Foraging Behavior

Behavior Models

Models are tools that an able or researcher to predict what an animal will do in a given circumstance.

Armed with these predictors, conservationists can protect important habitats, see that ecosystems are balanced, predict when a species may be in danger, etc.

Optimality Theory

“Optimality models predict which decisions an animal should make in order to maximize its inclusive fitness under a given set of conditions.” (text, page 256)

Optimality models have three parts; decisions, currency, constraints.

Optimality Theory

Decisions involve the choices available to an animal in a given set of circumstances.

“Should I eat this or continue hunting?”, “should I stay here or move on?”, “is this prey or is it a predator?”, etc.

Optimality Theory Currency. This is what is being optimized. In the

case of foraging it is energy. The constraints are the set of conditions with which

the animal is actually confronted and which can limit its ability to forage effectively.

These constraints can be internal in the sense that they are determined by the physiology of the animal such as limited night vision and inability to tolerate cold.

They can also be external in the sense that the environment is too dry, too humid, too densely foliated, etc.

Prey Model (profitability)

This model answers questions about what should be eaten to maximize fitness. Fitness will be maximized when caloric intake or energy is maximized.

In the formula, Ei is the energy derived from prey i and hi is the handling time involved in getting prey i.

ih

Ei

iProfitability of prey

Prey Model (profitability) When prey 1 is more profitable than prey 2:

The gain from eating prey 1 will be:

Where S = search time.

When an animal finds prey 2, should it eat it or search for prey 1? Yes, if:

2

2

1

1

h

E

h

E

11

1

hS

E

Prey Model (profitability)

Predictions of the model: Whether or not to eat prey 2 will depend, at

least partially, on the search time for prey 1. Search time for prey 2 is unimportant if the

formula above holds. The zero-one rule should apply and animals

should switch back and forth between prey species to optimize their energy.

11

1

2

2

hS

E

h

E

Constraints on the Model As is often the case, the animals don’t know

the formulas. The models are good first estimates but life is much more complicated.

Learning is important. Environments have to be sampled and information must be gathered in order to make the correct choice.

Energy may not be the correct currency. Minimizing search time may be more important.

Constraints on the Model Search images. With experience, animals

improve their ability to get specific prey. What seems to be happening is an increased attentional focus to the prey with which the animal is familiar. Studies with birds have supported this hypothesis.

Patch foraging Marginal value theorem. Used to predict

when to stay and when to leave a patch. See pp 260-261.

The theory predicts that foragers will spend less time in patches that are closer together than in widely dispersed patches. When the next patch is easy to find it pays to leave the old one and move on.

Patch foraging (When do I want to be alone?) Optimal foraging behavior will vary as food

distribution varies. Widely dispersed food favors solitary foraging whereas clumped food distribution favors foraging in groups.

If you’re “bringing home the bacon” other parameters are involved. How big a load can I carry? The answer to this question can determine when to leave a patch.

Patch foraging (risk assessment) Utility functions are useful to estimate when

an animal should take risks and when it should not. See graphs on page 262.

When food is sufficient animals should not be gamblers, but when it is not, it pays to gamble. It is better to try and loose than not to try at all

Feeding Behavior

Animals can modify their food supply in various ways: e.g. leaf cutter ants, prairie dogs, the mucous trails of limpets, and farming by ants of aphids.

Trap building: e.g. spiders and ant lions Many fish use electromagnetic fields to detect

prey.

Aggressive Mimicry

Many fish have structures that act as bait to other animals.

Firefly females can signal sexual receptiveness to males of another species and eat them when they come to investigate.

Tools Examples of tool use include rocks on sea

otters, cactus needles by woodpecker finches and the modified tools of chimpanzees who square leaves from a twig and then use it to catch insects.

Foraging and Social Behavior Animals foraging in groups can benefit in several

ways:  Cooperative hunting maneuvers

Mammals, Wolves with Dall sheep;  Lions, especially with large difficult prey; Wild dogs (between problems of capturing large prey and fighting off hyenas, probably couldn't survive unless cooperated); Hyenas - Killer whales (encircle porpoises and one whale feeds at a time until all the porpoises are eaten. Gang up on other whale species larger than themselves)

Higher social insects = ultimate coop. foragers. Waggle dance of bees is ultimate in foraging

communication.

Increased feeding efficiency. (Imitative foraging) Coordination of feeding or drinking

decreases the risks in harsh environments where shelter is removed from food and water.

Get benefits of pooled knowledge re. resources

Increased harvesting efficiency. Insectivorous birds. Group beats up more insects/bird than do individuals.

Prey Defenses Prey are not simply waiting around to get

eaten. They have many Defense strategies. Run away, freeze in place, cryptic coloration,

toxicity. Mimicry. Mullerian mimics evolve to look

alike in order to amplify the learning curve of the of the predator, e.g. monarchy and queen butterflies.

Batesian mimicry is more difficult to understand.

Social Strategies A group is harder to spot than an individual. Safety in numbers. The predator cannot eat

them all. Selfish herd concept. Hide behind the other

guy. It’s better to be in the center of the group.

The more eyes checking the safer you are. Confusion affect. Mobbing

Multi-species Fish Schools (benefits) Access to more food, particularly in cases like the

moon wrasse and the parrotfish, where the parrotfish disturbs food items that can be consumed by the smaller wrasse.

As with other groups there is safety in numbers. Fishes may use these larger schools to reduce

aggressive encounters with the territorial damselfishes which defend algal turfs over much of the reef surface. The latter can be very aggressive to single fishes (herbivores and non-herbivores) that enter their territory, but when 40 or 50 fishes enter at once to feed, the damselfish is overwhelmed and often "gives up the fight"!