Practise calculating Simpson’s index from species counts and interpreting values near zero or one to compare diversity, evenness and habitat effects.
Bears are several species of mammal in the family Ursidae.
Climate change and loss of habitats due to human activity have reduced the size of some bear populations in recent years.
Human activity has disturbed the habitat of many populations of spectacled bear, Tremarctos ornatus. The spectacled bear feeds on a variety of plant and animal species.
Scientists compared the diversity of the food eaten by two populations of spectacled bear by analysing their faeces. One population lived in an undisturbed habitat and the other population lived in a habitat that had been disturbed by road building.
The scientists analysed the faeces from 60 bears in each population. They identified the species present and the number of individuals of each species in the faeces.
The scientists calculated the diversity of species in the faeces of the two populations using Simpson's Index of Diversity.
The formula for Simpson's Index of Diversity is:
n= number of individuals of each species present in the sample
N= total number of all individuals of all species
Table 8.1 shows the results and some of the steps for calculating the D value for the disturbed population.
Table 8.1
Calculate Simpson's Index of Diversity by completing Table 8.1 in the spaces provided.
Write the value for Simpson's Index of Diversity on the dotted line.
The scientists calculated a D value of 0.833 for the undisturbed population.
Explain what is shown by the difference in the D values between the two populations of bear.