title: Primates in Human-Modified and Fragmented Landscapes: The Conservation Relevance of Modelling Habitat and Disturbance Factors in Density Estimation.
abstract: Accurate density estimations of threatened animal populations is essential for management and conservation. This is particularly critical for species living in patchy and altered landscapes, as is the case for most tropical forest primates. In this study, we used a hierarchical modelling approach that incorporates the effect of environmental covariates on both the detection (i.e. observation) and the state (i.e. abundance) processes of distance sampling. We applied this method to already published data on three arboreal primates of the Udzungwa Mountains of Tanzania, including the endangered and endemic Udzungwa red colobus (Procolobus gordonorum). The area is a primate hotspot at continental level. Compared to previous, 'canonical' density estimates, we found that the inclusion of covariates in the modelling makes the inference process more informative, as it takes in full account the contrasting habitat and protection levels among forest blocks. The correction of density estimates for imperfect detection was especially critical where animal detectability was low. Relative to our approach, density was underestimated by the canonical distance sampling, particularly in the less protected forest. Group size had an effect on detectability, determining how the observation process varies depending on the socio-ecology of the target species. Lastly, as the inference on density is spatially-explicit to the scale of the covariates used in the modelling, we could confirm that primate densities are highest in low-to-mid elevations, where human disturbance tend to be greater, indicating a considerable resilience by target monkeys in disturbed habitats. However, the marked trend of lower densities in unprotected forests urgently calls for effective forest protection.
authors: DICAM Department of Civil, Environmental and Mechanical Engineering, University of Trento, Trento, Italy.|Tropical Biodiversity Section, MUSE-Museo delle Scienze, Trento, Italy.
authors: Nathalie
authors: N
authors: Cavada
authors: Tropical Biodiversity Section, MUSE-Museo delle Scienze, Trento, Italy.|Biodiversity and Molecular Ecology Department, Research and Innovation Centre-Fondazione Edmund Mach, San Michele all'Adige (TN), Italy.
authors: Claudia
authors: C
authors: Barelli
authors: DICAM Department of Civil, Environmental and Mechanical Engineering, University of Trento, Trento, Italy.
authors: Marco
authors: M
authors: Ciolli
authors: Tropical Biodiversity Section, MUSE-Museo delle Scienze, Trento, Italy.|Udzungwa Ecological Monitoring Centre, Udzungwa Mountains National Park, Mang'ula, Tanzania.
authors: Francesco
authors: F
authors: Rovero
mesh_terms: D000818:Animals; D003104:Colobus; D017753:Ecosystem; D056727:Endangered Species / Q000706:statistics & numerical data*; D065928:Forests; D006801:Humans; D008962:Models, Theoretical; D011156:Population Density; D013636:Tanzania; D014329:Tropical Climate