Topic 5: Foraging

Question 1

What are some of the questions we ask when observing animals foraging behaviours?

Answer 1

• What to eat (body size and food types)
• What is the optimal foraging choices?
• Where to eat? (Optimal foraging theory and margin value theorem
• How do animals learn in terms of foraging?

Question 2

What is the biological determinant of diet choice? Is size the main component?

Answer 2

• Energy is the main determinant for food choice
• The energy you need to consume is directly related to the amount of energy you emit, and your need to maintain a constant internal temperature (homeostasis)
• the energy you need to maintain homeostasis is used to combat heat loss to environment, which is determined by surface area ratio (skin:core)
• if you are larger, this means you have less surface area for your volume, and are better at conserving energy/heat.
• ex. Gorillas eat leaves, low energy foods, while hummingbirds eat saps and sugars, high energy foods.

Question 3

High quality food has _________ abundance and distribution

low quality foods have ___________ abundance and distribution

Answer 3

High quality food have low abundance and distribution

low quality foods have high abundance and distribution

Question 4

What is optimal foraging theory?

Answer 4

• a subset of evolutionary theory, principles of natural selection to predict details of foraging behaviour
• cost benefit analysis on the best ways to forage, with a maximum energy return, and a minimum energy expenditure

Question 5

What are the four ‘levels’ of optimal foraging theory?

Answer 5

1. maximize rate food patches are encountered
2. optimize rate of intake within patches
3. optimize food choices within patches
4. optimize processing of food

Question 6

What is the horn model?

Answer 6

• The horn model predicts that if food is uniform and predictable, than animals will live in small groups or on their own (because food is not hard to obtain - reduce in competition)
• however, if food is clumped and unpredictable, animals will living in large groups in larger spaces (this will increase size of search and so increase encounter rate, reduces the chance of empty patches)

Question 7

Do groups cause a foraging problem? Are there any other benefits to living in groups?

Answer 7

• In general, with group living there is intra-group food competition
• as group size increases, food intake decreases
• as groups size decreases, food size increases
• however, with group living, also comes reduced predation risk.

Question 8

What are some ways to maximize the rate of food patches that are encountered?

Answer 8

• foraging optimally by living in a group
• visiting patches optimally (good spatial navigation)

Question 9

Give an example on how group size may become detrimental to the group of animals (horn model)

Answer 9

• Sunfish!
• sunfish forage in groups, and the amount of prey they can eat per minute is connected to group size
• it was found that each fish maximizes its fish intake with a group number of 4-5
• if in groups of 6+, intra-group food competition is too high, sunfish will fight over food, and prey captures per minute plumets

Question 10

How can having good spatial navigation maximize the rate of food patches encountered?

Answer 10

• good spatial navigation = visiting patches optimally = maximizes the rate of food patches encountered
• by knowing your area, and recognizing visual cues on home territory, this can lessen energy loss to capture food and bring it back home.
• ex. If given landmark cues, (ex pinecones), beewolf wasps will follow the cues to their nest. And even after the cues are moved, they will follow them.

Question 11

What is marginal value theorem?

Answer 11

• determines the optimal rate of food intake
• connects travel time, net gain, and patch type together to determine this
• determines when is the best time for an animal to move between patches

Question 12

At what point should an animal move between food patches? (MVT)

Answer 12

that animals should leave the current patch when the energy intake rate within the patch diminishes to the average energy-harvesting rate in the environment

Question 13

What are the three main aspects of marginal value theorem?

Answer 13

1. Stay in a patch until your average food intake falls below daily average
2. the greater the distance/time between patches, the longer you should stay in a patch
3. You should stay longer in a poor quality patch, than a good quality patch (increase the ratio of travel cost to foraging benefit)

Question 14

Do animals actually do marginal value theorem? give an example

Answer 14

• Sometimes!
• in lab experiments with great tits, used a metal tree with pots, each with varying amount of mealworms.
• the ‘travel time’ was how hard it was to open the pot
• The harder it was to remove the lid, the more time they spent at the pot.

Question 15

How do animals choose their prey, if there are multiple types of prey, or prey of varying size? examples

Answer 15

• they will choose which ever prey gives them maximum energy return, and a minimum energy expenditure
• Will choose prey that allow them to spend less energy to capture, even if this choice of prey doesn’t have the highest reward
• ex. Oyster catcher birds. OFT predicted they would go for the largest oysters, as they have the most energy gain. But OFT did not take into account that the largest oysters were not as profitable, as they were heavier to carry, and harder to crack open. Oyster birds instead ate more medium sizes oysters.

Question 16

If animals are given options for food- at the same time- in varying degrees of density and size, what should they choose?

Answer 16

In an example done with great tits, when given equal proportions of large and small prey, they will feed on them equally. However in any other scenario with differing densities, they almost always exclusively chose large prey- even if it was less abundant than small prey.

Question 17

How will animals maximize the difference between benefits provided and costs invested if food needs to be processed? example

Answer 17

• Try to maximize the size/density of prey while minimizing the energy it takes to process and consume the food
• ex. Crows eating whelks. Crows would drop whelks from 5ft in the air to crack and break them open, but would have to drop them multiple times. They would not drop high than 5 ft. Why?- if dropped too high, the whelks would shatter, and the food would be scattered everywhere, and attract food competitors.
• So would maximize the whelk size (energy benefits) while minimizing vertical flight energy costs, to open whelk, and minimize the “shatter scatter”

Question 18

What is an example of animals using tools to process their food?

Answer 18

• Brown Capuchin monkeys use stone rocks to open palm nuts that are very hard to open.
• high reward food, rely on the dense calories when little other food is available
• they learn this behavior from other capuchins, what size of stone, what kind of surface to break it on, and how to tell when the nut has a crack in the shell- so they don’t use unnecessary energy to continuously smash it.

Question 19

What is a major issue with optimal foraging theory? example?

Answer 19

• because it is a mathematical model- it doesn’t take into account other factors that may influence animals foraging behaviors, like environment or predators
• ex. Dugong’s have 2 types of foraging methods, cropping which simply strips leaves off vegetation, has low caloric value, and excavation, which is where they dig down and eat everything, including the root and is much higher in calories.
• OFT predicts that Dugongs should almost exclusively excavate, but in reality, they don’t, as it creates a lot of dust, and have their head down, so they can’t look for predators.
• the time spent excavating was less when there were a higher proportion of sharks in the area

Question 20

Does social learning effect foraging? example

Answer 20

• yes!
• in an experiment with pigeons in lab, they were made to complete a simple task (peck a hole thru paper) to get a food reward
• in 4 different scenarios, experimental pigeons would watch a model pigeon either do nothing, completed the task but got no food, get food from a preexisting hole, or complete the process to get food, the pigeons would learn how to complete the task to get food.
• the pigeons who were able to watch the complete demonstration (ol model) where the fastest to complete the puzzle, while those that did not have a model pigeon to watch were never able to complete the puzzle.