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Community Ecology: Species Interactions

Community Ecology: Species Interactions

Author: Sophia Tutorial

Identify the types of species interactions.

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what's covered
In this lesson, we'll discuss the important properties of community ecology, different types of species interactions, and the concept of ecological succession.

The specific areas of focus include:
  1. Properties of Community Ecology
  2. Species Interactions
  3. Ecological Succession
    1. Primary Succession
    2. Secondary Succession


Community ecology is the study of interactions between multiple species in a given time and area.

Community ecologists study four main properties:

  • Species Abundance: the number and relative abundance of each species in a community
  • Species Composition: which species exist in a community
  • Species Distribution: the way species are distributed relative to each other
  • Species Interactions: how species impact each other

Let's put these properties to use by considering a fictional forest community.


Let's say this community spans one square mile in the year 2015. A community ecologist would observe and record the different species in the forest community, such as squirrels, birds, trees, and shrub species. This is species composition.

The ecologist would then measure species abundance, and calculate the abundance of each species in relation to each other. The ecologist might discover that there is a large population of squirrels and a large population of nut-bearing trees, but a low number of swallow bird species.

Then the ecologist would observe the species distribution, and perhaps discover that there is a sparse but even distribution of oak trees; however, the population of a specific shrub seems to live in only one small portion of a community.

Finally, the ecologist would study the different types of relationships that the species are having, such as competition between different bird species or symbiotic relationships between microorganisms and tree roots.


We'll now delve a little deeper into the types of interactions that species can have.

There are three types of interactions:

  • Competition
  • Predation
  • Symbiosis

However, in terms of interaction outcomes, there are also three possible endings for an interaction:

  • Positive
  • Negative
  • Neutral

Interaction Description Outcome Example
Competition Two species compete for the same food or resources Negative - Negative

This always has a negative outcome for each species.
Two bird species compete for available materials to build their nests, or for food for their young.
Predation One species preys on or consumes another. Predation includes carnivores eating other species, herbivores consuming plants, or species laying eggs on or in another species. Positive - Negative

This is positive for the predator and negative for the prey.
An eagle catches and eats a snake — good for the eagle, bad for the snake.
Symbiosis Two species have a mutually beneficial interaction. Symbiosis is much more common in nature than people realize. Many species, including humans, rely on symbiotic relationships to help digest their food. Positive - Positive

This is positive on both sides.
Humans have bacteria in their digestive tract, which allows them to digest their food better. Cows also have a symbiotic digestive relationship with bacteria.


Ecological succession is the process of the creation of a new community, either on barren land or on highly-disrupted environments.

There are two different types of ecological succession:

  • Primary succession: When species begin inhabiting and establishing themselves in an environment that has never been inhabited before.


If land created from an oceanic volcano became inhabited by a pioneer species, like moss and algae, and eventually by shrubs, trees, and animals, this would be primary succession.
  • Secondary succession: When a disturbance damages communities or organisms in an already-established community enough that there is a vacuum, where new species can move in and establish themselves. This is the most common form of succession.


If a forest fire burned a large swath of forest, and over time, new species moved in and began growing (thus modifying the environment), this would be secondary succession. Other disturbances that can cause secondary succession are floods, fires, volcanoes, droughts, overgrazing, and human activity, such as deforestation and over-harvesting.

term to know

Ecological Succession
The process of the creation of a new community, either on barren land or on highly-disrupted environments.

In this lesson, you learned the important properties of community ecology, as well as the different types of species interactions: competition, predation, and symbiosis. Competition has a negative outcome for both species involved; predation has a positive outcome for the predator, and a negative outcome for the prey; symbiosis is positive for both sides.

You now understand that ecological succession is the process of the creation of a new community, either on barren land or on highly-disrupted environments. While there are two types of ecological succession, primary succession and secondary succession, the most common type is secondary.

Source: Adapted from Sophia tutorial by Jensen Morgan.

Terms to Know
Ecological Succession

the process of the creation of a new community, either on barren land or on highly disrupted environments