Editor: Shai Meiri
Scale effects on the body size frequency distributions of African birds: patterns and potential mechanisms
Article first published online: 26 SEP 2012
© 2012 Blackwell Publishing Ltd
Global Ecology and Biogeography
Volume 22, Issue 4, pages 380–390, April 2013
How to Cite
Coetzee, B. W. T., le Roux, P. C. and Chown, S. L. (2013), Scale effects on the body size frequency distributions of African birds: patterns and potential mechanisms. Global Ecology and Biogeography, 22: 380–390. doi: 10.1111/j.1466-8238.2012.00793.x
- Issue published online: 5 MAR 2013
- Article first published online: 26 SEP 2012
- National Research Foundation of South Africa
- Stellenbosch University
- Harry Crossley
- African avifauna;
- African birds;
- body mass;
- body size;
- range size;
- scaling effects
To describe and analyse the body size frequency distributions (BSFDs) of avian assemblages at several spatial scales in the Afrotropics. We also tested if the variation in median body size across assemblages at different spatial scales was related to environmental variables and whether purely stochastic processes could explain BSFDs.
The Afrotropical biogeographic realm.
Avian body masses for 1960 species where analysed at continental, biome, ecoregion and local spatial scales with standard metrics. Variation in median assemblage body size was modelled as a function of environmental and spatial explanatory variables to assess non-random assemblage structure. We tested if BSFDs of smaller spatial scale distributions are random subsets of the larger spatial scale assemblages in which they are embedded, and used three different null model randomizations to investigate the influence of stochastic processes on BSFDs.
The African avifauna's continental BSFD is unimodal and right-skewed. BSFDs generally become less skewed and less modal with decreasing spatial scale. The best-fit model explained 71% of median body size values at the ecoregion scale as a function of latitude, latitude2, longitude, species richness and species range size. BSFDs at smaller scales show non-random assembly from larger scale BSFDs distributions.
African avifaunal BSFDs are quantitatively dissimilar to African mammal BSFDs, which are bimodal at all spatial scales. Much of the change in median body size with spatial scale can be captured by a range-weighted null model, suggesting that differential turnover between smaller- and larger-bodied species might explain the shift in the central tendency of the BSFD. At the local scale, energy may well contribute to structuring BSFDs, but this pattern is less pronounced at larger spatial scales.