No description available.

Please read the abstract in the section 00front of this document / Thesis (DPhil (Entomology))--University of Pretoria, 2006. / Zoology and Entomology / unrestricted

The main aim of this study was to determine if Ischyrolepis sieberi, a common restiod species found at high altitudes in the Cederberg captures fog to supplement its water needs. This was done by comparing the isotopic ratios of δD and δ¹⁸O in captured fog, rainwater, and stream water and comparing these to the δD and δ¹⁸O values found in the xylem water of Ischyrolepis sieberi plants growing at the study site. The δD values of the collected fog samples were enriched relative to rainwater, stream water, and xylem water from I. sieberi, however these differences were not significant. The δ¹⁸O values of the I. sieberi xylem water were significantly (p < 0.01) more enriched than rain, stream, and fog water. The xylem water of I. sieberi was depleted in δD and enriched in δ¹⁸O relative to all other water sources. The plants therefore did not appear to be utilizing fog during the three months of this study. The δ¹⁸O values of I. sieberi were consistently 4-6‰ enriched compared to rainwater, suggesting that they are utilizing rainwater, which has undergone fractionation due to evaporation in the soil before being taken up by the plants. This study was run during the wet winter months. The δD and δ¹⁸O values from previous data suggest that the I. sieberi plants do utilize fog during the dry summer months.

No description available.

Graduation date: 1998

D. Tech. Biotechnology and Food Technology. / Assesses the symbiotic dependency of grain and shrub / tree legumes as well as shrub/tree legume species adaptation to different rainfall regimes within five agroecological zones in Botswana, leaves of the test species were sampled.

No description available.

Thermophysiological traits of two isolated Hoplodactylus maculatus populations were investigated to test adpatations to climate. Geckos were collected from Craigieburn (high altitude, generally cooler site) and Banks Peninsula. If climatic conditions at respective sites influenced physiology, I expected geckos from Craigieburn to exhibit cold-adapted physiological traits, whilst Banks Peninsula geckos would exhibit traits more characteristic of a warmclimate species. To this end I investigated four thermophysiological parameters: metabolism (SMR), preferred body temperature (PBT), locomotory performance and critical thermal minimum (CTMin). I hypothesized that if climate had an effect on SMR, Craigieburn geckos would exhibit higher levels of SMR which typically characterise other coolclimate reptiles. Craigieburn geckos displayed an average relative elevation of SMR over Banks Peninsula geckos of 26%. Furthermore, Craigieburn geckos appeared to be 'geared' towards lower body temperatures and exhibited a greater acclimatory and acclimatizatory ability of SMR. The PBT of Craigieburn geckos was consistently elevated above Banks Peninsula geckos. This finding was somewhat paradoxical in light of previous studies of this parameter. A closer examination of the ecology of the two populations is required to clarify the adaptive significance of a higher PBT in geckos from a cooler climate. With respect to locomotory performance, I hypothesized that if thermal extremes influenced activity, Craigieburn geckos would exhibit activity patterns which help ameliorate the adverse effects of cold temperature. Craigieburn geckos did in fact have greater independence of activity to temperature than Banks Peninsula geckos, especially over lower body temperatures. The final parameter investigated, that of the critical thermal minimum, failed to distinguish the populations decisively. However there was some evidence of a greater acclimatizatory and acclimatory range in Craigieburn geckos, providing somewhat limited support for a population difference. Investigations into all four parameters lead me to conclude that populations of Hoplodactylus maculatus from Craigieburn and Banks Peninsula are physiologically distinct and warrant a revision of nomenclature.

No description available.

Ecophysiological traits that vary in response to water stress, and that exhibit significant genotypic variation in Pinus radiata, may reveal a differentiation between genotypes in their ability to respond to and function under water-limitation. Where the genotypic variation of these ecophysiological traits is also genetically correlated with tree growth, they improve the understanding of the genetic variation in growth under water limitation in this species. Ultimately they could be used as selection criteria for improved growth in water-limited environments. The objectives of the thesis were to identify ecophysiological traits in Pinus radiata that responded significantly to water stress; to assess the genotypic variation of those ecophysiological traits in P. radiata; and to determine the genetic correlation between those genetically variable ecophysiological traits and growth. / The thesis assessed the genotypic variation in ecophysiological response to water stress in Pinus radiata, and the genetic correlation between ecophysiological response and growth. These assessments were carried out in seedlings in the glasshouse, in 10 year-old trees in two field trials, and in increment cores of three field trials. / The response of Pinus radiata to water stress was exhibited in a wide range of ecophysiological traits, including growth, respiration, gas exchange, carbon isotope discrimination, chlorophyll fluorescence and osmotic adjustment. Gas exchange and carbon isotope discrimination were not genetically variable in response to water stress, despite significant treatment effects. Some of the other ecophysiological traits, including chlorophyll fluorescence, respiration in growing tissues and osmotic adjustment, did exhibit significant genetic variation under water stress, suggesting some genetic plasticity in P. radiata in response to water stress. However, there were few significant genetic correlations between any of these ecophysiological traits and growth traits, and none of them were demonstrated to be suitable selection criteria for genetic improvement of growth under water stress. / The thesis concludes that genetic variation in ecophysiological response to water stress is limited in P. radiata, and that the growth response to water stress was remarkably homogeneous between genotypes, despite there otherwise being significant genetic variation in growth that was unrelated to water stress. These findings were consistent across several trials and degrees of water stress, in both seedlings and mature trees. They are an important contribution to discussion of the appropriate balance of genetic improvement and silviculture in the optimum management of P. radiata in water-limited environments or under a drying climate, particularly as they are in contrast to results of studies of other Pinus spp such as P. pinaster or P. elliottii x caribaea in growth response to water stress has been shown to be genetically variable.