Award Date

1-1-2001

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Science

First Committee Member

Daniel B. Thompson

Number of Pages

184

Abstract

Plant succession following disturbance in deserts is difficult to study because there is no well-defined series of species replacements and "successional stages" contain many of the same plant species. Persistence of the same species through successional stages introduces the possibility that desert species could respond to natural selection induced by disturbed environments. This study details changes in perennial vegetation, plant distribution, and small-scale abiotic environments on the scale of individual annual plants in order to examine corresponding changes in plant character phenotypes and natural selection in response to disturbance caused by fire. Two burned and two unburned populations of the Mojave Desert annual plant, Amsinckia tessellata were compared in a Coleogyne ramossisima dominated shrubland in Joshua Tree National Park; Perennial community composition was drastically altered by burning, and A. tessellata distribution did not significantly change. However, the microhabitat (light, temperature, and soil moisture) experienced by A. tessellata individuals differed between sites only sporadically, mostly during early spring months. The most dramatic effect of burning upon plant phenotypes was in altering plant response to microhabitat. Plants from burned sites responded to microhabitat in a less predictable and more temporally heterogeneous manner. Phenotypic variation and natural selection were estimated and compared between burned and unburned sites for three components of fitness and lifetime fitness. Phenotypic variation of plant characters and fitness variables was considerably higher in the novel burned environment for most of the plant characters measured. However, total linear selection was neither consistently stronger nor weaker in burned habitats for most character groups. Negative nonlinear (variance decreasing) selection coefficients were not more common in unburned sites compared to burned sites except for a single character group and fitness component. The two years showed highly variable selection, likely because the first sampling year was a high rainfall El Nino year while the second was an average rainfall year. Despite the temporal and spatial variation associated with the abiotic environment and selection between burned and unburned environments, A. tessellata populations could potentially diverge in response to changes in the environment wrought by disturbance.

Keywords

Amsinckia Tessellata; Annual; Annual Plant; Desert; Ecology; Evolution; Fire; Mojave Desert; Plant

Controlled Subject

Ecology

File Format

pdf

File Size

5447.68 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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