Abstract
Forest edges change micro-environmental conditions, thereby affecting the ecology of many forest-dwelling species. Understanding such edge effects is particularly important for Malagasy primates because many of them live in highly fragmented forests today. The aim of our study was to assess the influence of forest edge effects on activity budgets, feeding ecology, and stress hormone output (measured as faecal glucocorticoid metabolite – fGCM – levels) in wild Verreaux's sifakas (Propithecus verreauxi), a group living, arboreal lemur. We observed five habituated groups: three living in the forest interior and two at an established forest edge. There was no difference in average daily temperatures between edge and interior habitats; however, within the edge site, the average daily temperature incrementally increased over 450 m from the forest edge towards the interior forest of the edge habitat, and the population density was lower at the edge site. Activity budgets differed between groups living in the two microhabitats, with individuals living near the edge spending more time travelling and less time feeding. Groups living near the edge also tended to have smaller home ranges and core areas than groups in the forest interior. In addition, edge groups had elevated average fGCM concentrations, and birth rates were lower for females living in the edge habitat. Combined with lower levels of fruit consumption at the edge, these results suggest that nutritional stress might be a limiting factor for Verreaux's sifakas when living near a forest edge. Hence, Verreaux's sifakas appear to be sensitive to microhabitat characteristics linked to forest edges; a result with implications for the conservation of this critically endangered lemurid species.
Highlights
Tropical forest habitats continue to become increasingly fragmented, thereby disintegrating populations and reducing suitable habitats for many species (Laurance, 1999; Watson et al, 2004)
The aim of our study was to assess the influence of forest edge effects on activity budgets, feeding ecology, and stress hormone output in wild Verreaux’s sifakas (Propithecus verreauxi), a group living, arboreal lemur
There was no difference in average daily temperatures between edge and interior habitats; within the edge site, the average daily temperature incrementally increased over 450 m from the forest edge towards the interior forest of the edge habitat, and the population density was lower at the edge site
Summary
Tropical forest habitats continue to become increasingly fragmented, thereby disintegrating populations and reducing suitable habitats for many species (Laurance, 1999; Watson et al, 2004). Fragmentation of habitats results in additional abrupt boundaries, creating so-called edge effects. Edge effects refer to how abiotic and biotic conditions interact between two adjacent habitats separated by an abrupt boundary, altering the distribution, abundance, and behaviour of organisms (Murcia, 1995). As environmental conditions, such as temperature, light intensity, plant growth, and level of disturbance, change around edges, they can be considered as distinct ecosystems in comparison to undisturbed forest interiors (Laurance et al, 2000, 2011). Because species respond differently to living in edge habitats (Lehtinen et al, 2003; Lehman et al, 2006a, b; Delattre et al, 2009), studying edge effects is of key importance for species-specific conservation assessment
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