Local extinction of specialist species due to fragmentation is one of the major causes of biodiversity loss. Increased extinction rates in smaller fragments are expected to result from both smaller local population sizes, which increase the effect of environmental or demographic stochasticity, and increased edge effects. However, the relative effect sizes of these two factors are still poorly investigated. We attempt to disentangle these effects on ground beetle communities of temperate broadleaved woodland fragments situated in one of the most urbanized regions in Belgium. Assemblages were sampled along transects that extended from 30 m outside to 100 m inside both small and large historic forest fragments. Although species assemblages within the forest were highly distinct compared to those sampled outside the forest, species turnover along these transects was less pronounced within forest fragments indicating only weak edge effects. The magnitude of edge effects did not differ significantly between large and small fragments. However, larger differences in species composition were observed with respect to fragment size, wherein highly specialized species persisted only in the largest fragment. In sum, increased local extinction processes in smaller fragments, which led to a strong reduction of specialized and wingless forest species, appeared to be the most important factor that drives changes in species composition in this historic and fragmented woodland complex.
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The Antarctic shelf’s marine biodiversity has been greatly influenced by the climatic and glacial history of the region. Extreme temperature changes led to the extinction of some lineages, while others adapted and flourished. The amphipod genus Epimeria is an example of the latter, being particularly diverse in the Antarctic region. By reconstructing a time-calibrated phylogeny based on mitochondrial (COI) and nuclear (28S and H3) markers and including Epimeria species from all oceans, this study provides a temporal and geographical framework for the evolution of Antarctic Epimeria. The monophyly of this genus is not supported by Bayesian Inference, as Antarctic and non-Antarctic Epimeria form two distinct wellsupported clades, with Antarctic Epimeria being a sister clade to two stilipedid species. The monophyly of Antarctic Epimeria suggests that this clade evolved in isolation since its origin. While the precise timing of this origin remains unclear, it is inferred that the Antarctic lineage arose from a late Gondwanan ancestor and hence did not colonize the Antarctic region after the continent broke apart from the other fragments of Gondwanaland. The initial diversification of the clade occurred 38.04 Ma (95% HPD [48.46 Ma; 28.36 Ma]) in a cooling environment. Adaptation to cold waters, along with the extinction of cold-intolerant taxa and resulting ecological opportunities, likely led to the successful diversification of Epimeria on the Antarctic shelf. However, there was neither evidence of a rapid lineage diversification early in the clade’s history, nor of any shifts in diversification rates induced by glacial cycles. This suggests that a high turnover rate on the repeatedly scoured Antarctic shelf could have masked potential signals of diversification bursts.
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RBINS Staff Publications 2017
