An ecologist compared the biodiversity of ground-dwelling invertebrates in two agricultural wheat fields. Field A was managed using conservation headlands (leaving an unsprayed margin around the boundary), while Field B was managed using intensive herbicide and insecticide applications.
The table below shows the number of individuals of each ground beetle species captured in pitfall traps from each field:
| Species | Field A (Conservation) | Field B (Intensive) |
|---|---|---|
| Pterostichus melanarius | 10 | 17 |
| Nebria brevicollis | 5 | 1 |
| Amara aenea | 3 | 1 |
| Bembidion lampros | 2 | 1 |
Using the formula for the index of diversity:
d=N(N−1)∑n(n−1) d = \frac{N(N-1)}{\sum n(n-1)} d=∑n(n−1)N(N−1)where N N\,N is the total number of organisms of all species and n n\,n is the total number of organisms of each species, which of the following statements correctly evaluates the biodiversity of these two fields?
Field A has a higher species richness than Field B, but Field B has a higher species evenness.
Both fields have the same species richness, but Field A has a higher index of diversity (d≈3.22d \approx 3.22d≈3.22) than Field B (d≈1.40d \approx 1.40d≈1.40).
Field B has a higher index of diversity than Field A because the calculated ddd values are d≈0.72d \approx 0.72d≈0.72 for Field B and d≈0.31d \approx 0.31d≈0.31 for Field A.
Both fields have the same index of diversity (d≈1.05d \approx 1.05d≈1.05) because they have the exact same total population size (N=20N = 20N=20) and species richness.
