Competition and Coexistence in Neotropical Birds: A Latitudinal Comparison
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Brooks, D. M. 1998. Competition and Coexistence in Neotropical Birds: A Latitudinal Comparison. Texas A&M University. PhD Dissertation.
Abstract: I tested coexistence of Neotropical bird assemblages by examining congeneric character displacement (mutual divergence and competitive release), confamilial size adjustment and species packing mechanisms (comparing real pools against null pool) at three different latitudes, representing gradients of productivity and stability: the northern subtropics (Rio Grande Valley), the equatorial zone (Amazonian Peru) and the austral subtropics (Paraguayan Chaco). Size adjustment and assortment involve species competing for the same resources exhibiting spatially distinct characters in ecomorphological space, molded through evolutionary forces to reduce the chance for competition. Species packing is the number of species packed into ecomorphological space, with ecomorphological distance between species decreasing with increasing diversity.
I covered 7.3 km of transects during each of 9 sampling periods at the Rio Grande site, 8.4 km during each of 7 periods at the Amazon site, and 7.1 km during each of 12 periods at the Chaco site. Despite least intensive sampling effort at the Amazon site, it is the most speciose (238 species / 78 common) compared to the Chaco (147 / 76) and Rio Grande (61 / 24) sites. Only species that are common, spatially and temporally sympatric, sharing the same habitat and similar dietary resources, and not exhibiting social mimicry or phylogenetic constraints are used in analyses, as these represent the most likely competitors and thus are suitable for testing hypotheses.
My analyses revealed some interesting patterns. First, my results suggest that size adjustment is a pattern exclusive to plant consumers, with mutual divergence not evidenced, and character release occurring only at the Amazon site. Second, size assortment is the most pervasive pattern among the three sites, with most of the groups being animal consumers or omnivores, represented by a high percentage of insectivores. Third, species packing is most pervasive at the Chaco and Amazon sites, with all groups being animal consumers or omnivores.