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Behavioural Ecology

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


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



=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
• How does predator behaviour influence the size of predator
and prey populations?


Effects of Prey Density on Predator Behaviour

Functional Response


functional response

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


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)


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 \/


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)


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)


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


prey switching

switch to a more abundant prey type


What to feed on?



– Specialist

an individual takes one or a few prey types



an individual takes many prey types



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


Preferences will depend on:

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


Preferences can be switched

Switch may depend on the abundance of different prey types


Foraging Theory goal

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


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)


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


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


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)...


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


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
• 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,
• Predators may minimize their own risk of predation
Eg. take a less profitable prey type to avoid foraging near a predator