Role of different species in a community

Maria’s parents are building a small pond in their garden. And Maria’s job is to decide what plants and animals should live there. Maria puts some aquatic plants into the pond first. At the edges, she wants reeds, and in the middle of the pond, floating water lilies and duckweed. Now that the plants are all sorted, Maria thinks it would be nice to have some fish in there too.

She decides on goldfish. Maria is very happy with her pond! Then, Maria gets busy with school, and friends and forgets about the pond. When she remembers to check up on it after a couple of weeks, she’s very surprised to find all sorts of living things in and around the pond. Songbirds, ducks, dragonflies and other insects.

She can even hear a couple of frogs croaking! When Maria filled the pond with her plants and goldfish, she created an environment that other species would enjoy living in as well. Now all these different organisms live in the same place, at the same time and they interact with each other. Maria has created a biological community! The plants Maria picked provide food for all the animals living around the pond.

Plants play the role of the producers in the community. Animals that eat these plants are the consumers in the community. But these aren’t the only roles species can play in a community! Let’s have a look at the goldfish in Maria’s pond. When Maria first put goldfish into the pond, there weren’t any other animals around that ate these fish.

On top of that, Maria fed them nutritious pellets. So the goldfish reproduced very fast. Soon there were loads of goldfish! If you count all the animals at the pond, you see that there are many more goldfish than any other type of animal. The goldfish eat the most food, and sometimes prevent other animals from living there – for example, mosquitoes can’t live around the pond, because the fish eat their larvae.

Goldfish have the role of a dominant species in this biological community. Let’s leave Maria’s pond for a moment, and go under the sea. Let’s look at a biological community where sea stars are the only ones that eat sea urchins, mussels and some other shellfish. So, the role of the sea stars is to control the numbers of these other species, by eating them. If sea stars were suddenly all removed from this community, the populations of sea urchins and mussels would grow uncontrollably.

This might cause other types of animals, such as fish, to leave the area altogether. Without sea stars, the community would suddenly not be well-balanced or healthy anymore. Sea stars play the role of a species that keeps the whole community together — they are a keystone species. Maria modified her garden when she created the pond, and by creating a pond she produced a community. She maintains this community by occasionally feeding the ducks and the goldfish, and watering the plants in summer.

Because she modified an environment and created a community that she helps maintain, Maria is an ecosystem engineer. In all-natural communities, such as forests, or coral reefs, the ecosystem engineers will be specific plant or animal species. It’s one of many very important roles that species can play in their communities. Species may have one role, or multiple, depending on their community. Like goldfish in the pond, who are a consumer and a dominant species.

Regardless of how many roles they have, communities would not function well, or at all, without all species doing their part.