Antagonism: Definition & Biology

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  • 0:00 What Is Antagonism
  • 0:43 Types of Antagonism
  • 3:21 Defensive Measures
  • 4:08 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Carnivores, herbivores, omnivores, and microorganisms all have something in common: the desire to survive. Many species interactions are therefore antagonistic in nature. Find out what this means and learn about several different types of antagonism.

What Is Antagonism?

Do you have an annoying younger sibling who antagonizes you? Or maybe you can just picture a pesky one that does if you don't. What does your brother or sister do to annoy you? They probably make life difficult for you. That isn't too far off from the concept of antagonism as it relates to natural selection and evolution.

In biology, antagonism is an interaction between organisms so that one organism benefits at the expense of another, like your little brother or sister benefiting by pestering you while you study. You yell at them and then get in trouble for yelling, while they look like the innocent victim and gain favor. They win, you lose.

Types of Antagonism

Leaving annoying siblings behind, there are different types of antagonism. Let's explore some of them.


First is predation, or when a predator feeds on prey - for instance, a pack of wolves chasing down a deer. The deer is really just one big walking source of nutrition. The wolves eat the deer and gain life-sustaining nutrients. Had the deer been able to outrun the wolves, it might've been able to breed and pass on its genes to the next generation, but in this case, it's the wolves that survive another day and get the chance to pass on their genes instead.


Another type of antagonism is parasitism, where a parasite depends on, but usually does not kill, the host organism. Parasites often live on or in the host and feed directly from it. In this relationship, the parasite benefits while the host suffers. Why doesn't a parasite kill the host organism like the wolves killed the deer? Because if the host organism dies, so may the parasite.

The host organism is an endless market of food - and a home, to boot - for the parasite. If the parasite destroys the host, it has no source of nutrition, no place to live, and no place to reproduce. Thus, parasites usually gain as much as they can from the host without killing it.

Grazing and Browsing

Animals that eat plants are antagonizing them. In this case, the herbivores gain nutrients to grow and reproduce from plants. Grazers clip plants at low levels like lawn mowers. Animals like wildebeest, horses, or sheep are grazers. Browsers eat the leaves, wood, or green stems of plants. Animals like deer, caterpillars, or goats fit this category. Examples exist in water too, where animals eat aquatic plants or surface algae, such as manatees eating shoal grass or ducks eating algae.

Grazers and browsers harm the ability of the plant to gain its own nutrients through photosynthesis. However, like a parasite, they rarely kill off their source of food.


Competition is the negative relationship between organisms that both need the same resources. For example, plants (even of the same species) living in a small area may compete for light or mineral nutrition. Some plants will be able to outcompete other members, surviving to reproduce while others will die off.


Another kind of antagonism is cannibalism, where one animal eats another animal of its own kind. For some species of animals, this is an extremely rare practice that is either utilized in extreme survival situations, like a mother mouse eating her babies to save herself from starvation.

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