Insect communities and the spatial complexity of mountain habitats
Traditionally, mountain environments have been viewed as supporting only `simple' ecosystems, because there is generally a marked decrease in the number of species of organisms with increasing altitude. However, the high degree of spatial complexity of mountain landscapes suggests that mountain ecosystems should be very complicated. Here both directions of thought are explored. By reference to a number of case studies in which flies of the family Syrphidae (Diptera) serve as the primary models, the following argument is developed. First, `simple' communities of flies on mountain meadows may be affected by environmental changes caused by skiing, grazing intensity and other forms of human land use. These effects are not reflected by measures of `species diversity', but rather the life strategies (specialist, generalist, etc.) of the insects. Second, even with simple species assemblages, the difficulties inherent in defining the spatial limits of ecological communities in mountains are great. Consideration of an `ensemble' of mosaic patches, defined at a scale relevant to the organisms, is more realistic than examination of species assemblages within particular `human-defined' patches. Third, the complexity of the borders between patches in a mosaic may be just as important in determining species assemblage structure as patch content. Fourth, in a changing climate, mountain ecosystems are likely to be vulnerable to changes in the form and complexity of the microclimatic mosaic as well as to overall changes in average climatic conditions.
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