Wednesday, May 28, 2008 - 1:30 PM
434

Flood disturbance enhances deterministic control on community assembly in streams

Fabio Lepori, Department of Fish, Wildlife, and Conservation Biology, Colorado State University, 1474 Campus Delivery, Fort Collins, CO 80523-1474 and Björn Malmqvist, Department of Ecology and Environmental Science, Umeå University, Umeå, SE-901 87, Sweden.

In spite of much research, the processes that assemble biological communities remain poorly understood. We censused macroinvertebrate communities and measured flood disturbance in Scandinavian streams to assess the hypothesis that communities are shaped by stochastic processes under stable conditions, and increasingly by deterministic processes as disturbance becomes more severe. Each of 19 study streams was categorized into stable, intermediate, or disturbed ‘treatments’ depending on the severity of scouring floods. Within-treatment diversity, but not local (within-site) diversity was negatively affected by disturbance, suggesting that disturbance acted as a filter preventing the establishment at disturbed sites of species unable to cope with the stress involved. High site-to-site variation in composition suggests that communities within the stable treatment were assembled largely by stochastic processes. By contrast, lower site-to-site variation within the disturbed and intermediate treatments implies a stronger role of deterministic processes. In the study area, macroinvertebrate communities appear to be shaped by deterministic processes, which recruit potential colonists from the regional species pool depending on niche differences and disturbance conditions, and by stochastic processes, which distribute the selected species among local communities. Although often considered alternative, stochastic and deterministic processes acted hierarchically to shape the diversity of the communities studied. 


Web Page: community structure, diversity, invertebrate communities, spatial scale, species richness, similarity index, stochastic,

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