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Body size frequency distributions in African mammals are bimodal at all spatial scales

Authors

  • Douglas A. Kelt,

    Corresponding author
      *Correspondence: Douglas A. Kelt, Department of Wildlife, Fish, and Conservation Biology, University of California, One Shields Ave., Davis, CA 95616-8751, USA. E-mail: dakelt@ucdavis.edu
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  • Marc D. Meyer

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    • Present address: H. T. Harvey and Associates Ecological Consultants, 423 W. Fallbrook Ave., # 202, Fresno, CA 93711, USA.


*Correspondence: Douglas A. Kelt, Department of Wildlife, Fish, and Conservation Biology, University of California, One Shields Ave., Davis, CA 95616-8751, USA. E-mail: dakelt@ucdavis.edu

ABSTRACT

Aim  To examine frequency distributions of body sizes for mammal assemblages at several spatial scales and assess the generality of results heretofore obtained only for North and South America.

Location  Africa.

Methods  Terrestrial African mammals were allocated to major biomes, and regional and local assemblages were extracted from published and unpublished literature. We produced body size frequency distributions for local, regional, biomic and continental distributions, both for whole assemblages and for three foraging strata, and compared these with several standard metrics (e.g. mean and median size, interquartile range, skew, bimodality, etc.). Differences between distributions were quantified using t-tests and analysis of variance.

Results  African mammal faunas exhibit features in common with those of North and South America, most notably the gradual reduction in the modality and skew of body size distributions with decreasing spatial scale. Unlike other continents, however, the African mammal fauna exhibits a bimodal frequency distributions at all spatial scales. Our data suggest a role for competitive interactions in local assembly, as documented elsewhere, but further data on locally interacting assemblages are needed.

Main conclusions  The African fauna appears unique in the expression of bimodality at all spatial scales. The presence of a secondary mode at large body size may reflect co-evolutionary adjustments to proto-human hunters and consequent escape from anthropogenic Pleistocene extinctions, but the absence of species of intermediate body size (c. 250–4000 g) remains anomalous and is not readily explained by either historical or modern (ecological) factors. For the African mammal fauna, a key question in understanding the role of history versus ecology may not be why there are so many large species, but why there are so few intermediate-sized species.

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