Browsing by Subject "Ecology"
Now showing 1 - 20 of 24
Results Per Page
Sort Options
Item A sensitivity test for species distribution models used for gap analysis in New Mexico(Texas Tech University, 1996-12) Islas, Carlos Gonzalez-RebelesGap Analysis Program is a landscape-level evaluation of plant communities and animal richness and is useful in wildlife conservation. Models to predict species distributions are fundamental for Gap analysis to assess animal richness patterns. Basic models combine species' locality, together with their vegetation associations (base variables). Additional environmental variables (filter variables) are used for further adjustment and to represent particular habitat associations. However, there is a need to know the contribution that filter variables provide to the models. This research evaluated model sensitivity to simplification of habitat associations in the model, by systematically removing selected filter variables. This was done to quantify indirectly the value added by these variables and to examine if the response pattern was consistent with expected model performance. Distribution predictions from the New Mexico Gap Analysis Project (NMGAP) were used as baseline data for this study. A representative sample of species was evaluated by using subset combinations of filter variables as model input. Altered species distribution estimates were examined for differences in area relative to the full model. Model sensitivity to different single filter variables and combinations was found to be highly variable among different types of models (number of filter variables used) and the species they represented. Between extreme high and low values, results indicated that in general all filter variables presented some level of influence on the models (assumed adjustment). However, for those models formed with two or three filter variables most of their least influential variables did not differ (p>0.05) from a threshold value set as minimum acceptable change (5% change in area). This indicated that more risks of variables with no effect may occur when adding more than two filter variables (potential correlation). Consistent with model performance expectations, general response to perturbation suggested that each additional filter variable used in the model produced a cumulative effect for most models, and that this effect was greater (p<0.05) for models representing species with restricted distributions than for those with widespread species distributions. Sensitivity analysis is recommended at the stage of review of preliminary wildlife species distribution maps produced for Gap analysis to detect model weaknesses.Item An unwitting autobiography - Staked Plains ecological prehistory and history(Texas Tech University, 1991-12) Fenton, James IrvingNot availableItem Balance between humanity and ecology(2009) Spears, Steven Joseph, 1974-; Catterall, KateIncorporating aspects of public and environmental art practices into my professional endeavors as a landscape architect and urban designer has provided me with opportunities to work at a human scale, consider human needs, and focus on environmental issues that are closely interwoven with those needs. The public and environmental art process has presented greater opportunities to balance the sublime with the pragmatic and allows for a more overt communication between designer and audience, viewer or user. Functioning in this interstitial space allows me to communicate ideas clearly and to initiate a broader discussion on how society might find a balance between the stewardship of the natural environment in the face of the exponential growth of communities and the desire to own and develop land. My aim is to strike a balance between economic development and environmental imperatives through work bridging the practice of landscape architecture and public art. My objective is to use art and design work in the environment to persuade people to utilize all of their senses and to realize the undiscovered in their own journey, to stop and notice the world around them, and to act to protect the delicate balance between contemporary civilization and precious ecosystems. Using a method to register and then to make overt ephemeral elements in the environment, I aim to both demonstrate the ever-changing quality of nature and, more importantly, abuses of the natural environment in our society. Although my interest in the natural environment is multifaceted, water quantity and quality is a focus for my work. It is fast becoming a global issue with dire environmental and social ramifications. In the southwest United States and Australia, water is scarce. In the northwest United States and Finland, water quality remains an issue. In parts of Africa and Asia, water is being privatized and villages are left without a source of life and livelihood that has been a constant for generations. The more poetic aspect of my work focuses on natural time and revealing the abstract beauty of the environment. Shadows, sun, water and wind are all environmental systems that we can learn from and are revealed to us through natural time. It is through natural time that we may learn, respect and come into balance with the environment. In order for my work to succeed on all levels and reach the broadest possible audience, it needs to exist in the public realm. In order for it to communicate effectively it needs to be both, persuasive and poetic; while revealing possibilities for harmony between humanity and ecology. This can be achieved by communicating natures’ equilibrium surrounding environmental issues in the face of human civilization and time.Item Biodiversity associated with active and extirpated black-tailed prairie dog colonies(Texas Tech University, 2001-12) McCaffrey, Rachel ElizabethNot availableItem Community assembly, stability and food web structure(2009-05) Pawar, Samraat Shashikant, 1975-; Sarkar, SahotraNatural communities of species embody complex interrelationships between the structure of the interspecific interaction network, dynamics of species' populations, and the stability of the system as a whole. Studying these interrelationships is crucial for understanding the survival of species in nature. In this context, studying the food web (the network of who-eats-whom) embedded in each interaction network is particularly important because trophic interactions are the main channels of energy flow in all ecosystems. Using a combination of mathematical modeling and empirical data analyses, this study explores the interrelationship between food web structure and multi-species coexistence in local communities. Chapter 1 of this thesis places the overall dissertation study in context of the history of research on species interaction networks and food webs. In Chapter 2, I use a population dynamical model to show how the requirements of stable multi-species coexistence results in the emergence of specific, nonrandom configurations of food web structure during community assembly. These structural "signatures" can be used to empirically gauge the importance of interaction-driven dynamical stability constraints in natural communities. In Chapter 3, I extend the model analyzed in Chapter 2 by imposing biologically feasible constraints on its parameters. This is made possible by the allometric scaling between individual metabolism and body size, and the constraints on interspecific trophic interactions due to body size differences between pairs of interacting species. I show that, using this approach, it is possible to interlink three aspects of local communities that have typically been studied in isolation: the species' body mass distribution, the distribution of ratios of body sizes of consumer and resource species (e.g., predator and prey), and certain food web structural features. Some of these features have previously lacked explanatory models. Finally in Chapter 4, using empirical data from nine communities across a range of habitats, I test some theoretical predictions of the previous chapter. The results provide strong evidence that the food web structure of natural communities do indeed exhibit signatures of dynamical stability constraints, and that the model developed in Chapters 2 and 3 is successfully able to predict a number of empirically observed food web structural features.Item Distribution of mammals in the davis mountains, texas and surrounding areas(Texas Tech University, 2008-08) DeBaca, Robert S.; Zak, John; Bravo, Jorge S.; Phillips, Carleton J.; Mulligan, Kevin; Bradley, Robert D.This project focused on the dispersal and distribution patterns of mammals in or near the Davis Mountains, Texas. Data were obtained from existing museum and literature records and from extensive field sampling of the region, which resulted in the acquisition of more than 2,000 museum specimens and related data (Appendix A). The purpose of this research was to investigate regional and local patterns of mammalian biodiversity as these relate to dispersal and distribution in montane ecosystems at a regional scale in the Trans-Pecos and at a local scale in and near the Davis Mountains. In the first chapter, paleontological data suggested that now isolated mountain ranges in the Trans-Pecos were once connected in a north-south network. Research in that chapter examined modern patterns of biodiversity in the mountains that could have resulted from patterns inherited from Pleistocene distributions and dispersal routes of species in mixed-conifer forests or piñon-juniper-oak woodlands. Evidence presented in chapter one indicated that connectivity to source areas could have improved dispersal opportunities through highland corridors and montane areas. The second research chapter evaluated an observed pattern of greater species richness at a middle elevation study site in the Davis Mountains that was about 15 percent the size of a larger study site in the highlands of this mountain range. Rodents were the focus of research to find a partial explanation for this pattern, in which a dispersal filter may have allowed dispersal of some species but hindered others along an elevational gradient from lowlands to highlands. This pattern suggested a decrease in the body size of a lowland group of species along this gradient in response to a substrate that becomes more unavailable to larger burrowing rodents. That pattern was not statistically significant, but an alternative investigation showed that the smaller mid-elevation site likely had greater habitat variety in comparison to the high elevation one, which could have provided more microhabitats for more species to coexist at the smaller, more diverse site. In the final research chapter, biodiversity patterns were investigated for bats in relation to broad-scaled ecological patterns and site-specific resource partitioning that could account for the observed spatial and temporal distribution patterns. Along an elevational gradient, five species were specific to a smaller series of elevations and habitat types; whereas, twelve species were either too rare to analyze or were widespread throughout the sampled array of environmental conditions. Five species also showed elevational segregation by sex, with females occupying a lower range of elevations than males, which was a surrogate measure of warmer macrohabitat utilization by females. Lastly the most prolific sampling site, a semi-perennial pool, was analyzed for temporal differences in its use by month and by time of night. The results showed that vespertilionid bats dominated use of this resource during mid-summer and during the first two hours of the night and that molossid bats dominated its use after the first two hours and during the latter part of the summer. This partitioning could result from the thermoregulation constraints of the main vespertilionid species that concentrated activity early in the evening and during the warmer months of the sampling period. In response to vespertilionid use and to prevent collisions, the fast-flying, less maneuverable molossid bats may avoid the area until use by other bats dwindles both during the night and warmer months of the season.Item Diversity, distribution, and development of the Odonata of the Southern High Plains of Texas(Texas Tech University, 2009-05) Reece, Bryan A.; McIntyre, Nancy E.; Deslippe, Richard J.; Martin, Clyde F.; Mulligan, Kevin; Strauss, Richard E.The diversity, distribution, and developmental patterns of odonates (dragonflies and damselflies; Insecta: Odonata) were examined in the playa system of the Southern High Plains of Texas from 2003-2008. Comparisons were made in these factors between playas surrounded by the two dominant forms of land use (cropland, grassland). Controlled field and lab experiments were performed to examine the causal relationship between environmental variables and growth, development, and survival of larvae of a focal species. Land-use type did have an influence on certain variables, but not consistently or on all variables. Over one hundred new county records were discovered, indicating how little is known about this system. In addition, the dragonfly holdings at the Museum of Texas Tech University were sorted, identified, and compiled, revealing numerous other new county records.Item Ecological mechanisms underlying soil microbial responses to climate change(2013-12) Waring, Bonnie Grace; Hawkes, Christine V.Soil microbes influence the global carbon cycle via their role in the decomposition and formation of soil organic matter. Thus, rates of ecosystem processes such as primary production, soil respiration, and pedogenesis are sensitive to changes in the aggregate functional traits of the entire microbial community. To predict the magnitude and direction of microbial feedbacks on climate change, it is necessary to identify the physiological, ecological, and evolutionary mechanisms that underlie microbes’ responses to altered temperature and rainfall. Therefore, I examined microbial community composition and function in relation to manipulations of resource availability