Landscape Ecology Landscape ecology [Chpt 23] •Edges, ecotones and boundaries •Corridors •Island biogeography •Patch dynamics •Disturbance • LANDSCAPE ECOLOGY A LANDSCAPE consists of communities of varying sizes and compositions embedded in a MATRIX (=surrounding areas that differ in species structure or composition). • Natural patterns of PATCHES or landscape elements (distinct communities that make up the mosaic) within this landscape are affected by human disturbance i.e. introduced patches (altered patches that often involve the elimination of natural ecosystems / the introduction of exotic species) surround unmodified remnant patches (unmodified natural ecosystems). LANDSCAPE ECOLOGY Landscape elements: matrix, patches, edges, ecotones •A landscape consists of communities of varying sizes and compositions embedded in a matrix (surrounding areas that differ in species structure or composition). Natural patterns of patches or landscape elements (distinct communities that make up the mosaic) within this landscape are affected by human disturbance—introduced patches (altered patches that often involve the elimination of natural ecosystems, the introduction of exotic species, and maintenance activities) surround unmodified remnant patches (unmodified natural ecosystems). However, abiotic and biotic features of the landscape also influence human activities. The size, shape, area and orientation of PATCHES have an important influence on many physical and ecological processes. e.g. flow of wind, the dispersal of seeds, and the movement of animals, and on their suitability as habitats for plants and animals. o o Stream Corridor Elements of the landscape: matrices, patches, and corridors. Elements of the landscape: matrices, patches, and corridors. The edge of one patch meets the edge of another patch at a BORDER The ‘edge’ area s of two adjacent patches (plus border), is referred to as the BOUNDARY. o Although some adjacent patches have boundaries that are abrupt, with sharp contrasts between the two patches; o o Some patches do not have distinct boundaries and intergrade / blend into other patches in areas of community overlap, or ECOTONES. o In the ecotone, species common to each community mingle with species common to the edge, often resulting in a highly diverse and unique community in the boundary fig23 Edges are one of the most conspicuous features of the landscape. The place where the edge of one patch meets the edge of another is called a border. The two edges and the border combined make up the boundary. Edges are one of the most conspicuous features of the landscape. fig23 Some boundaries are abrupt with a sharp contrast between the adjoining patches. Others are less distinct, with low contrast between adjoining edges, such as between two forest communities. In this case, the vegetation of one patch blends with the other to form a sort of transition zone called an ecotone. Plant and animal species adapted to environmental conditions existing in the edges advance as far into either community as their abilities will allow. Thus, in the ecotone, species common to each community mingle with species common to the edge, often resulting in a highly diverse and unique community within these boundary environments. o inherent edges are stable, long-term features of a landscape. o induced edges are maintained by periodic disturbances. o The EDGE EFFECT refers to ecotones and edges being environmentally diverse and composed of species from each patch as well as species unique to the edge itself; o oconsequently, species richness is often higher along community edges and ecotones. •EDGES • •Some edges result from abrupt changes in soil type, topography, geomorphic features (such as rock outcrops), and microclimate. • •Under such conditions, long-term natural features of the physical environment determine adjoining vegetation types. • •Such edges, referred to as INHERENT, are usually stable and permanent. • •EDGES • •Other edges result from such natural disturbances as fire, storms, and floods • •or from such human-induced disturbances as livestock grazing, timber harvesting, agriculture, and suburban development. • •Such edges, maintained by periodic disturbances, are called INDUCED EDGES. • •Unless maintained, these disturbed areas will tend to revert to their original state – e.g. succession • Edge development Types of edges: inherent and induced, high contrast and low contrast. Inherent edges are most abrupt. Edges of high contrast exist between widely different adjacent communities, such as shrub and mature forest. Edges of low contrast involve two closely related successional communities, such as shrubs and sapling growth. 23D fig23 An induced edge is created, such as by clearing of a forested area for agriculture & there is an increase in light penetration into the adjacent woodland (a). Edges, like all communities, are dynamic and change in space and time. This figure shows typical changes in the boundary between two communities as time progresses. In the initial creation of an induced edge, such as by clearing of a forested area for agriculture, there is an increase in light penetration into the adjacent woodland (a). This increased light will raise air temperatures, increase evaporation, and result in the development of xeric conditions. In time, vegetation responds to changed conditions, including expansion of tree crowns and development of epicormic branching (b). Some shade-tolerant understory species may be unable to withstand the shock of exposure and may die. The high light, more xeric conditions will favor highly competitive, shade-intolerant plant species. Eventually, a dense understory of shade-intolerant woody seedlings and herbaceous plants develops. Because of the open conditions, edge vegetation invades the woodland. In time, increased expansion of tree crowns, increased growth of epicormic branches, and growth of edge understory plants close the gap between crown and edge vegetation and reduce the penetration of light into the adjacent forest (c). Some species disappear, and edge growth into the forest declines. At this point, edge vegetation experiences increased competition for light (d). Some species survive while others disappear, depending on their competitive ability. The number of dominant and codominant species in the edge declines, and such edge-oriented species as hawthorn, hickory, aspen, and oak replace shrubs such as blackberry (e). At this stage, a few large trees with branching close to the ground dominate the edge. Only minimal edge understory remains. When conditions permit, woody species may invade the adjacent field, developing an ecotone (f). Eventually, the edge becomes a mixture of shade-tolerant and shade-intolerant species. fig23 This increased light will raise air temperatures, increase evaporation, and result in the development of xeric conditions. In time, vegetation responds expanding tree crowns and branching (b). Edges, like all communities, are dynamic and change in space and time. This figure shows typical changes in the boundary between two communities as time progresses. In the initial creation of an induced edge, such as by clearing of a forested area for agriculture, there is an increase in light penetration into the adjacent woodland (a). This increased light will raise air temperatures, increase evaporation, and result in the development of xeric conditions. In time, vegetation responds to changed conditions, including expansion of tree crowns and development of epicormic branching (b). Some shade-tolerant understory species may be unable to withstand the shock of exposure and may die. The high light, more xeric conditions will favor highly competitive, shade-intolerant plant species. Eventually, a dense understory of shade-intolerant woody seedlings and herbaceous plants develops. Because of the open conditions, edge vegetation invades the woodland. In time, increased expansion of tree crowns, increased growth of epicormic branches, and growth of edge understory plants close the gap between crown and edge vegetation and reduce the penetration of light into the adjacent forest (c). Some species disappear, and edge growth into the forest declines. At this point, edge vegetation experiences increased competition for light (d). Some species survive while others disappear, depending on their competitive ability. The number of dominant and codominant species in the edge declines, and such edge-oriented species as hawthorn, hickory, aspen, and oak replace shrubs such as blackberry (e). At this stage, a few large trees with branching close to the ground dominate the edge. Only minimal edge understory remains. When conditions permit, woody species may invade the adjacent field, developing an ecotone (f). Eventually, the edge becomes a mixture of shade-tolerant and shade-intolerant species. fig23 This increased light will raise air temperatures, increase evaporation, and result in the development of xeric conditions. In time, vegetation responds expanding tree crowns and branching (b). etc etc. Edges, like all communities, are dynamic and change in space and time. This figure shows typical changes in the boundary between two communities as time progresses. In the initial creation of an induced edge, such as by clearing of a forested area for agriculture, there is an increase in light penetration into the adjacent woodland (a). This increased light will raise air temperatures, increase evaporation, and result in the development of xeric conditions. In time, vegetation responds to changed conditions, including expansion of tree crowns and development of epicormic branching (b). Some shade-tolerant understory species may be unable to withstand the shock of exposure and may die. The high light, more xeric conditions will favor highly competitive, shade-intolerant plant species. Eventually, a dense understory of shade-intolerant woody seedlings and herbaceous plants develops. Because of the open conditions, edge vegetation invades the woodland. In time, increased expansion of tree crowns, increased growth of epicormic branches, and growth of edge understory plants close the gap between crown and edge vegetation and reduce the penetration of light into the adjacent forest (c). Some species disappear, and edge growth into the forest declines. At this point, edge vegetation experiences increased competition for light (d). Some species survive while others disappear, depending on their competitive ability. The number of dominant and codominant species in the edge declines, and such edge-oriented species as hawthorn, hickory, aspen, and oak replace shrubs such as blackberry (e). At this stage, a few large trees with branching close to the ground dominate the edge. Only minimal edge understory remains. When conditions permit, woody species may invade the adjacent field, developing an ecotone (f). Eventually, the edge becomes a mixture of shade-tolerant and shade-intolerant species. fig23 Edge vegetation has increasing competition for light (d). Edges, like all communities, are dynamic and change in space and time. This figure shows typical changes in the boundary between two communities as time progresses. In the initial creation of an induced edge, such as by clearing of a forested area for agriculture, there is an increase in light penetration into the adjacent woodland (a). This increased light will raise air temperatures, increase evaporation, and result in the development of xeric conditions. In time, vegetation responds to changed conditions, including expansion of tree crowns and development of epicormic branching (b). Some shade-tolerant understory species may be unable to withstand the shock of exposure and may die. The high light, more xeric conditions will favor highly competitive, shade-intolerant plant species. Eventually, a dense understory of shade-intolerant woody seedlings and herbaceous plants develops. Because of the open conditions, edge vegetation invades the woodland. In time, increased expansion of tree crowns, increased growth of epicormic branches, and growth of edge understory plants close the gap between crown and edge vegetation and reduce the penetration of light into the adjacent forest (c). Some species disappear, and edge growth into the forest declines. At this point, edge vegetation experiences increased competition for light (d). Some species survive while others disappear, depending on their competitive ability. The number of dominant and codominant species in the edge declines, and such edge-oriented species as hawthorn, hickory, aspen, and oak replace shrubs such as blackberry (e). At this stage, a few large trees with branching close to the ground dominate the edge. Only minimal edge understory remains. When conditions permit, woody species may invade the adjacent field, developing an ecotone (f). Eventually, the edge becomes a mixture of shade-tolerant and shade-intolerant species. fig23 Some species survive while others disappear, depending on their competitive ability (e). etc etc. Edges, like all communities, are dynamic and change in space and time. This figure shows typical changes in the boundary between two communities as time progresses. In the initial creation of an induced edge, such as by clearing of a forested area for agriculture, there is an increase in light penetration into the adjacent woodland (a). This increased light will raise air temperatures, increase evaporation, and result in the development of xeric conditions. In time, vegetation responds to changed conditions, including expansion of tree crowns and development of epicormic branching (b). Some shade-tolerant understory species may be unable to withstand the shock of exposure and may die. The high light, more xeric conditions will favor highly competitive, shade-intolerant plant species. Eventually, a dense understory of shade-intolerant woody seedlings and herbaceous plants develops. Because of the open conditions, edge vegetation invades the woodland. In time, increased expansion of tree crowns, increased growth of epicormic branches, and growth of edge understory plants close the gap between crown and edge vegetation and reduce the penetration of light into the adjacent forest (c). Some species disappear, and edge growth into the forest declines. At this point, edge vegetation experiences increased competition for light (d). Some species survive while others disappear, depending on their competitive ability. The number of dominant and codominant species in the edge declines, and such edge-oriented species as hawthorn, hickory, aspen, and oak replace shrubs such as blackberry (e). At this stage, a few large trees with branching close to the ground dominate the edge. Only minimal edge understory remains. When conditions permit, woody species may invade the adjacent field, developing an ecotone (f). Eventually, the edge becomes a mixture of shade-tolerant and shade-intolerant species. •Successional process that occur in edge communities arises because environmental conditions in the newly formed edge are different from those of the adjacent vegetation communities, especially in the case of forests. • •Environmentally, such edges reflect steep gradients of wind flow, moisture, temperature, and solar radiation. • •Wind velocity is greater at the forest’s edge than within the forest, creating higher rates of evaporation and xeric conditions in and around the edge. • •With increased temperatures - transpiration increases, placing greater demands on soil moisture by plants. •Because changes in the penetration of solar radiation are influenced by aspect, north-facing and south-facing edges will differ in environmental conditions. • •In the Northern Hemisphere, a south-facing edge may receive 3 – 10 x more hours of sunshine a month during midsummer than a north-facing edge, making it much warmer and drier. • •Although the depth to which sunlight penetrates the vertical edge of the forest depends on a variety of factors, including