Animal Foraging

Question 1

What must be considered when looking at the prey model?

Answer 1

Competitive exclusion: two species are foraging on a single resource and will compete for access- generally one will be excluded

Question 2

What type of species are more and less at risk when a certain resource becomes scarce?

Answer 2

Highly specialised species are less able to adapt if specialised resources become scarce, e.g koalas and eucalyptus trees

More flexible generalist species are less at risk, e.g brown rat

Question 3

Who created the prey selection model?

Answer 3

MacArthur and Pianka (1966)

Paved the way for a huge body of research based around the principal of optimality

Question 4

What is the currency of fitness?

Answer 4

Often the net rate of energy intake

Question 5

What are the 3 possibilities considered in the prey model?

Answer 5

1. Only take the most profitable prey: increases fitness but longer search time
2. Take all prey encountered: reduced search time but decrease in fitness gain
3. Only take the least profitable prey (obviously not a rational strategy)

Question 6

What are some of the constraints to the prey model?

Answer 6

It implies prey are encountered sequentially- you can’t meet a group of prey

The animal has all necessary info regarding the available prey, encounter rates with each prey type and how profitable each is

Question 7

Give two examples of where the prey model is discredited:

Answer 7

Crab example: Elner and Hughes (1978)
At high density of mussels the crabs did not just take the large mussels, they also took the intermediate

Great tit: krebs et al. (1977) great tit took some smaller mealworms even when the larger ones were in high abundance

Question 8

Who first proposed the patch model and what is it also known as?

Answer 8

Eric Charnov (1976)

Marginal value theorem

Question 9

What is the theory behind the patch model?

Answer 9

As soon as the patch is depleted energy intake starts to decrease

Sooner or later this will reach a critical point or marginal value

At this point it’s better to find another patch than expend energy in the depleted area

Question 10

What is central place foraging?

Answer 10

It’s a variation on the patch model- prey are transported to a central location and at this location food is eaten, fed to young or cached

Question 11

What are the two main features of central place foraging?

Answer 11

1. Loading time: time taken filling beak, pouches etc.

2. Travel time: time spent moving from patch to burrow (included unloading time)

Question 12

What does central place foraging suggest?

Answer 12

As the travel time increases animals should spend a greater time loading up at any given patch of food

Patch richness also affects loading time as animals spend less time searching the patch for food

Question 13

Give an example that supports central place foraging

Answer 13

Eastern chipmunk by Giraldeau and Kramer (1982)

Load size of sunflower seeds increases with distance from the burrow

Question 14

What is a risk when looking at patches and foraging?

Answer 14

Choosing the variable patch

Question 15

What is the cost of social/group foraging and give the two types

Answer 15

Competition

1. Scramble competition: competitors are foraging on the same resource and resource remains depleted- long lived
2. Interference competition: dominant individual or extra individuals scaring off prey- short lived because prey move back after competitor leaves

Question 16

Why join a group?

Answer 16

Predation reduction

More efficient predation strategies- allows them to take larger prey

Question 17

What are the factors that cause predation reduction?

Answer 17

Dilution effect

Selfish herd (shield and hide behind)

Confusion effect

Greater predator detection

Group defensive behaviour towards a predator

Question 18

What is dispersion economy?

Answer 18

To maximise gain individuals in a group must spread out as much as possible

When aggregation occurs it’s due to lack of suitable patches

Question 19

What are the assumptions of the ideal free distribution?

Answer 19

Individuals will move to patch of highest quality (they are ‘free’)

Individuals also know the value of each patch (the knowledge is ‘ideal’)

Competition will reduce the value of the patch

Each individual is equal in ability to exploit patches

Question 20

When is equilibrium reached in ideal free distribution?

Answer 20

When the number of individuals in each patch is such that no benefit will be gained by joining the other group

Question 21

Why are most groups a stable group size rather than an optimal group size?

Answer 21

The group size is more than the optimal number but the payoff is still greater than if they were alone

Question 22

What is the producer/scrounger game?

Answer 22

The producer searches for and consumes food

The scrounger watches and shares their food

Eventually it reaches an equilibrium where there are a certain number of scroungers and producers