and precipitation in two contrasting ecosystems: a tropical rainforest at La Selva Biological Station, Costa Rica, and a semi-arid grassland in central Texas. I conducted a leaf litter decomposition experiment at La Selva to identify the physiological constraints on microbial allocation to extracellular enzymes, which degrade organic matter. I found strong evidence that microbial enzyme production is decoupled from foliar stoichiometry, consistent with weak links between leaf litter nutrients and decomposition rates at the pan-tropical scale. Next, to examine whether ecological trade-offs within microbial communities may drive shifts in carbon cycling at local spatial scales, I quantified changes in soil fungal and bacterial community composition in response to an in situ precipitation exclusion experiment I established at La Selva. Although drought-induced shifts in community structure were small, large increases in biomass-specific respiration rates were observed under dry conditions. These findings suggest that physiological adjustments to drought may constitute an important feedback on climate change in wet tropical forests. Finally, I focused on microbial community responses to climate change within a meta-community framework, using a reciprocal transplant experiment to investigate how dispersal shapes bacterial community structure along a natural rainfall gradient in central Texas. I found that soils from the wet end of the precipitation gradient exhibited more plastic functional responses to altered water availability. However, soil bacterial community composition was resistant to changes in rainfall and dispersal, preventing functional acclimatization to precipitation regime. Together, the results of these experiments emphasize the potential for physiological plasticity or microevolutionary shifts within microbial populations to drive ecosystem carbon cycling under climate change.Item Ecology of sympatric deer species in west-central Texas: methodology, reproductive biology, and mortality and antipredator strategies of adult females and fawns(Texas Tech University, 2007-12) Haskell, Shawn P.; Ballard, Warren B.; Wallace, Mark C.; Krausman, Paul; Bradley, Robert D.; McIntyre, Nancy E.Between the mid-1800s and -1900s mule deer (Odocoileus hemionus) declined to relict populations in west Texas. This event coincided with the advent of barbed-wire fencing and dug wells providing water by windmills, which brought an end to free-ranging livestock. Also coincident was rangeland conversion from grassland-savannah to more brush dominated habitats due to overgrazing and fire suppression. These conditions favored white-tailed deer (O. virginianus) that expanded their range westward with the brush into areas that were previously inhabited by mule deer only. Most local biologists would cite the west-Texas decline of mule deer as the result of unfavorable changes in rangeland habitats, which facilitated competitive exclusion by white-tailed deer. Others have speculated about effects of fragmentation and hybridization, although genetic introgression between deer species appears uncommon despite hybridization in sympatric contact zones. However, these conditions still exist in west Texas, and mule deer are making their comeback into their previous range that was only occupied by white-tailed deer 30 years ago. The question remains: why did mule deer disappear 100 years ago? We think we have the answer: diseases associated with livestock. To reach that overarching conclusion (as a hypothesis), we first: 1) refined our field methods, 2) studied reproductive biology, and 3) examined causes of death for adult females and fawns of both species in a contact zone in northwest Crockett County, Texas, an area that was inhabited only by mule deer 100 years ago and only by white-tailed deer 30 years ago. They are now of similar abundance. We also made a discovery regarding maternal antipredator strategies that seems interesting for both ecology and management. I will not expound here on detailed results, as each chapter has its own abstract of more appropriate form. Because we relied on deer location estimates by radiotelemetry to test hypotheses, I conducted a beacon study to determine errors and generate a predictive regression model. This model allowed me to assess whether or not objectives could be met given our field methods. I also created a common-sense approach to location estimation that incorporated subjective weighting by relative confidence in a signal received. I compared this approach to the commonly used maximum likelihood estimator. Other researchers may find my MATLAB files useful for beacon studies and location estimation by radiotelemetry triangulation (see http://www.rw.ttu.edu/haskell/ ). To interpret results from wildlife studies it is useful to know population densities. We used mark-resight and deer location data to generate a theoretically unbiased deer density estimate at our site in 2005 (approx. 30 deer/km2). We took advantage of this estimate to provide Texas Parks and Wildlife Department (TPWD) with the first scientifically valid field assessment of their deer survey methods from roads. As predicted, because of habituation behavior within (and perhaps beyond) the effective survey strip width, deer seemed to be clustered near roads as semi-permeable barriers to movement, although a displacement effect of approximately 30 m was also evident. We provided TPWD with recommendations to calibrate their non-random survey design to more defensible methods. Field methods for fawn studies have been continuously refined. Most prior studies suffered from potential positive survival biases because fawns were not captured as true neonates and survival rates may be lowest soon after birth. In fact, 9% of the fawns we captured died within 25 m of birth-sites; most of these were not handled prior to death. We agree with others that risk of marking-induced abandonment is low if females are allowed at least 3 hours postpartum to clean and nurse their young. We used vaginal implant transmitters (VITs) to locate birth-sites. We experimented with VIT design to determine variable efficacy. Despite previous behavioral observations from captive deer, we found that antennas protruding too far externally from the vulva were more likely to be prematurely expelled, presumably because deer pulled them out with their teeth. Also we found that previous models estimating ages of captive fawns by hoof growth predicted ages that were about 1.5 weeks too young for our free-ranging fawns. Thus, researchers should take considerable caution when applying models from captive deer to free-ranging populations. We found that white-tailed deer moved neonates farther faster from birth-sties than did mule deer females. We hypothesized that this observed phenomenon was due to differences in maternal antipredator strategies, to be discussed more later. I examined factors affecting birth dates of these sympatric species at 3 hierarchal levels. At the population level, white-tailed deer