solar angle, edge aspect, density and height of vegetation, latitude, season and time of day, in general the edge effect extends about 50 m into the forest. • fig23 This successional process that occurs in edge communities arises because environmental conditions in the newly formed edge are different from those of the adjacent vegetation communities, especially in the case of forests. Environmentally, such edges reflect steep gradients of wind flow, moisture, temperature, and solar radiation between extremes of open land and forest interior. Wind velocity is greater at the forest’s edge than within the forest, creating higher rates of evaporation and xeric conditions in and around the edge. With increased temperatures transpiration increases, placing greater demands on soil moisture by plants. Because changes in the penetration of solar radiation are influenced by aspect, north-facing and south-facing edges will differ in environmental conditions. In the Northern Hemisphere, a south-facing edge may receive three to ten times more hours of sunshine a month during midsummer than a north-facing edge, making it much warmer and drier. Although the depth to which sunlight penetrates the vertical edge of the forest depends on a variety of factors, including solar angle, edge aspect, density and height of vegetation, latitude, season and time of day, in general the edge effect extends about 50 m into the forest. CORRIDORS are strips of vegetation linking one patch with another. The vegetation of the corridor is similar to the patches it connects but different from the surrounding landscape in which they are set. o Narrow-line corridors include windbreaks, hedgerows, roads and roadside strips, and drainage ditches. o o Strip corridors (have both interior and edge environments) include strips of woodlands, power line rights-of-way & stream riparian (bank vegetation) zones. Corridors • Corridors are strips of vegetation linking one patch with another. The vegetation of the corridor is similar to the patches it connects but different from the surrounding landscape in which they are set. o Narrow-line corridors include windbreaks, hedgerows, roads and roadside strips, and drainage ditches. Strip corridors, consisting of both interior and edge environments, include strips of woodlands, power line rights-of-way, and stream riparian zones. o Corridors provide both unique habitat and passages between habitat patches. o Corridors act as filters, providing dispersal routes for some species but not others—the filter effect. o Corridors have both positive (i.e., promotion of gene flow) and negative (i.e., spread of disease, road-kill) effects. Corridors provide both unique habitat and passages between habitat patches. Often, corridors originate from human disturbance or development and are remnants of largely undisturbed land between agricultural fields and developments. o Corridors act as filters, providing dispersal routes for some species but not others—the filter effect. o o Corridors have both positive effects o (i.e., promotion of gene flow) and negative effects (i.e., spread of disease, road-kill) Corridors • Corridors are strips of vegetation linking one patch with another. The vegetation of the corridor is similar to the patches it connects but different from the surrounding landscape in which they are set. o Narrow-line corridors include windbreaks, hedgerows, roads and roadside strips, and drainage ditches. Strip corridors, consisting of both interior and edge environments, include strips of woodlands, power line rights-of-way, and stream riparian zones. o Corridors provide both unique habitat and passages between habitat patches. o Corridors act as filters, providing dispersal routes for some species but not others—the filter effect. o Corridors have both positive (i.e., promotion of gene flow) and negative (i.e., spread of disease, road-kill) effects. § CORRIDORS Habitat Corridors are strips of vegetation linking one patch with another on the landscape. The vegetation of the corridor is similar to the patches it connects but different from the surrounding landscape in which they are set. Usually, corridors originate from human disturbance or development and are remnants of largely undisturbed land between agricultural fields and developments. Some may be narrow-line corridors, such as lines of trees planted as windbreaks, hedgerows, roads and roadside strips, and drainage ditches. Wider bands of vegetation are called strip corridors, consisting of both interior and edge environments. Such corridors may be wide strips of woodlands or power line rights-of-way and belts of vegetation along streams. Corridors have two functional roles: they provide an often unique habitat for a variety of plants and animals, and they function as biological corridors—travel ways between habitat patches. Many corridors along streams and rivers provide important riparian habitat for animals. In suburban and urban settings, corridors provide habitat for edge species and act as stopover habitats for migrating birds. Corridors also provide protective cover for prey or scouting positions for predators, allowing them to remain concealed while hunting in adjacent vegetation patches. Corridors also act as conduits, providing dispersal routes and travel lanes for species between habitat patches, especially when corridors interconnect to form networks. They probably function best as travel lanes for individuals moving within the bounds of their home range. By facilitating the movement of individuals among different patches, corridors can facilitate gene flow between subpopulations occupying those patches, or the reestablishment of species in habitats that have experienced local extinctions. Corridors also act as filters, providing dispersal routes for some species but not others. Various sizes gaps in corridors allow certain organisms to cross and restrict others—the filter effect. Corridors can also have a negative impact on some populations by creating avenues for the spread of disease between patches or allowing the movement of predators. Four legs good…four wheels bad… •Two- to four-lane high speed roads are a major source of mortality for wildlife from large mammals to insects. • •They also effectively divide populations of many species. • •All types of roads alter or some way affect roadside vegetation. • •Most important, perhaps, road corridors allow people to access remote areas with often disastrous ecological effects. • •Where roads invade, people and development follow. • BUT… The effectiveness of biological corridors as a means of stimulating immigration between habitat patches has never been explicitly demonstrated. Beyond general observations of corridor use, there is little experimental evidence of the role of corridors in species dispersal. The use of corridors relates to the nature of the landscape mosaic in which it is set and to the probability of the disperser finding the corridor, using it, and successfully traversing it. Island Biogeography Theory The various patches that form the vegetation patterns across the landscape suggest ISLANDS of different sizes. The size of the patches and their distances from each other have a pronounced influence on the nature and diversity of the life they hold. o Darlington’s rule of thumb (1957): o “a tenfold increase in area leads to a doubling of the number of species.” Island Biogeography Theory • The various patches that form the vegetation patterns across the landscape suggest islands of different sizes. The size of the patches and their distances from each other have a pronounced influence on the nature and diversity of the life they hold. o Darlington’s rule of thumb (1957): “a tenfold increase in area leads to a doubling of the number of species.” o F.W. Preston (1962) formalized the relationship between the area of an island and the number of species present. When the two values are plotted as logarithms, the number of species varies linearly with island size. The steeper the slope of the line, the larger the increases in species richness per unit increase in island size. F.W. Preston (1962) formalized the relationship between the area of an island and the number of species present. When the two values are plotted as logarithms, the number of species varies linearly with island size. The steeper the slope of the line, the larger the increases in species richness per unit increase in island size. • Island Biogeography Theory • The various patches that form the vegetation patterns across the landscape suggest islands of different sizes. The size of the patches and their distances from each other have a pronounced influence on the nature and diversity of the life they hold. o Darlington’s rule of thumb (1957): “a tenfold increase in area leads to a doubling of the number of species.” o F.W. Preston (1962) formalized the relationship between the area of an island and the number of species present. When the two values are plotted as logarithms, the number of species varies linearly with island size. The steeper the slope of the line, the larger the increases in species richness per unit increase in island size. § ISLAND BIOGEOGRAPHY THEORY Number of bird species on various islands of the East Indies in relation to area. The abscissa gives areas of the islands. The ordinate is the number of bird species breeding on each island. The number of species varies linearly with island size: log S = log c + zlogA, where S is the number of species, A is the area of the island, c is a constant measuring the number of species per unit area, and z is a constant measuring the slope of the line relating S and A. The various patches, large and small, that form the vegetation patterns across the landscape suggest islands of different sizes. The size of these patches and their distances from each other on the landscape have a pronounced influence on the nature and diversity of the life they hold. Early naturalists and biogeographers noted that large islands hold more species than small islands. P. Darlington (1957) suggested a rule of thumb: a tenfold increase in area leads to a doubling of the number of species. In 1962, F. W. Preston formalized the relationship between the area of an island and the number of species present. When the two values are plotted as logarithms, the number of species varies linearly with island size, as shown here. This relationship can be expressed as: log S = log c + zlogA [or S = cA^z], where S is the number of species, A is the area of the island, c is a constant measuring the number of species per unit area, and z is a constant measuring the slope of the line relating S and A. The steeper the slope of the line, the larger the increases in species richness per unit increase in island size. The theory of island biogeography (MacArthur and Wilson 1963) states that the number of species of a given taxon established on an island represents a dynamic equilibrium between: o o the rate of immigration of new colonizing species and o the rate of extinction of previously established ones. o oThe rate at which one species is lost and a replacement gained is called the TURNOVER RATE. o The theory of island biogeography (MacArthur and Wilson 1963) states that the number of species of a given taxon established on an island represents a dynamic equilibrium between the rate of immigration of new colonizing species and the rate of extinction of previously established ones. The rate at which one species is lost and a replacement gained is called the turnover rate. o There are a number of limitations to this theory: § It examines species richness only. § It makes no assumptions about species composition—all species are treated as equivalents. § It does not address limitations related to the life history or habitat requirements of the species involved. § It assumes that the probabilities of extinctions and immigrations are the same for all species. oThere are a number of limitations to this theory: o § It examines species richness only. § It makes no assumptions about species composition—all species are treated as equivalents. § It does not address limitations related to the life history or habitat requirements of the species involved. § It assumes that the probabilities of extinctions and immigrations are the same for all species. o The theory of island biogeography (MacArthur and Wilson 1963) states that the number of species of a given taxon established on an island represents a dynamic equilibrium between the rate of immigration of new colonizing species and the rate of extinction of previously established ones. The rate at which one species is lost and a replacement gained is called the turnover rate. o There are a number of limitations to this theory: § It examines species richness only. § It makes no assumptions about species composition—all species are treated as equivalents. § It does not address limitations related to the life history or habitat requirements of the species involved. § It assumes that the probabilities of extinctions and immigrations are the same for all species. Immigrations and extinctions may not be independent. § For example: extinction of a dwindling population may be slowed or prevented by an influx of immigrants = the rescue effect. § Immigrations and extinctions may not be independent. For example, extinction of a dwindling population may be slowed or prevented by an influx of immigrants, the rescue effect. • Graphical representation of the island biogeography theory, involving both distance and area. Equilibrium species densities are labeled by corresponding value of S. Immigration rates decrease with increasing distance from a source area. Thus distant islands attain species equilibrium with fewer species than near islands, all else being equal. Extinction rates increase as the size of the island becomes smaller. [S3>S2 for large islands; S2>S1 for small islands.] T=the rate at which a species is lost and another is gained. Both the size and proximity of an island to the mainland strongly influence the rates of immigration, extinction, and turnover and consequently the predicted equilibrium species richness, as illustrated here. Extinction rates are higher on smaller islands than on larger ones, because large islands can hold bigger populations of any particular species. Immigration rates decrease with increasing distance from the mainland; thus, islands closer to the mainland have a higher immigration rate than distant islands. Considering both immigration and extinction rates, we can hypothesize that near islands reach equilibrium with more species than distant islands, and small islands reach equilibrium with fewer species than large islands. Interactions of size and distance from the mainland and equilibrium species richness are shown in this figure. Turnover rates are greater for near islands than for distant islands of the same size, because a source of replacement immigrants is closer. However, turnover rates for near, small islands are greater than for near, large islands because extinction rates are greatest on small islands. • An alternative approach to island biography is the HABITAT DIVERSITY THEORY. • The habitat diversity theory states that it is the diversity of habitats that supports species richness, not the area per se. Larger islands may have lower extinction rates and support more species than smaller islands because they have more diverse habitats. • o There is considerable evidence that habitat heterogeneity can override the influence of island size - with smaller islands with high habitat heterogeneity supporting greater species richness than large, more homogeneous islands. •An alternative approach to island biography is the habitat diversity theory. The habitat diversity theory states that it is the diversity of habitats that supports species richness, not the area per se. Larger islands may have lower extinction rates and support more species than smaller islands because they have more diverse habitats. o