Assessing Diversity Notes

Estimating Biodiversity Aim How we charactarise communities. Focus on population diversity and population growth (excluding factors such as mutualism, predation etc). How do characterise biodiversity? The diversity of lakes, grasslands, the diversity of insects and microflora within grasslands etc. They way diversity is characterised is fairly uniform. One approach would be to count all of the species and compare directly - the most basic way communities are characterised. There are obvious shortcomings. May not be able to see all the species, so what often happens is counting a subset and extrapolating. In both of these examples, there are 5 plants species, but it cannot be said that they are equally diverse, as there are more pink flowers on the right than on the left - the equitability of these communities is different. So we want a diversity estimate to characterise that one community is diverse but the other is experiencing dominance. Species richness is a matter of counting everything - has x number of species. Species diversity is a scale of richness and relative abundance. In the above example, the species richness is equal to 5 for both examples; however the species diversity is 0.698 and 0.0178 for the two samples respectively. Simpson's Diversity Index The simplest and most common diversity index. Higher values of D = higher diversity For a given richness, D increases with equitability For a given equitability, D increases with richness. So if there are two species that are equally represented, it will not be as diverse as 4 species that are equally represented. Shannon-Weaver Higher numbers again correlate to higher diversity. In most cases, giving the same information but some more sensitive to rare species than others. 

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