The nitrogen budgets of Eurotia lanata (Pursh.) Moq. and Atriplex confertifolia (Torr. and Frem.) S. Wats salt desert shrub plant communities were investigated. In each, a complete biomass and organic nitrogen inventory was made. In addition, investigations of the nitrogen fixation potential of soil surface microflora and inorganic soil nitrogen relationships were carried out. Greater total biomass and organic nitrogen was found in the above-ground portions, annual shoot productivity, and litter of the Atriplex community. However, the Atriplex community was exceeded by the Eurotia community in root biomass. Roots accounted for 74 and 87 percent of the plant biomass and 83 and 90 percent of the associated organic nitrogen in Eurotia and Atriplex communities respectively. Root biomass distribution at various depths was markedly different in the two communities. Differences between communities in relative amounts of various plant parts and litter are related to contrasting plant growth habit, and differences in soil texture and soil salinity. Total plant biomass estimates, which were 18,480 and 17,300 kilograms per hectare for Eurotia and Atriplex communities, were not significantly different and reflect the overriding influence of macroclimate and associated moisture limitation. Under laboratory conditions the soil surface microflora of the Atriplex community was able to fix significant amounts of atmospheric nitrogen while that of the Eurotia community did not. Nitrogen fixation potential in the Atriplex community was associated with the presence of abundant lichen cover and associated heterocvstcontaining blue-green algae of lichen interspaces. Differences between communities were found in rates of mineralization, downward flux, and pattern of utilization of inorganic soil nitrogen. Soil salinity appeared to strongly limit inorganic soil nitrogen mineralization as well as root growth and nitrogen uptake in the lower part of the Atriplex soil profile; however, this lack of biological activity was compensated for by a greater downward flux of inorganic soil nitrogen from decomposing litter and surface soil in the Atriplex community. Shoot and root litter appears to be the most readily available source of inorganic soil nitrogen for plant growth in salt desert shrub plant communities.

Kangaroo rats (Dipodomys spp.) are frequently characterized as keystone species for their role in altering soil characteristics, changing habitat structure through seed consumption and dispersal, and being important primary consumers in their ecosystem. They are arid adapted and known to forage in areas with sparse vegetation. Studies suggests densely vegetated habitat to be unsuitable for kangaroo rats because plants are an impediment to their locomotion and predator avoidance behaviors. This study focuses on an invasive grass, South African Veldt (Ehrharta calycina), that converts landscapes with sparse vegetation into dense grassland habitats, and the Lompoc kangaroo rat (Dipodomys heermanni arenae) that occupies some of those modified landscapes. I explored the proximate effects of Veldt grass by assessing the locomotion of D.h. arenae in three Veldt grass densities. I hypothesized that Veldt grass influences kangaroo rat locomotion, but that performance could also be influenced by experience with the grass. Kangaroo rats with long-term experience with Veldt grass (i.e., those occupying a habitat containing Veldt grass) and short-term experience (two-night habituation in an artificial Veldt grass patch) were tested by pursing the animals through runways of different grass densities and measuring the amount of time spent crossing the runway, amount of time spent stopped, average velocity, and amount of motivation required to initiate and sustain movement. I also monitored habitat use during the two-night habituation period in order to assess habitat utilization among three Veldt grass density habitat patches. I hypothesized that Veldt grass may influence normal habitat utilization patterns in D.h. arenae: specifically, the avoidance of the densest habitats and preference or disproportionate utilization of the most open habitat. I found, when the animals were left alone to forage and explore, they spent significantly more time in habitat patches containing Veldt grass than in a control patch containing zero percent cover. However, in locomotion trials, Veldt grass had a negative effect on locomotory performance. These effects seem to scale with grass density, and were ameliorated to some degree by familiarization: animals from a Veldt grass habitat of origin performed better in novel Veldt grass templates than animals from a non-Veldt habitat of origin; however, both groups performed equally well after two nights’ habituation to the templates. These results suggest that learning occurred in two nights and that it increased the kangaroo rats’ ability to locomote through the grass when pursued. I note that performance studies often do not take into account the amount of motivation employed to initiate and sustain running of the test animals, and suggest that this be considered in future studies. Furthermore, the learning capacity of a kangaroo rat, as well as a community level perspective that considers neutral or even positive trophic interactions among natives and invasives, must be considered in conservation and management decisions in the future.

