Award Date

1-1-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Science

Number of Pages

168

Abstract

Avian species richness, species diversity, and density were measured and compared over a 21 month period on six riparian sites in Lake Mead National Recreation Area (LMNRA), southern Nevada. Sites consisted of two lake shore areas with almost pure stands of Tamarix ramosissima and four stream side areas, two with mixed Tamarix and native vegetation and two with only native vegetation. Overall mean avian species richness, diversity, and density were lowest on lake shore sites, intermediate on mixed stream sites and highest on stream sites with native vegetation. Differences in these values were significant between lake shore and stream sites and between stream sites for density. Habitat variables within these sites that were measured and correlated with avian community factors included perennial species richness, perennial species diversity, relative percent cover of Tamarix, percent total cover native vegetation, foliage volume, and arthropod biomass. Perennial plant species richness and diversity decreased on sites as amount of Tamarix increased based on relative canopy coverage measurements. Significant differences were found in foliage volumes of Tamarix growing on different site types at all three heights measured during various seasons. No differences in foliage volumes of native vegetation growing on different site types were found at any height in any seaSon Foliage height profiles based on foliage volumes measured at three different heights were constructed. Age profiles and age-stem diameter relationships of Tamarix were determined for four populations growing in the two habitat types. Stream sites were found to have older populations with less recruitment and averaged slightly fewer number of growth rings/cm than lake shore populations. Arthropods were sampled monthly from three vegetation layers, were identified to family, and then dried and weighed to determine sample biomass. Estimates of biomass in g/m{dollar}\sp3{dollar} and in g/ha were calculated for each site. Taxonomic diversity of arthropods was highest in the sites with no Tamarix and lowest in sites with little native vegetation. Significant differences were found in arthropod abundance between native vegetation and T. ramosissima. Using linear models, arthropod biomass was the poorest predictor of the three bird community factors at all levels. Percent total cover of native vegetation was the best predictor of bird species diversity, richness, and density across the three site types. Values for r{dollar}\sp2{dollar} were improved slightly by using various nonlinear models for all factors at all levels. Multiple linear regression was used to construct a model to predict each avian factor using the five vegetation factors across all six sites and across the three site types. Values for r{dollar}\sp2{dollar} were similar for bird species diversity and richness and lower for bird density across all six sites. At the site type level, r{dollar}\sp2{dollar} values were higher, with the value for bird density being the highest. Perennial plant species that birds used in greater proportions relative to their abundance were identified and included Acacia greggii, Prosopis pubescens, Prosopis glandulosa and Larrea tridentata. Plant species that birds used less in proportion to their abundance included Phragmites australis and Baccharis sarothroides.

Keywords

Amounts; Areas; Avian; Diversity; Habitat; Nevada; Ramosissima; Richness; Riparian; Southern; Species; Species Richness; Tamarix

Controlled Subject

Ecology; Zoology

File Format

pdf

File Size

4218.88 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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