There is considerable evidence that habitat heterogeneity can override the influence of island size, with smaller islands with high habitat heterogeneity supporting greater species richness than large, more homogeneous islands. Patch Dynamics Patches are dynamic systems affected by both natural processes and human disturbances. The impact of fragmentation is related to the scale at which it occurs. o The probability of occurrence of interior species —those whose habitat begins some distance within the habitat patch— increases with patch size. o oSome species are area-sensitive because they require large territories or foraging areas. o o Area-insensitive species are found in small or large habitat units. o Patch Dynamics • Patches are dynamic systems affected by both natural processes and human disturbances. The impact of fragmentation is related to the scale at which it occurs. o The probability of occurrence of interior species—those whose habitat begins some distance within the habitat patch—increases with patch size. Some species are area-sensitive because they require large territories or foraging areas. Area-insensitive species are found in small to large habitat units. o As fragmentation continues and patch area is reduced, area-sensitive species go extinct while edge and area-insensitive species increase in numbers. o As fragmentation continues, species numbers follow a downward trend. As fragmentation continues and patch area is reduced – • area-sensitive species go extinct • • while edge and area-insensitive species increase in numbers. As fragmentation continues, species numbers follow a downward trend. o Patch Dynamics • Patches are dynamic systems affected by both natural processes and human disturbances. The impact of fragmentation is related to the scale at which it occurs. o The probability of occurrence of interior species—those whose habitat begins some distance within the habitat patch—increases with patch size. Some species are area-sensitive because they require large territories or foraging areas. Area-insensitive species are found in small to large habitat units. o As fragmentation continues and patch area is reduced, area-sensitive species go extinct while edge and area-insensitive species increase in numbers. o As fragmentation continues, species numbers follow a downward trend. fig23 Often these are species whose habitat begins some distance within the forest, shrubland, and grassland. Termed interior species, the probability of occurrence of these species increases with patch size, as shown here for several area-insensitive and area-sensitive interior bird species. Others are area-sensitive because they require large territories or foraging areas. As fragmentation continues and these species disappear, edge and area-insensitive species, ones at home in small to large units of habitat, increase in abundance. Although the number of species in a fragmented habitat may increase initially with the creation of edge environments, the number of species it contains will eventually decline as fragmentation continues. The minimum size of habitat needed to maintain interior species differs between plants and animals. For plants, patch size, per se, is not as important in species persistence and extinction as environmental conditions. For many shade-tolerant plant species found in the forest interior, the minimum area depends on the patch size required to allow for moisture and light conditions typical of the interior. That area depends in part on the nature of the edge about the stand—whether it is open or closed (reducing the penetration of light and wind)—on canopy closure, and on the ratio of edge to interior. If the stand is too small or too open, the interior environment becomes so xeric that mesic species, both herbaceous and woody, cannot survive and reproduce. There appears to be a pattern of maximum species diversity with patches of intermediate size. This pattern results from the negative correlation between edge species and the size of habitat patches combined with the positive correlation between interior species and increased area. However, as these figures suggest, bird species diversity in forest patches increases with patch size, but only up to a point. •The minimum size of habitat needed to maintain interior species differs between plants and animals. • •For plants, patch size, per se, is not as important in species persistence and extinction as environmental conditions. • •For many shade-tolerant plant species found in the forest interior, the minimum area depends on the patch size required to allow for appropriate moisture and light conditions. • •If the stand is too small or too open, the interior environment becomes so xeric that mesic species, both herbaceous and woody, cannot survive and reproduce. • Theoretically, although maximum diversity is achieved with patches of intermediate size • - many species that require large patches are excluded. • • Also, fragmentation of larger patches may not result in a significant decline in species diversity - but it may eliminate many species from the landscape. • Although maximum diversity is achieved with patches of intermediate size, many species that require large patches are excluded. Fragmentation of larger patches may not result in a significant decline in species diversity, but it may eliminate many species from the landscape. o Although species diversity is related to area, it also is a function of the ratio of edge (or perimeter) to area. The length of perimeter is directly proportional to the square root of the area. At some small size, all territorial islands are edge. If the depth of the edge remains constant as area increases, the ratio of edge to interior decreases as the habitat island size increases. o Configuration or shape of the island is also important. For example, long, narrow islands of sufficient size may still be all edge habitat. Although species diversity is related to area, it also is a function of the ratio of edge (or perimeter) to area. The length of perimeter is directly proportional to the square root of the area. At some small size, territorial islands are all edge. If the depth of the edge remains constant as area increases, the ratio of edge to interior decreases as the habitat island size increases. Configuration or shape of the island is also important. For example, long, narrow islands of sufficient size may still be all edge habitat. • Although maximum diversity is achieved with patches of intermediate size, many species that require large patches are excluded. Fragmentation of larger patches may not result in a significant decline in species diversity, but it may eliminate many species from the landscape. o Although species diversity is related to area, it also is a function of the ratio of edge (or perimeter) to area. The length of perimeter is directly proportional to the square root of the area. At some small size, all territorial islands are edge. If the depth of the edge remains constant as area increases, the ratio of edge to interior decreases as the habitat island size increases. o Configuration or shape of the island is also important. For example, long, narrow islands of sufficient size may still be all edge habitat. Relationship of island or fragment size to edge and interior conditions. (a) Functionally, all small islands of habitat are edge. Allowing the depth of edges to remain constant, the ratio of edge to interior decreases as island size increases. When island size is large enough to maintain mesic and interior conditions, an interior begins to develop. Although maximum diversity is achieved with patches of intermediate size, many species that require larger areas are excluded. Although fragmentation of larger forest patches may not result in a significant decline in species diversity, it will eliminate many species from the landscape. Managing for maximum diversity within any one patch may not maximize the total diversity of the landscape, nor provide adequate habitat for all species found within the region prior to fragmentation. Although species diversity is related to area, area alone is not the full story. What is important is the ratio of edge (or perimeter) to area. The length of perimeter is directly proportional to the square root of the area. At some small size all territorial islands or patches are edge. If we allow the depth of the edge to remain constant while increasing area, the ratio of edge to interior decreases as the habitat island size increases. When the island size becomes large enough to maintain interior conditions, an interior begins to develop. However, size alone is not a primary determinant of edge-interior conditions. Relationship of island or fragment size to edge and interior conditions. (c) A graph shows the relationship between edge and interior as island size increases. Below A, the woodland is all edge. As its size increases, interior area increases and the ratio of edge to interior decreases. This relationship of size to edge holds for circular or square islands. This relationship between patch size and the relative abundance of edge and interior habitats is further illustrated here. For small patches (size A or less on the x axis), only edge habitats are found and the patch cannot support interior species. As patch size increases, the interior area increases and the ratio of edge to interior decreases. This relationship of area to edge holds for circular or square patches, but not for irregularly shaped or rectangular islands. Long narrow woodland islands as shown in the previous slide, whose width does not exceed the depth of the edge, would be edge communities, even though their area might be the same as that of square or circular ones. Given that a number of relatively small patches will hold a higher species diversity in total than large patches, an overemphasis on managing for species diversity can lead to a decline and ultimate extinction of interior and area-sensitive species that exist in large or more homogeneous habitats. We must consider both species diversity and species composition in the conservation and management of lands. fig23 39 ha 47 ha Configuration or shape of the island is also critical. For example, the island at the top contains 39 ha, but it is entirely edge habitat; its width does not exceed the depth of its edge, or it has a high ratio of edge perimeter to area. Out of 16 species, none are interior. The square woodland contains 47 ha and has a core interior area of 20 ha. Six of its 16 species are interior species sensitive to fragmentation. Disturbance creates colonization sites, thereby increasing the abundance of opportunistic species and diversity while simultaneously initiating secondary succession. Disturbances can be characterized on the basis of intensity, frequency and scale: § Intensity is a measure of the magnitude of the physical force of the disturbance, usually expressed in terms of the proportion removed or mortality of individuals, species, or biomass. It is influenced by the magnitude of the physical force involved, morphological and physiological characteristics of the organisms that influence their response, and the nature of the substrate. Disturbance • Disturbance creates colonization sites, thereby increasing the abundance of opportunistic species and diversity while simultaneously initiating secondary succession. o Disturbances can be characterized on the basis of intensity, frequency and scale: § Intensity is a measure of the magnitude of the physical force of the disturbance, usually expressed in terms of the proportion removed or mortality of individuals, species, or biomass. It is influenced by the magnitude of the physical force involved, morphological and physiological characteristics of the organisms that influence their response, and the nature of the substrate. §Frequency is the rate of disturbance, or return interval—number of disturbances/time. §Scale is rather abstract but refers to the size of the disturbance and must be considered in the context of the scale of the community being affected. o Sources of landscape disturbance include fire (surface, crown, and ground fire), wind, ice, moving water, drought, and animals, and human activities such as timber harvest, land clearing, cultivation, and mining. oSome species have developed adaptations to periodic disturbances, such as fire. They may be loosely classified as “seeders, sprouters, or tolerators.” o The effects of disturbance on animals depend on the species affected and the size and type of disturbance. § Frequency is the rate of disturbance, or return interval—number of disturbances/time. § Scale is rather abstract but refers to the size of the disturbance and must be considered in the context of the scale of the community being affected. o Sources of landscape disturbance include fire (surface, crown, and ground fire), wind, ice, moving water, drought, and animals, and human activities such as timber harvest, land clearing, cultivation, and mining. o Some species have developed adaptations to periodic disturbances, such as fire. They may be loosely classified as “seeders, sprouters, or tolerators.” o The effects of disturbance on animals depend on the species affected and the size and type of disturbance. A wee break… [USEMAP] Ecosystem Productivity Ecosystem Productivity [Chpt 24] •Components •Nature of Energy •Laws of thermodynamics •Storage and utilization of energy by plants •Primary productivity around the world •Secondary production •Energy balance •Food chains or Energy flow • Structural and Functional Components of Ecosystems One of the primary functional processes of ecosystems is the flow and use of energy. o The biotic and abiotic components of the ecosystem exchange energy and materials. o All ecosystems have three structural and functional components: § Autotrophs-the energy-capturing base of the system. § Heterotrophs (consumers and decomposers)-organisms that utilize the energy stored by the autotrophs and ultimately decompose complex materials into simple, inorganic substances. § Inorganic and dead organic matter - the basis of the internal cycling of nutrients in the ecosystem. ECOSYSTEM PRODUCTIVITY Structural and Functional Components of Ecosystems • One of the primary functional facets of ecosystems is to process energy, its flow and use. o Ecosystems can be divided into biotic (all interacting organisms living in the community) and abiotic (the physical environment with which the organisms interact) components. The biotic and abiotic exchange energy and materials. o All ecosystems have three structural and functional components: § Autotrophs-the energy-capturing base of the system. § Heterotrophs (consumers and decomposers)-organisms that utilize the energy stored by the autotrophs. § Inorganic and dead organic matter o Inputs into the system are both biotic (includes other organisms that move into the ecosystem and influences imposed by other ecosystems in the landscape) and abiotic (energy, inorganic substances, mineral nutrients, organic compounds, and precipitation). o o The driving force of the system is the energy of the sun which causes other inputs to circulate through the system. o o Outflows from one system become inflows to another. o Energy is being used and dissipated as heat of respiration while chemical elements are being recycled. o Inputs into the system are both biotic (include other organisms that move into the ecosystem and influences imposed by other ecosystems in the landscape) and abiotic (energy, inorganic substances, mineral nutrients, organic compounds, and precipitation). o The driving force of the system is the energy of the sun which cause other inputs to circulate through the system. o Outflows from one system become inflows to another. Energy is being used and dissipated as heat of respiration while chemical elements are being recycled. o Consumers regulate the speed at which nutrients are recycled. o A given ecosystem on any