Backyard Species Diversity Lab

A blog post by Derik Verkest and Bo Nash

Introduction/Background

Species diversity and biodiversity as a whole not only is aesthetically pleasing when you look at an environment, it is also very important in the ecological balance of an ecosystem. Biodiversity is the number of species in a given area and species diversity combines two measurements: species evenness and species richness. Species evenness is a measure of how many individuals there are of one species while species richness is the amount of species present in that community. In this lab we will be showing two examples of biodiversity. This is a very simple exercise and all you need is a backyard, which is where our information comes from. Below you will see data that represents species diversity and species evenness in order to determine which backyard is more diverse. In order to do this we will use mathematical models and equations. Below are the symbols used for these equations and their respective meanings.

• Species richness (R)= the number of species
• Shannon-Wiener Index (H’): determined by the number of species and the species evenness
  • H = – ∑ (P_i log₂ P_i)
    • p_i = relative abundance of a given species = (n_i/N)
    • Log₂ = natural log of p_i
    • n_i = number of individuals in species i
    • N = total number of individuals in all species
• Species evenness (E)= how many individuals are in a species

Although these definitions and equations may seem complicated, we will be showing how the results have been calculated in order to determine our final result: which backyard is more diverse.

Importance of Biodiversity

Why is biodiversity important? You might be asking yourself this as you read this blog. Biodiversity is crucial to maintaining a balance in an ecosystem. Not only does it have dramatic and prolonged effects in a wild ecosystem, biodiversity also benefits humans in a huge way. We get medicine by observing diverse ecosystems. Without diversity in our crops we cannot determine if one plant species has a genetic edge over another. Without diversity, a community is more susceptible to a changing environment, which is what we’re undergoing right now. These are just some of the many reasons why biodiversity is important and why this experiment is being conducted.

Results

For the following data, two backyards had pictures taken of them and the species of vegetation within each picture was identified and counted to the best of our ability. The species diversity and evenness were then analyzed using this gathered information, evenness being how proportional the number of individuals of each species are in relation to the other species. The closer to 1 that the species evenness get to, the more even in population level each species is to each other. For the first backyard (Fig.1), the species diversity was calculated using the Shannon-Wiener Index (H’), resulting in a value of 1.53. The higher this value, the more diverse the environment. The species evenness (E=0.951) was then calculated using H’ and species richness (R=5).

In the second backyard (Fig.2), the species diversity was calculated to be 1.08. The species evenness was 0.983 and species richness 3.

When comparing the two backyards to one another, we see that the H’ for backyard 1 is greater than backyard 2, which implies that the environment for backyard 1 is more diverse. However, the species evenness is greater in backyard 2 due to being closer to 1. In backyard one, Tall Fescue and Southern Forager dominated most of the are, and this is most likely due to the two plants having an advantage in that particular environment, whether that’s moisture level or sun exposure. In backyard 2, there was no real dominance of one species over another, which is most likely due to a lack of competition from other species.

Characteristics of an ecosystem with a high Shannon-Wiener Index include places with a healthy balance of rain, warmth, sunlight, and soil nutrients. Duration and intensity of the warm seasons also effects the outcome of this measurement because some plants take months to bloom. The presence of invasive species can negatively effect the diversity due to the higher success in competition between the invading and native species, resulting in the reduced fitness of the native species. The higher diversity level of backyard 1 is due to a lack of maintenance and high moisture level in the area is resides in. Water collects heavily throughout that area and the vegetation is rarely disturbed or cut. Along with this, the spot gets plenty of sunlight even though it’s at the base of a tree. In backyard 2, the lower diversity level is most likely due to selective, regular maintenance of the area along with the dominance of trees shading most of the sunlight.

Results Analysis

After analyzing the two backyards, it was found that Backyard 1 had the greater biodiversity. This also means that this backyard will have the greater degree of ecological stability. The reason that there is a correlation between a high biodiversity and a high ecological stability has to do with the variation of the species. If there are few species in an environment and they are introduced to an outside stress, there is less of a chance that there could be a species that can adapt or survive that outside stress. If there is a greater diversity in species and number of individuals in that species, then there is a far greater chance that any one of those species can buffer the effects of that outside stress and survive.

Peer Review Article

Below is a research article in the widely renowned journal “Nature” that explains biodiversity as a whole and how it is under pressure in our ever-changing landscape and climate.

Anna Armstrong. (2017). Biodiversity. Nature, 546(7656), 47. https://doi.org/10.1038/546047a

Credit

• Bo Nash: Introduction/Background, Importance of Biodiversity, Peer Review Article, Results Analysis
• Derik Verkest: Results, Data Tables

Works Cited

• Anna Armstrong. (2017). Biodiversity. Nature, 546(7656), 47. https://doi.org/10.1038/546047a