Every ecosystem has a diverse community of species that interact with each other and their environment. Where they are located influences the composition of the species present in that location. Species diversity is the variety of species found in an ecosystem and the size of each population.

Ecosystems are most resilient to environmental changes when there are a variety of different species, known as species richness; and a healthy population size of each species, known as species evenness.

Each species has an important role to perform in its respective ecosystem (Remember the Food Chains in Lesson 1 and the essential roles that primary producers, consumers, and decomposers play in the cycling of nutrients and the transfer of energy). Having a healthy population size reduces the chances of a species disappearing. Having multiple species whose roles overlap ensures that if one species dies out or relocates, another will take its place.

The roles these different species perform support these core processes that are required to maintain the existence of self-sustaining ecosystems:

  • The cycling of nutrients through each trophic level and back into the soil
  • The cycling of water through Earth’s four spheres
  • The flow of energy from the sun through the food chain 
  • Community dynamics, which are the constant changes that occur due to species interactions

A species’ existence in an ecosystem is primarily controlled by environmental factors such as soil, climate, water and sunlight. Their population size is restricted or expanded by the interactions they have with other species in its community. Predators, for example, decrease their prey’s population size. Likewise, competition for resources regulates a species’ population growth around the availability of thpse resources. All these factors create what is called a species ‘niche’.

These roles can be performed on a large scale, such as how beavers create wetland ecosystems when they build dams thereby creating a whole new ecosystem for species to inhabit. Or they can occur on a microscopic, scale such how bacteria breaks down leaves in the stomach of a proboscis monkey to enable them to gain nutrition and energy which will later be passed on through the food chain. There are so many parts to an ecosystem that it requires a vast array of species that can perform these roles in different areas, at different magnitudes, and in different ways to ensure that all species can integrate as one fully functioning ecosystem.

Female proboscis monkey eating leaves in Borneo, Malaysia

Here a are a few examples of the roles of different species:

  • Pollinator species regenerate habitats for species to live in and increase the genetic diversity of plants.
  • Soil-dwelling species break down nutrients for other species to consume, bioturbate, and aerate the soil making it more fertile and habitable for plant and animal species.
  • Plants bring energy into the food chain and provide shelter and food resources for a multitude of higher trophic level species, which continue to pass on nutrients and energy.
  • Fungi decompose and recycle organic matter back into the soil for plants to use; they also interact with plant feeder-roots by providing nutrients and transferring information between plants throughout the ecosystem.
  • Bacteria act as both producers of energy and decomposers, recycling nutrients in the ecosystem; they also break down harmful chemicals into harmless compounds.

Now that we understand that species diversity ensures the essential roles of nutrient cycling and energy flow are performed, which are vital in keeping an ecosystem healthy, let’s take a look at the proboscis monkey and how this species interacts with other species and its environment.


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