Make Your Booking. Simpson's Diversity Index 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. Use of this website constitutes acceptance of our Privacy and Cookies Policy. A diversity index is a quantitative measure that reflects the number of different species and how evenly the individuals are distributed among those species.
Typically, the value of a diversity index increases when the number of types increases and the evenness increases. For example, communities with a large number of species that are evenly distributed are the most diverse and communities with few species that are dominated by one species are the least diverse.
We are going to examine several common measures of species diversity. An equivalent formula is:. Since the mean of the proportional abundance of the species increases with decreasing number of species and increasing abundance of the most abundant species, the value of D obtains small values in data sets of high diversity and large values in data sets with low diversity.
Using the inverse, the value of this index starts with 1 as the lowest possible figure. The higher the value of this inverse index the greater the diversity. This version of the index has values ranging from 0 to 1, but now, the greater the value, the greater the diversity of your sample. This compliment represents the probability that two individuals randomly selected from a sample will belong to different species. The Shannon-Weiner index Barnes et al. 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. For example, the diversity of the ground flora in a woodland, might be tested by sampling random quadrats. The number of plant species within each quadrat, as well as the number of individuals of each species is noted. There is no necessity to be able to identify all the species, provided they can be distinguished from each other. As an example, let us work out the value of D for a single quadrat sample of ground vegetation in a woodland.
Of course, sampling only one quadrat would not give you a reliable estimate of the diversity of the ground flora in the wood. Several samples would have to be taken and the data pooled to give a better estimate of overall diversity. How many samples? Putting the figures into the formula for Simpson's Index. These 3 different values all represent the same biodiversity. It is therefore important to ascertain which index has actually been used in any comparative studies of diversity.
A value of Simpson's Index of 0. Simpson's Index gives more weight to the more abundant species in a sample. The addition of rare species to a sample causes only small changes in the value of D.
Ecological Sampling Contents. Simpson's Diversity Index is a measure of diversity. They each have three species. But when we look at the data, it's clear that community two is mostly species A and you have very small groups of species B and species C, while community one is more evenly spread.
So just intuitively it feels like community one is maybe more diverse, but this was just on my intuition or our intuition, and the numbers are pretty clear here. It's evenly distributed amongst the species here, and here it's very heavily weighted on species A, but it might not always be this clear. So it'd be useful to have some type of quantitative way to measure the diversity of a population. And lucky for us, there is a quantitative way to do that called Simpson's, I'll write it down, Simpson's diversity index, and the way you calculate it, it's equal to one minus the sum of, for each species you take the number of that species divided by the community size squared.
So for each of the species, you do this calculation, square it and then you add it up for each of those species. So let's figure out Simpson's diversity index for both communities one and community two. And I encourage you you could pause the video and try to work on it on your own before I work through it with you. So let's start with community one. So I'll say diversity index for community one. I'll just put that in parentheses, is going to be equal to one minus, so we have over, over 1, squared.
Remember, we're gonna sum on each of these species plus , over 1, squared plus over 1, squared. And I need to close my parentheses, and I can simplify this a bit.
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