particular site is not a permanent entity, but part of a shifting pattern on the landscape. Biotic and abiotic components making up the ecosystem structure may change, biomass accumulate or decline, but functional processes still operate. o Consumers regulate the speed at which nutrients are recycled. o o A given ecosystem on any particular site is not a permanent entity, but part of a shifting pattern on the landscape. o oBiotic and abiotic components making up the ecosystem structure may change, biomass accumulate or decline, but functional processes still operate. o Inputs into the system are both biotic (include other organisms that move into the ecosystem and influences imposed by other ecosystems in the landscape) and abiotic (energy, inorganic substances, mineral nutrients, organic compounds, and precipitation). o The driving force of the system is the energy of the sun which cause other inputs to circulate through the system. o Outflows from one system become inflows to another. Energy is being used and dissipated as heat of respiration while chemical elements are being recycled. o Consumers regulate the speed at which nutrients are recycled. o A given ecosystem on any particular site is not a permanent entity, but part of a shifting pattern on the landscape. Biotic and abiotic components making up the ecosystem structure may change, biomass accumulate or decline, but functional processes still operate. fig24 All ecosystems are composed of two parts: the biotic and the abiotic. The biotic part consists of all interacting organisms living in the area, the community. The abiotic part embraces the physical environment with which the organisms of the community interact. The biotic and abiotic exchange energy and materials. The Nature of Energy Energy is the ability to do work; it is what happens when a force acts through distance. Energy can be potential or kinetic: o Potential energy - energy at rest and is capable of and available for work. o Kinetic energy - energy in motion. o Work that results from the expenditure of energy can either store or concentrate energy (as potential energy) or arrange or order matter without storing energy. o Energy is measured in joules ( 1 joule is 4.168 one-gram calories), calories (1 calorie is the amount of heat needed to raise 1 gram of water 1oC at 15oC), or kilogram calories (kcal or the amount of heat required to raise 1 kilogram of water 1oC and 15oC). The Nature of Energy • Energy is the ability to do work; it is what happens when a force acts through distance. Energy is either potential or kinetic: o Potential energy-energy at rest and is capable of and available for work. o Kinetic energy-energy in motion. o Work that results from the expenditure of energy can either store or concentrate energy (as potential energy) or arrange or order matter without storing energy. o Energy is measured in joules ( 1 joule is 4.168 one-gram calories), calories (1 calorie is the amount of heat needed to raise 1 gram of water 1^oC at 15^oC), or kilogram calories (kcal or the amount of heat required to raise 1 kilogram of water 1^oC and 15^oC). The Laws of Thermodynamics The first law of thermodynamics is concerned with the conservation of energy: energy is neither created nor destroyed. It may change form, pass from one place to another, or act on matter, transforming it to energy, but in the process there is no gain or loss in total energy from the system. o An exothermic reaction releases potential energy as heat into the surrounding. o When energy from outside flows into a system to raise it to a higher energy state, the reaction is endothermic. (i.e. heat goes in) The Nature of Energy • Energy is the ability to do work; it is what happens when a force acts through distance. Energy is either potential or kinetic: o Potential energy-energy at rest and is capable of and available for work. o Kinetic energy-energy in motion. o Work that results from the expenditure of energy can either store or concentrate energy (as potential energy) or arrange or order matter without storing energy. o Energy is measured in joules ( 1 joule is 4.168 one-gram calories), calories (1 calorie is the amount of heat needed to raise 1 gram of water 1^oC at 15^oC), or kilogram calories (kcal or the amount of heat required to raise 1 kilogram of water 1^oC and 15^oC). Much of the potential energy in any reaction is degraded in quality and becomes unable to perform further work. This energy ends up as heat, serving to disorganize or randomly disperse molecules. The measure of this relative disorder is termed entropy. The Nature of Energy • Energy is the ability to do work; it is what happens when a force acts through distance. Energy is either potential or kinetic: o Potential energy-energy at rest and is capable of and available for work. o Kinetic energy-energy in motion. o Work that results from the expenditure of energy can either store or concentrate energy (as potential energy) or arrange or order matter without storing energy. o Energy is measured in joules ( 1 joule is 4.168 one-gram calories), calories (1 calorie is the amount of heat needed to raise 1 gram of water 1^oC at 15^oC), or kilogram calories (kcal or the amount of heat required to raise 1 kilogram of water 1^oC and 15^oC). • The second law of thermodynamics states that when energy is transferred or transformed, part of the energy is lost as waste; The tendency, then, is to create disorder (entropy) out of order—the system is running down hill. The second law applies theoretically to isolated closed systems, in which there is no exchange of energy or matter between the system and its surroundings. • The second law of thermodynamics states that when energy is transferred or transformed, part of the energy is lost as waste; it assumes a form that cannot be passed on further. The tendency, then, is to create disorder (entropy) out of order—the system is running down hill. o The second law applies theoretically to isolated closed systems, in which there is no exchange of energy or matter between the system and its surroundings. Closed systems tend toward a state of minimum free energy (available to do work) and maximum entropy. o Biological systems do not seem to conform to the second law of thermodynamics. Ecological systems are open, steady-state systems in which entropy is offset by the continual input of free energy. • Any discussion of energy flow through ecosystems is fundamentally a discussion of solar energy and carbon. Biological systems do not seem to conform to the second law of thermodynamics. Ecological systems are open, steady-state systems in which entropy is offset by the continual input of free energy. Any discussion of energy flow through ecosystems is fundamentally a discussion of solar energy and carbon. • The second law of thermodynamics states that when energy is transferred or transformed, part of the energy is lost as waste; it assumes a form that cannot be passed on further. The tendency, then, is to create disorder (entropy) out of order—the system is running down hill. o The second law applies theoretically to isolated closed systems, in which there is no exchange of energy or matter between the system and its surroundings. Closed systems tend toward a state of minimum free energy (available to do work) and maximum entropy. o Biological systems do not seem to conform to the second law of thermodynamics. Ecological systems are open, steady-state systems in which entropy is offset by the continual input of free energy. • Any discussion of energy flow through ecosystems is fundamentally a discussion of solar energy and carbon. Storage and Utilization of Energy by Plants Primary production - energy accumulated by plants resulting from photosynthesis. Gross primary production (GPP)-all of the energy assimilated in photosynthesis. o Net primary production (NPP)-energy remaining after respiration and stored as organic matter [NPP = GPP – Respiration]. The storage of organic matter in plant tissue in excess of respiration. Storage and Utilization of Energy by Plants • Primary production-energy accumulated by plants resulting from photosynthesis. o Gross primary production (GPP)-all of the energy assimilated in photosynthesis. o Net primary production (NPP)-energy remaining after respiration and stored as organic matter [NPP = GPP – Respiration]. The storage of organic matter in plant tissue in excess of respiration. o Both gross and primary production are measured as the rate at which energy or biomass is produced per unit area per unit time [kcal/m^2/yr or g dry weight/m^2/yr]. o Standing crop biomass-the accumulated organic matter found on a given area at a given time. Because it represents accumulated biomass, a low-productivity ecosystem can accumulate a high standing crop biomass over a long period of time. Both gross and primary production are measured as the rate at which energy or biomass is produced per unit area per unit time [kcal/m2/yr or g dry weight/m2/yr]. Standing crop biomass - the accumulated organic matter found on a given area at a given time. Because it represents accumulated biomass, a low-productivity ecosystem can accumulate a high standing crop biomass over a long period of time. Storage and Utilization of Energy by Plants • Primary production-energy accumulated by plants resulting from photosynthesis. o Gross primary production (GPP)-all of the energy assimilated in photosynthesis. o Net primary production (NPP)-energy remaining after respiration and stored as organic matter [NPP = GPP – Respiration]. The storage of organic matter in plant tissue in excess of respiration. o Both gross and primary production are measured as the rate at which energy or biomass is produced per unit area per unit time [kcal/m^2/yr or g dry weight/m^2/yr]. o Standing crop biomass-the accumulated organic matter found on a given area at a given time. Because it represents accumulated biomass, a low-productivity ecosystem can accumulate a high standing crop biomass over a long period of time. • Levels of primary productivity vary immensely among ecosystems, between ecosystems of the same type, and within the same ecosystem from year to year. • In general, the productivity of terrestrial ecosystems is most influenced by temperature and precipitation patterns. • • At the local level, temporal and spatial variation in productivity can be related to nutrient availability, grazing pressure, outbreaks in plant disease or insect infestation, fire, and growing season length. • • Annual net production changes with age. In general, it increases in terrestrial ecosystems during succession or stand development, followed by a decline as time progresses. • Levels of primary productivity vary immensely among ecosystems, between ecosystems of the same type, and within the same ecosystem from year to year. In general, the productivity of terrestrial ecosystems is most influenced by temperature and precipitation patterns. • At the local level, temporal and spatial variation in productivity can be related to nutrient availability, grazing pressure, outbreaks in plant disease or insect infestation, fire, and growing season length. • Annual net production changes with age. In general, it increases in terrestrial ecosystems during succession or stand development, followed by a decline as time progresses. • Environmental controls on primary productivity Net primary productivity for a variety of terrestrial ecosystems. (a) as a function of mean annual precipitation, and (b) as a function of mean annual temperature. Productivity of terrestrial ecosystems is influenced by climate. Measured estimates of net primary productivity for a variety of different terrestrial ecosystems are plotted in these two figures as a function of annual precipitation (a) and mean daily temperature (b) for each site. As shown, NPP increases with increasing temperature and rainfall. These relationships between primary productivity and the environmental factors of temperature and precipitation are a result of their influence on the rates of photosynthesis, the amount of leaf area that can be supported, and the duration of the growing season. fig24 The influence of temperature and precipitation are interrelated. Warm temperatures result in high water demand. If temperatures are warm but water availability (precipitation is low), productivity will also be low. Likewise, if water availability is high but temperatures are low, productivity will be low. It is the combination of warm temperatures and adequate water supply to meet the demands of transpiration that results in the highest values of primary productivity. This pattern is reflected in this graph showing the the relationship between NPP of various ecosystems with the measured value of actual evapotranspiration, the combined value of surface evaporation and transpiration, which reflects both demand and supply of water. fig24 In any ecosystem, annual net production changes with age. In general, primary productivity in terrestrial ecosystems increases initially during succession or stand development, followed by a decline as time progresses, shown here as changes in above-ground NPP with age for a stand of white spruce in the Karelia region of Russia. Growth is initially slow, increases as leaf area develops, peaks as leaf area reaches its maximum, and declines thereafter. Energy Allocation Net primary production can be allocated to: (a) Growth – the build up of components such as stems, roots and leaves that promote further acquisition of energy and nutrients. (b) Storage - materials built up in the plant for future growth and other functions: § Accumulation - the increase of compounds that do not directly support growth (i.e.,starch, fructose, mineral ions). § Reserve formation - synthesis of storage compounds from resources that otherwise would be allocated directly to promote growth. § Recycling - recycling of material from aging tissue to new growth. Patterns of energy allocation change with age and size of the individual, species, and availability of water and nutrients. Energy Allocation • Allocation of net primary production: o Growth-the build up of components such as stems, roots and leaves that promote further acquisition of energy and nutrients. o Storage-photosynthate built up in the plant for future growth and other functions: § Accumulation-the increase of compounds that do not directly support growth (i.e.,starch, fructose, mineral ions). § Reserve formation-synthesis of storage compounds from resources that otherwise would be allocated directly to promote growth. § Recycling-recycling of material from aging tissue to new growth. • Patterns of energy allocation change with age and size of the individual, species, and availability of water and nutrients. • Primary productivity around the world • • The primary productivity of terrestrial ecosystems varies widely over the globe. • • The most productive terrestrial ecosystems are tropical rain forests with high rain fall and warm temperatures; their NPP ranges from 1000 to 3500 g/m2/yr. • • Temperate forests range between 600 and 2500 g/m2/yr. • • Shrublands have net productivities in the range of 700 to 1500 g/m2/yr. • • Desert grasslands produce about 200 to 300 g/m2/yr, whereas deserts and tundra range between 100 and 250 g/m2/yr. • • fig24 The primary productivity of terrestrial ecosystems varies widely over the globe as depicted here. The most productive terrestrial ecosystems are tropical rain forests with high rain fall and warm temperatures; their NPP ranges from 1000 to 3500 g/m^2/yr. Temperate forests range between 600 and 2500 g/m^2/yr. Shrublands have net productivities in the range of 700 to 1500 g/m2/yr. Desert grasslands produce about 200 to 300 g/m^2/yr, whereas deserts and tundra range between 100 and 250 g/m^2/yr. These differences in net primary productivity from tropic to arctic regions are reflected in litter production, which ranges from 900 to 1500 g/m^2/yr in tropical forests to 200 to 600 g/m^2/yr in