BIODIVERSITY

I. Introduction
Diversity is a characteristic of community level ecology. Community diversity can be compared between different habitats, over time in the same habitat, and between similar habitats in different locations. Diversity indices are calculated so mathematical (statistical) comparisons can be made. We will collect field data of invertebrate diversity from several different locations on campus.

The Brockport campus was once farmland. The land was plowed and crops were grown. Since the purchase of this land for the SUNY Brockport campus, buildings and athletic fields were constructed, lawns created, and parking lots paved. Some of the land however was left untouched, or was mowed for a short time, or mowed every few years. This has left areas in different stages of soil, plant, invertebrate and therefore community succession.

Calculating Community similarity and diversity Indices

Biological systems are organized on many different levels: molecules, cells, organisms, populations, communities and ecosystems. Species diversity is a characteristic unique to the community level of biological organization. Higher species diversity is generally thought to indicate a more complex and healthier community because a greater variety of species allows for more species interactions and indicates good environmental conditions. A variety of diversity indices can be calculated to compare ecological communities. In addition, pairs of communities can be compared using community similarity indices.

Species diversity has two parts. Richness refers to the number of species found in a community and evenness refers to the relative abundance of each species. A community is said to have high species diversity if many nearly equally abundant species are present. If a community has only a few species or if only a few species are very abundant, then species diversity is low. Consider a community with 100 individuals distributed among 10 species. It should make sense that if there are 10 individuals in each of the 10 species in the community it is more diverse than if there are 91 individuals in one species and one individual in each of the other nine species.

To give another example, we might have sampled two different fields for wildflowers. The sample from the first field consists of 300 daisies, 335 dandelions and 365 buttercups. The sample from the second field comprises 20 daisies, 49 dandelions and 931 buttercups (see the table below). Both samples have the same richness (3 species) and the same total number of individuals (1000). However, the first sample has more evenness than the second. This is because the total number of individuals in the sample is quite evenly distributed between the three species. In the second sample, most of the individuals are buttercups, with only a few daisies and dandelions present. Sample 2 is therefore considered to be less diverse than sample 1.

A community dominated by one or two species is considered to be less diverse than one in which several different species have a similar abundance.

As species richness and evenness increase, so diversity increases. Simpson's Diversity Index is a measure of diversity which takes into account both richness and evenness.

Simpson's Diversity Index is a measure of diversity. In ecology, it is often used to quantify the biodiversity of a habitat. It takes into account the number of species present, as well as the abundance of each species.

Simpson's Diversity Indices

The term 'Simpson's Diversity Index' can actually refer to any one of 3 closely related indices.

Simpson's Index (D) measures the probability that two individuals randomly selected from a sample will belong to the same species (or some category other than species). There are two versions of the formula for calculating D, either is acceptable, but be consistent.

The value of D ranges between 0 and 1

With this index, 0 represents infinite diversity and 1, no diversity. That is, the bigger the value of D, the lower the diversity. This is neither intuitive nor logical, so to get over this problem, D is often subtracted from 1 to give:

Simpson's Index of Diversity 1 - D

The value of this index also ranges between 0 and 1, but now, the greater the value, the greater the sample diversity. This makes more sense. In this case, the index represents the probability that two individuals randomly selected from a sample will belong to different species.

Another way of overcoming the problem of the counter-intuitive nature of Simpson's Index is to take the reciprocal of the Index:

Simpson's Reciprocal Index 1 / D

The value of this index starts with 1 as the lowest possible figure. This figure would represent a community containing only one species; the higher the value, the greater the diversity. The maximum value is the number of species (or other category being used) in the sample. For example if there are five species in the sample, then the maximum value is 5.

II. Assignment

Today we will sample leaf litter to determine the relative diversity of invertebrate. The three lab sections will sample from different locations on campus and share relative data. Using a 1 m x 1 m box transect you will leaf litter within for analysis. All leaf matter from this area will be collected and transferred back to the lab for analysis. The material will be placeed in a Berlese funnel apparatus consisting of of a funnel lined with screening (or a large piece of screening over a tray). A light source is placed above the funnel and heats the leaf litter. The purpose of this apparatus is to collect the tiny invertebrates from the sample as they fall into a sample collection jar located below the funnel. After a period of one hour, you will record the number of invertebrates and calculate the Simpson's Diversity Index (1-D) for the samples from all lab groups. Your assignment is to answer the following questions and include all relevant equations based on the data you collected, analyzed and interpreted.

Exercise 1: Simpson's Index of Diversity

Simpson's Index calculates the probability that two invertebrates sampled from a community will belong to different species (the more even the abundance of individuals across species, the higher the probability that the two individuals sampled will belong to different species). Simpson's Index values range from 0 to 1, with 1 representing perfect evenness (all species present in equal numbers). The formula for Simpson's Index of Diversity is:

Ds = 1 - Sum (ni*(ni-1))                          (Equation 2)

             Sum (N*(N-1))

--add all ni*(ni-1) values together, ni = the number of individuals in the ith species collected, and N = the total number of organisms in the sample. For example, suppose you collected 3 species with 40, 25 and 15 individuals, respectively.

Ds = 1 - 40(39) + 25(24) + 15(14)

                                80(79)

= 1 - 2370

        6320

= 1 - 0.375

= 0.625

**Calculate the Simpson's Diversity Index (1-D) for all areas samples (Wed morning lab, Wed evening lab and Fri morning lab).

Exercise 2: Calculating the Proportional Index of Community Percent Similarity

A good way to compare communities in different places (e.g., middle and lower Sandy Creek) or at different times (e.g., lower Sandy Creek in spring and fall), is to use measures of community similarity. We will use a simple measure, called Percent Similarity, to compare the invertebrate communities on campus. The table below gives an example for you to work through.

Table 1. The percent of hypothetical fish sampled for 5 categories in community 1 and community 2.

The lesser value for category A between community 1 and community 2 is 0% (community 2) therefore you take that value.

Example:

Community 1, Category B = 25 specimen out of 93 total

Community 2, Category B = 7 specimen out of 112 total

Therefore: =PS = 25/93= 26.88% 7/112 = 6.25% -à Lowest value, use it

Then: PS= 0% (from Category A) + 6.25% (from Category B) = 6.25 % (for the first 2 categories).

PS (Percent Similarity) = (lowest percent value between categories of communities), in this case:

PS = 0% + ?% + ?% + ?% + ?% = ??%

**Find the percent similarity for the invertebrate communities sampled by the classes with the lowest and highest Simpson's diversities.

.

*Highest diversity indicates the highest value for calculated 1-D from all three habitats sampled

**Lowest diversity indicates the lowest value for calculated 1-D from all three habitats sampled

In terms of habitat, and your answers to the questions above, explain why you think you got the results you did for 1-D and community percent similarity?