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12.8: Predation

Difficulty Level: At Grade Created by: CK-12
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Can insects hunt for food?

When you think of an animal hunting for its food, large animals such as lions may come to mind. But many tiny animals also hunt for their food. For example, this praying mantis is eating a grasshopper. To eat the grasshopper, the praying mantis first had to catch the grasshopper, which is a form of hunting.

Predation

Predation is another mechanism in which species interact with each other. Predation is when a predator organism feeds on another living organism or organisms, known as prey . The predator always lowers the prey’s fitness . It does this by keeping the prey from surviving, reproducing, or both. Predator-prey relationships are essential to maintaining the balance of organisms in an ecosystem.

There are different types of predation, including:

  • true predation.
  • grazing.
  • parasitism.

True predation is when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large prey. They tear it apart and chew it before eating it ( Figure below ). Others, like bottlenose dolphins or snakes, may eat their prey whole. In some cases, the prey dies in the mouth or the digestive system of the predator. Baleen whales, for example, eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance.

This example of a true predator shows a pair of lions actively hunting prey.

In grazing , the predator eats part of the prey but does not usually kill it. You may have seen cows grazing on grass. The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed) can regrow after being eaten by fish.

Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species . These are species that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a detrimental effect on the whole ecosystem. In this example, the wolves would be a keystone species.

Prey also have adaptations for avoiding predators. Prey sometimes avoid detection by using camouflage ( Figure below ). Camouflage means that species have an appearance (color, shape, or pattern) that helps them blend into the background. Mimicry is a related adaptation in which a species uses appearance to copy or mimic another species. For example, a non-poisonous dart frog may evolve to look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry can be used by both predators and prey ( Figure below ).

Parasitism is a type of symbiotic relationship and will be described in the Symbiosis concept.

Camouflage by the dead leaf mantis makes it less visible to both its predators and prey. If alarmed, it lies motionless on the rainforest floor of Madagascar, Africa, camouflaged among the actual dead leaves. It eats other animals up to the size of small lizards.

An example of mimicry, where the Viceroy butterfly ( right ) mimics the unpleasant Monarch butterfly ( left ). Both species are avoided by predators to a greater degree than either one would be otherwise.

Vocabulary

  • camouflage : An appearance (color, shape, or pattern) that helps a species blend into the background.
  • fitness : The relative ability of an organism to survive and produce fertile offspring.
  • grazing : Predation in which the predator eats part of the prey but does not usually kill it.
  • keystone species : Species that plays an especially important role in its community so that major changes in its numbers affect the populations of many other species in the community.
  • mimicry : When a species uses appearance to copy another species.
  • parasitism : Symbiotic relationship in which one species benefits while the other species is harmed.
  • predation : Relationship in which members of one species consume members of another species.
  • predator-prey relationship : An interaction between two organisms of unlike species; one organism acts as predator that captures and feeds on the other organism, which serves as the prey.
  • prey : Species that is consumed by another species.
  • producer : An organism that can absorb the energy of the sun and convert it into food through the process of photosynthesis; i.e. plants and algae.
  • symbiosis : A close and long-term interaction between different species.
  • true predation : Predation in which a predator kills and eats its prey.

Summary

  • Predation happens when a predator organism feeds on another living organism or organisms, known as prey.
  • Predators can be keystone species, a species that can have a large effect on the balance of organisms in an ecosystem.

Practice

Use the resources below to answer the questions that follow.

Traces of Early Animal Life at Shape of Life http://shapeoflife.org/video/scientist/whitey-hagadorn-paleontologist-traces-early-animal-life (6:11)

  1. What does the fossil record suggest about how predation affected the diversity of life? Can you think of a reason, other than predation, for the pattern in the fossil record?
  2. How many years were sessile organisms the dominant life form on Earth? What factors do you think contributed to the shift away from the dominance of sessile life forms?
  3. Is it possible for sessile life forms to be predators? How does this situation relate to your answer to question 2?
  4. What sort of systems allow an organism to develop directed movement?

Dragonfly Larva Hunts Newt at Shape of Life http://shapeoflife.org/video/behavior/arthropods-dragonfly-larva-hunts-newt (2:06)

  1. Notice the dragonfly larva's movements. How deliberate do its movements appear to be? Given that this is a young individual, what sort of behavior do you think this represents, innate or learned? Explain your reasoning.
  2. What predation-related attributes or adaptations do you see in the newt and the dragonfly larva?
  3. What sort of predation occurs between the dragonfly larva and the newt? What sort of predation occurs between the dragonfly larva?

Review

  1. What's the difference between grazing and true predation?
  2. What sorts of adaptations do prey have for avoiding predators?
  3. What are some of the effects predation has on ecosystems and ecosystem dynamics?

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Difficulty Level:

At Grade

Concept Nodes:

Grades:

7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Sep 02, 2014
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