METAPOPULATION EXTINCTION IN FRAGMENTED LANDSCAPES - USING BACTERIA AND PROTOZOA COMMUNITIES AS MODEL-ECOSYSTEMS

Extinction is notoriously difficult to study because of the long times cales involved and the difficulty in ascertaining that extinction has actually occurred. The effect of habitat subdivision, or fragmentation , on extinction risk is even harder to study, as it requires copious r eplication of habitat patches on large spatial scales and control of a rea effects between treatments, I used simple small-scale communities of bacteria and protozoa to study extinction in response to habitat lo ss and habitat fragmentation. I studied several different community co nfigurations, each with three trophic levels, Unlike most metapopulati on studies (experimental as well as theoretical), which have tended to deal with inherently unstable species interactions, I deliberately us ed community configurations that were persistent in large stock cultur es. I recorded the time to extinction of the to;; predator in single h abitat patches of different sizes and in fragmented systems with diffe rent degrees of subdivision but the same amount of available habitat, Habitat loss reduced the time to extinction of isolated populations, F ragmented systems went extinct sooner than corresponding unfragmented (continuous) systems of the same overall size. Unfragmented population s persisted longer than fragmented systems (metapopulations) with or w ithout dispersal corridors between subpopulations. In fact, fragmented systems where the fragments were linked by dispersal corridors went e xtinctly significantly sooner than those where subpopulations were com pletely isolated from each other. If these results extend to more ''na tural systems, it suggests a need for caution in management programs t hat emphasize widespread establishment of wildlife corridors in fragme nted landscapes.