Fragment quality and distribution of the arboreal primate Propithecus verreauxi in the spiny forest of south Madagascar

Fragmentation can randomly distribute animals among forest patches and across fragmented habitat and surrounding matrix. Local populations can survive only if the colonized forest remnants are adequate and/or dispersal is possible. Subsequently, a non-random distribution can result from local populations either remaining connected but distinct (metapopulation) or merging into a single large but patchy population. Such distribution can be dictated by different aspects of fragment quality, including size and vegetation variables (e.g. tree species diversity, large-tree abundance and food plant availability). This study evaluates the population status and distribution of the Malagasy primate Propithecus verreauxi in six spiny forest fragments of south Madagascar. Propithecus verreauxi (Verreaux’s sifaka) is a lemur particularly sensitive to habitat disruption because it is strictly arboreal (vertical climber and leaper) and has an energetically poor diet (mainly folivorous). Our results suggest that intrinsic factors (density and sex-ratio) do not shed light on population viability (due to their heavy fluctuation) and that,among extrinsic factors, vegetation structure overrides fragment size in dictating animal distribution in the small spiny-forest fragments.