Chapter 11- Foraging

Question 1

Flight paths in bats study (Fujioka)

Answer 1

Researchers built a mathematical simulation that allowed them to predict how a foraging bat would behave if it flew along the optimal path to obtain one prey item vs the optimal path to obtain both of 2 prey items. It was found that bats tended to fly along paths that took into account the best way to obtain both food items, rather than just one. Bats that were able to plan ahead were more successful in obtaining both prey items, while bats that just tried to capture the first item usually weren’t successful in capturing the second.

Question 2

Foraging behavior

Answer 2

Searching for and consuming food. Animals spend much of their time foraging

Question 3

Granivores

Answer 3

Animals that eat seeds, nuts, and berries

Question 4

Scavengers

Answer 4

Animals that eat dead animals

Question 5

Search image theory (Tinbergen)

Answer 5

States that when animals encounter a prey type more frequently, they form a representation of that prey type. This representation becomes more detailed with experience, so the animal gets better at finding that type of prey. The search representation could be a representation of the entire prey item, or it could be a salient attribute of the prey.

Question 6

Why did search images evolve?

Answer 6

Probably evolved as a response to the difficulty of finding prey, and to assess what is prey and what’s not

Question 7

Optimal foraging theory

Answer 7

A mathematical model used to predict aspects of animal foraging behavior within a set of constraints. There are multiple types of models

Question 8

3 questions addressed by optimal foraging models

Answer 8

1. What food items should a forager eat?
2. How long should a forager stay in a certain food patch?
3. How does variance in food supply affect a forager’s decision about what food types to eat?

Question 9

Why is deciding what to eat a problem for an animal?

Answer 9

There are many different food items an animal could choose from, so the animal has to decide which items will be in its diet

Question 10

Optimality models of prey choice

Answer 10

Predicting which prey an animal will choose. An animal might have to choose between two different types of food or between 2 different size food items of the same type. The model assumes that foragers will compare the energy value of prey, encounter rate (how often the forager will encounter the prey), and handling time

Question 11

In the optimality model of prey choice, how is profitability of a prey item defined?

Answer 11

Energy divided by handling time. The greater this ratio, the greater the profitability of a prey time

Question 12

The optimality model of prey choice assumes (5)

Answer 12

1. Energy intake from prey can be measured in a standard currency like calories
2. Foragers can’t simultaneously handle one prey item and search for another
3. Prey are recognized instantly and accurately
4. Prey are encountered sequentially
5. Natural selection favors foragers that maximize their rate of energy intake

Question 13

What does the optimality model of prey choice predict an animal will do when deciding to add a second, lower profitability prey item to its diet?

Answer 13

The model predicts that the encounter rate with the second prey type does not effect whether that item should be added to the diet. The model states that there is a critical encounter rate with the other more profitable item. If the encounter rate the predator experiences for prey 1 is above the critical value, only prey 1 is taken. If it’s not above the critical value, both prey 1 and 2 are taken. The critical value is like the limit for the time that is devoted to the encounter rate. Therefore, the decision of whether to take prey 2 depends on the encounter rate for prey 1.

Question 14

Optimal prey choice model in the great tit study (Krebs)

Answer 14

Birds were placed in front of a moving conveyer belt. Researchers used two different sized pieces of mealworm as the two different prey item types. They controlled the rate at which the two prey items were encountered by the birds, the energy provided by the prey, and the handling time associated with the size of the mealworm. They used the model to determine when the birds would take the most profitable prey type vs both prey types. Consistent with the model, it was found that the encounter rate of the most profitable prey determines whether the great tits took the least profitable items

Question 15

Why is determining where to eat a problem for animals?

Answer 15

Animals need to decide how long to stay in one food area if there are other food areas available, and they need to decide how long to spend foraging in one place. Traveling between patches comes with the cost of energy, time, and increased risk of predation.

Question 16

Patch

Answer 16

A clump of food that can be depleted by a forager

Question 17

Marginal value theorem

Answer 17

Makes predictions regarding patch residence time

Question 18

According to the marginal value theorem, how long should a forager stay in a patch?

Answer 18

Until the marginal rate of food intake is equal to that of the average rate of food intake across all patches available. A forager should stay in a patch until the point in time where marginal food intake in the patch to equal to the average amount of food it could get in other patches, given the cost of getting to another patch

Question 19

Marginal rate of food intake

Answer 19

The rate of food intake associated with the next food item in its patch

Question 20

According to the marginal value theorem, what will cause an animal to stay longer in a patch?

Answer 20

1. The greater the time between patches, the longer a forager should stay in a patch. More travel time is a greater cost
2. If patch quality in the environment is poor vs rich. Staying in a poor quality patch makes up the cost of travel because the forager obtained a fixed amount of energy

Question 21

Marginal value theorem in great tits study

Answer 21

A series of artificial trees with multiple branches were built in an aviary. Buckets of mealworms were attached to the branches. Travel time could be manipulated. The amount of time a bird spent in a patch matched the optimal time predicted by the marginal value theorem

Question 22

In which situations can the marginal value theorem be used to calculate optimal patch time?