temperate forests, and 0 to 200 g/m^2/yr in arctic and alpine regions. • NPP in the open ocean is generally quite low. • • Tropical waters tend to have low productivity – due to low nutrients. • • Productivity in the open waters of the cool temperate oceans tends to be higher than those of the tropics. • • However, in some areas of tropical upwelling, such as the Humbolt current (the band of high productivity off the west coast of South America), net productivity can reach 1000 g/m2/yr. • • Coastal ecosystems and the continental shelves generally have higher productivity than the open waters - input of nutrients from terrestrial ecosystems via rivers. • • Coastal swamps and marshes have net productivities ranging up to 4000 g/m2/yr. • • Estuaries, because of input of nutrients from rivers and tides, can have a net productivity up to 2500 g/m2/yr. • • Likewise coral reefs – although coral reefs are found in nutrient poor waters – symbiotic algae in coral help compensate for low nutrients. • • High levels of productivity can be found in polar regions, especially Antarctica. • • Despite cold temperatures – 24 hours of sunlight in the summer plus nutrient upwellings lead to high productivity. FG14_14 Midlatitude Productivity Upwellings are 4x more productive than coastal areas and 5x more productive than the open ocean But coastal area is 100x larger than upwelling areas → greater biomass Upwellings can be more productive than rainforest or plantations Secondary Production Net primary productivity is the energy available to the heterotrophic components of the ecosystem. Rarely is all of it available and utilized by these organisms, including the decomposers. Energy, once consumed, either is diverted to maintenance, growth and reproduction, or is passed from the body as waste products. The energy content of the waste products is transferred to the detrivores. Secondary Production • Net primary productivity is the energy available to the heterotrophic components of the ecosystem. Rarely is all of it available and utilized by these organisms, including the decomposers. o Energy, once consumed, either is diverted to maintenance, growth and reproduction, or is passed from the body as waste products. The energy content of the waste products is transferred to the detrivores. o Of the energy left after these losses, part is utilized as heat required for metabolism above the basal or resting metabolism. The remaining net energy is available for maintenance, production and reproduction. o Maintenance costs are highest in small, active warm-blooded animals and are fixed or irreducible. In small invertebrates, energy can vary with temperature, and a positive energy balance exits only within a narrow range of temperatures. Of the energy left after these losses, part is utilized as heat required for metabolism above the basal or resting metabolism. The remaining NET ENERGY is available for maintenance, production and reproduction. Maintenance costs are highest in small, active warm-blooded animals and are fixed or irreducible. In small invertebrates, energy can vary with temperature, and a positive energy balance exits only within a narrow range of temperatures. Secondary Production • Net primary productivity is the energy available to the heterotrophic components of the ecosystem. Rarely is all of it available and utilized by these organisms, including the decomposers. o Energy, once consumed, either is diverted to maintenance, growth and reproduction, or is passed from the body as waste products. The energy content of the waste products is transferred to the detrivores. o Of the energy left after these losses, part is utilized as heat required for metabolism above the basal or resting metabolism. The remaining net energy is available for maintenance, production and reproduction. o Maintenance costs are highest in small, active warm-blooded animals and are fixed or irreducible. In small invertebrates, energy can vary with temperature, and a positive energy balance exits only within a narrow range of temperatures. fig24 Energy, once consumed, either is diverted to maintenance, growth and reproduction or is passed from the body as waste products—feces, urine and fermentation gasses. The energy content of feces is transferred to the detritivores. Of the energy left after these losses, part is utilized as heat increment, which is heat required for metabolism above the basal or resting metabolism. The remainder of the energy is net energy, available for maintenance, production, and reproduction. It includes energy involved in capturing or harvesting food, muscular worked expended in the animal’s daily routine, and energy needed to keep up with the wear and tear on the animal’s body. The energy used for maintenance is lost as heat. Maintenance costs, highest in small, active warm-blooded animals, are fixed or irreducible. In small invertebrates, energy can vary with temperature, and a positive energy balance exists only within a fairly narrow range of temperatures. Energy remaining from maintenance and respiration—net energy—goes into secondary or consumer production—fat, growth, and the birth of new individuals. Within secondary production there is no portion known as gross production — what is analogous to gross production is actually assimilation. Secondary production depends on the quantity, quality and availability of net primary production as a source of energy. Therefore, any of the environmental constraints on primary productivity, such as climate, soil fertility, and water availability, will also act to constrain secondary productivity. • o Energy remaining from maintenance and respiration—net energy—goes into secondary or consumer production—fat, growth, and the birth of new individuals. o Within secondary production there is no portion known as gross production—what is analogous to gross production is actually assimilation. o Secondary production depends on the quantity, quality and availability of net primary production as a source of energy. Therefore, any of the environmental constraints on primary productivity, such as climate, soil fertility, and water availability, will also act to constrain secondary productivity. •Energy remaining from maintenance and respiration—net energy—goes into secondary or consumer production—fat, growth, and the birth of new individuals. Within secondary production there is no portion known as gross production—what is analogous to gross production is actually assimilation. fig24 Secondary production depends on the quantity, quality and availability of net production primary productivity as a source of energy. Therefore, any of the environmental constraints on primary productivity, such as climate, will also act to constrain secondary productivity within the ecosystem. Figure (a) shows the observed relationship between mean annual rainfall and the productivity of large herbivores in African ecosystems. The increase in large herbivore production with increasing rainfall is a direct result of the corresponding increase in net primary productivity. A similar relationship between phytoplankton production (primary productivity) and zooplankton production (secondary production) in lake ecosystems is shown in figure (b). Energy Balance or budget A consumer’s energy budget is given by: C = A + (F + U) where C is the energy ingested or consumed; A is the energy assimilated; and F and U are the energy lost through feces and nitrogenous wastes (urine). Energy Balance or Budget • A consumer’s energy budget is given by: C = A + (F + U); where C is the energy ingested or consumed; A is the energy assimilated; and F and U are the energy lost through feces and nitrogenous wastes (urine). • Differences among heterotrophs in energy balance can be understood from the viewpoint of three measures of assimilation and production efficiency: o Assimilation efficiency-the ratio of assimilation to consumption or ingestion, A/I. It is an index of the efficiency of the consumer in extracting energy from the food it consumes. It relates to food quality and effectiveness of digestion. Production efficiency = the ratio of production to assimilation, P/A This is an index of the efficiency of a consumer in incorporating assimilation energy into new tissue (growth), or secondary production. It reflects the relative balance of the energy allocation to production and respiration. Production to consumption (P/I) -this index reflect how much energy consumed by the animal is converted into production. It’s measure of the efficiency with which energy is made available to the next group of consumers. o Production efficiency-the ratio of production to assimilation, P/A. This is an index of the efficiency of a consumer in incorporating assimilation energy into new tissue (growth), or secondary production. It reflects the relative balance of the energy allocation to production and respiration. o Production to consumption (P/I)-this index reflect how much energy consumed by the animal is converted into production and is a measure of the efficiency with which energy is made available to the next group of consumers. o Homeotherms use about 98 percent of their assimilated energy in metabolism and only about 2 percent in secondary production. Poikilotherms convert about 44 percent of their assimilated energy to secondary production. However, homeotherms have a much higher assimilation efficiency. Homeotherms use about 98% of their assimilated energy in metabolism and only about 2% in secondary production. Poikilotherms convert about 44% of their assimilated energy to secondary production. However, homeotherms have a much higher assimilation efficiency. Assimilation efficiency A/I = assimilation to consumption or ingestion (I) An index of the efficiency of the consumer in extracting energy from the food it consumes. It relates to food quality and effectiveness of digestion. Therefore, poikilotherms have to consume more to obtain sufficient energy for maintenance, growth, and reproduction. o Production efficiency-the ratio of production to assimilation, P/A. This is an index of the efficiency of a consumer in incorporating assimilation energy into new tissue (growth), or secondary production. It reflects the relative balance of the energy allocation to production and respiration. o Production to consumption (P/I)-this index reflect how much energy consumed by the animal is converted into production and is a measure of the efficiency with which energy is made available to the next group of consumers. o Homeotherms use about 98 percent of their assimilated energy in metabolism and only about 2 percent in secondary production. Poikilotherms convert about 44 percent of their assimilated energy to secondary production. However, homeotherms have a much higher assimilation efficiency. Assimilation Efficiency and Production Efficiency For Homeotherms and Poikilotherms All All Efficiency Homeotherms Poikilotherms Assimilation A/I 77.5+/-6.4 41.9+/-2.3 Production P/A 2.46+/-0.46 44.6+/-2.1 P/I 2.0+/-0.46 17.7+/-1.0 A/I=assimilation to consumption or ingestion, an index of the efficiency of the consumer in extracting energy from the food it consumes. It relates to food quality and effectiveness of digestion. P/A= production to assimilation, P/A, an index of the efficiency of a consumer in incorporating assimilation energy into new tissue. P/I= production to consumption, a measure of the efficiency with which energy is made available to the next group of consumers. The ability of the consumer population to use the energy it ingests varies with the type of consumer and the species, as shown in this table. Homeotherms use about 98 percent of their assimilated energy in metabolism and only about 2 percent in secondary production. Poikilotherms convert about 44 percent of their assimilated energy to secondary production. They turn a greater proportion of their assimilated energy (A) into biomass (P). However, there is a major difference in assimilation efficiencies between the two: poikilotherms have an efficiency of about 42 percent and homeotherms over 70 percent. Therefore, the poikilotherm has to consume more calories to obtain sufficient energy for maintenance, growth, and reproduction. Consumer Efficiency (Secondary Production/ Secondary Consumption) Growing PRODUCERS HERBIVORES CARNIVORES Season Efficiency Efficiency Efficiency Habitat (days) Production (%) Production (%) Production (%) Shortgrass plains 206 3.767 0.8 53 11.9 6 13.2 Midgrass prairie 200 3.591 0.9 127 16.5 37 23.7 Tallgrass prairie 275 5.022 0.9 162 5.3 15 13.9 A wide range of conversion efficiencies exists among various feeding groups, as suggested in this table. Production efficiency in plants (net productivity/light absorbed) is low, ranging from 0.34 percent in some phytoplankton to 0.8 to 0.9 percent in grassland vegetation. • Herbivores use plant production with varying degrees of efficiency • • - depending on whether they are poikilotherms or homeotherms. • • Because they eat foods already converted to animal tissue, carnivores, both poikilothermic and homeothermic, have high assimilation efficiencies. • • On North American midwestern grasslands, average herbivore production efficiency, involving mostly poikilotherms, ranges from 5 – 16%; • • carnivores have production efficiencies ranging from 13 - 24 %. • Food Chains and Energy Flow Energy stored by plants is passed along through the ecosystem in a series of steps of eating and being eaten known as a food chain. Feeding relationships within a food chain are defined in terms of trophic or consumer levels. o oAt the first level are the primary producers, oAt the second level are the herbivores, oAnd the higher levels are the carnivores. o o Some consumers occupy a single trophic level while others, such as omnivores, occupy more than one trophic level. Food Chains and Energy Flow • Energy stored by plants is passed along through the ecosystem in a series of steps of eating and being eaten known as a food chain. Feeding relationships within a food chain are defined in terms of trophic or consumer levels. o From a functional rather than a species view, all organisms that obtain their energy in the same number of steps from the autotrophs belong to the same trophic level. o At the first level are the primary producers, at the second level are the herbivores, and the higher levels are the carnivores. Some consumers occupy a single trophic level while others, such as omnivores, occupy more than one trophic level. o Food chains are descriptive with major feeding groups defined on the basis of a common source of energy. Each feeding group is then linked to others in a manner that represents the flow of energy. There are two basic types of food chains: o o grazing (autotrophs are the primary source of energy for the initial consumers) and o detrital (the initial consumers, primarily bacteria and fungi, use dead organic matter as their source of energy). o Food chains are descriptive with major feeding groups defined on the basis of a common source of energy. Each feeding group is then linked to others in a manner that represents the flow of energy. o There are two basic types of food chains: grazing (autotrophs are the primary source of energy for the initial consumers) and detrital (the initial consumers, primarily bacteria and fungi, use dead organic matter as their source of energy). o In terrestrial systems, only a small portion of primary production goes by way of the grazing food chain. o In terrestrial and littoral ecosystems, the detrital food chain is the major pathway of energy flow. In a yellow poplar forest, 50 percent of gross primary productivity goes into maintenance and respiration, 13 percent is accumulated as new tissue, 2 percent is consumed by herbivores, and 35 percent goes into the detrital food chain. oIn terrestrial systems, only a small portion of primary production goes by way of the grazing food chain. o In terrestrial and littoral ecosystems, the detrital food chain is the