Predation – what is it?Predation – what is it?

One animal kills another for food

( + - interaction )

One animal kills another for food

( + - interaction )

Parasitism / ParasitoidismParasitism / Parasitoidism

HerbivoryHerbivory

Any ecological process in which energy and matter flow from one species to another.

Any ecological process in which energy and matter flow from one species to another.

PredationPredation

One organism consumes another in the classic “+ -” interaction:

carnivore herbivore

parasite / parasitoid (virus, bacteria, etc)

‘cannibalism’

One organism consumes another in the classic “+ -” interaction:

carnivore herbivore

parasite / parasitoid (virus, bacteria, etc)

‘cannibalism’

Why do we care?Why do we care?

1. Predation can act as a force to structure communities.1. Predation can act as a force to structure communities.

2. Predation can act as a mechanism for natural selection.2. Predation can act as a mechanism for natural selection.

3. Predation can control species distribution or density.3. Predation can control species distribution or density.

Keystone predatorKeystone predator

RegulationRegulation

Trophic cascadesTrophic cascades

Lotka-Volterra: classic 2-species model

Primary AssumptionsPrimary Assumptions

● all individuals represented by the average● all individuals represented by the average

● linear relationship between predator and prey● linear relationship between predator and prey

● no time lag in response● no time lag in response

● exponential growth, no K● exponential growth, no K

(Begon et al. 1996 p. 118)

RealityReality

Gause 1934 – rotifer vs. protist Gause 1934 – rotifer vs. protist

unmanipulatedunmanipulated

prey refuge addedprey refuge added

“immigration”“immigration”

Huffaker 1958 – mites and oranges Huffaker 1958 – mites and oranges

Initial results – similar to Gause, simple systems

were incapable of sustaining coexistence

Initial results – similar to Gause, simple systems

were incapable of sustaining coexistence

Coexistence was only possible with extreme

environmental heterogeneity

“hide and seek”

Coexistence was only possible with extreme

environmental heterogeneity

“hide and seek”

Eotetranychus sexmaculatusvs.

Typhlodromus occidentalis

Adding reality to model predictions: C.S. Holling 1959

Adding reality to model predictions: C.S. Holling 1959

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III IV

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Prey density

2 types of predator response:2 types of predator response:

2. Numerical: Increase in the total number of predators

- reproduction- aggregation

2. Numerical: Increase in the total number of predators

- reproduction- aggregation

1. Functional: Change in the rate of predation by an individual predator - ‘search image’ - ‘prey switching’

1. Functional: Change in the rate of predation by an individual predator - ‘search image’ - ‘prey switching’

Holling 1959 Holling 1959

2 types of predators:2 types of predators:

GeneralistsGeneralists SpecialistsSpecialists

Krebs et al. 2001

Specialist numerical response:Specialist numerical response:

Quick reviewQuick review

Simple dynamics (L-V) predicts a steady cycle

This cannot be re-created empirically without interference by the investigator

In reality, we observe a wide variety of dynamics

- cycles - stability- extinction - chaos- periodic fluctuations

Simple dynamics (L-V) predicts a steady cycle

This cannot be re-created empirically without interference by the investigator

In reality, we observe a wide variety of dynamics

- cycles - stability- extinction - chaos- periodic fluctuations

What factors control whether predator/prey interactions are stable?

What factors control whether predator/prey interactions are stable?

StabilizingStabilizing

Factors influencing stabilityFactors influencing stability

DestabilizingDestabilizing

Type III functional response

RefugiaRefugiaGeneralist predatorGeneralist predator

Low predator efficiencyLow predator efficiency

Complex systems multiple predator spp. multiple prey spp. prey switching

Complex systems multiple predator spp. multiple prey spp. prey switching

Time lags Time lags

Specialist predatorSpecialist predator

High predator efficiencyHigh predator efficiency

Simple systemsSimple systems

SummarySummary

● Factors that influence coexistence:predator efficiency, system complexityrefugia, time lags

● Factors that influence coexistence:predator efficiency, system complexityrefugia, time lags

● Predation involves energy and matter flowing from one species into another (+ -).● Predation involves energy and matter flowing from one species into another (+ -).

● Holling’s Type I, II, III curves● Holling’s Type I, II, III curves

● Generalist vs. specialist, numerical vs. functional● Generalist vs. specialist, numerical vs. functional

● Predation can: act as an agent of selectionstructure communitiesregulate populations

● Predation can: act as an agent of selectionstructure communitiesregulate populations