Predator-Prey Interactions

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All organisms need energy to survive. For example, gazelles are herbivores that feed on plants. On the other hand, cheetahs are carnivores that hunt gazelles. This predator–prey interaction is called predation, in which the cheetah acts as the predator and gains energy by consuming the gazelle, its prey.

A predator uses a range of sensory adaptations to detect prey, depending on the species. These may include sight, smell, and hearing. Specialized physical features, such as teeth or claws in cheetahs, allow the predator to capture and consume the prey.

As prey evolve traits to avoid predation, predators also evolve traits that improve hunting success, such as the cheetah’s increased speed.

For example, some birds have evolved exceptional eyesight, including color vision, which helps them locate and hunt prey. A defense called crypsis helps prey avoid visual detection by blending into their environment. For example, peppered moths have colors and patterns that match the bark and branches of their host trees.

In other cases, prey do not hide. For example, monarch butterflies show their toxicity with bright, patterned wings. This warning coloration, called aposematism, acts as a visual cue to predators that the butterfly is harmful or inedible. Birds that ignore this warning experience a bad taste or nausea and later avoid similar butterflies.

When a species’ warning coloration works well, other species that face the same predators may evolve to copy its appearance.

One such pattern is Müllerian mimicry, in which species that are toxic or unpalatable to predators evolve similar warning signals and both benefit as predators learn to avoid them. Viceroy butterflies, for example, are toxic and closely resemble monarch butterflies. When predators try one species, they learn to avoid the other species rather than risk another unpleasant feeding experience.

Alternatively, Batesian mimicry happens when a harmless species mimics a harmful species. For instance, predators avoid the bright, tricolor banded pattern of venomous coral snakes. Nonvenomous king snakes benefit from this pattern by mimicking the coral snake’s appearance.

Predator-prey interactions resemble an evolutionary arms race, driving the evolution of adaptations in both predators and prey. This mutual evolutionary change between interacting species is called coevolution.

Overview

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Predators consume prey for energy. Predators that acquire prey and prey that avoid predation both increase their chances of survival and reproduction (i.e., fitness). Routine predator-prey interactions elicit mutual adaptations that improve predator offenses, such as claws, teeth, and speed, as well as prey defenses, including crypsis, aposematism, and mimicry. Thus, predator-prey interactions resemble an evolutionary arms race.

Although predation is commonly associated with carnivory, for example, cheetahs hunting gazelles, a closely related type of interaction exists. Herbivory is the consumption of plants by animals known as herbivores. Plants typically deter herbivores by employing an array of defenses, including morphological defenses like an acacia tree’s thorns, and chemical defenses such as a milkweed’s toxins. However, some herbivores evolve adaptations to bypass plant defenses. Giraffes, for example, have long, dexterous tongues that allow them to consume the acacia’s leaves while avoiding its thorns. Monarch butterfly caterpillars evolved immunity to milkweed toxins, and instead ingest milkweed to store the toxins in their tissues as a defense against their own predators.

Predator and prey population sizes can increase and decrease in cycles, due in part to predation. For instance, the lynx and snowshoe hare populations in northern Canada cycle about every 10 years, with the lynx population changes lagging 1-2 years behind the hare population. As the hare population increases, the lynx population—which prefers to feed on snowshoe hares—increases as well. However, as lynx capture hares, the hare population begins to decline. Scarcity of hares eventually reduces the lynx population, allowing hares to thrive and the cycle to repeat. Other factors, such as vegetation availability and predation by other predators, also impact the hare population cycle by limiting its peak population size and growth rate.