Name: foraging trade-offs in animals
Uploaded: 2019-03-11T09:21:38.000Z
Duration: 48 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Life Science

LS.6

LS.6.b

Optimal Foraging

Animals need to forage. That is, find and eat food to survive. Optimal foraging theory postulates that evolution favors foraging behaviors that balance the benefits of getting food with the costs of obtaining it, such as energy expenditure, and the risk of predation.

One example is the Northwestern crow, which picks up whelks, sea snails, then flies upwards and drops them onto the rocks below to crack open the shell, allowing the crow to eat the insides. The crow repeats this process until the shell is broken. If it flies higher, the shell will break with fewer drops.

However, that uses more energy. Scientists have found that the crows, on average, fly to a height that yields the most amount of food relative to the energy used to obtain it.

optimal foraging

How animals obtain and eat their food is called foraging behavior. Foraging can include searching for plants and hunting for prey and depends on the species and environment.

Optimal foraging theory states that natural selection favors foraging strategies that balance the benefits of a particular food, such as energy and nutrients, with the costs of obtaining it, such as energy expenditure and the risk of predation. Optimal foraging maximizes benefits while minimizing costs.

<h4>For the Crows</h4>

Optimal foraging theory is supported by evidence from several species. One example is the Northwestern crow&rsquo;s strategy for eating whelks (sea snails). To eat a whelk, a crow must crack open its shell, which it achieves by flying with the whelk and then dropping it onto rocks beneath. Crows will do this repeatedly until the shell cracks.

Flying higher will break the shell sooner, but requires more energy. By dropping whelks from various heights, scientists calculated the optimal height that will break the shell using the least amount of energy. The crows, on average, fly close to this height to crack whelk shells&mdash;supporting the idea that this foraging behavior has evolved to be optimal for energy balance.

Larger whelks also break more easily than smaller whelks, in addition to containing more caloric energy. Crows further optimize their strategy by selecting large whelks and making many attempts to crack a single whelk, rather than expending extra energy to find another whelk.

<h4>Mule Deer</h4>

The risk of being attacked by predators can be another cost of foraging. Researchers found that mule deer spend more time foraging in open areas although there is slightly less food available than at the edges of the forest. This is due to a lower risk of predation by mountain lions in open areas.

This observation further supports the idea that foraging is a trade-off between benefits and costs, and that evolution favors strategies that are optimized to balance the two.

How animals obtain and eat their food is called foraging behavior. Foraging can include searching for plants and hunting for prey and depends on the ...

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KEY TERMS AND CONCEPTS

foraging trade-offs in animals

Foraging trade-offs shape how animals find and use food. Foraging behavior includes searching for plants and hunting prey, and it varies with the species and the environment. Optimal foraging theory says natural selection favors strategies that balance the benefits of food, such as energy and nutrients, against the costs of getting it, such as energy use and the risk of predation.

Crows show how this balance can work in real life. Northwestern crows eat whelks, which are sea snails with hard shells. To open a whelk, a crow flies with it and drops it onto rocks below. The bird repeats this until the shell cracks. Dropping the whelk from a higher place can break it sooner, but it also costs more energy.

Scientists tested different drop heights and found the height that cracked the shell using the least energy. On average, the crows flew close to that height. This supports the idea that their foraging behavior has evolved to be efficient. Larger whelks are also easier to break and provide more calories. Crows improve their strategy by choosing large whelks and making many attempts on one whelk instead of spending extra energy to find another one.

Predation risk can also shape foraging choices. Mule deer spend more time feeding in open areas, even though those areas have slightly less food than the edge of the forest. Open areas lower the chance of attack by mountain lions. This shows that foraging is a trade-off between benefits and costs, and that evolution favors strategies that balance both.

Foraging Trade-offs in Animals

types of behavior

How Animals Act and Adapt

Animal behavior is the set of actions an organism performs. These actions can help it find food, reproduce, defend against threats, and carry out many other tasks. Behavior can also include movement in the environment, such as migration, and social interactions within a species or population. Many behaviors involve motor output. Motor output means muscle movement. Other behaviors are less visible. Learning is one example of a behavior that does not always show up as an obvious physical action.<br...

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Stickleback Courtship and Attack Signals

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imprinting

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communication

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Foraging trade-offs shape how animals find and use food. Foraging behavior includes searching for plants and hunting prey, and it varies with the species and the environment. Optimal foraging theory says natural selection favors strategies that balance the benefits of food, such as energy and nutrients, against the costs of getting it, such as energy use and the risk of predation. Crows show how this balance can work in real life. Northwestern crows eat whelks, which are sea snails with hard...

mate choice

Sexual Selection in Mate Choice

Mate choice is a form of sexual selection in which animals choose partners based on traits that can affect reproduction. It is also called intersexual selection because it happens between the sexes. In many species, one sex is choosy, and it is often the female. Choosy animals may select mates by looking at appearance or behavior. They often prefer showier males with brighter coloration, more elaborate ornamentation, like a peacock’s tail, or more complex songs and courtship displays. These...

parental care

How Animals Care for Their Young

Parental care is the behavior animals use to feed, groom, and protect their young. It is common in mammals and birds, which often have offspring that are born relatively helpless. Some insects, fish, and amphibians also show this kind of care. In birds, parental care can begin before hatching. Parents sit on eggs to incubate them, which helps the embryos develop. After the chicks hatch, the parents bring food and may brood the young to keep them warm. Depending on the species, both the male...

altruism

Altruism in Animal Groups

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inclusive fitness

How Kin Selection Spreads Helpful Traits

Inclusive fitness explains why animals may help relatives even at a personal cost. It describes how an individual can pass on genes through its own offspring and through the offspring of close relatives that share those genes. When help increases a relative’s reproductive success, the helper’s inclusive fitness can also rise. A clear example appears in eusocial animals such as bees and naked mole rats. These species live in colonies with one reproductively capable female, called the queen. The...

key terms and concepts

Explore how animals balance food benefits, energy use, and predator risk through optimal foraging, with examples from crows and mule deer.

Foraging Trade-offs in Animals | JoVE K12

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ecosystems-interactions-energy-and-dynamics

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LS.6.d

Foraging Trade-offs in Animals

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