abstract: Riparian systems in the arid southwest are heavily altered and, based on relative land-area, provision a disproportionately high number of native wildlife. Amphibians and reptiles are collectively the most threatened vertebrate taxa and, in the Sonoran Desert, are often reliant on riparian habitat. The link between amphibians and environmental water characteristics, as well as the association between lizards and habitat structure, make herpetofauna good organisms for which to examine the effects of environmental change. My objective was to relate capture rates of a fossorial anuran and lizard abundance to aspects of native, invaded, and shrub-encroached riparian habitats in order to forecast the potential winners and losers of riparian habitat xerification and invasion. I measured habitat and monitored herpetofauna at 18 sites near the confluence of the San Pedro River and Gila River in Pinal County, Arizona in 2016 and 2017. Sites were divided into three categories based on dominant tree genus; Populus-Salix, Prosopis, and Tamarix, which represented native riparia, xeric riparia, and invaded riparia, respectively. Habitat measurements indicated that sites varied significantly in structure, and that dominant tree species was a useful descriptor of habitat physiognomy. Results from herpetofauna trapping demonstrated that Scaphiopus couchii, a fossorial anuran, occupy Prosopis sites at a much higher rate than at Tamarix sites, which were almost completely avoided. S. couchii was also found to be closely tied to xero-riparian habitat components present at Prosopis sites and soil analyses indicate that aspects of soil moisture and texture play an important role in the partitioning of this species across altered riparian habitats. Lizard abundance was found to be significantly lower in Tamarix habitat, with the majority of captures attributed to the generalist whiptail Aspidoscelis tigris. Additionally, more than half of lizard species that were analyzed displayed a negative association to Tamarix habitat. Of the three habitat types considered, Populus-Salix supported the greatest abundance of lizards. Based on this study, the deleterious effects of xerfication on a riparian herpetofauna community may be lesser than those of Tamarix invasion. These two forms of riparian habitat shift often co-occur, with the ultimate cause being changes in hydrologic regime. This may imply that a bottom-up approach, wherein historic hydrology is restored to restore or maintain native habitats, to riverine management is appropriate for riparian herpetofauna conservation. / Dissertation/Thesis / Masters Thesis Applied Biological Sciences 2018

Ants are ubiquitous in most communities and many form opportunistic mutualisms with honeydew-producing hemipterans (e.g. treehoppers). Hemipterans excrete honeydew, a carbohydrate rich substance, that ants harvest and, in return, ants protect their honeydew-producing partners from parasitoids, predators, and competitors. Given the efficacy of tending ants in removing hemipteran antagonists, and the strong roles that ants play within their communities as predators, competitors, and seed dispersers, surprisingly little is known of the effects of ant-hemipteran mutualisms (AHM) on the invertebrate communities in which they are embedded or on the plants that host AHM. Using observational and manipulative field experiments, I examined the long-term effect of AHM on their host plant’s, honey mesquite (Prosopis glandulosa), reproductive potential and quality. In addition, I measured how the presence of AHM affects the abundance, richness, diversity, and composition of the invertebrate communities living on honey mesquite. Plants hosting AHM may indirectly benefit (through the removal of herbivore arthropods) or suffer (through the loss pollinators) due to the defensive behavior of tending ants. To determine the effects of AHM on their host plant, I established a four-year press experiment in which I removed AHM from 50 randomly trees, while leaving 50 as controls. In addition, I marked and followed 30 trees from which AHM were naturally absent. To assess if mesquite quality differed between trees hosting AHM and trees in which AHM were naturally absent, in 2012 I assayed foliar condensed tannin concentrations, a secondary defense compound, and, in 2015, I measured foliar nitrogen, phosphorous, potassium, magnesium, and iron as they are essential for growth and reproduction. I compared the reproductive potential between AHM present and removed trees by counting flowers and fruits across all 4 years of the study. Mesquite that hosted AHM contained significantly less condensed tannins and significantly higher concentrations of N%, Mg, and Fe. Furthermore, over the duration of the study mesquite hosting AHM contained significantly more flowers than those from which AHM were removed or naturally absent. My results indicate that AHM select trees of high quality and their continued presence is associated with high levels of reproductive potential. Most studies that have evaluated community-level effects of AHM compare total abundance and species richness in communities (or host plants) with and without AHMs. However, both measures are dependent on sampling effort, complicating comparisons across different studies. To examine the effects of AMH on the arthropod community in mesquite, I first compared family richness and alpha diversity using standardized rarefaction and extrapolation curves. I then measured beta diversity and turnover in community composition from one year to the next. The removal of AHM increased invertebrate diversity and significantly altered community composition. Although treatments did not statistically differ in turnover rates, replacements occurred among treatments at the family level which may be biologically meaningful. Furthermore, herbivore and predator populations increased, and pollinator populations decreased following the removal of AHM. These results suggest that the presence of AHM can alter the composition of arthropod communities and food-web dynamics. However, these effects were significant in some years and not others, suggesting the importance of temporal variation in drivers of communities. Overall, my work demonstrates that AHM can be drivers of community composition and illustrate the importance of examining their effects across multiple seasons.

