What is metapopulation biology?
What is it?
WWW links
Metapopulation biology
- by country
- by info. content
- by habitat
- by organism
Landscape ecology
- a few links
- US-IALE
Thus, a balance may be reached when, on average, an equal number extiction and colonisation events occor each year. Then a quite constant fraction of the patches is always occupied, although exactly which differs from year to year. If habitat patches are destroyed one by one, the metapopulation will become extinct before all patches are destroyed. Also, a metapopulation may become extinct even if only "empty" (in a given year) habitat patches are destroyed. These properties of metapopulations are important reasons for the interest in metapopulation biology in connection with species/biodiversity conservation.
The concept was introduced in 1969 by R.A. Levins, but it was not in common use until the eighties. (Levins' mathematical model is presented in the end of this lecture by Alexei Sharov.) In the nineties, it became rapidly a buzzword in ecology and conservation, and the rate of publishing on the subject continues to grow. Recently, Ilkka Hanski and Michael Gilpin have edited a new book devoted to metapopulation biology (Metapopulation Biology: Ecology, Genetics, and Evolution; Academic Press 1997). In the introduction, the authors note that the meaning of the concept seems to have been expanded; among other things, one may still talk about a metapopulation even though extinction of populations has not been observed. It is also evident that the classical metapopulation view of the world as binary (habitat/non-habitat) often is too simple when it is to be applied in the real world.
Many people treats metapopulation biology as a part of the wider field of landscape ecology, which is quite logical if landscape ecology is seen just as the science of landscapes in general. However, it appears that many authors see landscape ecology and metapopulation ecology as two different branches of science. The reason for thois appears to be that there are two traditions of landscape ecology: (1) The European tradition, founded by geographers, has a holistic and applied approach of landscape ecology. In this tradition, landscape ecology is applied as a tool in landscape planning; thus, it is naturally quite hopeless to model the population dynamics of every plant and animal species and every aspect of hydrology and nutrient movement, and one often has to resort to "rules of thumb" - e.g., "habitat fragmentation is not good" or "corridors enhance animal movement and thus the survival of animal populations". Thus, metapopulation biology is one of several sub-sciences that allow a landscape ecologist to give advice on landscape planning. (2) The American tradition, however, was founded by biologists (ecosystem ecologists); it has a more reductionistic approach (it tries to understand landscape processes "from the bottom and up", and has less tradition as a landscape planning tool. It is for a large part based on mathematical models (or computer simulations) of e.g. nutrient movement, forest fires, or movement of animals in landscapes.
In case of animal movement, the latter breed of landscape ecologists stress variation in patch quality, variation in the quality of the surrounding environment (the matrix), boundary/edge effects, and how the landscape pattern affects connectivity (Wiens 1997, in the Hanski and Gilpin book). In metapopulation biology, this is often much simplified: it is assumed that the patches all are alike, at least in quality (if not in size), the matrix is viewed as homogenous, and the probability that an individual can move from one patch to atother depends only on the distance between the patches. When the habitat patches are very small compared to the landscape (essentially points in the landscape), these assumptions may not cause great errors, while these errors become increasinlgly important in landscapes where a significant portion of the landscape is covered by habitat. Thus, defining LC and HC landscapes as landscapes with resp. low and high coverage of habitat, Hanski and Gilpin concludes that "there appears to be a real difference between the two traditions here, as the have largely been largely concerned with either LC landscapes (metapopulation ecology) or HC landscapes (landscape ecology)". As both these authors and John Wiens stress, an important task is to establish common ground for these two branches of science.