Spatial Distribution and abundance of two Hylobatidae species in relation to canopy structure and disturbance in a Sumatran lowland dipterocarp forest.

Authors: Hankinson, E., Korstjens, A.H., Hill, R., Wich, S.A. and Nowak, M.

Start date: 21 August 2016

Forest degradation drastically alters canopy structure and habitat quality of tropical rainforests, directly influencing ranging behaviour of arboreal primates to obtain crucial resources. Relatively little is known on hylobatid distribution in relation to canopy structure and more specifically, why densities differ across degraded forests with altered structural complexity. Highly stratified, structurally complex uninterrupted canopies are hypothesised to hold high hylobatid densities, whilst disturbed degraded forest with lower canopy levels contain smaller populations. We present data on two sympatric gibbon species that are extremely sensitive to forest disturbance; the lar gibbon Hylobates lar and siamang Symphalangus syndactylus. Forest structure and hylobatid density were sampled in four alluvial and hill forest areas displaying a gradient of disturbance within a 40km2 area of lowland dipterocarp forest in Sikundur, North Sumatra. In each area, forest structure was classified through five vegetation plots and gibbon density obtained by recording morning vocalisations over four consecutive days using three linearly placed listening posts; 8 arrays over a 6 month period. Spatially explicit capture re-capture models (SERC) were used to calculate density and GLM’s to identify structural vegetational characteristics best describing primate densities. Our results indicate altered structural complexity of degraded forests directly influence hylobatid ranging behaviour and habitat use emphasising the importance of habitat quality in sustaining critically endangered gibbon populations. More information available at the LEAP research group website:

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