Biological communities

Selma and her family belong to a neighbourhood association, along with other local families. In this association, every household has a role to play. Selma and her sister often cook meals for neighbourhood events. Some of their neighbours are gardeners who maintain the common green spaces. Others make sure common areas are kept clean.

Selma and her family, together with their neighbours, form a community. But it’s not just people who form communities. Let’s have a look at the garden behind Selma’s house. There is a lawn, some flowers grow here and there, and bushes in the corner. There are earthworms in the soil; bees, butterflies and other insects flying or crawling around, and birds nest in the bushes.

Every group of living things has a role to play in the garden. The grass, the flowers and the bushes all provide food for the birds and the insects — they are the “cooks” of the garden. The insects and the birds pollinate and help disperse seeds — they are the “gardeners”. The earthworms clean up everyone’s mess — they break down matter and return nutrients to the soil. All these organisms live in the same place at the same time.

They interact with each other and each type of organism has a role to play. They form a biological community — a bit like the neighbourhood community Selma and her family belong to! There are different kinds of biological communities. Selma’s garden is one, so is a small stream, a forest or a coral reef. Communities can differ in a number of ways.

One way is by how many organisms live in a community. This number is called abundance. The more different species there are, the more complex the community — communities differ in species richness. For example, a tropical aquarium might only have 10 fish, meaning the community has low abundance. But if every fish is a different species, the species richness will be rather high!

A community also differs depending on its food chain. Let’s look at Selma’s garden again. Here, the grasses, flowers and bushes are the sources of food — they are the first link in the food chain, the producers. The insects and birds that eat these plants are the consumers. But since nothing in the garden eats these insects and birds, the only other links in the food chain are the earthworms.

Earthworms break down dead matter - they are decomposers. And communities can have many more links in their food chain than this garden. Communities can be very complex. Interactions between different species in a community, also depend on the space and nutrients available. The smaller the space and the fewer the nutrients, the more competition there is between species!

Some species will be better at competing than others, maybe because of their body size or large numbers. And this might lead to them becoming dominant in their community. But communities also depend on species working together. Bees eat nectar from flowers, for example, and then carry pollen from one plant to the next. There are countless different biological communities.

Each contains species carrying out different roles which allow the community to function. Selma and her family would never want to change the community in their neighbourhood. Even if being part of it, sometimes means a lot of cooking and hard work.