What is a keystone species?

A keystone species is a species that plays a critical role in maintaining the structure of an ecological community and whose impact on the community is greater than would be expected based on its relative abundance or total biomass.

Here are the steps to understand this concept:

1. Understanding the term 'Species': A species is a group of living organisms that can interbreed to produce fertile offspring. For example, lions, tigers, humans, etc.

2. Understanding the term 'Ecological Community': An ecological community is a group of actually or potentially interacting species living in the same place. A community is bound together by the network of influences that species have on one another.

3. Understanding 'Keystone' in the context of ecology: In architecture, a keystone is the piece at the top of an arch that holds the other pieces in place. Similarly, in an ecological community, a keystone species is one which other species largely depend, and if removed, the ecosystem would change drastically.

4. Role of Keystone Species: Keystone species have a large effect on their ecosystems and help to maintain biodiversity. They can be predators, prey, competitors, mutualists, or even ecosystem engineers. Their removal can lead to a domino effect, impacting other species and potentially leading to ecosystem collapse.

5. Examples of Keystone Species: Sea otters, wolves, and bees are examples of keystone species. Sea otters are predators that control sea urchin populations, which would otherwise damage kelp forest ecosystems. Wolves control the population of herbivores like deer, preventing overgrazing. Bees are pollinators vital to many ecosystems.

So, in summary, a keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species affect many other organisms in an ecosystem and help to determine the types and numbers of various others species in a community.