PredationPredation

• Competition (intra- and inter-) involve interactions between same trophic level

• Predation involves interactions between trophic levels

• One species negatively effects the other• Very important for management goals

– Conservation– Control– Harvesting

Types of predationTypes of predation

• Herbivory– Animals prey on green plants– Death of plant not usual

• Parasitism– Usually don’t kill host

• Carnivory– Predator kills and eats prey

• Cannibalism– Predator and prey same species

Predator behavior and prey Predator behavior and prey survivalsurvival

• Herbivores gain nutrition from plants– Have to deal with plant defenses – chemical and physical

• Must also avoid predators– Protective shapes and coloration– Active defense– Alertness and swiftness– Protective cover– morphology

• Predators must catch prey– Speed, agility, claws, teeth, smell, vision, etc

PredationPredation

• Many different techniques

• Normally involves large investment of time and effort per unit food

• Usually target physically weakened or in a vulnerable place

• Typically 4.5 to 10.8 % capture success

• e.g. 124 moose, 7% success rate by wolves

PredationPredation• Often select prey by

oddity– Color– Behavior– Location

PredationPredation

• Conspicuousness and crypsis

PredationPredation• Conspicuousness and crypsis

• Prey change behavior in absence of predators

PredationPredation

• Conspicuousness and crypsis

• Prey change behavior in absence of predators

• Marginal habitat

Effect of predators on prey Effect of predators on prey densitydensity

CATEGORY LOCATION DENSITY PER KM2

PREDATORS ABSENT Slate islands 4-8

Norway 3-4

Newfoundland 8-9

South Georgia 2

MOUNTAIN-DWELLING Finlayson 0.15

(predator more intense Little Rancheria 0.1

and frequent) Central Alaska 0.2

FOREST-DWELLING Quesnel Lake 0.03

(predation high and Ontario 0.03

constant) Saskatchewan 0.03

Effect of predators on prey Effect of predators on prey densitydensity

• Predator numbers also correlated with prey numbers

• Based on correlations • Are predators keeping prey below food

supply, or killing only those that are malnourished?

• Need to understand the behavior of predators

The behavior of predatorsThe behavior of predators

How do predators respond to:

1. Changes in prey density?

2. Changes in predator density?

3. Differences in the degree of clumping of prey?

Response to changes in prey Response to changes in prey densitydensity

Response of predators to prey depends on:

1. Feeding behavior of individual predators• Functional response

2. Response of the predator population through reproduction, immigration and emigration

• Numerical response

Functional responseFunctional response1. Searches randomly for its prey2. Has an unlimited appetite3. Spends a constant amount of time searching

– Then the number of prey found will increase in direct proportion to prey density

– Type I response

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Functional ResponseFunctional Response

• Assumptions are usually unrealistic• Some predators show an approximation of

a type 1 function response – Reindeer feeding on lichens

• No animal has an unlimited appetite.• Constant search time unlikely• Handling time – more prey eaten per unit

time, more time is taken up with handling and less for searching.

Functional responseFunctional responseNa = (aTtN) / (1 + ahN)

• Type II response

• Number eaten per time increases to an asymptote as prey density increases

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Functional responseFunctional response

• Type III response

• Prey switching

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Functional responseFunctional response

• Success at catching depends on prey density• Predators react to individuals of own species by

dispersing– Territoriality– Eviction

• Interference• Interference reduces the searching efficiency of

the predator as predator density increases• Interference stabilizes predator numbers

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 thereby have a regulating effect on prey numbers

Numerical responseNumerical response

• Trend of predator numbers against prey numbers

• Predators increase as prey density increases• Due to

1. Increased rate of predator reproduction when prey are abundant

• Numerical response

2. Attraction of predators to prey aggregations• Aggregational response

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

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

Behavior of preyBehavior of prey

• How does the behavior of the prey influence predation?

• Migration

• Herding and spacing

• Birth synchrony

MigrationMigration

• If 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 predators 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

• 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

• Unlikely predation is cause of synchrony, but likely intensifies it.

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 with predation depensatory

• 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

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