major pathway of energy flow. o e.g. In a yellow poplar forest, 50% of gross primary productivity goes into maintenance and respiration, -13% is accumulated as new tissue, -2% is consumed by herbivores, and -35% percent goes into the detrital food chain. o Food chains are descriptive with major feeding groups defined on the basis of a common source of energy. Each feeding group is then linked to others in a manner that represents the flow of energy. o There are two basic types of food chains: grazing (autotrophs are the primary source of energy for the initial consumers) and detrital (the initial consumers, primarily bacteria and fungi, use dead organic matter as their source of energy). o In terrestrial systems, only a small portion of primary production goes by way of the grazing food chain. o In terrestrial and littoral ecosystems, the detrital food chain is the major pathway of energy flow. In a yellow poplar forest, 50 percent of gross primary productivity goes into maintenance and respiration, 13 percent is accumulated as new tissue, 2 percent is consumed by herbivores, and 35 percent goes into the detrital food chain. fig24 Within any ecosystem there are two major food chains, the grazing food chain and the detrital food chain. The two food chains are distinguished by their source of energy or food for the initial consumers. In grazing ecosystem, autotrophs, or living plant tissues, are the primary source of energy for the initial consumers. In the detrital food chain, the initial consumers, primarily bacterial and fungi, use dead organic matter, detritus, as their source of energy. fig24 Golley (1960) worked out a grazing food chain for old-field vegetation, meadow mice, and weasels. The mice are almost exclusively herbivorous and the weasels live mainly on mice. The vegetation converts about 1 percent of the solar energy into net production, or plant tissue. The mice consume about 2 percent of the plant food available to them, and the weasels about 31 percent of the mice. Of the energy assimilated, the plants lose about 15 percent through respiration, the mice 68 percent, and the weasels 93 percent. The weasels use so much of their assimilated energy in maintenance that a carnivore preying on weasels could not exist. • In a very general way, energy transformed through the ecosystem by way of the grazing food chain is reduced by a magnitude of 10 from one level to another. • • Thus if an average of 1000 kcal of plant energy is consumed by herbivores, • • about 100 kcal is converted to herbivore tissue, • • 10 kcal to first-level carnivore production, and • • 1 kcal to second-level carnivores. • • The amount of energy available to second- and third-level carnivores is so small that few organisms could be supported if they depended on that source alone. • • For all practical purposes, each food chain has from three to four links, rarely five. The fifth link is distinctly a luxury item in the ecosystem. • The sun is the original source of energy (100,000 units of energy) Plants capture <1% of the available light energy for biomass production by photosynthesis (1,000 units of energy) Herbivores consume about 10% of the plant biomass produced (100 units of energy) Carnivores capture and consume about 10-15% of the energy stored by herbivores (10 units of energy) so01038_ na01441_ an01125_ AN00058_ In a very general way, energy transformed through the ecosystem by way of the grazing food chain is reduced by a magnitude of 10 from one level to another. Thus if an average of 1000 kcal of plant energy is consumed by herbivores, about 100 kcal is converted to herbivore tissue, 10 kcal to first-level carnivore production, and 1 kcal to second-level carnivores. The amount of energy available to second- and third-level carnivores is so small that few organisms could be supported if they depended on that source alone. For all practical purposes, each food chain has from three to four links, rarely five. The fifth link is distinctly a luxury item in the ecosystem. FG14_22 FG14_24 o The grazing and detrital food chains are linked, with the initial source of energy for the decomposer food chain being the input of waste material and dead organic matter from the grazing food chain. o The main difference between the two food chains is that the flow of energy between trophic levels in the grazing food chain is unidirectional, with net primary production providing the energy source for herbivores, herbivores providing the energy for carnivores, and so forth. o o In the decomposer food chain, the flow of energy is not unidirectional; the waste materials and detritus in each of the consumer trophic levels are recycled, returning as input to the detritus box at the base of the food chain. o The grazing and detrital food chains are linked, with the initial source of energy for the decomposer food chain being the input of waste material and dead organic matter from the grazing food chain. o The main difference between the two food chains is that the flow of energy between trophic levels in the grazing food chain is unidirectional, with net primary production providing the energy source for herbivores, herbivores providing the energy for carnivores, and so forth. In the decomposer food chain, the flow of energy is not unidirectional; the waste materials and detritus in each of the consumer trophic levels are recycled, returning as input to the detritus box at the base of the food chain. fig24 The two major food chains, grazer and detrital, are combined here to produce a generalized model of trophic structure and energy flow through an ecosystem. The two food chains are linked, with the initial source of energy for the decomposer food chain being the input of waste material and dead organic matter from the grazing food chain, indicated as a series of arrows from each of the trophic levels in the grazing food chain going toward the box designated as detritus (dead organic matter). There is one notable difference in the flow of energy between trophic levels in the grazing and decomposer food chains: in the grazing food chain the flow is unidirectional, with net primary production providing the energy source for herbivores, herbivores providing the energy for carnivores, and so forth. In the decomposer food chain, the flow of energy is not unidirectional. The waste materials and detritus in each of the consumer trophic levels are recycled, returning as an input to the detritus box at the base of the food chain. In addition to the flow of detritus and waste materials from the grazer to the decomposer food chains, these two food chains are also interconnected via the process of predation. In addition to breaking down dead organic matter, decomposer organisms are also food to numerous other animals. A recap… For herbivores, food is plentiful, but the diet is constrained by low protein levels and the relative indigestibility of cellulose in plant material. Adaptations in herbivores are related to increasing the digestion and assimilation of plant materials. • Carnivores are usually not constrained by diet quality, but by obtaining sufficient amounts of food through the capture of elusive prey. Adaptations in carnivores are generally related to increasing success of prey capture. • For herbivores, food is plentiful, but the diet is constrained by low protein levels and the relative indigestibility of cellulose in plant material. Adaptations in herbivores are related to increasing the digestion and assimilation of plant materials. • Carnivores are usually not constrained by diet quality, but by obtaining sufficient amounts of food through the capture of elusive prey. Adaptations in carnivores are generally related to increasing success of prey capture. The relative importance of the two food chains and the rate at which energy flows through the various trophic levels can vary widely among different types of ecosystems. • The concept of trophic levels has several weaknesses: o It discounts detrital material, decomposers, and saprophages (the detrital food chain). o Consumers, especially above the herbivore level, often occupy more than one trophic level and their contribution to biomass must be apportioned. o The concept does not take into account the availability of energy — all the energy at any level is not available to consumers. o The concept gives the false impression that energy does not cycle through ecosystems. • The relative importance of the two food chains and the rate at which energy flows through the various trophic levels can vary widely among different types of ecosystems. • The concept of trophic levels has several weaknesses: o It discounts detrital material, decomposers, and saprophages (the detrital food chain). o Consumers, especially above the herbivore level, often occupy more than one trophic level and their contribution to biomass must be apportioned. o The concept does not take into account the availability of energy—all the energy at any level is not available to consumers. o The concept give the false impression that energy does not cycle through ecosystems. A comparison of energy flow through four distinct ecosystem types is presented in these figures. The relative size of each box represents the amount of energy in each trophic level of the food chain, and the arrows represent the relative flow of energy between trophic levels. The open water ecosystem and associated phytoplankton community have the highest consumption efficiency (proportion of NPP consumed), with the grazing food chain playing a greater role in energy flow than in the other three ecosystem types. In terrestrial ecosystems, the grazing food chain is much more important in grassland than in forest ecosystems. In forest ecosystems, the vast majority of net primary productivity is not consumed as living tissues by herbivores; rather, it is stored as woody standing crop biomass that eventually makes its way to the detrital food chain as dead organic matter. Stream ecosystems have extremely low net primary productivity, and the grazing food chain is minor. The detrital food chain dominates and depends on inputs of dead organic matter from adjacent terrestrial ecosystems. [USEMAP] BIOGEOCHEMISTRY: NUTRIENT CYCLING • The living world depends on the flow of energy and the circulation of matter through ecosystems. Both influence the abundance of organisms, the rate of their metabolism, and the complexity and structure of the ecosystem. • Energy and matter flow through the ecosystem together as organic matter; one cannot be separated from the other. The link between energy and matter begins in the process of photosynthesis. Biogeochemical Cycles • Biogeochemical cycles-chemical exchanges of elements among the atmosphere, rocks of the Earth’s crust, water, and living things. BIOGEOCHEMISTRY: NUTRIENT CYCLING • The living world depends on the flow of energy and the circulation of matter through ecosystems. Both influence the abundance of organisms, the rate of their metabolism, and the complexity and structure of the ecosystem. • Energy and matter flow through the ecosystem together as organic matter; one cannot be separated from the other. The link between energy and matter begins in the process of photosynthesis. Biogeochemical Cycles • Biogeochemical cycles-chemical exchanges of elements among the atmosphere, rocks of the Earth’s crust, water, and living things. The interrelationship between nutrient cycling and energy flow in the ecosystem. The living world depends on the flow of energy and the circulation of matter through ecosystems. Both influence the abundance of organisms, the rate of their metabolism, and the complexity and structure of the ecosystem. Energy and matter flow through the ecosystem together as organic matter; one cannot be separated from the other. The link between energy and matter begins in the process of photosynthesis. Organic matter, the tissues of plants and animals, is composed not only of carbon, but a variety of essential nutrients, as outlined in the first lesson and Chapter 3 of the text. Because of this link between energy and matter, the general model of energy flow through an ecosystem presented in the last chapter (25) provides a basic framework for examining the flow of matter through ecosystems. • There are two types of biogeochemical cycles based on the primary source of the nutrient input to the ecosystem: o Gaseous cycles-the main source of nutrients possessing a gaseous cycle are the atmosphere and ocean and, therefore, have global circulation patterns. o Sedimentary cycles-the main reservoirs of nutrients are the soil and the rocks of the Earth’s crust. Sedimentary cycles vary from one element to another, but essentially each has two abiotic phases: the salt solution phase and the rock phase. When in the soluble salt phase, unless absorbed by plants the nutrients can move through the soil into lakes and streams and eventually to the seas, where they can remain indefinitely. • There are two types of biogeochemical cycles based on the primary source of the nutrient input to the ecosystem: o Gaseous cycles-the main source of nutrients possessing a gaseous cycle are the atmosphere and ocean and, therefore, have global circulation patterns. o Sedimentary cycles-the main reservoirs of nutrients are the soil and the rocks of the Earth’s crust. Sedimentary cycles vary from one element to another, but essentially each has two abiotic phases: the salt solution phase and the rock phase. When in the soluble salt phase, unless absorbed by plants the nutrients can move through the soil into lakes and streams and eventually to the seas, where they can remain indefinitely. o Although all of the cycles of the various nutrients vary in detail, from the perspective of the ecosystem, they all have a common structure, sharing three basic components: inputs, internal cycling, and outputs. o The rate of internal cycling of nutrients depends on the rates of primary productivity and decomposition which, in turn, are affected by climate (faster in warmer and wetter climates), the number and type of organisms in the ecosystem, and availability of nutrients. o Nutrients can be lost (outputs) from the ecosystem to the atmosphere, by the migration of organisms, water flow, and harvesting. o Although all of the cycles of the various nutrients vary in detail, from the perspective of the ecosystem, they all have a common structure, sharing three basic components: inputs, internal cycling, and outputs. o The rate of internal cycling of nutrients depends on the rates of primary productivity and decomposition which, in turn, are affected by climate (faster in warmer and wetter climates), the number and type of organisms in the ecosystem, and availability of nutrients. o Nutrients can be lost (outputs) from the ecosystem to the atmosphere, by the migration of organisms, water flow, and harvesting. § MODEL OF NUTRIENT CYCLES A generalized model of nutrient cycling in a terrestrial ecosystem. The three common components of inputs, internal cycling and outputs are shown in bold. The key ecosystem processes of net productivity and decomposition are italicized. Although the biogeochemical cycles of the various essential nutrients required by autotrophs and heterotrophs differ in detail, for the perspective of the ecosystem, all biogeochemical cycles have a common structure, sharing three basic components: inputs, internal cycling, and outputs. • Internal cycling The cycle of 134Cs in white oak, an example of the pathways of nutrients through plants. Primary productivity in ecosystems depends on the uptake of essential mineral (inorganic) nutrients by plants and their incorporation into living tissues. Nutrients in organic form, stored in living tissues, represent a significant proportion of the total nutrient pool in most ecosystems. As these living tissues senesce, the nutrients are returned to the soil or sediments in the form of dead organic matter. Various microbial decomposers transform the organic nutrients