Abstract
Habitat fragmentation caused by dams and road passes can lead to extinctions of fish populations, while species introductions can cause extinctions of isolated fish populations and a homogenization of the fish fauna at the landscape level. To increase our understanding of fragmentation effects we will quantify extinction and colonization rates. Extinction rates as a function of habitat size will be quantified from the incidence of species in isolated habitats under the highest coast line. To distinguish introduced populations from those surviving since land elevation isolated the lake from the sea, we will use remains of fish scales and zooplankton in lake sediments. Effects of introductions will be quantified by comparing diversity patterns before vs. after introductions. To build models that can be used to predict effects of fragmentation and introductions we will use data on the outcome of introductions to formulate habitat dependent assembly rules. These rules specify how the probability that two or more species can coexist depends on habitat size and presence of other species. We will use an existing data set that cover all lakes in an area around Öviks kommun (1500 lakes). It contains data on all fish assemblages, on a large number of introductions (500 lakes) including "before and after" data on fish assemblages, and documentation of dispersal barriers.
Sweden