Global climate change is already contributing to the extirpation of numerous species worldwide, and sensitive species will continue to face challenges associated with rising temperatures throughout this century and beyond. It is especially important to evaluate the thermal ecology of endangered ectotherm species now so that mitigation measures can be taken as early as possible. A recent study of the thermal ecology of the federally endangered Blunt-Nosed Leopard Lizard (Gambelia sila) suggested that they face major activity restrictions due to thermal constraints in their desert habitat, but that large shade-providing shrubs act as thermal buffers to allow them to maintain surface activity without overheating. We replicated this study but added a population of G. sila with no access to large shrubs to facilitate comparison of the thermal ecology of G. sila in shrubless and shrubbed populations. We found that G. sila without access to shrubs spent more time sheltering inside rodent burrows than lizards with access to shrubs, especially during the hot summer months. Lizards from a shrubbed population had higher midday body temperatures and therefore poorer thermoregulatory accuracy than G. sila from a shrubless population, suggesting that greater surface activity may represent a thermoregulatory tradeoff for G. sila. Lizards at both sites are currently constrained from using open, sunny microhabitats for much of the day during their short active seasons, and our projections suggest that climate change will exacerbate these restrictions and force G. sila to use rodent burrows for shelter even more than they do now, especially at sites without access to shrubs. The continued management of shrubs and of burrowing rodents at G. sila sites is therefore essential to the survival of this endangered species.

The sand dunes lying ten miles northwest of Kanab in Kane County, Utah, support a sparse plant cover with four species dominating the vegetation: Psoralea stenostachys, Sophora stenophylla, Oryzopsis hymenoides, and Wyethia scabra var. attenuata. Of these Psoralea and Wyethia are endemic to the dunes or to a limited area which includes the dunes. The pineer species gain a start in the valleys between dunes and occupy the area only until sand covers them or until sand is blown away from their roots. Stabilization of the soils is not permanently in the interdune valleys and the dunes continue to wander. The low fertility of the soils, the low moisture content, the extremes of temperature, light, and other environmental factors limits the number of individual plants which can occupy the dunes. The region will continue to have actively moving dunes until major climatic changes occur permittimg a denser plant cover which would tend to stabilize the sands.

During the summer of 1934 this investigation was conducted to determine the effect of overgrazing on the mortality of desert browse in the vicinity of the Desert Range Branch experiment station. Range lands of western United States have, as a whole been subjected to overgrazing. Utah has about 24 million acres of public acres of public domain that can only be utilized from grazing. An effort has been made to put this area under control. The "Taylor Grazing Act" passed by Congress June 28, 1934 is a big step in the direction of the control of this vast area of unappropriated range land. This control is necessary in order to rid these ranges of the evils of overgrazing, and save one of the chief resources of the Western States.

Phylogeographic studies have relied on surveying neutral genetic variation in natural populations as a way of gaining better insights into the evolutionary processes shaping present day population demography. Recent emphasis on understanding putative adaptive variation have brought to light the role of epigenetic variation in influencing phenotypes and the mechanisms underlying local adaptation. While much is known about how methylation acts at specific loci to influence known phenotypes, there is little information on the spatial genetic structure of genome-wide patterns of methylation and the extent to which it can extend our understanding of both neutral and putatively adaptive processes. This research examines spatial genetic structure using paired nucleotide and methylation genetic markers in the Sonoran bark beetle, Araptus attenuatus, for which we have a considerable knowledge about its neutral demographic history, demography, and factors influencing ongoing genetic connectivity. Using the msAFLP approach, we attained 703 genetic markers. Of those, 297 were polymorphic in both nucleotide (SEQ) and methylation (METH) were assayed from 20 populations collected throughout the species range. Of the paired SEQ and METH locis, the METH were both more frequent (16% vs. 7%), maintained more diversity (Shannon IMeth = 0.361 vs. ISeq=0.272), and had more among-population genetic structure (ΦST; Meth = 0.035 vs. ΦST; Seq= 0.008) than their paired SEQ loci. Interpopulation genetic distance in both SEQ and METH markers were highly correlated, with 16% of the METH loci having sufficient signal to reconstruct phylogeographic history. Allele frequency variation at five loci (two SEQ and three METH) showed significant relationships with at-site bioclimatic variables suggesting the need for subsequent analysis addressing non-neutral evolution. These results suggest that methylation can be as informative as nucleotide variation when examining spatial genetic structure for phylogeography, connectivity, and, identifying putatively adaptive genetic variance.

