Metapopulation processes and persistence in remnant water vole populations

We examined the spatial distribution of water vote populations in four cons ecutive years and investigated whether the regional population processes of extinction, recolonisation and migration influence distribution and persis tence, We examined how such regional processes are influenced by spatial va riation in habitat quality. In addition, we assessed the relevance of metap opulation concepts for understanding the dynamics of species that deviate f rom classical metapopulation assumptions and developing conservation measur es for them. Populations were patchy and discrete, and the patchy distribut ion was not static between years. Population turnover occurred even in the absence of predatory mink, which only influenced the network of populations at the end of the study. Most populations were clustered close together in the upper tributaries. Local population persistence was predominantly infl uenced by population size: large populations were more persistent. Recoloni sation rates were influenced by isolation and habitat quality. The isolatio n estimates which best explained the distribution of water vote populations incorporated straight-line distances, suggesting water votes disperse over land. The distribution of recolonised sites indicated that dispersing votes actively selected habitat on the basis of its quality. Water votes depart from some of the assumptions made by frequently used metapopulation models. In particular there is no clear binary distinction between suitable and no n-suitable habitat. Accounting for variation in habitat quality before inve stigating temporal changes in population distribution allowed us to demonst rate that the key metapopulation processes were important. The significance of regional population processes relative to local population processes ma y have increased in declining, fragmented populations compared to pristine regional populations. We hypothesise that although mink predation is likely to eventually cause regional extinction in many areas, metapopulation proc esses have delayed this decline. Consequently, conservation measures should take into account mink predation rates and regional population processes, before considering aspects of habitat quality.