PREDATIONPREDATION

• One of the least well developed areas of ecological theory

• Management problems occur with a lack of information– Biological data on predators and prey– Explanation of the Ecosystem

PREDATORSPREDATORS• Change in feeding behavior of individual

predators to different prey densities

– Functional Response

• Response of predator population through reproduction, immigration, and emigration

– Numerical Response

Functional ResponsesFunctional Responses

Type l Type ll Type lll

Prey Density

Pre

dato

r D

ensi

ty

Pre

dato

r D

ensi

ty

Pre

dato

r D

ensi

ty

Prey Density Prey Density

prey switching

DEFINITIONSDEFINITIONS

• PREY SWITCHING– Changing preference toward the more

abundant prey.– Ignoring rare prey– Concentrating search in more rewarding

areas– Any of these behaviors result in:

Type III Functional Response

PREDATIONPREDATION

• Population Models are uniquely related to predator-prey dynamics – ½ equation – Density Dependence

• Place where prey are most vulnerable to predation, predators have the least effect.– At K– Low population density prey are in good

condition and more dispersed. – Predators have have greatest effect, but prey

are least vulnerable in body condition.

Population Model of PreyPopulation Model of PreyR

ecru

itmen

t R

ate

Population Size (N) Nt

Nt+

1

Steepness of the line Size of “hump” above no growth line

Potential to be resilient to offtake by a predator

N

Predator PitsPredator Pits

Nt

Nt+1

Losses to predators

K

No Predators in System

Equilibrium

Equilibrium

Functional responseFunctional response

• Prey live in small patches of high density and low density in between

• Clumped distribution

• Predators concentrate on areas of high density

• Predators may have a regulating effect on prey numbers

Numerical responseNumerical response

• Trend of predator numbers against prey numbers

• Predators increase as prey density increases• Increased rate of predator reproduction when

prey are abundant• Numerical response

• Attraction of predators to prey aggregations• Aggregational response (short term)• immigration

Numerical responseNumerical response

• Reproduction and mortality rate of predators depends on predation rate

• More prey, more energy• Predator numbers increase to an asymptote

– determined by interference

• Interference such as territoriality can cause reduction or stabilization of predators.– High density: 20% adult wolves, 50% juveniles

disperse

Total responseTotal response• Total number eaten = number eaten by one

predator multiplied by number of predators• Can be plotted as Total response curves• Need to also incorporate recruitment rate of

prey• Different types of curves indicate different

types of relationships– Predators regulate prey population– Prey regulated by intraspecific competition for food– Multiple stable states

Population CyclesPopulation Cycles

• Strongest representation at high latitude

• Specialist predator

• Lynx - hare cycle

• Weasel – microtine cycle

• Red grouse – possibly gut nematodes.

Mid-16th century, Archbishop of Uppsala, Sweden published 2 reports on cyclic fluctuations of northern small rodents.

In early 1900s, wildlife biologists analyzed the fur trading records of the Hudson’s Bay Company, including those for the Canadian lynx.

POPULATION CYCLES

•Period is amount of time it takes population to go through complete cycle.

•Amplitude can be defined as difference between maximum population size and population size at midpoint, but some researchers refer to peak-to-trough amplitudes.

•In general, periods tend to be fairly consistent for a particular cyclic population, whereas amplitudes are more variable.

Population CyclesPopulation Cycles

Behavior of preyBehavior of prey

• How does the behavior of the prey influence predation?

• Migration

• Herding and spacing

• Birth synchrony

MigrationMigrationIf a prey species can migrate beyond the range of its

predators the population can escape predator regulation

Predators have slow growing young and are restricted to a small area to breed

Ungulates have precocial young that can move within a few hours

Thus prey follow food resource, predators cannot

Herding and spacingHerding and spacing

• Animals reduce risk of predation by forming groups– Group size predicted to increase with increasing

predator densities– Group size increases with distance from cover– More animals in group, more vigilance of groups, less

per individual.

• Can also leave group when most vulnerable– Leave group when give birth as predators are

concentrated around herds

Birth synchronyBirth synchrony

• Synchronize births to reduce predation rate

• Predator swamping

• Also influenced by seasonal availability of resources

Conservation and managementConservation and management

• Predator and prey populations usually coexist– Prey at low density by regulation– Prey at high density by intraspecific competition for

food.

• Both systems can operate in one area– Type III functional response or density-dependent

numerical response– Disturbance moves from one state to other– Explains outbreaks of pest species, decline of hunted

species

Conservation and managementConservation and management

• Prey population can become extinct– Type II response with no prey refuge, no alternative

prey– Important in management where there are habitat

changes– Small populations or exotics

• Which situation occurs depends on – Ability of predator to catch prey– Ability of prey to escape predation– Reproduction