how could a community appear to have a relatively small diversity even though it is rich in species?

Species diversity is determined not only by the number of species within a biological community—i.e., species richness—but also by the relative abundance of individuals in that community. Species abundance is the number of individuals per species, and relative abundance refers to the evenness of distribution of individuals among species in a community. Two communities may be equally rich in species but differ in relative abundance. For example, each community may contain 5 species and 300 individuals, but in one community all species are equally common (e.g., 60 individuals of each species), while in the second community one species significantly outnumbers the other four.

These components of species diversity respond differently to various environmental conditions. A region that does not have a wide variety of habitats usually is species-poor; however, the few species that are able to occupy the region may be abundant because competition with other species for resources will be reduced.

Trends in species richness may reveal a good deal about both past and present conditions of a region. The Antarctic continent has few species because its environment is so inhospitable; however, oceanic islands are species-poor because they are hard to reach, or, as is the case with the Lesser Sunda Islands in south-central Indonesia, because they are of rather recent origin and organisms have not had enough time to establish themselves.