Distribution of abundance across the range in eastern North American trees

Abstract

Aim We analysed spatial datasets of abundance across the entirety, or near entirety, of the geographical ranges of 134 tree species to test macroecological hypotheses concerning the distribution of abundance across geographical ranges.Location Our abundance estimates came via the USDA Forest Service Forest Inventory and Analysis Eastwide Database, which contains data for 134 eastern North American tree species. MethodsWe extracted measures of range size and the spatial location of abundance relative to position in the range for each species to test four hypotheses: (a) species occur in low abundance throughout most of their geographical range; (b) there is a positive interspecific relationship between abundance and range size; (c) species are more abundant in the centre of their range; and (d) there is a bimodal distribution of spatial autocorrelation in abundance across a species range. ResultsOur results demonstrate that (a) most species (85%) are abundant somewhere in their geographical range; (b) species achieving relatively high abundance tend to have larger range sizes; (c) the widely held assumption that species exhibit an 'abundant-centre distribution' is not well supported for the majority of species; we suggest 'abundant-core' as a more suitable term; and (d) there is no evidence of a bimodal distribution of spatial autocorrelation in abundance.Main Conclusions For many tree species, high abundance can be achieved at any position in the range, though suitable sites are found with less frequency towards range edges. Competitive relationships may be involved in the distribution of abundance across tree ranges and species with larger ranges (and possibly broader niches) may be affected more by biotic interactions than smaller ranging species.

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Central-marginal population dynamics in species invasions

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