into a mineral form, a process called mineralization (see Chapter 9), and the nutrients are once again available to the plants for uptake and incorporation into new tissues. This process is called internal cycling and is an essential feature of all ecosystems. It represents a recycling of nutrients within the ecosystem. Weatherspoon et al. (1961, 1964) demonstrated how internal cycling works in a study using radioisotopes of elements to quantify the cycling of nutrients through the ecosystem. Cesium behaves like potassium, is highly mobile, cycles rapidly in an ionic form, and is easily leached from plant surfaces by rain. About 40 percent of the 134Cs inoculated into the white oaks in April moved into the leaves in early June. Leaching from the leaves began when the first rains fell. By September, this loss amounted to 13 percent of the maximum concentration in the leaves. Seventy percent of this rainwater loss reached the mineral soil; the remaining 30 percent found its way into the litter and understory. When the leaves fell in autumn, they carried twice as much radiocesium as had leached from the crown. Over the winter, half was leached to the mineral soil where 92 percent remained in the upper 10 cm nearly two years after inoculation. Eight percent was confined to an area within the crown perimeter, and 19 percent was located in a small area about the trunk. In spring, cesium retained over winter in the wood and minimal transfers from the soil moved back into the leaves. Influence of (a) root nitrogen uptake on leaf nitrogen concentrations and (b) leaf nitrogen concentrations on maximum observed rates of net photosynthesis for a variety of species from differing habitats. • Ecosystem processes influencing the rate of nutrient cycling Cycling of nutrients through the ecosystem depends on the processes of primary productivity and decomposition. Primary productivity determines the rate of nutrient transfer from inorganic to organic form (nutrient uptake), and decomposition determines the rate of transformation of organic nutrients into inorganic form (nutrient release). Therefore, the rates at which nutrients are cycled will be directly related to the rates at which these two processes occur. These two processes interact to limit the rate of internal cycling of nutrients through their interdependence. These two figures show the direct link between soil nitrogen availability, rate of nitrogen uptake by plant roots, and the resulting leaf nitrogen concentrations. The maximum rate of photosynthesis is strongly correlated with leaf nitrogen concentrations, because a large portion of leaf nitrogen is contained within compounds directly involved in photosynthesis. The availability of nitrogen in the soil will therefore directly affect rates of ecosystem primary productivity via its influence on photosynthesis and carbon uptake. Reduced productivity results in reduced input of dead organic matter, and its associated nitrogen, to the decomposers. Since the rate of decomposition and nitrogen mineralization are directly related to both quantity and quality of organic matter, the lower nutrient concentrations in the dead organic matter promote immobilization of nutrients from the soil and water to meet the nutrient demands of the decomposers. This immobilization further reduces nutrient availability to the plants, adversely affecting primary productivity and dead organic matter production in the future. Feedback that occurs between nutrient availability, net primary productivity, and nutrient release in decomposition for initial conditions of low and high nutrient availability. The previous discussion is an illustration of the feedback system that exists in internal cycling of nutrients within an ecosystem. Reduced nutrient availability can have the combined effect of reducing both the nutrient concentration of plant tissues and net primary productivity. This reduction lowers the total amount of nutrients returned to the soil in dead organic matter. The reduced quantity and quality of organic matter entering the decomposer food chain increases immobilization and reduces the availability of nutrients for uptake by plants. In effect, low nutrient availability begets low nutrient availability. Conversely, high nutrient availability encourages high plant tissue concentrations and high net primary productivity. In turn, the associated high quantity and quality of dead organic matter encourages high rates of net mineralization and nutrient supply in the soil. Comparison of nitrate production following logging for a loblolly pine plantation in the southeastern U.S. Data for the reference stand (no harvest) are compared with those of a whole-tree harvest clear-cut. The removal of trees in clearcutting and other silvicultural (forest management) practices increases the amount of radiation (including direct sunlight) reaching the soil surface. The resulting increase in soil temperature promotes decomposition and results in an increase in net mineralization rates. Temporal changes in the nitrate concentration of streamwater for two forested watersheds in Hubbard Brook, New Hampshire. The forest on one watershed was clear cut, while the other remained undisturbed. Note the large increase in concentrations of nitrate in the stream on the clear cut watershed. This increase is due to increased decomposition and nitrogen mineralization following the removal of the trees. The nitrogen was then leached into the surface and groundwater. This increase in nutrient availability in the soil occurs at the same time that demand for nutrients is low because plants have been removed and net primary productivity is low. As a result, there is a dramatic increase in the leaching of nutrients from the ecosystem in surface waters. This export of nutrients from the ecosystem results from decoupling the two processes of nutrient release in decomposition and nutrient uptake in net primary productivity. Nutrient Cycling in Terrestrial versus Aquatic Systems • In virtually all ecosystems there is a vertical separation between zones of production and decomposition. In terrestrial ecosystems, the plants themselves bridge this physical separation. • In aquatic systems this is not always the case. Here, the vertical structure of the aquatic system forms a warm, low-density surface layer of water (epilimnion) on top of a denser, cold layer of deep water (hypolimnion) separated by a rather thin zone of the thermocline (metalimnion). The deeper layer is nutrient rich, but cannot support high productivity while the surface layer is nutrient poor and can support high productivity. o Nutrient replenishment to the surface layer occurs through a process of turnover where the surface waters become cooler than the deeper waters, resulting in a breakdown of the thermocline and a mixing of the water column. o Although all of the cycles of the various nutrients vary in detail, from the perspective of the ecosystem, they all have a common structure, sharing three basic components: inputs, internal cycling, and outputs. o The rate of internal cycling of nutrients depends on the rates of primary productivity and decomposition which, in turn, are affected by climate (faster in warmer and wetter climates), the number and type of organisms in the ecosystem, and availability of nutrients. o Nutrients can be lost (outputs) from the ecosystem to the atmosphere, by the migration of organisms, water flow, and harvesting. § CONTRASTING NUTRIENT CYCLING IN TERRESTRIAL AND AQUATIC ECOSYSTEMS Comparison of the vertical zones of production and decomposition in (a) a terrestrial (forest) and (b) an open water (lake) ecosystem. Note that in the forest ecosystem the two zones are linked by the vegetation. This is not the case in the lake ecosystem. The process of nutrient cycling is an essential feature of all ecosystems and represents a direct (cyclic) link between net primary productivity and decomposition. However, the nature of this link varies among ecosystems, particularly between terrestrial and aquatic ecosystems. In virtually all ecosystems there is a vertical separation between the zones of production (photosynthesis) and decomposition, as shown in this illustration. In terrestrial ecosystems (a), the plants themselves bridge this physical separation between the zone of decomposition at the soil surface and the zone of productivity in the plant canopy—the plants physically exist in both zones. The root systems provide access to the nutrients made available in the soil through decomposition, and the vascular system within the plant transports these nutrients to the sites of production. In aquatic systems, this is not always the case. In shallow water environments of the shoreline, emergent vegetation such as cattails, cordgrasses, and sedges are rooted in the sediments. Here, as in terrestrial ecosystems, the zone of decomposition and production are linked directly by the plants. Likewise, submerged vegetation, such as seagrasses and kelps, is rooted in the sediments with the plants extending up the water column into the photic zone, the shallower waters where light levels support higher productivity (b). However, as water depth increases, primary production is dominated by free-floating phytoplankton, which migrates vertically within the upper waters (photic zone). Here exists a physical separation between the zones of decomposition in the bottom, or benthic zone, and the surface waters where temperatures and light availability support primary productivity. This physical separation between where nutrients become available through decomposition and the zone of productivity where nutrients are needed to support photosynthesis and plant growth is a major factor controlling the productivity of open water ecosystems. Seasonal dynamics in the vertical structure of an open water ecosystem in the Temperate Zone. (a) Winds mix the waters within the epilimnion during the summer, but the thermocline isolates this mixing to the surface waters. (b) Turnover occurs during the winter months with the breakdown of the thermocline, allowing mixing and nutrients flow to the surface from the epilimnion. Although winds blowing over the water surface cause turbulence that mixes the waters of the epilimnion, this mixing does not extend into the colder, deeper waters because of the thermocline. As autumn and winter approach in the temperate and polar zones, the amount of solar radiation reaching the surface decreases and the temperature of the surface water declines. As the water temperature of the epilimnion approaches that of the hypolimnion, the thermocline breaks down and mixing throughout the profile can take place. If surface waters become cooler than the deeper waters, they will begin to sink, displacing deep waters to the surface. This process is called turnover. With the breakdown of the thermocline and mixing of the water column, nutrients are brought up from the bottom to the surface waters. With the onset of spring, increasing temperatures and light in the epilimnion give rise to a peak in productivity with the increased availability of nutrients in the surface waters. As the spring and summer progress, the nutrients in the surface water are used, reducing the nutrient content of the water, and a subsequent decline in productivity occurs. Seasonal dynamics of: (a) the thermocline and associated changes in (b) the availability of light and nutrients, and (c) net primary productivity of the surface waters. The resulting annual cycle of productivity in these ecosystems is a direct function of the dynamics of the thermocline and the resulting behavior of the vertical distribution of nutrients. The Carbon Cycle • The source of all fixed carbon is carbon dioxide found in the atmosphere and dissolved in water. • Carbon is assimilated by photosynthesis and the flow of carbon through an ecosystem is essentially the flow of energy. In fact, measurement of productivity is commonly expressed in terms of grams of carbon fixed per m2 per year. • The concentration of carbon dioxide in the atmosphere around plants fluctuates throughout the day and seasonally. • Carbon dioxide is fixed by plants, passed through the food chain, and returned to the atmosphere and water through respiration and decomposition. • Similar cycling occurs in aquatic environments but carbon dioxide is found as a dissolved gas—bicarbonate at pH of 4.3 to 8.3 or carbonate at pH above 8.3. The Carbon Cycle • The source of all fixed carbon is carbon dioxide found in the atmosphere and dissolved in water. • Carbon is assimilated by photosynthesis and the flow of carbon through an ecosystem is essentially the flow of energy. In fact, measurement of productivity is commonly expressed in terms of grams of carbon fixed per m^2 per year. • The concentration of carbon dioxide in the atmosphere around plants fluctuates throughout the day and seasonally. • Carbon dioxide is fixed by plants, passed through the food chain, and returned to the atmosphere and water through respiration and decomposition. • Similar cycling occurs in aquatic environments but carbon dioxide is found as a dissolved gas—bicarbonate at pH of 4.3 to 8.3 or carbonate at pH above 8.3. • The Carbon Cycle Although the main reservoir is the gas CO2, considerable quantities are tied up in organic and inorganic compounds of carbon in the biosphere. Because it is a basic constituent of all organic compounds and a major element in the fixation of energy by photosynthesis, carbon is so closely tied to energy flow that the two are inseparable. In fact, the measurement of productivity is commonly expressed in terms of grams of carbon fixed per square meter per year. The source of all fixed carbon is carbon dioxide, found in the atmosphere and dissolved in water. To trace its cycling through the ecosystem is to redescribe photosynthesis and energy flow, as shown in this diagram. The cycling of carbon dioxide involves assimilation by plants and conversion to glucose. From glucose, plants synthesize polysaccharides, proteins, and fat and store them in the form of plant tissue. When digesting plant tissue, herbivores synthesize these compounds into other carbon compounds. Meat-eating animals feed on herbivores, and the carbon compounds are redigested and resythesized into other forms. Some of the carbon is returned directly by both plants and animals in the form of CO[2] as a by-product of respiration. The remainder for a time becomes incorporated in the living biomass. Assorted decomposer organisms release carbon contained in animal following death. The rate of release depends on environmental conditions such as soil moisture, temperature, and precipitation. Similar cycling occurs in freshwater and marine environments. Carbon dioxide diffuses into the upper layers of water according to equilibrium reactions that depend on pH. At pH <4.3 most carbon dioxide is found as a dissolved gas, between 4.3 and 8.3 as bicarbonate (HCO[3]^-), and >8.3 as carbonate (CO[3]^2-). Together these forms are called dissolved inorganic carbon (DIC). Phytoplankton utilizes the dissolved inorganic carbon and converts it into carbohydrates. The carbohydrates so produced pass through the aquatic food chains. Plankton are consumed by zooplankton, and eventually all are consumed by decomposers. The carbon dioxide produced by respiration is reutilized by the phytoplankton in the production of more carbohydrates. The Nitrogen Cycle • Nitrogen is an essential constituent of protein and is a major component of the atmosphere (79 percent). However, in its gaseous state, it is unavailable to most life and must be converted to a usable form. • The nitrogen cycle consists of four processes: o Fixation is the conversion of nitrogen in its gaseous state to a usable form. High energy fixation by lightning or occasionally cosmic radiation converts N2 to ammonia (NH3). Biological fixation by mutualistic bacteria living in association with leguminous and root-nodulated nonleguminous plants, by