birthed 1 month earlier than mule deer, and both species birthed later when rain was reduced during the pre-rut and rut periods. We suggest that the different birthing (and presumably breeding) periods for these sympatric species was not the result of selective pressure against hybridization, but instead was the result of some degree of phylogenetic constraint from parent populations. That is, the white-tailed deer expanded from central Texas where birthing is in mid-June, whereas the mule deer (O. h. eremicus) originated from southwestern deserts where birthing is synchronized with convective rain storms later in summer. At the individual level, older and heavier females birthed earlier. Reproductive success from the previous year may have greater effect on timing of breeding and birthing at other sites than at our study site because females seemed to invest relatively little energy in rearing fawns at our site. Also, deer birthed later on the more overgrazed ranches, suggesting an inter-generational effect after other factors were accounted for in multiple regression. This deer herd likely exists near a K-carrying capacity that responds positively to rain. As predicted, white-tailed adult females survived better during a period of greater rain than during drought. Unexpectedly, mule deer females that had nearly 100% survival during drought had reduced survival 2 years after the substantial rains of 2004. We hypothesize that the rains of 2004 directly and indirectly created an environment more favorable for disease transmission. Reproductive rates were high for both species, but were reduced in 2006 following reduced rain in the pre-rut and rut period of 2005, although mule deer females may have been stressed for the reason previously cited. Hemorrhagic diseases were chronically endemic in both species, but white-tailed deer are thought to have previously obtained enzootic stability in Texas. Overall, mule deer fawns succumbed more to sickness and starvation, and white-tailed fawns were killed more by bobcats (Lynx rufus). Even in 2004, one of the wettest summers in west Texas history, sickness-starvation was the biggest killer of mule deer fawns. Apparent diseases were numerous, and diseases associated with domestic sheep may have been more pathogenic than those associated with cattle. Mule deer kept fawns nearby and close together to protect them from seemingly overabundant small predators (e.g., bobcats and foxes), in the absence of larger predators such as coyotes (Canis latrans). In contrast, white-tailed females separated fawns and were generally removed from them during the fawn hider phase, 3 weeks postpartum. Given the long evolutionary history of white-tailed deer with many large predators, this loose cohesion antipredator strategy may be adaptive in the presence of large predators, but was maladaptive in their absence because extirpation of large predators can release populations of smaller predators that could be defended against. While bobcats tended to kill healthy fawns, bobcat predation may be to some degree compensatory, as the only appreciable top-down limiting factor on this deer herd, if the long-term effect is to alleviate negative density-dependent consequences of life near K-carrying capacity. Data from adult female weights and survival and fawn survival, thymus glands, weight gain, new hoof growth, birth dates, and weaning dates indicated that this deer population was chronically stressed near a carrying capacity that fluctuated with rain, and that females invested relatively energy in rearing fawns. We suggest that it was pathogens introduced by livestock ranchers that were responsible for the historic decline of a naïve mule deer herd in west Texas. Mule deer appear to have developed some immunity and may eventually achieve enzootic stability similar to white-tailed deer. Human use of these private lands and the unhealthy deer herd has been consistent for decades and likely will remain so. Responsible deer management is impossible where human land-use practices affect ecology and demographics across fence-lines and top-down limitation is negligible. We recommend research into alternative economic means and public ecological education of youth and adults as the management action with greatest potential for desirable results.Item Effects of cattail management on invertebrate production and migratory bird use of Cheyenne Bottoms, KS(Texas Tech University, 2002-12) Kostecke, Richard MichaelDense monotypic cattail (Tvpha spp.) stands are a management problem in many prairie wetlands as they exclude desirable plants and migratory wetland birds. Cheyenne Bottoms Wildlife Area (CBWA), a Wetland of International Importance located in central Kansas, has experienced a large increase in cattails and a subsequent decrease in avian use. As a consequence, intensive cattail management is practiced at CBWA. However, dense emergent vegetation also influences production of Invertebrates, an important food source for migratory wetland birds. Effectiveness of different techniques in reducing cattail at CBWA was assessed from fall 1999 to spring 2001. Cattail management also was evaluated based on its impacts on invertebrate production and migratory wetland bird use and behavior. In addition, aquatic invertebrate succession (i.e., temporal patterns in density, biomass, familial richness, familial diversity, and trophic structure) and migratory wetland bird community structure (i.e. nestedness and species co-occurrence patterns) also were assessed. Treatments to reduce cattail (i.e., burned, control, disked, and grazed) were applied at CBWA during 1999 and 2000. Disking and high-intensity grazing (20 head/11.05 ha) resulted in the lowest cattail densities and biomass. Reduction of cattail within these treatments lasted for at least 1 year. In the short term, cattail management by disking and high-intensity grazing was at the expense of higher plant species richness, plant species diversity, and non-cattail productivity. Within 1 year, however, plant species richness, plant species diversity, and non-cattail productivity had recovered (i.e., increased) in the disked and high intensity-grazed treatments. The more heavily vegetated burned and control treatments had greatest invertebrate production. However, maintaining large stands of such vegetative cover to benefit invertebrates is counter to migratory bird management goals at CBWA. While invertebrate food resources may be greater in areas of greater vegetative cover, such areas exclude most wetland birds. It should be noted, that while invertebrate production was lower in the more open disked and grazed treatments, invertebrate densities were adequate (> 100/m^) to support some migratory wetland bird use within these treatments. However, invertebrate densities were generally < 1600/m^ within all cattail management treatments. Invertebrate densities of 5000/m^ may be needed to support large (0.5 million birds) populations of migratory wetland birds at CBWA. Aquatic invertebrate succession