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Competition and Symbiosis_MrSapora
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Least Auklets - Saint George Island, Alaska. These tiny seabirds compete not only for food but also for breeding territory. In this picture, these birds are displaying and chattering away at each other establishing their social status (and probably showing off a bit too...they are total show-boaters).

Does there have to be a winner?

We have spent a lot of time learning about how abiotic (non-living) factors influence and shape an ecosystem.  It is now to time to explore a few of the biotic factors that shape the world around us, and even shape us!  Biotic factors are those that involve living things interacting with one another.  We will start with competition and then learn about another set of interactions called symbiosis.

When animals compete? Yes. Animals, or other organisms, will compete when both want the same thing. One must "lose" so the winner can have the resource. But competition doesn't necessarily involve physical altercations.

Competition

Competition is a relationship between organisms that strive for the same resources in the same place. The resources might be food, water, or space. There are two different types of competition:

  1. Intraspecific competition occurs between members of the same species. For example, two male birds of the same species might compete for mates in the same area. This type of competition is a basic factor in natural selection. It leads to the evolution of better adaptations within a species.
  2. Interspecific competition occurs between members of different species. For example, predators of different species might compete for the same prey.  Think "international", as in different countries competeing for a resource.  This is how I remember the difference between "intra-" and "inter-" at least.

Interspecific Competition and Extinction

Interspecific competition often leads to extinction . The species that is less well adapted may get fewer of the resources that both species need. As a result, members of that species are less likely to survive, and the species may go extinct - or at least it might be pushed out of the specific geographic region where it is forced to directly compete for a resource with a rival species.

Interspecific competition might also lead to "niche-partitioning" - where each species shares a habitat, or even a resource, but utilizes it in different ways - such as one becoming nocturnal (active at night), while the other develops a diuranal (active during the day) strategy.  


Do interactions between species always result in harm?

Not all biotic interactions between organisms result in direct cometition - sometimes they may even benefit each other.  What are some ways that we human animals interact to benefit one another?  Here in Tillamook many of us rely on farming for a way of life, where we directly interact with other species (cows) to benefit ourselves, but we also have to be mindful to not harm the species (cows again) we are benefiting from.  These types of interactions, where species interact but do not kill or directly consume the other are called symbiotic relationships .

Symbiotic Relationships

Symbiosis  is a close relationship between two species in which at least one species benefits. For the other species, the relationship may be positive, negative, or neutral. There are three basic types of symbiosis: mutualism, commensalism, and parasitism.

Mutualism

Mutualism  is a symbiotic relationship in which both species benefit. An example of mutualism locally involves moss growing on the branches of certain trees - mainly the big leaf maple (Acer circinatum).  You may think at first glance that these big mats of moss covering the branches are harming the trees, but scientists have discovered that the trees actually produce roots from out of their branches that trail through the moss beds and collect decomposing nutrients and water.  In this relationship - both species benefit: the tree gains water and nutrients, while the moss gains a lofty and sunny perch to grow on and gather sunlight.  I think of this as a (+/+) relationship, where both species benefit so both are a plus (+).

Moss, ferns, even huckleberries grow on branches of trees in our area. The trees also benefit though - they produce roots to collect nutrients and water from this elevated gardens. Plants that grow on other plants are called "epiphytes" and our temperate rain forest, along with tropical rain forests, are full of them!

 

Anemone fish - or clown fish - have a mutualistic relationship with sea anemones. The fish protect the anemone from annoying predators and parasites, and the fish gain a defended fortress to live and breed in! Koh Tao, Thailand.

Commensalism

Commensalism  is a symbiotic relationship in which one species benefits while the other species is not affected. One species typically uses the other for a purpose other than food. For example, mites attach themselves to larger flying insects to get a “free ride.” Hermit crabs use the shells of dead snails for homes. This is more of a (+/0) relationship, where one species benefits while the other species is not affected or could care less.  Barnacles on a whale are also a good example fo this...or the sea turtle below, hosting a nice coat of green algae growing on its shell.

This sea turtle has a coat of green algae growing on its back. The algae is not harmed is protected from other grazers, while the turtle is not harmed but is also not really helped. Koh Tao, Thailand.

Parasitism

Parasitism  is a symbiotic relationship in which one species (the  parasite ) benefits while the other species (the  host ) is harmed. Many species of animals are parasites, at least during some stage of their life. Most species are also hosts to one or more parasites.  Parasitism can be defined as a (+/-) relationship, where one species benefits (the + or parasite), and the other species is harmed (the - or host).

Some parasites live on the surface of their host. Others live inside their host. They may enter the host through a break in the skin or in food or water. For example, roundworms are parasites of mammals, including humans, cats, and dogs (see  Figure   below ). The worms produce huge numbers of eggs, which are passed in the host’s feces to the environment. Other individuals may be infected by swallowing the eggs in contaminated food or water.

Some parasites kill their host, but most do not. It’s easy to see why. If a parasite kills its host, the parasite is also likely to die. Instead, parasites usually cause relatively minor damage to their host.

Summary

  • Competition is a relationship between organisms that strive for the same resources in the same place.
  • Intraspecific competition occurs between members of the same species. It improves the species’ adaptations.
  • Interspecific competition occurs between members of different species. It may lead to one species going extinct or both becoming more specialized.
  • Symbiosis is a close relationship between two species in which at least one species benefits.
  • Mutualism is a symbiotic relationship in which both species benefit.
  • Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected.
  • Parasitism is a symbiotic relationship in which one species (the parasite) benefits while the other species (the host) is harmed.

Practice I

Use this resource to answer the questions that follow.

  1. What are the three general types of interactions within a community?
  2. Define competition.
  3. What are some of the resources organisms compete for?
  4. What is the main outcome of competition? ( Hint : affects the niche)
  5. Describe an example of interspecific competition.
  6. Why might intraspecific competition occur?
  1. What are the three types of symbiotic relationships?
  2. Describe the three symbiotic relationships.
  3. Describe an example of a symbiotic relationship involving humans.
  4. Describe a symbiotic relationship involving plants and bacteria.

Practice II

Review

1. What is competition?

2. Compare and contrast the evolutionary effects of intraspecific and interspecific competition.

1. Define mutualism and commensalism.

2. Explain why most parasites do not kill their host. Why is it in their own best interest to keep their host alive?

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