The Big Picture from Small Landscapes Investigations of Spatial Patterns and Processes using a Model Metacommunity

Habitat fragmentation is a major current threat to natural environments. Still, fundamental questions of what influences ecological communities in spatially structured habitats are unanswered. In this thesis, microarthropods in moss patches were used in a model system, where both biotic and abiotic factors could be manipulated. In four studies, I investigated how isolation distance, connectivity, habitat size, dispersal barriers, matrix quality, and environmental quality influenced the occurrence, abundance and diversity of mites (Acari), and springtails (Collembola). First, I show that the effects of habitat fragmentation was profound and species specific. Inter-patch dispersal between isolated patches was low in natural settings compared to mainland-island dispersal, and populations in the mainland had a large influence even on distant communities. Secondly, I show that connecting fragmented patches by habitat corridors increased the dispersal throughout the landscape, but that this had complex and unpredictable results. Habitat corridors interacted with the surrounding matrix which led to counterintuitive patterns. For predatory mites and collembolans, habitat corridors had a negative impact when the corridors intersected a matrix of poor quality, severely reducing their abundance, probably due to increased edge effects. Moreover, oribatid mites decreased in landscapes with corridors, likely due to increased predation, caused by increased connectivity, favoring predators. Thirdly, I show that community assembly following a disturbance event was predictable, based on random colonization of individuals from the surrounding pool of individuals. In contrast, community disassembly following habitat fragmentation was highly unpredictable, and could not be explained by a random loss of individuals. The fourth study examined natural situations and show that while the spatial factors connectivity and distance had a lasting influence on local communities, habitat area was the major determining factor for both density and species richness.