lecture 7

Question 1

Behavioural Ecology

Answer 1

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

Question 2

Consumer-Resource Interactions

Answer 2

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

Question 3

predation

Answer 3

=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?

Question 4

Effects of Prey Density on Predator Behaviour

Answer 4

Functional Response

Question 5

functional response

Answer 5

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

Question 6

consumption rate depends on

Answer 6

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)

Question 7

Type I

Answer 7

• 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 \/

Question 8

Type II

Answer 8

• 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&raquo_space; h)
As prey density ^^, search time is zero but handling remains constant (h&raquo_space; s)

Question 9

Type III

Answer 9

• 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)

Question 10

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

Answer 10

not enough prey encounters to learn high capture efficiency

• prey switching
• high availability of cover for prey (refuge) at low densities

Question 11

prey switching

Answer 11

switch to a more abundant prey type

Question 12

What to feed on?

Answer 12

• specialist

- generalist

Question 13

– Specialist

Answer 13

an individual takes one or a few prey types

Question 14

Generalist

Answer 14

an individual takes many prey types

Question 15

Preference

Answer 15

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

Question 16

Preferences will depend on:

Answer 16

• Energy content of prey

* Nutritional content of prey (eg. vitamins, minerals)

Question 17

Preferences can be switched

Answer 17

Switch may depend on the abundance of different prey types

Question 18

Foraging Theory goal

Answer 18

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

Question 19

Foraging Theory assumptions

Answer 19

– 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)

Question 20

Diet Model

Answer 20

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

Question 21

diet model decision

Answer 21

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

Question 22

diet model optimal strategy

Answer 22

• 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)…

Question 23

Diet Model – Predictions

Answer 23

1. If Searching time&raquo_space; 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&raquo_space; 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

Question 24

Does this model predict foraging strategies

observed in nature?

Answer 24

• 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