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Calculating Diversity Aquatic Ecology Why quantify biodiversity? • Initially thought that more diversity = more stable ecosystem • Now used to measure and track changes How do we measure biodiversity? • Use functional categories – Ecosystem, species, genetics Describing Communities • Two methods – Describe physical attributes (e.g. age, class, size class) – Describe number of species and their abundance Biodiversity • • • • Diversity of living things Term often misused and overused Current focus in conservation studies Includes interest in genetic, species and ecosystem diversity • We will use species as our focus but concepts can be used for genetic and ecosystem diversity as well. Species Richness • • • • Number of species in a community The simplest measure Can count all spp only is few simple ecosystems Does not consider number of individuals Evenness • Evenness is a measure of the relative abundance of the different species making up the richness of an area. • • • • • • Numbers of individuals Flower Species Sample 1 Daisy 300 Dandelion 335 Buttercup 365 Total 1000 • What is the Richness? • What is the Evenness? Sample 2 20 49 931 1000 Species diversity • Species richness not very informative • Each community has 5 spp & 50 individuals Comm A Comm B Spp 1 Spp 2 Spp 3 Spp 4 Spp 5 10 10 10 10 10 46 1 1 1 1 Diversity indices • To get a better description of the community we need to get a measure of spp richness and evenness of their distribution • We usually use an index to represent several different measures – E.g. stock markets, air pollution, etc. Diversity indices • Over 60 indices used in ecology • Indices used to measure proportional abundance • Two major forms: – Dominance indices (e.g. Simpson index) – Information indices (e.g. Shannon Weiner index) Simpson Diversity Index (D) – Simpson’s index considered a dominance index because it weights towards the abundance of the most common species. – measures the probability two individuals randomly selected from a sample will belong to the same category – For example, the probability of two trees, picked at random from a tropical rainforest being of the same species would be relatively low , whereas in the boreal forest would be relatively high. Simpson Diversity Index (D) I = (n1(n1 -1)/N(N-1)) Where: Ds = 1-I n1 = number of individuals of spp 1 N = Total number of spp in community In this form as diversity increases index value gets smaller Simpson Diversity Index (D) Mayflie stonefl Damself Midge Gilled Total s ies lies Snails # Species 56 48 12 6 ((56*55)/(125*124))+ ((48*47)/(125*124)) + …………. ….((3*2)/125*124)) = 0.35509 3 125 Simpson Diversity Index (D) • • • • Complimentary form = 1-I = 1-0.35509 = 0.6449 Reciprocal 1/I = ds 1/0.35509 = 2.816 Questions?