The Importance of Population Processes for the Maintenance of Biological Diversity

Abstract

The central question in ecology is why a certain species is present at a given site and absent at others. A common view is that the physical site conditions determine the distribution and abundance of species, and therefore patterns of species and ecosystem diversity. Results from research in population biology, including examples from our own multidisciplinary biodiversity research programme, demonstrate, however, that observed patterns of species diversity can often only be understood if the underlying population dynamic mechanisms and patterns of genetic diversity are also studied. Interactions among species and stochastic processes within and regional processes among local populations are important factors shaping communities and ecosystems. We show, for example, that effects of global change may lead to evolutionary adjustments within species, calling into question the predictions of models that treat themas invariant. Similarly, habitat destruction and fragmentation may not extinguish entire populations but alter biotic interactions or decrease genetic variation, which in turn reduces their chances for further survival. This was for example observed in isolated populations of the rare plant Gentianella germanica. A continued exchange of individuals and genes among local populations would be essential for the survival of this species. A parallel study demonstrated the importance of regional processes for the community ecology of bumble-bees: it revealed a positive correlation between local abundance and regional abundance among species. Scientists and conservationists should recognize that the protection of sites alone may not be sufficient to preserve biological diversity.The maintenance of interactions among species can be of equal importance. This requires the protection of populations of sufficient size or systems of connected populations known as metapopulations.