Answer 22

Whenever a resource depletes as a function of use and costs are associated with traveling between patches of that resources are present. Can be used to predict mate choice/time mating also

Question 23

Risk

Answer 23

Variance in food intake between patches- refers to a greater chance of loss or gain in each patch. Does not refer to actual danger. Risk sensitive foraging models view risk in this sense.

Question 24

3 basic value or utility functions a forager can have, according to risk sensitive foraging models

Answer 24

1. A linear utility function- every food item is valued equally
2. Convex utility function
3. Concave utility function

Question 25

Convex vs concave utility functions in risk sensitive foraging models

Answer 25

In a convex utility function, every additional food item has less value. This is typical of a satiated forager because additional food isn’t really necessary. In a concave utility function, every additional food item is worth more and more to a limit, which is usually the case for a hungry forager

Question 26

Risk sensitive foraging model

Answer 26

Predicts that satiated foragers have a convex utility function and are predicted to be risk averse- they prefer to forage in patches with low variance. Hungry foragers should be risk prone and prefer high variance patches. Foragers with a linear utility function should be indifferent to foraging related variance.

Question 27

Why are foraging environments with high variance favored by hungry animals?

Answer 27

A satiated forager doesn’t view an additional food item as being worth a lot, so it should opt for a consistent food source. A hungry forager might require much more food, and is more likely to take a risk to get more food items because the consistent environment with less food overall won’t be enough to help it survive

Question 28

Foraging behavior in yellow-eyed juncos study

Answer 28

Researchers presented birds with two trays containing birdseed. Once a bird made a choice to go to one tray, the other tray was removed immediately. One tray had a fixed amount of food while the other had a more variable amount. Concave and convex utility functions were calculated. Consistent with the risk sensitive foraging model, birds with convex utility functions chose the fixed trays and birds with concave utility functions chose the variable trays

Question 29

Which animals grow their own food?

Answer 29

Fungus-growing ants. These ants also use antibiotics produced by streptomyces bacteria to kill parasites that grow in their fungal gardens. Only females have streptomyces, which they use when they start new nests. Parents also pass the bacteria to their offspring. In addition, the bacteria produces antibiotics that only wipe out certain parasitic diseases that pose a threat to the garden. The ants also have mechanisms to remove infected fungus from the garden

Question 30

How does increasing the number of foragers affect the amount of food obtained?

Answer 30

Increasing the number of foragers in a group can increase the amount of food each forager receives. This could be because more foragers flush out more prey or because cooperative hunting makes the group more successful. It reduces the time that any individual needs to devote to antipredator activities as well.

Question 31

Foraging in bluegills

Answer 31

Bluegill sunfish feed on small aquatic insects that live in dense vegetation. Group foraging helps with flushing the prey out of the vegetation. Researchers found a positive relationship between foraging group size and individual foraging success up to a group size of 4 fish. More prey was flushed with increased group size and prey clumped together, so other group members would often get food when one member found the prey. Bluegills don’t search for food in a coordinated manner, however.

Question 32

Hunting behavior in chimps

Answer 32

In Tai chimps, hunting success was positively correlated with group size, but with each new hunter, all group members receive more additional food than they did when the last new hunter was added (rather than individual increases in the amount of food). Tai chimps also hunt in a cooperative manner and have social rules that regulate access to prey

Question 33

Public information

Answer 33

Information based on the actions of others as a cue to changes in environmental conditions. This helps the forager to assess environmental variables

Question 34

How is public information different from social learning?

Answer 34

In social learning, individuals learn something specific. With public information, individuals use the actions of others as a means of assessing the condition of the environment and therefore helps to reduce environmental uncertainty

Question 35

What does public information models predict about patch residency for social foragers vs solitary foragers?

Answer 35

Predicts that social foragers in poor patches should leave the patches earlier than solitary individuals. This is because social foragers can use the failed foraging attempts of their groupmates to gain information about when they should leave a patch

Question 36

Foraging behavior in starlings

Answer 36

In one study, starlings fed at an artificial feeder containing cups that were either empty or contained a few seeds. A bird could forage alone or paired with a second bird. Paired birds left empty feeding patches earlier than solitary birds. Paired birds also left patches the earliest when paired with birds that had complete information about the patches

Question 37

Memory, hippocampal volume, and food caching in corvid birds study

Answer 37

The hippocampal region in birds is associated with food retrieval, and corvids have a lot of variation in food storing behavior. Researchers studied two species that rarely cache food, 4 species that food caching plays some role, and one species where food caching is very important. There was a strong positive relationship between food caching behavior and hippocampal volume- the more food storing behavior, the greater the volume

Question 38

How does availability of food resources impact hippocampal size?