patterns, including temporal patterns in trophic structure, following inundation at CBWA were assessed in order to understand the controls on aquatic invertebrate assemblage structure. Invertebrate density, biomass. familial richness, and familial diversity generally increased following inundation. Detritivores were rapid colonizers of newly flooded wetland habitat and were always the most abundant trophic group. Herbivores were most abundant during later successional stages. Predators followed a bimodal distribution with both early and late peaks. The early peak in predators was attributable to the presence of macroveliids. Predators also became more abundant during later successional stages. Although abundance of herbivores and predators increased over time, detritivores were always the most abundant trophic group at CBWA. Aquatic invertebrate succession has been hypothesized to occur in 3 phases (Lake et al. 1989, Schneider and Frost 1996, Moorhead et al. 1998). Increasing densities, biomass, familial richness, and familial diversity of aquatic invertebrates at CBWA are consistent with the first phase of succession, colonization and establishment. Familial richness and diversity generally stabilized within 2 weeks following Inundation, however, suggesting that the invertebrate assemblage at CBWA had entered the second phase of succession. This phase is characterized by the increasing influence of competition and/or predation, which prevents richness and diversity from increasing further. Aquatic invertebrate assemblages at CBWA failed to reach the third phase of succession dominated by predation. Temporal differences in trophic structure did not exist. Detritivores were always the dominant trophic group at CBWA. Failure to reach an assemblage dominated by predators may be related to timing of inundation. Studies of aquatic invertebrate succession have generally followed succession beginning with spring/early summer inundation. However, inundation occurred in late summer/early fall at CBWA. Abiotic factors (e.g., temperatures) and development of habitat structure (i.e., plant succession) are likely to differ between these time periods. Thus, controls on aquatic invertebrate assemblage structure are also likely to differ among these time periods. Therefore, the model of aquatic invertebrate succession posited by Lake et al. (1989), Schneider and Frost (1996), and Moorhead et al. (1998) may not hold for wetlands flooded in the fall. Greatest densities, species richness, and species diversity of migratory wetland birds were found in the disked and high-intensity grazed treatments. Foraging and resting were the most commonly observed behaviors. Foraging and resting behaviors generally did not vary among treatments, suggesting that the greatest difference among treatments in regards to migratory wetland bird use is the number of birds that can be accommodated. Treatments, such as the disked and high-intensity grazed, which had lower densities of cattail excluded fewer birds than treatments, such as the burned and control, which had higher densities of cattail. Models to predict migratory wetland bird species richness, species diversity, and densities were variable. However, results suggest that water depth is often an important variable influencing use by migratory birds. More species were accommodated at CBWA in spring 2001, when mean water depth was 12 cm. than in fall 1999 and 2000. when mean water depths were > 41 cm. In addition, high (5000/m^) densities of invertebrate prey may be needed to support large and diverse populations of migratory wetland birds. Vegetation variables included in models generally suggest that lightly vegetated and open areas should be maintained in order to increase migratory wetland bird use of CBWA. Such conditions were found in the disked and high-intensity grazed treatments, where migratory wetland bird species richness, species diversity, and densities were greatest. Nonrandom assemblages of migratory wetland birds exist at CBWA. In particular, nested patterns of species occurrence among cattail-management treatments have important conservation implications. Because assemblages in species-poor treatments (i.e., burned and control) were subsets of those found in species-rich treatments (i.e., disked and grazed) (i.e. assemblages were nested), effective cattail management can be applied without reducing overall migratory wetland bird species richness. Mutually exclusive (i.e. checkerboard) patterns of co-occurrence existed for many migratory wetland bird species pairs. Ecologically and morphologically similar species often did not co-occur (e.g., green-winged Anas crecca and blue-winged teal A. discors). However, such co-occurrence patterns are unlikely to be due to proximate competitive exclusion as the majority of associations among species pairs were positive. In most instances, checkerboard patterns of co-occurrence can probably be attributed to inter-specific differences in migration chronology. Disking and high-intensity grazing were effective means of reducing cattail for 1 year. Highest densities, species richness, and species diversity of migratory wetland birds also occurred in the disked and high-intensity grazed treatments. Cattail-management treatments exhibited a nested structure where the species found in little used treatments (i.e., burned and control) were subsets of those found in the highly used disked and high-intensity grazed treatments. This nested structure suggests that cattail management can be implemented without reducing overall species diversity. Because behavior did not vary among treatments, the largest difference among treatments in regards to migratory wetland bird use was in the number of birds that could be accommodated. Intensive cattail management did reduce invertebrate production; however, invertebrate production in disked and grazed treatments was presumably adequate (> 100/m^) to ensure use by migratory wetland birds.Item Effects of prescribed fire on small mammals and beetle assemblages in conservation reserve program (CRP) grasslands(Texas Tech University, 1998-05) Davis, Stephen SethThe Conservation Reserve Program (CRP) was established as a portion of the 1985 Food Security Act. The CRP removed highly erodible farmland from production by seeding perennial grasses. Acreage enrolled in CRP could not be grazed or harvested for 10 years. Since 1985, 400,000 ha in the Southern High Plains have been enrolled in CRP providing the unique opportunity for scientists to study a variety of animals in relatively homogenous man-made habitats. The stands of CRP in the Southern High Plains are dominated by weeping lovegrass (Eragrostis curvula). Information on community structure and microhabitat use of small mammals in homogenous CRP grasslands is severely lacking. Therefore, the hypothesis that rodents within CRP grasslands differed in microhabitat use was examined. Small mammals were live-trapped on 12 study plots from 11 to 15 March 1996 in Lynn County, Texas. First captures of small mammals were