Independent effects of habitat loss, habitat fragmentation and structural connectivity on the distribution of two arboreal rodents

Abstract

Summary 1.Habitat loss must be distinguished from habitat fragmentation so that appropriate conservation management can be applied. Few studies have evaluated the independent effects of habitat loss and habitat fragmentation on the distribution of vertebrates, and none has evaluated the independent effect of changes in structural connectivity. We carried out a landscape-scale experiment to assess the independent contribution of these three processes and to examine what landscape scale factors affect the distribution of two forest-dependent arboreal rodents: the hazel dormouse Muscardinus avellanarius and the red squirrel Sciurus vulgaris. 2. Habitat loss, rather than habitat fragmentation per se, was the major driver of distribution patterns for both species. As predicted, structural connectivity (hedgerow networks) played an important role in determining the distribution of the hazel dormouse, but not of the red squirrel. 3. Our models predict that long lengths of hedgerows (>30 km) are unlikely to increase the probability of occurrence of hazel dormouse in landscapes where there are low levels of forest cover (<5%-10%). 4. Synthesis and applications. Our empirical findings indicate that structural connectivity and habitat loss may have additive effects on vertebrate distribution. For the hazel dormouse, improving structural connectivity will be ineffective if the amount of forest cover in the landscape is less than 5-10%. The key message from this study is that resources should not be invested in landscape linkages until their efficacy for the given level of suitable habitat has been assessed.

Responses of small mammals to clear-cutting in temperate and boreal forests of Europe: a meta-analysis and review

“…Red squirrels are able to travel relatively long distances on open ground, thus are not as strongly affected by fragmentation as are other arboreal species (Wauters et al 2010;Mortelliti et al 2011). However, the amount of forest cover in the landscape is an important factor related to squirrels' presence (Mortelliti et al 2011) and red squirrels avoid clear-cuts (Hansson 1994). Indirect evidence (changes in the diet of avian predators) suggests that red squirrels are declining in numbers in Fennoscandia where gray squirrels do not occur (Selonen et al 2010).…”

“…Moderately intense forest harvest is not considered to be a threat because populations of red squirrels often remain viable in fragmented landscapes (Andrén and Delin 1994;Delin and Andrén 1999;Verbeylen et al 2003). Red squirrels are able to travel relatively long distances on open ground, thus are not as strongly affected by fragmentation as are other arboreal species (Wauters et al 2010;Mortelliti et al 2011). However, the amount of forest cover in the landscape is an important factor related to squirrels' presence (Mortelliti et al 2011) and red squirrels avoid clear-cuts (Hansson 1994).…”

“…Red squirrel Habitat loss (Mortelliti et al 2011). Minor: remain viable in fragmented landscapes but rely on mature trees for food.…”

“…Hazel dormouse Fragmentation (Bright and Morris 2008;Mortelliti et al 2011). Moderate: prone to isolation in forest fragments, but extensively use mid-successional clear-cuts.…”

Quantifying Landscape-Scale Patterns of Temperate Forests over Time by Means of Neutral Simulation Models

“…Although the accurate description of the huge ecological consequences of such transformations is beyond the scope of this work, we can point out possible effects, such as an increment in true forest species [93,94], a stronger connectivity for forest vertebrates [76,95], an improvement in CO 2 sink services [96], regulation of water drainage [97] and landslide prevention [98].…”