In a warm, dry grassland in southeastern Arizona dominated by C₄ grasses the only C₃ grass found was restricted to dry, exposed ridge crests within the hottest and driest part of the region. This was precisely the opposite of what one would predict from physiological and biogeographic considerations, which would lead one to expect a C₃ grass in this environment to be growing on cooler or moister areas that would mitigate the effects of the inhospitable climate. Cover of C₄ grasses was very low on these ridge crests, and increased downslope with the greater volume of water available to high values on the lower slopes and in washes. It was suggested that this C₃ grass, Stipa neomexicana, had a very high tolerance of water stress, but a very poor tolerance of competition, and was limited to unfavorably dry sites by its competitively superior C₄ neighbors. Most species, regardless of photosynthetic type, could not survive in the harsh ridge crest environment, which therefore offered a refuge from competition. The hypothesis of competitive exclusion was tested by removal experiments conducted at ridge crest, midslope and lower slope positions along the topographic gradient of decreasing Stipa neomexicana and increasing C₄ grass cover. The predictions made under this hypothesis were confirmed. The presence of competitors limited the growth of mature plants, flower production, seedling establishment and seedling survival. The beneficial effects of the removal of competitors increased downslope. Competition depressed estimated finite rates of population increase for Stipa neomexicana. This depression was most severe on the lower slope. It was concluded that increasing competition from C₄ grasses along the topographic gradient was responsible for restricting Stipa neomexicana to the unfavorable ridge-crest sites.

Includes bibliographical references (leaves 235-258). Estimates the primary production and investigates the photosynthetic performance of temperate turfs at West Island, off the coast of South Australia. These communities play a fundamental role in reef ecology, being the main source of food for grazers, both fishes and invertebrates. Turfs also have an important function in benthic algal community dynamics, being the first colonizers on disturbed and bare substratum.

Includes bibliographical references (leaves 235-258). / xxi, 274 leaves, [8] leaves of plates : ill. (chiefly col.), map 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Estimates the primary production and investigates the photosynthetic performance of temperate turfs at West Island, off the coast of South Australia. These communities play a fundamental role in reef ecology, being the main source of food for grazers, both fishes and invertebrates. Turfs also have an important function in benthic algal community dynamics, being the first colonizers on disturbed and bare substratum. / Thesis (Ph.D.)--University of Adelaide, Dept. of Environmental Biology, 2002