Recall that there are two components of Darwinian fitness: Survival and Fecundity (Reproduction). We expect adaptations to have evolved that increase animals' chances of survival.

Foraging for food is a major component of survival, and one that animals spend a lot of their time performing. Therefore, foraging has become the topic of much research in behavioral ecology.

Note that adaptive radiations are often reflected in behavior and morphology related to foraging.

Example: Hawaiian honey creepers

There are a number of categories that scientists use to describe a given species' foraging behavior.

I. Generalization vs. specialization

II. Predation vs. herbivory

III. Sit and wait vs. Active (roughly, grazing vs. browsing)

For sit and wait predators, site choice is very important. They often possess adaptations for choosing areas where they are likely to encounter prey.

For predators, active searchers often possess sensory adaptations for finding prey.

Some sit and wait foragers have special adaptations for increasing their encounter rates by attracting prey.

Note that this categorization can also be roughly applied to herbivores:

Grazers are akin to sit-and-wait predators. These are plant-feeding species that are more sedentary during feeding bouts (although they may need to move long distances in search of appropriate food- think of the mass migrations on the African plains, and of bison in North America. Grazers also tend to specialize more during feeding bouts.

Browsers move about actively, consuming small amounts of tissue from a diversity of plant individuals or species.

Optimality approaches to understanding foraging behavior: If natural selection has operated strongly on foraging behavior, then foraging behavior should be adaptive. One major prediction of this theory is that foraging behavior will be optimal in terms if maximizing RS.

Optimal Foraging Theory (OFT): An important application of behavioral ecology theory to the decisions animals make when collecting food. Assuming that foraging is optimized by evolution under natural selection, we can test what costs and benefits (proxies for RS) are important in explaining a given species' foraging behavior. OFT is used to generate models and predictions about foraging behavior, based on the key assumption that natural selection maximizes the efficiency of foraging (Why is this reasonable to assume, given what you know about how natural selection operates?).

We often employ OFT to try to understand foraging selectivity by animals:

-Why do animals reject some edible food items?

-Why do animals give up on some food items that they have started to process?

-How do foragers move when searching for or collecting food (fast/slow; straight/winding; fly/walk)?

-How do foragers choose which patches of food to visit?

-Why do animals stop foraging in an area (patch) before all of the food is consumed?

Any behavioral trait can have fitness costs and benefits. Natural selection should maximize the value of the difference,

(Benefit - Cost).

 Some important components of optimal foraging models:

-Foraging behavior must vary, either within or among individuals.

-Behavioral phenotypes must have associated benefits and costs that can be measured (as we noted earlier, the benefits and costs are often measured by proxies for RS).

-Generate a model and predictions to explain behavioral variation in terms of costs and benefits. If the predictions aren't met, you can modify the original model by taking additional benefits and costs of behavior into account.

 Two important currencies (RS proxies) are often used in optimal foraging models:

-Time (search within patches, handling of food items, travel between patches)

-Calories (energy gained per food item, energy expended getting it)

A good example study was performed on shorebirds (oyster catchers) that foraged on mussels.

 Some OFT studies have been criticized as being too simplistic. To improve the models, we might consider some additional currencies and selective forces:

-Animals may need to consider their intake of other nutrients (not just calories!)

-Some animals may behave so as to minimize their risk of starvation

-Not all prey are as easy to eat as wonder bread; it may be necessary to avoid prey defenses (Example- plant switching by herbivores).

 The problem of food availability:

Many animals occasionally face shortages of food. Sometimes these shortages are predictable, for example, when food becomes scarce in winter.

Fat stores are can be increased prior to predictable food shortages by many animals.

-In some mammals, decreased day length as winter approaches triggers hormonal changes that increase weight gain.

-Body fat has some costs (e.g., increased risk of predation). It is also limited by physiology (you can only get so fat…).

-Food hoarding is an alternative behavioral adaptation that counteracts environmental variation in food availability. Hoarding has evolved independently in different groups of animals.

 Species that form social groups can cooperate in food collection: this may function to decrease variation in food-finding success. Cooperation can also increase an individual's average performance, even when potential competitors are nearby.

The most complex forms of cooperative foraging involve division of labor: this means that individuals divide up the work and take on different roles when foraging.

 Cooperation in foraging can involve complex communication.

-Incidental information transfer occurs when animals observe others' success and copy them.

-Some species have evolved special foraging communication signals that increase other individuals' chances of finding food. This is best developed in some kinds of social insects (bees, ants, and termites), where colony mates lead each other to food.

Many animals feed directly on plant tissues. Foraging on plants takes three major forms, depending on which plat tissue is consumed:

-Herbivory

-Pollination

-Frugivory/seed dispersal

 Coevolution occurs when organisms reciprocally and strongly select on each other's traits. Plant charateristics and animal behavior provide many good examples of this process.

In some cases, current plant design is difficult to explain given current selective regimes (i.e., animal faunas). It appears that extinct animals have shaped some plants' fruiting and defense strategies.

 Some animals feed primarily on other living animals (predators). Foraging by predators has strongly affected adaptations in prey species. Most, if not all, species are subject to predation and exhibit antipredator adaptations.

 Evolutionary arms races: cycles of reciprocal adaptive responses between species (or other classes of individuals) with competing evolutionary goals.

 Constitutive defenses are those that are a permanent part of an animal's body structure. 

 Aposematism: originally, warning coloration; typically associated with chemical defenses. A better definition is honest communication of unprofitability,which can can be in any sensory modality

 Some animals exhibit predator misdirection adaptations: structures that deflect attack to unessential body parts.

 Mimicry: In general, can be defined as deceptive predator/prey communication. The prey have been selected to resemble something else.

There are two main classes of mimicry- Batesian (palatable species resemble unpalatable) and Mullerian (unpalaqtable resemble each other).

 Predator avoidance through crypsis: Cryptic prey are difficult to distinguish from their backgrounds.

 Anti-predator behavior: Elicited in prey in response to attack, or perceived detection by predators.