Identifier

etd-03312010-083400

Degree

Doctor of Philosophy (PhD)

Department

Biological Sciences

Document Type

Dissertation

Abstract

Although birds of the forest canopy are an important component of tropical forest ecosystems, difficulty accessing the forest canopy has limited the advancement of knowledge pertaining to this group of species. Here I test methods for the study of canopy birds in lowland Neotropical rainforests, and identify recurring patterns of community structure in canopy bird assemblages as well as processes potentially responsible for these patterns. I used three methods to assess differences in ground-based and canopy-based methods for detecting forest birds in a 100-ha plot of lowland rainforest in northern Honduras: (1) point counts from the ground; (2) repeat censuses from two canopy trees; and (3) single censuses from multiple canopy trees. Ground methods significantly underestimated species and familial richness as well as abundances of individuals in the canopy stratum, and I predict that ground methods miss 25 to 50% of the species richness for some migrant and resident families and underestimates the density of some species by as much as 25%. I compared two distant canopy bird assemblages based on >11,000 detections at lowland rainforest sites in Honduras and Amazonian Brazil. Richness of canopy birds was similar between sites, despite overall higher forest bird richness in Brazil. Honduras and Brazil differed significantly in abundance distributions, with greater evenness characterizing the Brazil assemblage. Long-distance migrants and species of forest edges and open habitats were underrepresented at both sites when compared to null expectations drawn from regional species pools. Long-distance migrants were relatively more important in Honduras, where they constituted a third of canopy birds. Species richness of omnivores amongst core canopy species was greater than expected at both sites, and omnivores dominated the canopy in terms of species richness and individual abundance. Functional morphology analyses indicated that core canopy birds are more similar phenotypically than would be expected by chance. Similarity in functional morphology may result from environmental filtering selecting for phenotypes optimally suited for survival in the harsh canopy environment. Phylogeny seems to be an important underlying component of morphological similarity, however, and may exert a structuring force on the canopy bird assemblage through phylogenetic niche conservatism.

Date

2010

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Remsen, J. V., Jr.

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