Stano Pekár"Populační ekologie živočichů"
dN
= Nr
dt
mortality of prey increases with the prey density due to predation
Total response of a predator
- increasing consumption rate of individual predators  functional
response
- increasing density of predators  numerical response
Holling (1959) found that predation rate increased with increasing prey
population density
- defined three types of functional responses
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 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 respond to kairomones
predators develop search image
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, "area of discovery", or "search rate"
Type I
consumption rate of a predator is unlimited
TH = 0
Sa aHTH =
HS TTT +=
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
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
haHS +=+=
h
a
aHT
aHT
H
+
=
1
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
attraction of predators to prey aggregations
- immediate response
- aggregated distribution makes search
of predators more profitable
conversion of prey into predators
e .. conversion efficiency
d .. mortality of predators
H
rp
0
dPeaHPrp -=
H Ha
5 2.5
10 4
20 7.9
40 9
80 12.6
160 11.6
Minks are kept in large-sized cages (10 m2) individually, different
number of prey (H) was released and after 2 days (T) captured prey was
counted.
1. What type of functional response minks have?
2. Estimate search efficiency (a) and handling time (Th).
h
a
aHT
aHT
H
+
=
1
T
T
HTaH
h
a
+=
111
TTh =

1
=a
xy  +=
H<-c(5,10,20,40,80,160)
Ha<-c(2.5,4,7.9,9,12.6,11.6)
plot(H,Ha)
y<-1/Ha
x<-1/(H*2)
plot(x,y)
lm(y~x)
1/3.38547
0.06446*48