separated into four vegetation categories based on canopy cover at the trap site. Eight species of small mammals were captured during 6000 trapnights. The deer mouse (Peromyscus maniculatus) and the hispid pocket mouse rChaetodipus hispidus) differed from the expected distribution of captures (chi square, 3 df, P < 0.001 and P = 0.001) with more captures in open trap sites. In contrast, the cotton rat (Sigmodon hispidus) and the western harvest mouse (Reithrodontomys megalotis^ differed from the expected distribution of captures (chi square, 3 df, P < 0.001 and P = 0.058) with more captures in densely vegetated trap sites. Results suggest rodents living in weeping lovegrass monocultures select different microhabitat cover. The effects of prescribed fire on small mammals and beetle assemblages in CRP grasslands have yet to be documented. Small mammals and beetles were sampled on six burned and six non-burned areas over the summers of 1996 and 1997. Small mammal trapping revealed 2532 captures of 1380 individuals of 10 species. R. megalotis and S. hispidus decreased dramatically following fire (P = 0.001 and P = 0.003). The northern grasshopper mouse (Onychomys leucogaster) increased following fire ( P = 0.044). Three other species, the spotted ground squirrel (Spermophilus spilosoma). P. maniculatus. and C. hispidus. all exhibited burn by time interactions and increased in at least one time period on burned areas. Rodent postfire succession in CRP grassland is a dynamic process. Habitats are continually being optimized by changing groups of rodents even when grasses return to preburn densities. Beetle trapping revealed 13 different beetle families, with six families captured in sufficient numbers for statistical analysis. Scarabaeidae, Tenebrionidae, and Meloidae beetles were not affected by fire. Carabidae and Cicindelidae, although not significant at the P < 0.05 level, had trends which suggested possible fire effects. Elateridae beetles decreased 16 months postburn but did not differ in previous samples. Beetles seem to be resilient to fire and families that are affected most are those depended on litter and detritus for habitat.Item Effects of simulated precipitation on nitrogen cycling and microbial processes in a grassland ecosystem at Big Bend National Park, Texas(Texas Tech University, 2003-12) Nagy, Amber MelanieVariations in the timing and magnitude of precipitation events have the potential to influence microbial dynamics and subsequent ecosystem level processes on a variety of scales leading to irreversible changes in vegetation structure and composition. According to the Hadley Climate Change Model #2, the Big Bend region of far west Texas is expected to receive 25% more precipitation in both the winter and summer months. The effects of changes in precipitation amounts and timing on nitrogen dynamics and microbial processes in the Sotol-grasslands at Big Bend National Park were studied. The objectives for this thesis were to: (1) monitor changes in soil nitrogen dynamics in response to variations in precipitation timing and amounts, (2) evaluate impacts of increased precipitation on soil microbial dynamics, and (3) examine, using a greenhouse experiment, the impacts of rainfall pH on soil nitrogen dynamics and microbial biomass production. The field experimental site was in the Sotol-grasslands along the Pine Canyon Watershed at Big Bend National Park, Dominant species plots, containing either Side-Oats grama, Sotol, or Brownspined Prickly-Pear cacti, and also community plots containing all three plant species, were established to examine the impacts of additional precipitation on soil microbial and nitrogen dynamics. Four water treatments (control, summer water only, winter water only, and summer and winter water) were applied beginning in January 2002. Winter water treatments were applied once during the winter season and summer watering took place over three different watering events. Additional water amounts were determined during the first year of the experiment by adding an additional 25% of the past 100 years precipitation averages. During the second year of the experiment, additional moisture was an additional 25%. of the previous three months' precipitation. This approach accounted for yearly precipitation variation. Plant type and season of water addition influenced the rate of N-mineralization, N-mineralization rates in the dominant species plots were significantly different among dates during the winter and spring, but not during the summer and warmer periods of the year. Plots with Side-Oats grama experienced the highest average rate of N-mineralization across date while Sotol plots had the lowest average rate of mineralization. Across the two years, ammonification rates were positive during the ApriI-June (2002) sample dates in all treatments and after the summer and winter watering events. For the remainder of the sampling periods, ammonification rates were negative. The negative rates are indicative of NH4+-N loss through either plant uptake and/or the process of nitrification. An increase in nitrification across plant types was found during the spring months and also early autumn months. The increase in nitrification rates does not appear to be directly related to water addition, but is a seasonal interaction for both the single species and community plots. Microbial biomass carbon production was directly related to soil moisture in that, for both plot types, plots watered in both the summer and winter contained the largest amounts of microbial biomass on average over the duration of the experiment. In the dominant species plots, vegetation type had a direct impact on the amounts of microbial biomass carbon and the levels of extractable NH4+-N and extractable NO3- -N contained within the plots. In the greenhouse experiment using soil from the Sotol-grasslands treated with water of varying pH's to simulate acid rain, it was found that water addition initially stimulated the release of immobilized or otherwise unavailable nitrogen, thereby allowing that nitrogen to become available for N-mineralization, It was also found that, like the field study at the Sotol-grasslands, nitrification is the primary contributor in N-mineralization, Microbial biomass carbon amounts were found to increase when treated with water pH 4,5, but levels of microbial biomass carbon declined initially when treated with water at pH at 3.5 and 5, The increase may be attributed to an increase in bacterial and fungal activity resulting from the changes in soil conditions, namely nitrogen and water availability, in response to acidic precipitation. Together, the field and greenhouse results suggest that alteration in precipitation patterns and amounts coupled with changes in rainfall chemistry as a result of pollution will have significant impacts on soil microbial activity and subsequently nitrogen dynamics in a complex manner within the Sotol grasslands at Big Bend National Park,.Item Evolution of microbial populations with spatial and environmental