Biodiversity of Different Habitats

The index of diversity lets biologists compare biodiversity between habitats in a fair, quantitative way. The habitat with the higher value of D has the greater biodiversity.To make a valid comparison, the sampling method must be the same in each habitat: the same type and size of quadrat or trap, the same number of samples, random placement, the same time of year, and the same method of identifying organisms.Worked example. A student samples ground beetles with pitfall traps in a woodland and in a field of wheat.Woodland: 5 species with 8, 6, 5, 4 and 2 individuals.N = 25, so N(N − 1) = 25 × 24 = 600.Σn(n − 1) = 56 + 30 + 20 + 12 + 2 = 120.D = 600 / 120 = 5.0.Wheat field: 3 species with 20, 3 and 2 individuals.N = 25, so N(N − 1) = 600.Σn(n − 1) = 380 + 6 + 2 = 388.D = 600 / 388 = 1.55.The woodland is far more diverse. It has more species, and its individuals are spread more evenly.Differences like this have biological explanations. Natural habitats such as woodland, hedgerows and wetlands usually have many different plant species, several layers of vegetation and a range of microhabitats, so they provide more niches and support more animal species. Farmland monocultures, especially where pesticides and herbicides are used, provide few niches, so fewer species survive and a few tolerant species dominate.Because a single sample may not be representative, repeated samples should be taken and statistical tests used to decide whether a difference in diversity is significant.