Answer 38

Researchers hypothesized that individuals from populations where food resources are scarce would be better at storing and recovering food, and would have a larger hippocampus than individuals from a food rich environment. Natural selection likely favors better storage and retrieval in a harsh foraging environment, and a larger hippocampus would also be favored in this situation

Question 39

Foraging and hippocampus size in black capped chickadees

Answer 39

The birds were tested on their ability to retrieve seeds that had stored. Birds from a food scarce population stored a greater percentage of seeds than the birds from the food rich population. The food scarce birds also found more of their stored seeds than the other birds did. The hippocampal volume of the food scarce birds was greater, and their hippocampuses contained more neurons

Question 40

Phylogenic history of caching in corvids

Answer 40

The most likely ancestral state of caching in corvids is moderate caching- they aren’t entirely dependent on storing food for survival. Some corvid species evolved toward specialized storage, while others evolved to not use food storage at all- in this case, the cost of a large hippocampus wasn’t worth it

Question 41

Birth weight and foraging behavior in honeybees

Answer 41

There was a positive correlation between birth weight and foraging related learning at 3 weeks of age. Bees that were heavier at birth developed into foragers that learned better than bees with a lower weight. There was still a lot of variation in learning abilities in heavier bees, mostly due to how quickly an individual extended its proboscis when exposed to a sugary liquid after emerging from the cell

Question 42

Foraging, learning, and brain size in birds

Answer 42

Researchers hypothesized that larger forebrains are associated with better learning abilities. They examined whether there was a relationship between foraging innovations and forebrain size in British and North American bird groups. In both populations, relative forebrain size correlated with foraging innovation. Birds with larger forebrains had higher incidences of foraging innovation

Question 43

Foraging innovation

Answer 43

Either the ingestion of a new food type or the use of a new foraging technique

Question 44

What benefits do birds experience from having a large forebrain?

Answer 44

Large brains relative to body size could be beneficial when a population is introduced into new or altered environments, when innovation would be important. Researchers found that frequency of foraging innovation is positively correlated with the ratio of forebrain mass to brain stem mass. There was also a positive relationship between brain size and the birds’ success in novel environments- this is due to innovative use of new foraging techniques, which increased the birds’ rate of new food intake. This suggests there is a correlation between fitness and large brains (and therefore innovation).

Question 45

Flexible stem hypothesis

Answer 45

Darwin’s finches have a very high diversification rate. These species may have high levels of phenotypic variation and an ability to colonize that allows them to occupy diverse niches. The hypothesis proposes that evolvability is likely when members of a clade possess flexible behavioral strategies.

Question 46

Behavioral flexibility and Darwin’s finches study

Answer 46

Researchers used instances of foraging innovations to test the flexible stem hypothesis. It was found that the birds’ superfamily had a higher frequency of innovations than any of the other avian superfamilies analyzed

Question 47

Which foraging dilemma is faced by pigeons?

Answer 47

Pigeons are scavengers, so they have to decide which new food items are safe and which are dangerous.

Question 48

Cultural transmission and pigeon foraging behavior

Answer 48

Observer pigeons were tasked to learn a task- piercing the red half of a red and black piece of paper. There were seeds located under the paper. In one group, observer pigeons saw no model, so they didn’t learn how to get the hidden food. The second group saw the model eating but did not see how they got the food, so they took longer to learn. In the other two groups, birds either saw a model pierce the paper but get no food, or saw a model pierce the paper and eat. These birds quickly learned the task

Question 49

Producers and scroungers in pigeons

Answer 49

Producers find food, scroungers follow producers and eat the food the producers uncover. When birds are tested in groups, only a few birds seem to learn new feeding behaviors. Researchers hypothesized that scrounging behavior could inhibit cultural transmission. Flocks of pigeons were allowed to feed together, using test tubes placed in a row- some contained food and some didn’t. Birds had to learn how to open the tubes, and any pigeon in the group could eat the food once the tube was opened. Only 2/16 pigeons learned to open tubes- scrounging seemed to inhibit learning how to open tubes through observation. Scroungers focused more on where producers were than what they did to get food, and they just never learned the skill. When one observer was paired with one demonstrator, the observers could open the tube, but having access to the food impaired their ability to learn

Question 50

Puma foraging strategy

Answer 50

We can use the Search Image theory to explain how the puma learn about preys. As they mature, they become able to identify and hunt bigger prey

Question 51

In optimal foraging theory, each prey item has (3)

Answer 51

1. Energy value (calories)
2. Encounter rate
3. Handling time (capture and ingestion)

Question 52

Specific nutrient constraints

Answer 52

Some animals need specific nutrients (like trace element, e.g. zinc) in order to stay healthy. Such nutrition constraint will impact foraging rules. Particularly important in herbivores that need large amount of low-energy food to survive

Question 53

Risk-sensitive optimal foraging model

Answer 53

This is not a risk of danger, but rather a risk of not eating. Variance of availability of prey plays an
important role in animal foraging behavior

Question 54

Risk-sensitive optimal foraging models account for (3)

Answer 54

1. Energy costs of foraging
2. Predation risk costs
3. Missed opportunity costs

Question 55

Seed caching

Answer 55

Some animals cache their food and can remember to retrieve it in a time of need. It requires a good spatial memory (hippocampus) to remember where the food is stored