What is the Difference Between Species Richness and Species Evenness

The main difference between species richness and species evenness is that species richness is the total number of species in an ecological community whereas species evenness is how evenly distributed the species are in the ecosystem.

Species richness and species evenness are the two main components of measuring the species diversity in an ecosystem.

Key Areas Covered

1. What is Species Richness
   • Definition, Characteristics, Importance
2. What is Species Evenness
   • Definition, Characteristics, Importance
3. Similarities Between Species Richness and Species Evenness
   • Outline of Common Features
4. Difference Between Species Richness and Species Evenness
   • Comparison of Key Differences

Key Terms

Alpha Diversity, Beta Diversity, Gamma Diversity, Shannon Index, Simpson Index, Species Evenness, Species Richness

What is Species Richness

Species richness is the number of species within a defined region. Generally, species richness counts the number of species in a particular ecosystem. However, it does not describe the abundance of the species in that particular ecosystem. It’s possible to measure the species richness through either sampling or a census. In addition, species richness can be divided into three components: alpha diversity, beta diversity, and gamma diversity. Alpha diversity or point diversity is the species richness that occurs within a given area that is smaller than the entire distribution of the species. Beta diversity, on the other hand, is the rate at which the species richness increases with the change of the habitat from one to another. Moreover, gamma diversity is the species richness within the entire region.

Figure 1: Global Species Richness in Mammals

Furthermore, species richness does not describe the distribution of the species within a particular geological area. It only describes the number of species in the above particular geological area. Although species richness is synonymous with species diversity, species diversity accounts for both species richness and species evenness.

What is Species Evenness

Species evenness is the number of species and the relative abundance of species in a particular community. There are several indices to describe species evenness and the two most common measures of evenness are the Shannon index (H) and the Simpson index (D). The Shannon index (H) is a measure of the information content of a community rather than that of a particular species. On the other hand, the Simpson index (D) measures the dominance of a multispecies community and can be thought of as the probability that two individuals selected from a community will be of the same species.

Figure 2: World Crop Evenness

Moreover, species evenness is important for scientists to know the abundance of species in an ecosystem. The measurement of the species’ evenness is an area-based count. These area-based accounts are important for species that are immobile. Another method of measuring species evenness is the distance-based method that uses the number of individuals per unit area. In mobile organisms, the mark-recapture method is important to take measurements. Here, marked individuals are given time to move, and their recapture gives a measurement of the total number of individuals in the population.

Similarities Between Species Richness and Species Evenness

• Species richness and species evenness are two components important in measuring the biological diversity of an ecosystem.
• Both measures describe the species living in a particular area.

Difference Between Species Richness and Species Evenness

Definition

Species richness refers to the number of different species represented in an ecological community while species evenness refers to how evenly distributed the species are in the ecosystem.

Significance

Moreover, species richness describes the number of species in the ecosystem while species evenness describes the distribution of the species in the ecosystem.

Measurement

Species richness measures the number of species in a particular area while species evenness measures the abundance of species in a defined area.

Conclusion

In brief, species richness and species evenness are two measurements that help to measure the biological diversity of a particular ecosystem. Here, species richness describes the number of species in a particular geological area. In contrast, species evenness describes how even the species are distributed in a particular ecological area. Therefore, the main difference between species richness and species evenness is the type of measurement.

References:

1. “Species Richness.” Species Richness – an Overview | ScienceDirect Topics.
2. “Species Evenness.” Species Evenness – an Overview | ScienceDirect Topics.

Image Courtesy:

1. “Global Mammal Richness Grids, 2015 Release, All Mammals (28871815285)” By SEDACMaps – Own work (CC BY 2.0) via Commons Wikimedia
2. “World crop eveness” By Bioversity International – Own Work (CC BY-NC-ND 2.0) via Commons Wikimedia