No description available.

The purpose of this study is to investigate the level and distribution of genetic variation in Astragalus jaegerianus by using molecular markers. The objectives of the study are: to estimate levels of genetic variation within and among populations of Astragalus jaegerianus; to test the hypothesis that levels and patterns of genetic variation in species of restricted ranges and few individuals is low and partitioned at the population level; and to discern whether, or how well, genetic partitioning of Lane Mountain milk vetch correlates with its geographic partitioning in the field.

Climate change models predict an increase in frequency and amplitude of extreme weather events, including heat waves. To better predict how the composition and distribution of plant assemblages might respond to these changes in temperature, it is important to understand how species currently respond to these extremes. Photosynthetic thermal tolerance (T25)and photosynthetic recovery (RT25) were quantified in 27 species. We also studied the relationships between T25, RT25 and leaf mass per area (LMA). Leaf temperature was also monitored in the field. Leaves used in this study were collected from two distinct environments representing desert and montane plant assemblages. T25 and RT25 were measured using a chlorophyll fluorescence protocol incorporating sub-saturating light and short duration heat stress. Mean T25and LMA were significantly different between environments. Mean RT25 was not significantly different between environments. There was a positive relationship between T25 and LMA in both environments. The ability to recover from heat stress does not differ between two biomes that experience vastly different mean maximum temperatures during the summer months. LMA is a predictive leaf trait for thermal tolerance.

Deserticolous birds inhabit an environment characterised by high ambient temperatures and low rainfall that has low primary productivity. The combination of these factors may lead to the evolution of adaptations that minimise food and water requirements. One physiological adaptation that has been found in many deserticolous birds is the reduction of basal metabolic rate (BMR). I measured metabolic rate in the laboratory using four species of African lovebirds (Agapornis) , and four species of Australian grass parakeets (one Neopsephotus and three Neophema), all similar in body mass. Tests for differences between groups were carried out using both conventional and phylogenetically independent methods. The BMRs of the lovebird and grass parakeet species were not statistically correlated with habitat type. These results confirm the findings of previous studies on the effect of desert conditions on the BMR of parrots. I also found no significant differences in BMR between the species assemblages from different continents. The lack of significant differences in BMR between deserticolous and nondeserticolous parrots supports the idea that birds are "ex-adapted" to living in desert environments. I suggest that the results may have been affected by phenotypic plasticity in BMR, as recent evidence has shown that the scaling exponent of BMR differs between captive-raised and wild-caught birds. To elucidate the effect of origin (captive-raised vs. wild-caught) on the BMR of birds used in this study a large scale analysis of bird BMR data was undertaken. BMR and body mass data for 242 species of birds were obtained from the literature, this study, and unpublished data from various sources. A phylogeny was constructed using molecular and morphological phylogenies from the literature, and analysed using conventional and phylogenetically independent methods. The conventional analysis found significant differences in the scaling exponents of BMR of captive-raised and wild-caught birds. However the phylogenetically independent method showed non-significant differences between these two groups. Conventional analysis of differences between parrots and all other birds yielded significant differences between these two groups, with parrots having significantly higher BMRs than other birds. Again the phylogenetically independent analysis found non-significant differences between these VII two groups. A test of homogeneity of variance between these two groups found significant differences between the variances ofthe two groups, probably due to disparity in sample size and range of body sizes. The conventional and phylogenetically independent tests for differences between captive-raised and wild-caught parrots yielded non-significant results, suggesting that the parrots are not subject to the phenotypic adjustments postulated for all other birds. The lack of significant differences between captive-raised and wild-caught parrots suggests that the analyses of differing habitat type for African and Australian parrots is indeed valid. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.