free living bacteria, and by cyanobacteria (blue-green algae) accounts for roughly 90 percent of the fixed nitrogen contributed to Earth each year. The Nitrogen Cycle • Nitrogen is an essential constituent of protein and is a major component of the atmosphere (79 percent). However, in its gaseous state, it is unavailable to most life and must be converted to a usable form. • The nitrogen cycle consists of four processes: o Fixation is the conversion of nitrogen in its gaseous state to a usable form. High energy fixation by lightning or occasionally cosmic radiation converts N[2] to ammonia (NH[3]). Biological fixation by mutualistic bacteria living in association with leguminous and root-nodulated nonleguminous plants, by free living bacteria, and by cyanobacteria (blue-green algae) accounts for roughly 90 percent of the fixed nitrogen contributed to Earth each year. oMineralization or ammonification, the conversion of amino acids in organic matter to ammonia. In this process, proteins in dead plant and animal material are broken down by bacteria and fungi to amino acids. The amino acids are oxidized to carbon dioxide, water, and ammonia, with a yield of energy. Ammonia, or the ammonia ion, is absorbed directly by plant roots, incorporated into amino acids, and passed through the food chain. oNitrification is a biological process which oxidizes ammonia to nitrites and nitrates yielding energy. This process involves Nitrosomonas or Nitrobacter bacteria. oMineralization or ammonification, the conversion of amino acids in organic matter to ammonia. In this process, proteins in dead plant and animal material are broken down by bacteria and fungi to amino acids. The amino acids are oxidized to carbon dioxide, water, and ammonia, with a yield of energy. Ammonia, or the ammonia ion, is absorbed directly by plant roots, incorporated into amino acids, and passed through the food chain. oNitrification is a biological process which oxidizes ammonia to nitrites and nitrates yielding energy. This process involves Nitrosomonas or Nitrobacter bacteria. o Denitrification is also a biological process that reduces nitrates to gaseous nitrogen to obtain oxygen. The denitrifiers, represented by fungi and the bacteria Pseudomonas, are facultative anaerobes. They prefer an oxygenated environment, but if oxygen is limited, they can use NO3- instead of O2 as the hydrogen acceptor. In doing so they release N2 in the gaseous state as a by-product. • Most of the nitrogen cycle is driven by microbes. o Denitrification is also a biological process that reduces nitrates to gaseous nitrogen to obtain oxygen. The denitrifiers, represented by fungi and the bacteria Pseudomonas, are facultative anaerobes. They prefer an oxygenated environment, but if oxygen is limited, they can use NO[3]^- instead of O[2] as the hydrogen acceptor. In doing so they release N[2] in the gaseous state as a by-product. • Most of the nitrogen cycle is driven by microbes. • The Nitrogen Cycle The bacterial process involved in nitrogen cycling. The width of each arrow is an approximation of the process rate. Nitrogen is an essential constituent of protein, a building block of all living material. It is also a major constituent, about 79 percent, of the atmosphere. The paradox is that in it gaseous state, nitrogen is unavailable to most life. It must be converted to some chemically usable form. Getting it into that form makes up a major part of the nitrogen cycle. The nitrogen cycle, showing major sources, compartments, and processes. The nitrogen cycle consists of four processes. 1. Fixation is the conversion of nitrogen in its gaseous state to a usable form. High energy fixation by lightning or occasionally cosmic radiation converts N2 to ammonia (NH3). Estimates suggest that less than 35 mg N/ha/yr arrives on Earth by this method. Biological fixation by mutualistic bacteria living in association with leguminous and root-nodulated nonleguminous plants, by free living bacteria, and by cyanobacteria (blue-green algae) accounts for roughly 90 percent of the fixed nitrogen contributed to Earth each year (about 1.4 to 7.0 kg N/ha/yr in natural ecosystems). 2. Mineralization or ammonification, the conversion of amino acids in organic matter to ammonia. In this process, proteins in dead plant and animal material are broken down by bacteria and fungi to amino acids. The amino acids are oxidized to carbon dioxide, water, and ammonia, with a yield of energy. Ammonia, or the ammonia ion, is absorbed directly by plant roots, incorporated into amino acids, and passed through the food chain. 3. Nitrification is a biological process which oxidizes ammonia to nitrites and nitrates yielding energy. This process involves Nitrosomonas or Nitrobacter bacteria. 4. Denitrification is also a biological process that reduces nitrates to gaseous nitrogen to obtain oxygen. The denitrifiers, represented by fungi and bacteria Pseudomonas, are facultative anaerobes. They prefer an oxygenated environment, but if oxygen is limited, they can use NO[3]^- instead of O[2] as the hydrogen acceptor. In doing so they release N[2] in the gaseous state as a by-product. Most of the nitrogen cycle is driven by microbes. The Sulfur Cycle • Sulfur has a long-term sedimentary phase tied up in organic (coal, oil, and peat) and inorganic (pyritic rocks and sulfur deposits) form. It is released by weathering of rocks, erosional runoff, decomposition of organic matter, and industrial production and carried to terrestrial and aquatic ecosystems in a salt solution. • The bulk of sulfur first appears in gaseous phase as hydrogen sulfide in the atmosphere from the combustion of fossil fuels, volcanic eruptions, and gasses released in decomposition. It is quickly oxidized into sulfur dioxide where it is carried back to Earth in rainwater as weak sulfuric acid. • Oceans are another source of gaseous sulfur where dimethysulfide is produced during the decomposition of phytoplankton. The Sulfur Cycle • Sulfur has a long-term sedimentary phase tied up in organic (coal, oil, and peat) and inorganic (pyritic rocks and sulfur deposits) form. It is released by weathering of rocks, erosional runoff, decomposition of organic matter, and industrial production and carried to terrestrial and aquatic ecosystems in a salt solution. • The bulk of sulfur first appears in gaseous phase as hydrogen sulfide in the atmosphere from the combustion of fossil fuels, volcanic eruptions, and gasses released in decomposition. It is quickly oxidized into sulfur dioxide where it is carried back to Earth in rainwater as weak sulfuric acid. • Oceans are another source of gaseous sulfur where dimethysulfide is produced during the decomposition of phytoplankton. • Sulfur is taken up by plants and incorporated into amino acids such as cysteine. From the producers, the sulfur in amino acids is transferred to consumers and ultimately back to the soil and the bottoms of aquatic habitats. • Sulfur, in the presence of iron and under anaerobic conditions, will precipitate as ferrous sulfide, a highly insoluble compound under neutral and alkaline conditions. It is firmly held in mud and wet soil. • Sulfur is taken up by plants and incorporated into amino acids such as cysteine. From the producers, the sulfur in amino acids is transferred to consumers and ultimately back to the soil and the bottoms of aquatic habitats. • Sulfur, in the presence of iron and under anaerobic conditions, will precipitate as ferrous sulfide, a highly insoluble compound under neutral and alkaline conditions. It is firmly held in mud and wet soil. • The Sulfur Cycle The sulfur cycle. Note the two components, sedimentary and gaseous. Sulfur has a long-term sedimentary phase, in which it is tied up in organic material (coal, oil, and peat) and inorganic form (pyritic rocks and sulfur deposits). Sulfur is released by the weathering of rocks, erosional runoff, decompositon of organic matter, and industrial production, and it is carried to terrestrial and aquatic ecosystems in a salt solution. However, the bulk of sulfur first appears in the gaseous phase as a volatile gas, hydrogen sulfide (H[2]S), in the atmosphere. Hydrogen sulfide comes from several sources: the combustion of fossil fuels, volcanic eruptions, and gasses released in terrestrial and aquatic decomposition. It quickly oxidizes into another volatile form, sulfur dioxide (SO[2]). Atmospheric sulfur dioxide, soluble in water, is carried back to Earth in rainwater as weak sulfuric acid (H[2]SO[4]). The oceans are another source of gaseous sulfur, dimethylsulfide [(CH[3])[2]S]. Dimethylsulfide (DMS) is produced during the decomposition of phytoplankton. The majority of DMS is degraded by microbes in the surface waters. Although only a small percentage of the total production in DMS is lost to the atmosphere, recent estimates suggest it constitutes the largest atmospheric emission of sulfur gas. In the atmosphere, DMS is rapidly oxidized by OH radicals, forming sulfate aerosols that are deposited in rainfall. Whatever the source, sulfur in soluble form is taken up by plants and incorporated through a series of metabolic processes, beginning with photosynthesis, into such sulfur-bearing amino acids as cysteine. From the producers, the sulfur in amino acids is transferred to consumers. Excretions and death carry sulfur in living material back to the soil and to the bottoms of ponds, lakes, and seas, where sulfur-reducing bacteria release it as hydrogen sulfide or as a sulfate. Other microorganisms in the forest soil convert inorganic sulfate to organic forms and incorporate it into forest ecosystems. Sulfur, in the presence of iron and under anaerobic conditions, will precipitate as ferrous sulfide (FeS[2]). This compound is highly insoluble under neutral and alkaline conditions and is firmly held in mud and wet soil. The Phosphorus Cycle • Phosphorus occurs only in very minute amounts in the atmosphere and none of its known compounds have an appreciable vapor pressure. • The main reservoirs of phosphorus are rock (especially the mineral apatite) and natural phosphate deposits, from which the element is released by weathering, leaching, erosion, and mining for agricultural use. • Some of the phosphorus passes through terrestrial and aquatic ecosystems as organic phosphorus from plants to grazers, predators, and parasites. It is returned to the ecosystem by excretion, death and decay. • In terrestrial ecosystems, organic phosphates are reduced by bacteria to inorganic phosphates. The Phosphorus Cycle • Phosphorus occurs only in very minute amounts in the atmosphere and none of its known compounds have an appreciable vapor pressure. • The main reservoirs of phosphorus are rock (especially the mineral apatite) and natural phosphate deposits, from which the element is released by weathering, leaching, erosion, and mining for agricultural use. • Some of the phosphorus passes through terrestrial and aquatic ecosystems as organic phosphorus from plants to grazers, predators, and parasites. It is returned to the ecosystem by excretion, death and decay. • In terrestrial ecosystems, organic phosphates are reduced by bacteria to inorganic phosphates. • The Phosphorus Cycle The phosphorus cycle in terrestrial and aquatic ecosystems. Phosphorus, unlike sulfur, occurs in only very minute amounts in the atmosphere, and none of its known compounds have an appreciable vapor pressure. Therefore, the phosphorus cycle can follow the hydrological cycle only partway, from land to sea. Under undisturbed natural conditions the source of phosphorus in the soil is the mineral apatite, a phosphate of calcium. Phosphorus also occurs in secondary forms as compounds of calcium and iron, and in organic combination. Under the best of conditions, the amount of available phosphorus is small. Phosphates are freely soluble only in acid solutions and under reducing conditions. Its natural limitation in aquatic ecosystems is emphasized by the explosive growth of algae in water with heavy discharges of phosphorus-rich wastes. The main reservoirs of phosphorus in the biosphere are rock and natural phosphate deposits, from which the element is released by weathering, by leaching, by erosion, and by mining for agricultural use. Some of it passes through terrestrial and aquatic ecosystems as organic phosphorus by the way of plants, grazers, predators, and parasites; and it is returned to the ecosystem by excretion, death and decay. In terrestrial ecosystems, organic phosphates are reduced by bacteria to inorganic phosphates. Some are recycled to plants, some become unavailable in chemical compounds, and some are immobilized in microorganisms. Some of the phosphorus of terrestrial ecosystems escapes to lakes and seas, both as organic phosphates and as particulate organic matter. In marine and freshwater systems, the phosphorus cycle involves three major fractions: (1) particulate organic phosphorus (POP), which includes phosphorus contained in both dead particulate matter and phytoplankton; (2) dissolved inorganic phosphates (DIP), mostly soluble orthophosphate that comes from various sources, both aquatic and terrestrial; (3) dissolved organic phosphorus (DOP), which is excreted by organisms, especially zooplankton. In most aquatic environments, particulate phosphorus is in greatest abundance, followed by DIP and then DOP. Uptake by primary producers and bacteria is responsible for the low phosphate concentrations typical of surface waters. Phosphorus in phytoplankton may be ingested by zooplankton or by detritus-feeding organisms as dead organic matter. The principal means of regenerating DIP is by the decay of POP and by animals. Zooplankton may excrete as much phosphorus daily as is stored in its biomass. By excreting phosphorus, zooplankton is instrumental in keeping the aquatic cycle going. More than half of the phosphorus zooplankton excretes is DIP, which is taken up by phytoplankton. The remainder of the phosphorus in aquatic ecosystems is in organic forms (DOP). These are utilized by bacteria, which fail to regenerate much dissolved inorganic phosphate (DIP) themselves. Instead, the bacteria are eaten by microbial grazers, who then excrete the phosphate they ingest. Part of the phosphorus in aquatic ecosystems is deposited in deep and shallow sediments. Precipitated largely as calcium compounds, much of it becomes stored for long periods of time in bottom sediments. In marine ecosystems, seasonal overturns and upwellings return some of the phosphorus to surface waters, where it is available to phytoplankton. During the growing season, much of the phosphorus is tied up in organic matter, and only by a rapid turnover in its populations can phytoplankton meet its phosphorus requirements. Linkages among Biogeochemical Cycles • All of the biogeochemical cycles are linked in various ways. o They may be linked through common membership in compounds that form an important component of their cycles, such as the link between calcium and phosphorus in the mineral apatite. o In general, they all travel together through the process of internal cycling because they are all components of living organisms. o Because of the specific quantitative relationships among the various elements involved in the processes related to carbon uptake and plant growth, the limitation of one nutrient can affect the cycling of all the others. Linkages among Biogeochemical Cycles • All of the biogeochemical cycles are linked in various ways. o They may be linked through common membership in compounds that form an important component of their cycles, such as the link between calcium and phosphorus in the mineral apatite. o In general, they all travel together through the process of internal cycling because they are all components of living organisms. o Because of the specific quantitative relationships among the various elements involved in the processes related to carbon uptake and plant growth, the limitation of one nutrient can affect the cycling of all the others.