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What may be the most common way different species interact?

Biomes as different as deserts and wetlands share something very important. All biomes have populations of interacting species. Species interact in the same basic ways in all biomes. For example, all biomes have some species that prey on others 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 fly. To eat the fly, the praying mantis first had to catch the fly, 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. Examples of predator-prey relationships include the lion and zebra, the bear and  fish , and the fox and rabbit.  Predator-prey relationships such as these account for most energy transfers in food chains and food webs.

There are different types of predation, including:

  • true predation.
  • grazing.
  • parasitism.

This lion is an example of a hunting predator

This lion is an example of a hunting predator.

This lion is an example of a predator on the hunt.

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. 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. Certain traits enable organisms to be effective hunters. These include camouflage, speed, and heightened senses. These traits also enable certain prey to avoid predators.

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.

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

Keystone Species

Some predator species are known as keystone species. A  keystone species  is one that plays an especially important role in its community. Major changes in the numbers of a keystone species affect the populations of many other species in the community. For example, some sea star species are keystone species in coral reef communities. The sea stars prey on mussels and sea urchins, which have no other natural predators. If sea stars were removed from a coral reef community, mussel and sea urchin populations would have explosive growth. This, in turn, would drive out most other species. In the end, the coral reef community would be destroyed.

Adaptations to Predation

Both predators and prey have adaptations to predation that evolve through natural selection. Predator adaptations help them capture prey. Prey adaptations help them avoid predators. A common adaptation in both predator and prey is  camouflage  Figure  below  ).  Camouflage  means that species have an appearance ( color , shape, or pattern) that helps them blend into the background.  Camouflage in prey helps them hide from predators. Camouflage in predators helps them sneak up on prey.  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  ). 

This dead leaf mantis is camouflaged by the actual dead leaves

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.

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.

The Viceroy butterfly mimics the unpleasant Monarch butterfly

An example of mimicry, where the Viceroy butterfly ( right ) mimics the unpleasant Monarch butterfly ( left ). Both butterfly species are avoided by predators to a greater degree than either one would be without mimicry.

An example of mimicry, where the Viceroy butterfly (  right  ) mimics the unpleasant Monarch butterfly (  left  ). Both butterfly species are avoided by predators to a greater degree than either one would be without mimicry.

Predation and Population

A predator-prey relationship tends to keep the populations of both species in balance. This is shown by the graph in Figure below . As the prey population increases, there is more food for predators. So, after a slight lag, the predator population increases as well. As the number of predators increases, more prey are captured. As a result, the prey population starts to decrease. What happens to the predator population then?

Predator-Prey Population Dynamics. As the prey population increases, why does the predator population also increase?

Summary

  • Predation is a relationship in which members of one species (the predator) consume members of another species (the prey).
  • A predator-prey relationship keeps the populations of both species in balance.

Review

1. Give an example of a predator and prey from your local area.

2.  As the prey population increases, why does the predator population also increase? 

3. Refer to the figure below for the following questions:

     a.   What is the population of wolves around the year 1980?  

     b.  The moose population increases from the years 1957 to 1973.  What may have caused the decline in    moose population from years 1973 to 1980?    

     c.  What is the moose population in the year 1993?

     d.  What is the wolf population in the year 1993? 

     e.  What might have caused the moose population to spike in the year 1993?   

License: CC BY-NC 3.0

[Figure1]

4. What is a keystone species? 

5. Why is a sea star considered a keystone species?

6. Give an example of an organism that uses camouflage that is not mentioned in this section.

Image Attributions

  1. [1]^ License: CC BY-NC 3.0

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