The control of mesquite is a major range problem in the Southwest. Mesquite is a thorny, woody shrub or tree that has infested 75 million acres of valuable range and pasture land in this region. It competes with grasses and other valuable plants for sunlight, moisture, and plant food. Mesquite also acts as a serious barrier to the handling of cattle on the range.

No description available.

In central Mexico's semi-arid highlands, mesquite (Prosopis spp.) pods are utilized for food and livestock feed. In 1975, a union of 53 rural communities opened a storage and processing facility for mesquite pods. A study of the operation and the regional collection, sales, and use of mesquite was conducted to evaluate the industry's potential. Twenty-six communities were visited, and formal interviews were held with 35 subsistence farmers, 12 mesquite feed dealers, eight large-scale ranchers, and members of the mesquite union. The effect of climatic factors on mesquite pod harvests was analyzed. The study examined opportunity costs for land and labor and the costs and returns of improvements to the operation. The mesquite facility has increased income production for rural farmers and provided a local source of nutritious livestock feed. Potential improvements to the industry include pest control, production of mixed feeds, improved management, and marketing. Similar operations could succeed in areas with dense mesquite woodlands, a history of pod collection and use, and a need for seasonal income production.

No description available.

Woody plant encroachment (WPE) into historic grasslands not only alters ecosystem structure but also yields a mosaic of vegetative growth-forms that differ in their inherent physiological capacities and physical attributes. C₃ plants tend to have a relatively broad range of temperature function but at the expensive of a lower optimum rate of photosynthesis. In contrast, C₄ grasses have a greater capacity for maximum uptake but across a relatively narrow range of temperatures. In considering which of these functional groups will outcompete the other within these regions undergoing WPE, one must account not only for these leaf physiological traits, but also the growth form induced differences in rooting depth, and therefore, potential access to deeper subsurface water. Laid upon these competitive interactions is an ever-changing environment, which for the semiarid southwestern US is predicted to become progressively warmer and characterized by highly variable precipitation with longer interstorm periods. In addition to aboveground changes in CO₂ assimilation, WPE influences soil nutrient, water, and carbon cycling. The objectives of this dissertation were to quantify: (1) the influence that temperature and available soil moisture have on regulating soil respiratory efflux within the microhabitats that results from WPE to estimate the influence this vegetative change will have on ecosystem CO₂ efflux; (2) the sensitivity of CO₂ uptake within grassland and woodland ecosystems to temperature and precipitation input in an effort to characterize how WPE might influence regional carbon and water balance; and (3) the role access to stable groundwater has in regulating the temperature sensitivity of ecosystems and their component fluxes. Major findings and contributions of this research include illustrating seasonal patterns of soil respiration within the microhabitats that result from WPE, such that an analysis of the relative contributions of these different components could be made. We found that soil respiration was not only consistently greater under mesquites, but that the relative contributions of these microhabitats varied significantly throughout the year, the duration of soil respiration after each rain was habitat-specific, and that the relationship between soil respiration and temperature followed a hysteretic pattern rather than a linear function (Appendix A). We found that a woodland ecosystem demonstrated a lower temperature sensitivity than a grassland across all seasonal periods of varying soil moisture availability, and that by maintaining physiological function across a wider range of temperatures throughout periods of limited precipitation, C₃ mesquites were acquiring large amounts of carbon while C₄ grasses were limited to functioning within a narrower range of temperatures (Appendix B). Finally, we found that having a connectivity to stable groundwater decoupled leaf and ecosystem scale temperature sensitivities relative to comparable sites lacking such access. Access to groundwater not only resulted in the temperature sensitivity of a riparian shrubland being nearly half that of the upland site throughout all seasonal periods, but also actual rates of net ecosystem productivity and leaf level rates of photosynthesis being dramatically enhanced (Appendix C).

