Abstract
Habitat loss and fragmentation represent the most serious extinction threats for many species and have been demonstrated to be especially detrimental for mammals. Particularly, highly specialized species with low dispersal abilities will encounter a high risk of extinction in fragmented landscapes. Here we studied the edible dormouse (Glis glis), a small arboreal mammal that is distributed throughout Central Europe, where forests are mostly fragmented at different spatial scales. The aim of this study was to investigate the effect of habitat fragmentation on genetic population structures using the example of edible dormouse populations inhabiting forest fragments in south western Germany. We genotyped 380 adult individuals captured between 2001 and 2009 in four different forest fragments and one large continuous forest using 14 species-specific microsatellites. We hypothesised, that populations in small forest patches have a lower genetic diversity and are more isolated compared to populations living in continuous forests. In accordance with our expectations we found that dormice inhabiting forest fragments were isolated from each other. Furthermore, their genetic population structure was more unstable over the study period than in the large continuous forest. Even though we could not detect lower genetic variability within individuals inhabiting forest fragments, strong genetic isolation and an overall high risk to mate with close relatives might be precursors to a reduced genetic variability and the onset of inbreeding depression. Results of this study highlight that connectivity among habitat fragments can already be strongly hampered before genetic erosion within small and isolated populations becomes evident.
Highlights
Habitat loss, degradation and fragmentation represent the most serious extinction threats for mammals, affecting 40% of the species assessed [1]
We considered different genetic sources that can explain the genetic variation of populations and which might be different in the populations of the continuous forest and the forest fragments, i.e. genetic differences between locations (Tubingen and Ulm), among populations of the two locations (Tubingen: HEcont and HLcont; Ulm: BGfrag, BSfrag, SFfrag and JHfrag), among yearly samples of populations, among individuals within populations, and within individuals
The number of private alleles found in both study sites within the continuous forest (n = 8) was similar to that detected in the fragments (n = 9)
Summary
Degradation and fragmentation represent the most serious extinction threats for mammals, affecting 40% of the species assessed [1]. Forests are the ones that are most strongly suffering from worldwide human impact, due to exploitation for timber and to clear cutting for agriculture [2] Such an ongoing habitat loss and fragmentation leads to the continuous isolation of suitable habitat patches across landscapes. Arboreal mammals with low dispersal ability face the problem that they become increasingly subdivided into comparatively small and isolated populations [3], which are subject to genetic drift and inbreeding, eventually resulting in a loss of genetic variation [4;5;6] Such forest habitat specialists can be considered as especially vulnerable to habitat fragmentation as the decrease in the level of genetic variation, inbreeding and the concomitant inbreeding effects can be expected to reduce their individual fitness and to obstruct adaptive responses to environmental stressful conditions [7]. Arboreal species, common ringtail possums (Pseudocheirus peregrinus) and Australian squirrel gliders (Petaurus norfolcensis), were shown to display lower levels of allelic richness and observed heterozygosity in small isolated populations compared to populations inhabiting larger habitat patches [5;6]
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