How Animals Interact in an Ecosystem

Grizzly Bear Feeds on a Jumping Salmon, Alaska
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Animals interact with each other in numerous, complex ways. However, we can make some general statements about these interactions. This enables us to better understand the role that species play within their ecosystems and how individual species can positively or negatively affect the species around them.

Of the various types of interactions between species, most involve resources and consumers. A resource, in ecological terms, is something (such as food, water, habitat, sunlight, or prey) that is required by an organism to perform a vital function such as growth or reproduction. A consumer is an organism that consumes a resource (such as predators, herbivores, or detritivores). Most interactions between animals involve one or more competitor species vying for a resource.

Species interactions can be categorized into four basic groups based on how the participating species are affected by the interaction. They include competitive interactions, consumer-resource interactions, detritivore-detritus interactions, and mutualistic interactions.

Competitive Interactions

Competitive interactions are interactions involving two or more species that are vying for the same resource. In these interactions, both of the species involved are negatively affected. Competitive interactions are in many cases indirect, such as when two species both consume the same resource but do not directly interact with each other. Instead, they affect each other by reducing the availability of the resource. An example of this type of interaction might be seen between lions and hyenas. Since both species feed on the same prey, they negatively affect each other by reducing the amount of that prey. One species may have trouble hunting in an area where the other is already present.

Consumer-resource Interactions

Consumer-resource interactions are interactions in which individuals from one species consume individuals from another species. Examples of consumer-resource interactions include predator-prey interactions and herbivore-plant interactions. These consumer-resource interactions affect the species involved in different ways. Usually, this type of interaction has a positive impact on the consumer species and a negative impact on the resource species. An example of a consumer-resource interaction would be a lion eating a zebra, or a zebra feeding on grass. In the first example, the zebra is the resource, while in the second example it is the consumer.

Detritivore-detritus Interactions

Detritivore-detritus interactions involve a species that consumes the detritus (dead or decomposing organic matter) of another species. The detritivore-detritus interaction is a positive interaction for the consumer species. It has no impact on the resource species since it is already dead. Detritivores include small creatures such as millipedes, slugs, woodlice, and sea cucumbers. By cleaning up decomposing plant and animal matter, they play an important role in maintaining the health of ecosystems.

Mutualistic Interactions

Mutualistic interactions are interactions in which both species--resource and consumer--benefit from the interaction. An example of this is the relationship between plants and pollinators. Nearly three-quarters of flowering plants rely on animals to help them pollinate. In exchange for this service, animals such as bees and butterflies are rewarded with food in the form of pollen or nectar. The interaction is beneficial for both species, plants, and animals.

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Klappenbach, Laura. "How Animals Interact in an Ecosystem." ThoughtCo, Sep. 6, 2021, Klappenbach, Laura. (2021, September 6). How Animals Interact in an Ecosystem. Retrieved from Klappenbach, Laura. "How Animals Interact in an Ecosystem." ThoughtCo. (accessed May 29, 2023).