Identifying environmental versus phylogenetic correlates of behavioural ecology in gibbons: implications for conservation management of the world's rarest ape.

Jessica V Bryant,Valérie A Olson,Samuel T Turvey,Helen J Chatterjee

doi:10.1186/s12862-015-0430-1

Jessica V Bryant, Valérie A Olson + Show 2 more

Open Access

https://doi.org/10.1186/s12862-015-0430-1

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Abstract

BackgroundFor conservation of highly threatened species to be effective, it is crucial to differentiate natural population parameters from atypical behavioural, ecological and demographic characteristics associated with human disturbance and habitat degradation, which can constrain population growth and recovery. Unfortunately, these parameters can be very hard to determine for species of extreme rarity. The Hainan gibbon (Nomascus hainanus), the world’s rarest ape, consists of a single population of c.25 individuals, but intensive management is constrained by a limited understanding of the species’ expected population characteristics and environmental requirements. In order to generate a more robust evidence-base for Hainan gibbon conservation, we employed a comparative approach to identify intrinsic and extrinsic drivers of variation in key ecological and behavioural traits (home range size, social group size, mating system) across the Hylobatidae while controlling for phylogenetic non-independence.ResultsAll three studied traits show strong phylogenetic signals across the Hylobatidae. Although the Hainan gibbon and some closely related species have large reported group sizes, no observed gibbon group size is significantly different from the values expected on the basis of phylogenetic relationship alone. However, the Hainan gibbon and two other Nomascus species (N. concolor, N. nasutus) show home range values that are higher than expected relative to all other gibbon species. Predictive models incorporating intraspecific trait variation but controlling for covariance between population samples due to phylogenetic relatedness reveal additional environmental and biological determinants of variation in gibbon ranging requirements and social structure, but not those immediately associated with recent habitat degradation.ConclusionsOur study represents the first systematic assessment of behavioural and ecological trait patterns across the Hylobatidae using recent approaches in comparative analysis. By formally contextualising the Hainan gibbon’s observed behavioural and ecological characteristics within family-wide variation in gibbons, we are able to determine natural population parameters expected for this Critically Endangered species, as well as wider correlates of variation for key population characteristics across the Hylobatidae. This approach reveals key insights with a direct impact on future Hainan gibbon conservation planning, and demonstrates the usefulness of the comparative approach for informing management of species of conservation concern.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0430-1) contains supplementary material, which is available to authorized users.

Highlights

For conservation of highly threatened species to be effective, it is crucial to differentiate natural population parameters from atypical behavioural, ecological and demographic characteristics associated with human disturbance and habitat degradation, which can constrain population growth and recovery
Irrespective of whether we use high or low home range estimates for the species, we show that Hainan gibbon social groups in the remnant population at Bawangling have larger home ranges than expected in the context of the strong phylogenetic signal that exists for this trait within the Hylobatidae
Once these phylogenetic signals are accounted for, variation in these key traits is driven by a combination of social and external factors: variation in gibbon home range size is explained by gibbon group density at a site along with mating system and social group size; gibbon social group size is linked to mean annual rainfall and mating system; and, while no explanatory variables were statistically associated with mating system, gibbon mating system, group size and home range appear to be inherently linked traits, with these factors being important, inter-correlated predictors of each other

Summary

Introduction

For conservation of highly threatened species to be effective, it is crucial to differentiate natural population parameters from atypical behavioural, ecological and demographic characteristics associated with human disturbance and habitat degradation, which can constrain population growth and recovery These parameters can be very hard to determine for species of extreme rarity. It is of particular importance to determine natural population parameters for highly threatened species that have been reduced to only a handful of surviving individuals, as such species of extreme rarity will likely require urgent and intensive conservation management [5] These parameters may be hard to determine for such species; for example, direct assessment of variation in population-level responses to different environmental conditions is impossible if a species of concern is restricted to a single site. Successful evidence-based conservation of species of extreme rarity may necessitate using alternative investigative approaches to determine their expected natural behavioural, ecological and demographic characteristics and environmental requirements

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