structure(2010-05) Miller, Eric Louis; Meyers, Lauren Ancel; Bennett, Philip C.; Bull, James J.; Hawkes, Christine V.; Hillis, David M.Rarely are natural conditions constant, but generally biologists study microbes in artificially constant environments in the laboratory. I relaxed these assumptions of constant environments through time and space as I investigated how microbial populations evolve. First, I examined how bacteriophage evolved in the presence of permissive and nonpermissive hosts. I found that bacteriophage evolved discrimina- tion in mixed environments as well as in one of two environments with homogeneous, permissive hosts. This showed the asymmetry of host-shifting in viruses as well as the possibility of large, and somewhat unpredictable, pleiotropic effects. Secondly, I reconstructed ancestral environmental conditions for soil bacteria groups using phy- logenetics and environmental variables of extant species’ habitats. These generaliza- tions suggested characteristic phenotypes for several phylogenetic groups, including uncultured Acidobacteria. Lastly, I collected genetic sequences and global collection information for 65 bacteria genera across the domain. In examining the relation- ship between genetic distance, environmental conditions, and geography, I observed positive relationships specifically between genetic distance and geography or genetic distance and environmental conditions for bacteria from land sites but not from wa- ter sites. Phylogenic classifications or phenotypes of the genera could not predict these correlations. In all of these projects, variations in the environment created evolutionary signals that hinted at past environments of microbial populations.Item Field and laboratory studies of venezuelan equine encephalitis virus ecology in Chiapas, Mexico.(2009-03-05) Eleanor Rose Deardorff; Scott WeaverThe emergence of Venezuelan equine encephalitis virus in Chiapas Mexico was examined from a field approach and from a laboratory approach. This virus was not previously associated with equine disease in Mexico. The evolution of the equine virulent phenotype was thought to have resulted in a mosquito vector switch from Culex (Melanoconion) taeniopus to Aedes (Ochlerotatus) taeniorhynchus as a result of land-use changes. Wild rodents and mosquitoes were captured over the course of one year and little evidence of virus circulation was found. Wild rodents from five species were then imported into the lab for experimental evaluation as virus amplifying hosts. It was found that a VEEV strain from the study area may use a variety of rodents as amplifying hosts in the laboratory. Lastly a breeding colony of Culex (Mel.) taeniopus mosquitoes was established and experimentally evaluated for the ability of these mosquitoes to transmit equine virulent VEEV. It was found that equine virulent virus infects and is transmitted by this mosquito with high efficiency and is likely maintained in transmission foci by Culex (Mel) taeniopus during inter-epizootic periods.Item Health and design(2003-12) Anderson, Steven R.Today, humans spend the majority of their lives indoors, and this has been shown to cause ill health effects in many, due to the poor design of our residential and business structures. By incorporating natural and healthy products and design ideas into our buildings we can begin to preserve and improve the health of the occupants, as well as the environment. My health care background, coupled with my lifelong interest and love for building and design, will hopefully ad a unique perspective to a growing interest and importance of the need to consider health in the design of our structures. In this study, Gulf Dunes is a proposed luxury residential community designed for the active adult. The development includes ten homes with common areas including a community clubhouse, fitness center and pool area. A research survey was conducted to determine which amenities would be most desirable to include in the development, which also helped to influence the design. The development is situated on the Gulf of Mexico south of Port Aransas, Texas, just across the bay from Corpus Christi. The beautiful North Padre Island location allows easy access to an abundant of year round activities in a natural environment (Figure 1 ).Item Medium of modulation: the contradictory configurations of power in video games(2016-05) Fong, Byron Tuck; Scott, Suzanne, 1979-; Mallapragada, MadhaviVideo games have formal structural properties that create tensions between simplicity and complexity, transparency and obfuscation, systems of power and individual empowerment. This thesis investigates these tensions in two directions of inquiry: 1) video games as software and 2) video games as assemblages within media ecologies. One dives into video games’ code. The other challenges video games’ boundaries to understand how they intertwine with other media systems. These two perspectives complement each other to expose the contradictions of power within video games as a medium. Drawing on Wendy Chun and Alexander Galloway, this thesis uses software studies to investigate how the properties of software condition video games’ ludological structures. A theoretical approach to video games’ existence as software exposes that they are not media objects with clearly defined, static boundaries. Instead, a video game is an assemblage of many component parts and interacting systems. Using Gilles Deleuze and Felix Guattari’s understanding of assemblages, I argue that video games are constituted not only of the software contained within the game’s executable code; they are always-already interacting with other media systems, which in turn become component parts of the game. Matthew Fuller’s theorization of media ecologies provides a framework for conceptualizing video games as software-based assemblages within intersecting media ecologies. Player-encoders, a term I develop in the thesis, are a site where both perspectives visibly intersect. Player-encoders are players who create paratextual media to complement existing video games. They decode games’ structures, and then re-encode this knowledge into paratexts that other players can utilize. By encoding new media objects through the process of decoding existing games, player-encoders expose the tensions between powerful systems and individual empowerment. Video games as software, as assemblages in ecologies, and as affected by player-encoded paratexts, reveals them to be unstable media objects modulating within contradictory configurations of power.Item Natural enemies and mortality factors of the coffee leafminer Leucoptera coffeella (Guerin-Meneville) (Lepidoptera: Lyonetiidae) in Chiapas, Mexico(2009-05-15) Lomeli-Flores, RefugioThrough field surveys and laboratory experiments, this study assessed in part the impacts of host plant, natural enemies, and weather variables on coffee leafminer Leucoptera coffeella distribution and abundance at two elevations and two rainfall levels in coffee farms in Chiapas, Mexico. In