Community Composition
The mix of different species present in an ecosystem at a given time, including their relative abundance and diversity.
The specific array of species inhabiting an ecosystem, including which organisms are present and in what proportions. It describes both the identity and abundance of plants, animals, and microorganisms in a community, and changes in composition reflect shifts in ecosystem health, environmental conditions, or disturbance history.
What this means in real life
A forest's community composition might shift from mostly oak and maple trees to more pine and birch after a fire, or a pond's fish community might change from native species to invasive carp after pollution, altering the entire ecosystem balance.
What it isn’t
It is not the same as biodiversity or species richness alone—those measure only how many species exist, whereas community composition also captures which specific species are present and their relative numbers.
Commonly misused online
Often conflated with 'biodiversity' on social media, but composition describes the actual species present and their proportions, while biodiversity is a broader measure of variety that doesn't specify which species matter.