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)
oligophagous (few prey types)
polyphagous/euryphagous (many prey
types)
- not capable of consuming all prey types
predators choose most profitable prey
- select prey items for which the gain is
greatest (energy intake per time spent
handling)
Krebs (1978)
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 )
- 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)