Foraging

Question 1

What is the cost animals pay for moving from patch to patch as the first patch runs out of food?

Answer 1

The cost associated with travelling. Not eating during travel.

Question 2

What is the currency used by most optimal foraging models?

Answer 2

(Energy gained) / (time spent foraging)

ie. rate of energy intake

Question 3

As travel time between patches increases, residence time at each patch ____?_____

Answer 3

As travel time between patches increases, residence time at each patch ‘increases as well’

This idea allows you to quantitatively predict what an animal will do in an area with patches.

Question 4

What is the prey choice model predicting?

Answer 4

Basically deciding ‘what to eat?’

Question 5

What are the three constraints of the prey choice model?

Answer 5

• Energy per item
• Handling time (eg. cracking shell)
• Search time (how long it takes to find that food)

Question 6

If you encounter a hamburger and there are french fries nearby, which one should you eat?

Answer 6

• Eat the hamburger if it’s nearby
• Eat fries if hamburger far away

Eat either hamburger or both hamburger and fries

Question 7

True or false? When a hamburger is common, you eat mostly hamburgers ‘regardless’ of the abundance of french fries

Answer 7

true

Question 8

How does an animal’s internal state determine choice of prey?

Answer 8

Animals optimal choice determined by their state.

For example, animals will take more risk-prone options if they require more than average amount of food (ie. if they’re starving)

Question 9

If you give a hungry stickleback with different densities of food, what do they do? How does this change when a predator (eg. kingfisher) is introduced?

Answer 9

Prefer to go for the higher densities of food. More first attacks at high density foods.

When a kingfisher was present, this was reversed. More first attacks on lower density foods to increase their ability for vigilance.

Question 10

What is search image?

Answer 10

All the various things a predator uses to increase its expectations for seeing patterns (eg. good at seeing symmetry in a busy background to see moths)

Question 11

What is the best way cryptic prey adapt to predator’s search image?

Answer 11

With variance, this prevents predators from linking a conserved pattern.

Question 12

What is aposematism?

Answer 12

Warning coloration that signals to predators that they’re no good to eat.

Question 13

What are the two fundamental models of optimal foraging? What is the driving force for each of these?

Answer 13

• The patch model (diminishing food drives choice)

- The prey choice model (the quality of one food or another and the time/energy it takes to find it drives this model)

Question 14

What are each of these for the patch model:

Decision
Constraints
Currency

Answer 14

Decision: How long to stay in patch

Constraints: The shrinking gain curve and travel time

Currency: Energetic efficiency (ie. E gained/E spent) or rate of energy intake (E gained/time spent)

Question 15

What is the marginal value theorem?

Answer 15

A result of the patch model of optimal foraging.

Predicts how long an animal will stay in a patch (residence time) based on travel time. A line is drawn from 0,0 and tangential to the gain curve. With shorter travel time the line will be steeper and therefore fall shorter on the gain curve (predicting a shorter residence time than if travel time is long)

Question 16

What are each of these for the prey choice model:

Decision
Constraints (3)
Currency

Answer 16

Decision: Prey A or prey B?

Constraints: Energy per item, handling time, search time

Currency: Rate of energy gain (energy of time)/(handling + searching time)

Question 17

For the prey choice model, which food should an animal eat?

Answer 17

Whichever food has the highest rate of energy gain

(energy of item)/(handling + searching time)

Unless there are special circumstances (eg. life and death)

Question 18

How was the prey choice model tested?

Answer 18

An animal given the choice between A or B, A had more energy.

• When both were rare, they were eaten equally
• When B rare and A common, A eaten much more often
• When B common and A common, A eaten much more often (no change from when B rare)

This shows that when food of any type is rare, the animal doesn’t discriminate and eats what it encounters. When a higher energy food item is present, even among an abundance of other lower energy food, it will take the higher energy food more often.

Question 19

How do the prey choice and patch model change when the internal state (needs) change to require:

A) more energy than average
B) less energy than average

Answer 19

A) Less energy needed: be risk averse and take the less variable option where mean payoff is greater than a variable option

B) More energy needed: Be risk-prone and take the variable option where you might get a lot of food or none at all