Extreme and complex variation in range-wide abundances across a threatened Neotropical bird community

Marsden, SJ, Devenish, C, Buchanan, G and Smith, G (2017) Extreme and complex variation in range-wide abundances across a threatened Neotropical bird community. Diversity and Distributions, 23 (8). pp. 910-921. ISSN 1366-9516

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Abstract

Aim: Understanding patterns and drivers of variation in abundance across full species ranges is crucial in conservation science, but our knowledge of these forms and pro-cesses is limited, especially in the tropics. This study aims to: (1) identify patterns in variation of abundance across sites; (2) examine congruence of abundance hotspots across species and spatial autocorrelation of abundance within species; and (3) assess the nature and strength of environmental correlates of abundance (topography, habi-tat and human pressure).Location: Twenty- six sites across the full ranges of 14 dry forest bird species in north-ern Peru.Methods: Study sites in this patchy habitat were selected within strata derived from species distribution models, while also ensuring geographic representation. Species abundance data from variable- width transects were compared across sites and across range core versus edge; relationships between abundance and environmental varia-bles were examined using GAMs, and spatial autocorrelation was examined with mul-tivariate Mantel tests.Results: Although most species were recorded at most sites, local abundance varied by one or two orders of magnitude. Several species showed a humped rather than the classic skewed abundance distribution, with abundance not necessarily highest at the centre of species’ ranges. Spatial autocorrelation in species’ local abundance was evi-dent only at distances less than 55 km. Sites of maximum abundance for individual species did not coincide—nine different sites held highest densities of at least one species. Relationships between local abundance and almost all environmental corre-lates were non- linear.Main conclusions: The extreme variation in species abundances and the complexity in their relationships with environmental variables have important implications, both for design of conservation- motivated surveys for which we offer some recommendations, and for the need for multiple reserves to capture high local abundances of key species.