Shifting patterns of precipitation associated with climate change may affect water-limited ecosystems to a greater degree than atmospheric CO2 or temperature changes, yet we lack a mechanistic understanding of the effects of water in these ecosystems. In water-limited ecosystems, annual net primary productivity correlates strongly with total annual precipitation. However, precipitation in these ecosystems arrives in episodic events, suggesting that biophysical investigations should focus on the implications of discrete precipitation events. Further, examining dynamics of ecosystem processes over a period of days or weeks promises to link our leaf-level mechanistic understandings with larger scale patterns and temporal dynamics of ecosystem photosynthetic CO2 uptake, respiration and evapotranspiration.The objectives of this dissertation were to quantify: (1) the influence of biotic and abiotic features of an ecosystem (e.g., species composition and soil physical characteristics) on short-term patterns of resilience and resistance to a precipitation pulse; (2) the role of antecedent climatic conditions and the seasonal timing of rainfall in limiting ecosystem carbon exchange in response to precipitation events; and (3) the effect of changes in woody plant abundance on seasonal ecosystem carbon dynamics in relation to the North American Monsoon.Major findings and contributions of this research include defining the concepts of ecosystem functional resistance and resilience and their implications in the presence of a dominant nonnative bunchgrass in semi-arid grasslands (Appendix A); a better understanding of the influence of warm-season precipitation variability and the seasonal timing of rainfall on ecosystem carbon dynamics in a semi-arid grassland (Appendix B); the use of flux duration analysis, a novel approach to analyzing ecosystem carbon and water flux time-series data to distinguish between "pulse-driven" or "steady-state" ecosystems (Appendix C); and, finally, the application of flux duration analysis to quantify the sensitivity of ecosystem carbon exchange in response to seasonal rainfall in a riparian grassland and shrubland and the role that plant functional type diversity may play in constraining carbon exchange sensitivity (Appendix D).

Thesis (D. Min.)--Dallas Theological Seminary, 2006. / Includes abstract. Includes bibliographical references (leaves 59-60).

abstract: Die-off of screwbean mesquite (Prosopis pubescens), a species native to the American Southwest, has been documented regionally within the last decade. Historical causes for episodic mortality of the more widely distributed velvet mesquite (Prosopis velutina) and honey mesquite (Prosopis glandulosa) include water table declines and flood scour. Causes of the recent die-offs of P. pubescens have received little study. Numerous riparian restoration projects have been implemented regionally that include screwbean mesquite. Restoration propagules from foreign sources can introduce diseases, and low genetic diversity plantings may allow for disease irruptions. I asked: 1) Are die-offs associated with a particular age class, 2) Is die-off suggestive of a pathogen or related to specific environmental stressors, 3) Are mortality influences and outcomes the same between restoration and local populations, 4) Are particular land uses and management associated with die-off, and 5) Are populations rebounding or keeping pace with mortality? I documented the screwbean mesquite population status at rivers and wetlands in Arizona with varying levels of restoration. I used logistic regression and Pearson correlation analysis to explore mortality response to site factors and disease related variables. I compared mortality response and disease severity between local and restoration populations. Biotic damage surfaced as the most important factor in statistical analyses, suggesting that mortality was caused by a pathogen. Mortality was greatest for young size classes (3 to 14 cm), and biotic damage was higher for individuals at infrequently flooded areas. Strong differences were not found between local and restoration populations – however restoration populations were less stressed and had lower biotic damage. Novel urban and restored sites may provide refuge as site conditions at other locations deteriorate. A culmination of past water diversion, development and land use may be surfacing, rendering riparian species vulnerable to diseases and triggering such events as region-wide die-off. / Dissertation/Thesis / Masters Thesis Plant Biology 2016