Date of Award:

5-1980

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

James A. MacMahon

Committee

James A. MacMahon

Abstract

The structure of Sonoran Desert bird communities was studied along both a vegetation gradient (at Organ Pipe Cactus National Monument, Arizona) and a latitudinal gradient (from Burro Creek, Arizona to Sierra Libre, Sonora, Mexico). The vegetation gradient consisted of 4 sites which varied in vegetation structure from complex (large cactus-subtree dominated community) to simple (shrub dominated community). Along the vegetation gradient, bird species diversity, bird species richness and consuming biomass decreased with decreasing structural complexity of the vegetation. Bird species equitablility did not change significantly along the gradient. Using both principal component and cluster analyses on foraging behavior data plus information on foraging behavior and diet taken from the literature, I recognized 10 guilds. Guild richness decreased with decreasing structural complexity from 10 guilds on the most complex site to 4 guilds on the least complex site.

Five measures of vegetation structure (foliage height diversity, plant species diversity, physiognomic cover diversity, foliage volume, and percent vegetation cover) were selected as possible determinants of bird community structure. All vegetation measures were significantly correlated with bird species diversity, bird species richness and consuming biomass. These results were apparently due to interdependence among the vegetation variables. To determine the possible controlling variable(s), multiple regression analysis was employed to determine the relative importance of each variable in accounting for variation in the bird community variables. Foraging behavior and foliage use of bird species was studied to determine if the vegetation variables selected were actually important to the birds. Results of these analyses suggest that foliage height diversity and physiognomic cover diversity are required to accurately predict bird species diversity in Sonoran Desert avian communities.

Along the latitudinal gradient, bird community structure was examined in 3 plant communities of similar vegetation structure. Bird species diversity and bird species richness did not change significantly along the latitudinal gradient; bird species equitability was positively correlated with latitude; consuming biomass and density (pairs/10 ha) were negatively correlate with latitude; and guild structure shifted from insectivore dominated communities in the north to granivore dominated communities in the south. Increasing consuming biomass and population density in the southern Sonoran Desert was correlated with greater annual and it is argued that greater precipitation may have contributed to two these patterns through its effect on greater productivity and resource availability. Changes in guild structure are correlated to differences in seasonal precipitation regimes and their apparent effect on the relative abundance of food types (i.e. insects and seeds). Patterns of bird community structure along these gradients are related to results from studies along with other vegetation gradients and their significance discussed.

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