Domains of Diversity

摘要

Leaving an English winter, Charles Darwin was soon writing gushing prose to his family about Brazil's biodiversity. He expected such variety because for centuries naturalists had returned from the tropics with unusual and colorful specimens. Yet, even today, pointed disagreements persist about why the tropics have more species than other latitudes. The many hypotheses reflect three deeply different approaches. Two date back to the time of Wallace: One stresses ecological processes, such as a location's temperature and rainfall, the other historical factors, such as whether a region was covered in ice during recent glaciations. The third approach is a newcomer that explains species richness as a simple, statistical consequence of the observation that some species have large geographical ranges, whereas others have small ranges. This explanation echoes a classic debate about the patterns of communities. (By "pattern," ecologists mean such features as how many species a community houses, or how similar those species are morphologically.) Proponents and critics of all three approaches have recently exchanged salvos.