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In this lesson, you’ll learn what species richness is and what factors can influence the index of species richness. You’ll also discover why it is an important index to measure in terms of conservation.


Species richness, very simply, is a count of the different species in a given ecosystem, region or particular area. You make the assumption that each organism constitutes a single species.

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Imagine a picture of a lake. How many different species might you see? You might see three different types of organisms: birds, fish and plants. So, in this lake community, the species richness would have a value of three.One important thing to keep in mind is the difference between species richness and species diversity.

Species diversity takes the abundance, or number of individuals, of different species into account, while species richness does not. If we again think about our lake community, you might note that there are four fish and three birds. Therefore, the species diversity would be higher for fish.

However, the species richness index would remain the same.

Sampling Considerations

The level of species richness can vary depending on a few variables, one of which is how you sample. For example, an index of species richness would greatly vary if you were counting species in an entire mesic hardwood forest, versus a one-meter-by-one-meter plot in the same forest.How you sample the environment in question is determined by what you want to gain by a species richness index.

If you are more interested in how many different types of trees are in the forest, sampling a small plot won’t tell you much. However, if you are interested in what insects live on the forest floor, sampling the entire forest would take years!You may be asking why we should care about species richness. Why is knowing what species are in a given ecosystem important? Species richness is an important index when thinking about conservation of a given habitat. Areas or habitats with rare species are considered to be a conservation priority.

An accurate species richness index can help determine what conservation measures need to be taken to provide a habitat where species can survive and thrive.


Another consideration when determining species richness is taxonomy. Taxonomy is the science of classifying things. In biology, we classify things in a certain order, which is: kingdom, phylum, class, order, family, genus and species.

The mnemonic phrase ‘King Phillip Crossed Oceans For Good Spices’ can help you remember the order.Let’s take a quick look at an example, and classify humans:

  • Our kingdom is Animalia, because we are animals
  • Our phylum is Chordata, which is for chordates, or animals with a backbone
  • Our class is Mammalia, since we are mammals
  • Our order is Primate, since we are evolutionarily considered to be primates
  • Our family is Hominidae, which is a family specifically for humans
  • Our genus is Homo
  • Our species is Homo sapiens

Note that when talking about a specific species, you include both the genus and species name.So if we can identify specific species in a given environment versus labeling organisms as just a fish, plant or bird, then our species richness index may dramatically change.Let’s think about our lake community again. Before, when we assumed that each organism was a single species (fish, bird or plant), we had a species richness index of three.

Now, if we take a closer look, you might note there are four different species of fish, three different species of bird and two species of plant. Our species richness index just went up to nine!


From our lake community example, you can see why standardizing sampling practices can be so important. The same ecosystem can be sampled and very different species richness indices can be counted, depending on how you sample and how specific you are when counting different species.

If you sent two scientists out to sample our lake community and only told them to count species, you could end up with a species richness index of three or nine. However, if you told these scientists to standardize their sampling practices to a specific taxonomic level, you should get the same species richness index from both scientists. This can be useful when comparing ecosystems in different areas – for example, the species richness index of a lake in Colorado versus a lake in Scotland.

Lesson Summary

Species richness is a count of the number of species in a given habitat or ecosystem. Unlike species diversity, species richness does not take species abundance into account.

One factor which is important to consider when measuring species richness is sampling methodology. The size of your sampling area, as well as how species-specific you are, can greatly influence the species richness index in a given community. Therefore, standardizing sampling practices is very important.No matter how you sample or the size of habitat you are sampling, species richness is a useful index for conservation practices.

Learning Outcomes

Once you have seen this video, you should be able to:

  • Understand what species richness is
  • Differentiate between species diversity and species richness
  • Explain why it’s important to standardize sampling practices

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