Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology, Ecology

Date of Defense

7-29-2008

Graduate Advisor

John G Blake

Committee

Bette Loiselle, Ph.D.

Robert E. Ricklefs, Ph.D.

Robert M. Zink, Ph.D.

Abstract

Aridlands of northern Venezuela are important from an ornithological perspective because of the occurrence of habitat specialist birds that depend exclusively on desert scrubs and are endemic to this region. Currently, long-term survival of habitat specialists is threatened by ongoing changes in vegetation but the effects of such changes on bird assemblages are unknown. The goal of this study was to characterize bird assemblages found in six arid zones in northern Venezuela at both ecological and genetic levels, and to generate information relevant for conservation planning. The study involved assessments of patterns of avian species richness, abundance, community composition and genetic diversity, as well as specific bird-habitat associations. Through systematic surveys, 96 bird species were recorded throughout the study areas. Even though the six areas support a homogeneous habitat type, species richness, composition, and abundance varied among them. The most abundant birds in all six areas were widespread generalists, and only one of the habitat specialists had high densities in all areas. Species richness was not a good indicator of an area?s conservation value, because the protection of the area with highest number of species does not guarantee the effective conservation of all habitat specialist birds. Vegetation analyses indicated differences in mean values of both floristic and structural vegetation variables among the six study areas but, overall, the six areas had relatively similar vegetation. Habitat specialists differed in their responses to vegetation variables, which may be related to differences in foraging strategies. Even though habitat specialists did not respond strongly to vegetation variables, results of this study suggest that some structural attributes are important for the survival of this particular group of species. Molecular techniques were used to investigate patterns of genetic diversity in three codistributed specialist birds. Multiple analyses indicated geographic structure in the three species, but the extent of geographic structure varied among them as a result of different levels of population isolation during historical times. The assessment of genetic diversity and geographic structure of these three restricted birds showed incongruent patterns, which evidence different evolutionary histories.

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