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1

Behavioural Ecology

Behavioural Ecological increases our understanding of how biotic factors influence distribution/abundance of organisms

2


Consumer-Resource Interactions

Fitness depends on an individual’s ability to grow, survive, & reproduce – Require:
• Suitable environmental conditions (abiotic factors) • Sufficient resources
– Acquire appropriate quantities of energy
– Acquire energy efficiently (gain > loss)

Behavioural strategies of foraging have evolved under these pressures to maximize fitness

3

predation

=consumption of prey by a predator, where the prey is alive when attacked
A number of important questions...
• Where to feed?
• What to feed on?
• How are predators affected by the density of their prey?
– Help us understand:
• How has natural selection favoured particular behavioural
patterns?
• How does predator behaviour influence the size of predator
and prey populations?

4

Effects of Prey Density on Predator Behaviour

Functional Response

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functional response

the relationship between prey density and predator consumption rate
-3 types

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consumption rate depends on

1. prey abundance per unit area
(prey density) – all prey species
2. search efficiency for prey
(search time, s)
3. time to pursue, subdue & ingest prey
(handling time, h)

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Type I

• Rarely observed
• search time varies with prey density
• handing time is constant but near zero
Eg. passive predators (spiders, filter feeders, herbivores)
- occurs if prey densities do not become high enough for As prey density ^, encounter rates ^, search time \/

8

Type II

• Most common
• search time varies with prey density
• handling time is constant
→ Predator consumption rate levels off at high prey densities
As prey density ^, search time \/ because easier to find prey (s >> h)
As prey density ^^, search time is zero but handling remains constant (h >> s)

9

Type III

• Rarely observed
• search time and handling time vary with prey density
→ Predator consumption rate is lower at low prey densities
At low prey density, search time ↑ and handling time ↑ (=pursue, subdue & ingest prey)

10

Why do handling and searching time increase at low prey densities?


not enough prey encounters to learn high capture efficiency
- prey switching
- high availability of cover for prey (refuge) at low densities

11

prey switching

switch to a more abundant prey type

12

What to feed on?

-specialist
-generalist

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– Specialist

an individual takes one or a few prey types

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Generalist

an individual takes many prey types

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Preference

proportion of a prey type in the diet is higher than in the environment

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Preferences will depend on:

• Energy content of prey
• Nutritional content of prey (eg. vitamins, minerals)

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Preferences can be switched

Switch may depend on the abundance of different prey types

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Foraging Theory goal

predict the optimal (or best) foraging strategy under certain conditions – basedonmathematicalmodelsderivedfromeconomics
– offersapowerfulwaytounderstandforagingdecisionsofpredators

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Foraging Theory assumptions

– Foraging behaviour enhances fitness (ie. a foraging strategy = a behavioural trait

favoured by natural selection in the past) Animalsmaximizenetenergygain(ensureshighfitness)
• Predators must expend energy to obtain prey – Energy loss: searching & handling time
– Energy gain: consumption
– profitability depends on: energy gain - energy loss (= net energy)

20

Diet Model

Specialist – energy lost searching ~ consume more profitable prey
Generalist – consume less profitable prey ~ low energy searching


Strategies have similar net energy gain under different environmental conditions... predators switch between these two strategies depending on conditions

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diet model decision

Should a predator expand its diet to include the next most profitable prey item (preytypei)? (specialist→generalist)
Examine this question by quantifying net energy gain of each prey type... Assume the predator has encountered prey type i

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diet model optimal strategy

- pursue prey type i when:
net energy of prey type i > of current diet
- ignore prey type i when:
net energy of current diet > of prey type i
Investigate situations where prey items have different search + handling times (components of energy loss)...

23

Diet Model – Predictions

1. If Searching time >> Handling time → Generalists
 A predator should consume all prey types when overall prey abundance is low
 Predators should be generalists in an unproductive environment
2. If Handling time >> Searching time → Specialists
Eg. Lions
• Live in constant sight of prey
– Searching is negligible
– Handling is time-consuming
Expect lions to be specialists and only take the highest quality prey

24

Does this model predict foraging strategies
observed in nature?

• Underlying model assumptions:
– Predators know everything about their foraging environment
– Predators perform complex mathematics to determine the profitabilities of a variety
of prey types
• We should not expect a perfect match
– Model predicts: Individuals that approach the optimal strategy will have higher
fitness
• Predators may use “general rules”
Eg. take the less profitable prey type after searching for a fixed amount of time

• Predators may not maximize net energy gain
Eg. take a less profitable prey type with a specific dietary requirement – nutrient,
vitamin
• Predators may minimize their own risk of predation
Eg. take a less profitable prey type to avoid foraging near a predator