BIODIVERSITY IN LEAF LITTER PURPOSE: The purpose of this lab is to measure the biodiversity of organisms found in a sample of leaf litter. Species diversity is a characteristic that is unique to a community level of biological organization. The biodiversity in different communities has been severely affected by human activities. A community is said to have high species diversity if it has many species present in approximately equally abundant numbers. If it is composed of only a few species or if only a few species are abundant, then the biodiversity is considered to be low. If a community had 100 individuals distributed among 10 species then the maximum possible diversity would occur if there were 10 individuals in each of the 10 species. The minimum possible diversity would occur if there were 91 individuals belonging to one species and only 1 individual in each of the other nine species. The number of species in a community is very important. There seems to be evidence that the greater the species diversity, the more stable the community; and with severe disturbance such as pollution, diversity may decline severely. In this lab we will use Simpson's Index of Diversity and the Shannon- Weiner Diversity Index. We will first determine the relative abundance of each individual species. Abundance compares the number of organisms of a particular species with the total number of organisms found in the sample. After we have determined the abundance we will measure the dominance. A species with a high diversity will have a low dominance and this is a good measure of species diversity. The following are examples of how to calculate abundance and also how to use Simpson's Index to determine diversity. Species i Abundance n i Relative Abundance p i 1 50 50/85 = 0.588 2 25 25/85 = 0.294 3 10 10/85 = 0.118 S = 3 N = 85 Once you determine the abundance, then you determine the dominance. See the attached page to understand how to do this. Dominance is a determination of diversity. It is the probability that two randomly selected individuals would belong to different species. The diversity index is an expression of the number of times one would have to take pairs of individuals at random from the entire community to find a pair from the same species.
MATERIALS: Compound microscope Berlese funnel (w/ screen, vial) leaf litter Identification sheet light source isopropyl alcohol (or methyl alcohol) To collect small organisms the Berlese funnel is commonly used. A sample is taken and put in the funnel with a wire screen below the litter. A bright light is placed above the funnel and a container with alcohol is placed below the funnel. The invertebrates fall into the alcohol. Use the attached data table to classify your organisms. Bug identification sheets available in the laboratory. When you have finished with the classification, you will be able to determine species abundance and species diversity. Species Name Number of Organisms 1 2 3 4 5 6 7 8 9 10 11 12 13 14 If you are unable to identify a species, just call it x, y, z, etc.
DISCUSSION: 1. How is the Berlese funnel able to separate the organisms from the leaf litter? 2. What does this indicate about the living conditions which these various organisms prefer? 3. Using your answer from the Diversity Index, summarize whether you think this particular location from which the litter came is an area of high or low diversity. If the diversity is low, try to give some reasons why it might be low.
A diversity index is a mathematical measure of species diversity in a community. Diversity indices provide more information about community composition than simply species richness (# species present). They also take into account the relative abundances of different species Simpson's (1949) Diversity Index Ds = 1 - Σ [ ni(ni-1) ] / N(N-1) Species i Abundance n i Relative Abundance p i Snail A 50 50/85 = 0.588 Snail B 25 25/85 = 0.294 Insect A 10 10/85 = 0.118 S = 3 N = 85 Ds = 1 - [ {50(49) + 25(24) + 10(9)} / 85(84) ] Ds = 1-3140 / 7140 Ds = 1-0.44 Ds = 0.56
Shannon-Weiner Diversity Index (H) Equitability (Evenness) (E H ) Total Number of Species (S) H = - Σ p i ln p i E H = H/H max = H / ln S Name # p i ln p i p i ln p i