addition, a checklist of Neotropical coffee leafminer parasitoids was assembled from field collections and literature review. Coffee leafminer field incidence was positively correlated with leaf nitrogen content and age, but in laboratory experiments coffee leafminers grew larger, developed faster, and had higher survivorship on leaves with moderate (2.9?0.01%) versus low (2.5?0.04%) or high (3.4?0.01%) nitrogen level, and on tough versus soft leaves. Ovipositional preference was not generally for leaves that maximized offspring performance. Coffee leafminer incidence was higher during the rainy versus dry season, and at low versus high elevation. Shade cover reduced ambient temperatures within coffee farms, but did not significantly affect coffee leafminer incidence. The coffee leafminer predator complex included 16 morphospecies, ~88% of them ants (Formicidae), and contributed >58% of real mortality. Predation rates were higher at high versus low elevation, and under high versus low rainfall. Predation was the main source of coffee leafminer mortality throughout the year, and was highest during the rainy season, when coffee leafminer incidence was highest. Neotropical coffee leafminer parasitoids included 23 species of Eulophidae and seven of Braconidae. In Chiapas, 22 larval parasitoid morphospecies were collected. Egg and pupal parasitoids were not recovered. Parasitism accounted for <10% of real mortality, and rates were 8-10-fold higher at low versus high elevation. Parasitism rates were not significantly influenced by temperature or rainfall. Coffee leafminer oviposited mostly during the night, and less under low versus high temperatures. Average monthly temperature minima, which occur during the night, were generally lower at high (~18 oC) versus low (~20 oC) elevation farms. The incidence and abundance of coffee leafminer may differ between elevations due to differences in temperature, because at high elevation lower temperatures likely reduced coffee leafminer oviposition, and may have increased its mortality rate as a consequence of longer development time and exposure to natural enemies.Item The origins, maintenance, and conservation of biodiversity in spatial networks(2009-08) Economo, Evan Philip; Keitt, Timothy H.Biodiversity is distributed unevenly across geographic space and the tree of life. A key task of biology is to understand the ecological and evolutionary processes that generate these patterns. I investigate how the structure and geometry of a landscape, for example the sizes and arrangements of islands in an archipelago, affects processes contributing to the generation and conservation of biodiversity patterns. In the first chapter, I integrate two disparate bodies of theory, ecological neutral theory and network theory into a powerful new framework for investigating patterns of biodiversity in a complex landscape. I examine the consequences of network structure, such as size, topology, and connectivity, for diversity patterning across the metacommunity. The second chapter focuses on how the position of a node within a network controls local community (node) diversity. Network statistics, such as node centrality, are found to predict diversity patterns with more central nodes accumulating the most diversity. In the third chapter, I use the theory to evaluate how well fundamental concepts in conservation biology perform when neutral metacommunity processes generate diversity patterns. I find that contemporary diversity patterns are poor predictors of the long-term capacity of a network to support diversity, challenging a host of conservation concepts and applications. In the fourth chapter, I consider biodiversity dynamics in a network with a different model of speciation, where spatial structure is needed for divergence. In this case, speciation hotspots form where the dispersal properties of an organism and the spatial structure of the landscape coincide. In the final chapter I study the biodiversity of a natural structured metacommunity, the ants of the Fijian archipelago. I used a variety of collecting techniques to inventory the ant species occurring across a system of islands in the southwest Pacific. Approximately 50 new species were discovered, and the distributions of the ant species across the islands are firmly established. Radiations are observed in the genera Pheidole, Camponotus, Lordomyrma, Leptogenys, Cerapachys, Strumigenys, Poecilomyrma, and Hypoponera.Item Plant community dynamics governed by red harvester ant (Pogonomyrmex barbatus) activities and their role as drought refugia in a semi-arid savanna(Texas A&M University, 2005-11-01) Nicolai, Nancy CarolThis study examined modifications made by Pogonomyrmex barbatus, by their processes of granivory and nest construction, to forb and grass dynamics under large-scale disturbances of fire, recent drought and long-term, large-mammalian herbivory using comparative studies, field experimental manipulations, and a simulation model on the Edwards Plateau, Texas. Ant nests are refugia for grass survival during extreme droughts as demonstrated during the drought of 1998 to 2002. Significantly greater cover of grasses and lower abundance and cover of forbs was found beside nests compared with surrounding habitat throughout the drought and recovery. Grasses near nests may be the seed source for surrounding habitats during recovery. Seeds were differentially collected among most forbs and grasses despite seed abundance. Harvest was significantly reduced in the fall relative to spring. During preference experiments, harvest differences were found between grazing treatments for two of four species, but only during the spring. High lipid content seeds were unpreferred in fall compared to high protein and carbohydrate content seeds. Granivory influences on seedling establishment were studied by comparing seedling recruitment among sown and naturally occurring seeds excluded and open to foragers. Exclosures were placed in three nest densities and two burn treatments. Seeds in exclosures produced significantly more seedlings than open arenas only during the first year of drought recovery. Densities of grasses and annual forbs were higher in open arenas the second year due to indirect effects of granivory. By reducing seeds ants release seedlings from competition. Sown seedling abundance was unaffected by colony density and fire. Colony density and distribution were influenced by topography, soil types, soil depth and woody cover, but not by historical grazing treatments. Cleared vegetation on nest disks impacted less than 1% of total surface area and losses were compensated by greater basal cover of grasses next to disks compared to surrounding habitats. Foraging areas influenced 17.3-73.6% of surface area and could diminish seed populations for potential seedlings. Model results agree with experimental observations that communities may be modified by P. barbatus presence due to differential responses of grass species to interaction between nests or granivory and rainfall amounts.