Stano Pekár“Populační ekologie živočichů“
 dN
= Nr
dt
True predators - catch several animals and gain sustenance for their
own fitness (spiders, lions)
Parasitoids - consume about single host, free adults but larvae
developing on or within a host, consuming it prior to pupation
(Hymenoptera, Diptera)
Parasites - live in close association with a host, gain sustenance
from the host, but often do not cause mortality (Acari, Trematodes)
Herbivores - feed on plants, may totally consume plants (seedeaters)
or partially (aphids, cows)
 monophagous (single prey type), stenophagous (few prey types)
 oligophagous (more prey types)
 polyphagous/euryphagous (many prey types)
- not capable of consuming all prey types
 type can based on taxonomy, size, sex,
ontogenetic stage
 predators choose most profitable prey
- select prey items for which the gain is
greatest (energy intake per time spent
handling)
Krebs (1978)
 Ecological context – stenophagy vs. euryphagy/polyphagy
 Evolutionary context – generalist vs. specialist
Euryphagous
generalist
Stenophagous
generalist
Euryphagous
specialist
Stenophagous
specialist
Pekár & Toft (2015)
Ecological dimension
Evolutionary
dimension
 predators tend to specialise to a greater or lesser extent during evolution
- monophagy evolved where prey is abundant and exerts pressures which
demands adaptations (e.g. morphological, behavioural, metabolic)
- polyphagy evolved where prey was unpredictable
 true predators - majority are polyphagous
 parasites - commonly monophagous due to intimate association with
hosts, their life-cycle is tuned to that of their host
 parasitoids - often monophagous but some are polyphagous presumably
because adults are free living
 herbivores - rather polyphagous, many insect herbivores
are specialised as a result of adaptation to plant
secondary metabolites (Drosophila pachea consumes
rotten tissues of Senita cactus which contain poisonous
alkaloids)
 even polyphagous predators prefer certain prey
- constant preference irrespective of prey density
- switching to more common prey
Thais preferred Mytilus edulis over M.
californianus
Murdoch & Oaten (1975)
Murton et al. (1964)
Seasonal shift in Columba
 predation has positive effect on population of prey because reduce
intraspecific competition - stabilise prey population dynamic
 true predators and parasitoids reduce fitness of individual prey to „0“
- Mustela consumed mainly solitary and injured individuals, so it has
little effect on the Ondatra population growth
 caterpillars defoliate partially so
that re-growth can occur, but cause
reduction in fertility
 parasites - reduce fitness partially,
effect is correlated with the burden
Negative effect of mite
parasites on Hydrometra
Lanciani (1975)
 mortality of prey increases with the prey density due to predation
Total response of a predator is composed of:
- individual response to changing prey density  functional response
- population response to changing desnity of prey  numerical response
 Holling (1959) found that predation rate of individual predator
increased with increasing prey density
- defined three types of functional responses
- more types were defined later
Type I
 number of captured prey is proportional to density
- prey mortality is constant
 less common
 found in passive predators (web-building spiders)
 the handling time exerts its effect suddenly
Daphnia feeding on Saccharomyces - above 105 cells
Daphnia is unable to swallow all food
Rigler (1961)
Type II
 predators cause maximum mortality at low prey density
 as prey density increases, search becomes trivial and handling takes up
increasing portion of the time
 saturation (due to handling) of predation at high densities
- prey mortality declines with density
Thompson (1975)
Ischnura eating Daphnia
Type III
 when attack rate increases or handling time decreases with increasing
density
 predators develop search image (e.g. respond to kairomones)
 polyphagous predators switch to the most abundant prey
- prey mortality increases then declines
Notonecta switched from Cleon to Asellus
based on its abundance
Lawton et al. (1974)
T .. total time
TS .. searching time - searching for prey
TH .. handling time - handling prey (chasing, killing, eating, digesting)
H .. prey density
Ha .. number of captured prey
a .. capture efficiency or “search rate”
Type I
 consumption rate of a predator is unlimited
 TH = 0 so
Sa aHTH 
HS TTT 
STT 
Type II
 consumption rate of a predator is limited because even if no time is
needed for search, predator still needs to spend time on prey handling
 TH > 0 so
predator captures Ha prey during T
Th .. time spent on handling 1 prey
at low density predator spends most
of the time searching, at high
density on prey handling
haH THT 
aH
H
TaHTH a
SSa 
aH
H
THTTT a
haSH 
h
a
aHT
aHT
H


1
HS TTT 
n
h
n
a
HaT
aTH
H


1
Type III
 consumption increases at low densities and decreases at higher
densities
n .. rate of increased consumption at higher densities
if n = 1  Type II
a .. rate of increase at low densities
H
Ha
T/Th
a
0
n
Increase of predator population may result from:
 increased rate of reproduction
- the more prey is consumed the more energy can predator allocate to
reproduction
- delayed response
 parasitoids - one host is sufficient
 predators, herbivores, parasites
- certain quantity of prey tissue is required
for basic maintenance = lower threshold
Growth rate in Linyphia
Turnbull (1962)
 conversion of prey into predator numbers (P):
f .. conversion efficiency
d .. mortality of predators
 Ivlev (1955) model
V .. amount of prey
a .. search rate
f .. conversion efficiency
d .. mortality of predators
H
rp
0
dear fV
 
)1(
dPfaHP
t
P

d
d
 attraction of predators to prey aggregations
- immediate response
- aggregated distribution makes search of predators more profitable
 instead of concentration on profitable patches
perspective predators and prey may play “hide-and-seek”
 Huffaker (1958): Typhlodromus captured Eotetranychus
that fed upon oranges
- Eotetranychus maintained fluctuating density
- addition of Typhlodromus led to extinction of both
Experimental setup Eotetranychus population dynamic Predator-prey dynamic
 making environment patchy
- by placing Vaseline barriers
- facilitating dispersal by adding sticks
 each patch was unstable but whole microcosmos was stable
- patch with prey only  rapid increase of prey
- patches with predators only  rapid death of predator
- patches with both  predator consumed prey
Sustained oscillations of the predator-prey systemAltered experimental setup
Refuge
 For fixed proportion of prey - certain proportion
of Ephestia caterpillars buried deep enough in flour
are not attacked by Venturia with short ovipositors
 For fixed number of prey
- adult Balanus occur in the upper zone
where Thais can not get during short high
tide thus consumes only juveniles
- a fixed number of Balanus is protected
from predation irrespective of Thais density
both refuge types stabilise the interaction
Connell (1970)