The Tropics as the Norm in Biogeography?

Abstract

inputs vary, but still this is a common characteristic for most of the biomes about which we will be taking. When we come, however, to consider precipitation, it is a little more difficult, because regions with this high radiant energy input embrace areas ranging from those with plentiful rainfall and high humidity throughout the year to nearly rainless deserts and through many climates with complex gradations between these two extremes. When we consider the concept of 'the norm', therefore, we may well be forced to limit our definition to, say, a true core area, such as the genuine lowland tropical rain forest and Koppen's Af climates. The tropics are also a region in which chemical and biological changes are noted for their speed of reaction, and we shall have to see whether the speed and nature of these reactions differ by degree only or in fundamental principle from those obtaining elsewhere on the globe. And, finally, we must accept, initially at least, a traditional view of the lowland tropical rain forest belt, namely that it is very old and has been but little affected by the climatic and other environmental changes incident on the Quaternary glaciations. However, I suspect that Dr Flenley may have a few caveats to enter concerning that common view and we may have to consider anew the so-called stability of a core community of lowland tropical rain forest. Let us now consider the second word, that enigmatic concept of a 'norm'. The main thesis underlying the question mark of this meeting is that, perhaps, because so much biogeographical and ecological theory has been developed from work in the boreal and temperate regions of the world, this theory has turned what is essentially the abnormal?the simple and the geologically young?into the normal, and that it could be misleading to have developed most of our basic principles in regions with soils and vegetation which are, in the main, less than 10 000 years old. Should not the tropics be the norm for developing theory and basic principles and not these clearly juvenile and ill-developed areas? I shall quote, as an example of the dilemma, one extreme instance. If the wilder theories of certain writers, such as those of the Russian, Federov (1966), were proved to have substance, and speciation (the creation of new species) in lowland tropical rain forest was seen to be governed by the random processes of genetic drift and not the clearly adaptive neo-Darwinistic principles of natural selection, then there would be no obvious and essential ecological relationship between habitat and species. The fundamental tenet of most ecological thinking would, in fact, be brought into question. This extreme case illustrates well the problem which we are confronting. In this instance, the differences would not be of degree only, but of principle. Many workers, on the other hand, regard the differences as of degree rather than of principle. The