Quiz 22: Geographic Ecology
The plot of the logarithms of area and species number should yield the tightest relationship between area and species richness.
The sample size is an important consideration in small-scale and large-scale ecological studies. The sample size determines the accuracy and the reliability of the statistical analysis. An appropriate sample size makes the sample, a true representative of the population. The sample size depends on the heterogeneity or variability of the sample and the scale of the study. Global or large-scale ecological studies may need collection of samples from different regions of a continent or from different continents. For global studies such as determination of population census, the whole population has to be analyzed. Hence, sample size becomes equal to population size. Large number of samples may be required to make generalizations at the global-level. This proves laborious and is practically not feasible. Hence, computer-based collection and analysis of data are being used for the global studies. Published data is also used for the large-scale statistical analysis.
MacArthur and Wilson studied the effect of isolation on species richness on islands. New Guinea was considered as a source of species for the surrounding islands. The islands selected for the study of species richness were isolated by variable distance from New Guinea. They were classified as islands near New Guinea, islands at intermediate distance from New Guinea and islands far from New Guinea. The islands selected were of similar area to avoid the influence of area in the study. Their study showed that islands located near New Guinea showed higher species richness than the islands at intermediate and far distance.The species richness was least in the islands far from New Guinea. This observation supported the hypothesis that isolation is one of the factors affecting species richness and it lowers species richness.