Forest Bird Community Structure in Central Panama: Influence of Spatial Scale and Biogeography

• Published in: Ecological monographs 2000-05, Vol.70 (2), p.209-235
• Main Authors: Robinson, W. Douglas, Brawn, Jeffrey D., Robinson, Scott K.
• Format: Article
• Language: English
• Subjects: Amazonia; Animal and plant ecology; Animal populations; Animal, plant and microbial ecology; Aves; Biodiversity; biogeographic history; Biogeography; Biological and medical sciences; biomass; Birds; Communities; Community structure; Ecosystems; Forest birds; Forest ecology; Forest fauna; Fundamental and applied biological sciences. Psychology; Limbo; neotropical forest; Old growth forests; Panama; Population density; Population estimates; Rainforests; spatial scale; Species; species diversity; species richness; Synecology; Terrestrial ecosystems; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0012-9615; 1557-7015
• DOI: 10.1890/0012-9615(2000)070[0209:FBCSIC]2.0.CO;2

Historical and biogeographic contexts can play important, yet sometimes overlooked, roles in determining structure of local communities. In particular, few examinations of historical influences on patterns of species richness and relative abundances in tropical communities have been conducted. In part, that gap in our knowledge has been caused by a paucity of data on tropical communities, even for relatively well-studied taxa such as birds. In the Neotropics, only two sites, a 97-ha plot in lowland Peru and a 100-ha plot in French Guiana, have been inventoried on a spatial scale sufficient to estimate population densities for a majority of resident bird species. Results from those studies revealed extremely similar species richness, community biomass, and patterns of relative abundance. A third site in lowland Panama was originally censused in 1968-1969 and has often been compared with many other tropical and temperate sites. Results from Panama suggested an exceptionally different community structure from that observed at the Amazonian sites. Informative comparisons among sites have been hampered, however, by differences in sampling protocols. The Panama site was sampled on a much smaller spatial scale (2 ha) than the two Amazonian sites. To improve comparisons, we censused a 104-ha area (the Limbo plot) encompassing the original 2-ha Panama study area and used several census methods, including those used at the Amazonian sites. As expected, spatial scale had a strong effect on estimates of species richness. We detected 252 species on the Limbo plot, compared with 161 detected on the original 2-ha area. Estimates of total individual birds per 100 ha were similar, but estimates from the original study were based on densities measured for one-third fewer species than we measured on our larger study area. Of the 53 species for which both Panama studies estimated population densities, a significant number of estimates were higher in the original study. Thus, the small spatial scale of the original study apparently led to inflated density estimates. The primary cause of disparities appeared to result from undersampling in the smaller plot of many species with patchy distributions and large territory sizes. Compared with Amazonian communities, the Panama community had far fewer rare species. Although 33% of species in Amazonian sites had densities of ≤1 pair/100 ha, only 17% were equally rare in Panama. Furthermore, eight species in Panama were, by tropical sta