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.