The loss of biodiversity has many consequences that we understand, and many that we do not. It is apparent that mankind is willing to sustain a great deal of biodiversity loss if there are concomitant benefits to society; we hope they are net benefits. In many cases, the benefits seem to accrue to a few individuals only, with net societal loss. However, as noted below, it is extremely difficult to estimate the future costs of losses in biodiversity, or of environmental damage. As stated by Tilman (2000), “The Earth will retain its most striking feature, its biodiversity, only if humans have the prescience to do so. This will occur, it seems, only if we realize the extent to which we use biodiversity.”
Losses in biodiversity in rainforests cause significant changes in ecosystem functioning. About ecosystem functioning in tropical rain forests we know very little, but we do know that ecosystems are affected by changes in the number and kinds of species which they contain, an idea originally conceived by Charles Darwin and Alfred Russel Wallace. Intact ecosystems function best, since the organisms composing them are specialized to function in that ecosystem to capture, transfer, utilize and, ultimately, lose both energy and nutrients. The particular species making up an ecosystem determine its productivity, they affect nutrient cycles and soil contents, and they influence environmental conditions such as water cycles, weather patterns, climate and other no-biotic aspects.
What regulates the normal functioning of an ecosystem? There are many interrelated, complex (and little-known) factors which ensure this function. There appear to be certain keystone species which are critical in the functioning of any ecosystem, as well as other species which are of more marginal importance, the loss of which would not be catastrophic. In some ecosystems it is possible that many species can disappear without serious degradation of most of the functional aspects of the ecosystem (Grime, 1997). Many ecologists nevertheless feel that the total number of species has a great effect on ecosytem functioning, and there is some evidence that it does (Loreau and Hector, 2001; Loreau, et al., 2001, for example). However, it cannot be simply the number of species, but also the fact that different species utilize different resources in a particular environment (“niche complementarity”) that affects function. Species, existing in proximity to each other, nevertheless utilize different microhabitats and nutrient combinations, and so are capable of exploiting all aspects of the environment. Conversely, reducing biodiversity may lead to a diminishment of productivity because of the loss of some of these niche roles; that is, a loss of functional diversity. However, how many species can be lost without serious alterations of an ecosystem; which species can be lost without serious consequences; and under what circumstances species loss will cause the destruction of the ecosystem, we do not know, for the most part.
One important fact that is often forgotten is that ecosystems are, as it were, living structures. They are constantly changing and subject to evolution, so that at various times they will be composed of different organisms. According to pollen data and information gathered from fossil bones, few modern ecosystems are the same as they were 10,000 years ago. They originate bit by bit as the environment changes, and as species become extinct or shift their geographical range or their anatomy or behavior.
As we continue to lose species at a rapid rate, we must discover which losses will have the most deleterious consequences on ecosystems. At present, we know little, and what we do have is information on short-term, small-scale experimental plots. We need to know more, much more. It is vital to realize, then, that biodiversity does not mean simply the number and kinds of living organisms present. Biodiversity depends upon the habitats and ecosystems which support them. As John Muir said, “When we try to pick out anything by itself, we find it hitched to everything else in the universe.”