Species richness, species abundance and species diversity

In scientific literature, you will often find these terms being used: “species richness”, “species abundance” and “species diversity”. While they sound quite similar (and mistakenly used interchangeably), they are three different concepts. I’d like to dedicate this blog to explaining what they mean, and why each of them are equally important in sustaining the ecosystems on Earth.

Species richness

Species richness is the number of species in an area. It’s merely a numerical characteristic of an ecosystem.

Species abundance

Species abundance is the number of individuals of each species in an area. It is also a numerical characteristic.

Species diversity

Species diversity is a term used to define the different number of species in an area (Species richness) and its abundance and the distribution of these species in that ecosystem. It’s a measure of the variety in the ecosystem.

Species diversity is a combination of species richness and species abundance.

Having one is not a guarantee that the others are also present in the ecosystem

You could have high species richness but low abundance and therefore, low species diversity in an ecosystem. An aquarium with many different species of animals, but very few individuals of each species confined to a small space is an example.

Likewise, you could have an ecosystem with high abundance, low species richness and therefore, low species diversity. An Oak forest is an example of this. Most of the trees in the forest are Oak; other tree species are limited in numbers and have poor distribution throughout the forest.

Such conditions (high-low) are commonly found in man-made ecosystems.

Having any one or two of the above conditions is not ideal in a natural ecosystem.

Why is species diversity important?

• Diversity is important because first and foremost, it helps buffer environmental stresses on an ecosystem. A diverse ecosystem has a better chance of surviving rapid changes with minimal losses.
• Diversity plays an important role in providing a variety of diets for the organisms in the ecosystem. It is diversity that leads to a food web; this is decidedly a better situation to have than a real food chain.
• It is also important aesthetically. As a person, you like to see a forest with different kinds of trees and animals, rather than rows and rows of the same tree with nothing in between.
• Diverse ecosystems can sustain complex ecological interactions between biotic and abiotic components in an ecosystem.

Large scale interactions are important, because it ensures that the ecosystem will not collapse after a short while. For example-

This is an example of a food web which clearly shows high species richness (so many different organisms). Now imagine an ecosystem where only a maximum of 5 individuals of each organism is present (low abundance): low species diversity. With all the eating they will be doing, how long do you think it’ll take for this ecosystem to die?

All conservation efforts that focus on species diversity need to improve species richness and abundance and their spatial distribution.