Browsing by Subject "endangered species"
Now showing 1 - 20 of 21
Results Per Page
Sort Options
Item Abundance and distribution trends of the West Indian manatee in the coastal zone of Belize: implications for conservation.(Texas A&M University, 2004-09-30) Auil, Nicole EricaThe coastal zone of Belize is home to the largest recorded number of the threatened Antillean manatee (Trichechus manatus manatus) within the species' Caribbean range. The objectives of my study were: (1) to determine long-term trends in aerial survey counts and indices of the manatee population in the coastal zone of Belize; and (2) to examine the seasonal change in manatee distribution among habitats in the coastal zone. Standardized extended-area aerial surveys were conducted along the entire coastline of Belize in the dry and wet seasons of 1997, and 1999 - 2002. Manatees were counted in five habitat categories: cay, coast, estuary, lagoon, and river. Total sightings per survey ranged from 90 to 338; the greatest number was counted in the 2002 wet season. Calf percentage ranged from 5 to 13. A slight negative trend in total counts was significant for dry-season, not wet-season surveys, indicating an interactive effect of season and year. Based on analysis of variance, the Abundance Index (transformed manatee sightings per hour) did not differ significantly among years, although it varied significantly within year by season and habitat by season. In applying a spatial approach, the general survey route was buffered 1 km on both sides, and 1 km grids were overlaid and classified by habitat type. The presence or absence of each cell for each survey was used in likelihood ratio tests of the single and interactive effect of season and habitat. The Index for river habitat was higher in the dry season, while cay habitat was higher in the wet season. Overall, near-shore habitat (estuary, lagoon, and river) showed a higher Index than did the offshore habitat (cay and coast) although the total number of sightings was higher offshore. Considering the interactive effect of year, season, and habitat, long-term studies are needed, in both seasons, and among all habitats to account for variation. Continued broad-scale surveys, along with metapopulation analysis would fine-tune the understanding of specific sites, enhancing integrated coastal zone management for protected species and their habitat systems.Item An environmental assessment of Bermuda's caves(Texas A&M University, 2005-02-17) Gibbons, Darcy AnnThe current environmental status of the majority of Bermuda?s one hundred sixty-six known caves was investigated. This survey replicated a historical cave study performed in 1983, wherein each was analyzed for positive and negative features. Statistical analysis of the data showed a significant difference between the historical and current survey ratings, with an overall decrease in environmental status. A water quality study was performed on twenty different caves with sea level pools in various locations around the island. Nitrate, nitrite, ammonia, and phosphate levels were measured from varying depths in these caves. Fifteen of these caves were also tested for the presence of fecal bacterial contamination. High nitrate levels were discovered in some of the caves, particularly in surface samples. Additionally, bacterial contamination was detected in some caves. No obvious relationship between cave size or location and contamination existed for any of the pollutants sampled. Three separate caves from this group were dived and analyzed using a Hydrolab Sonde 3 Multiprobe Logger to acquire in situ water column data including depth, temperature, pH, salinity, and dissolved oxygen. Each cave studied had its own unique trends in hydrology at varying depths in the water column. A later water sampling study with a randomized experimental design was created and caves were divided into four classes based on size and location. Surface and subsurface samples were gathered from twelve randomly selected caves, three from each class. Each sample was analyzed for nitrate, nitrite, and ammonia concentrations. The results were analyzed using multiple analysis of variance statistics. A significant difference between the nitrate concentrations in the surface and subsurface water samples was discovered. None of the other comparisons were statistically significant. To represent the data visually, a Bermuda Cave and Karst Information System (BeCKIS) was created using the environmental survey data and water quality information. Some of the maps generated highlighted regions where negative environmental impacts on caves were concentrated geographically, thus demonstrating how this geographic information system could be used as a conservation tool.Item Binational collaboration in recovery of endangered species: the Mexican wolf as a case study(Texas A&M University, 2004-09-30) Bernal Stoopen, Jose FranciscoThe goal of this inductive study was to identify factors that facilitate and inhibit binational collaboration in the recovery of endangered species in the northern Mexico borderlands, focusing on the Mexican wolf (Canis lupus baileyi). A conceptual model was developed using qualitative techniques, providing the basis for design of a mail survey. The target population included participants with experience in recovery efforts for over a dozen species at risk in the region. Long interviews were recorded with 44 participants from Mexico and the United States. Thematic hierarchical analysis was used to develop a conceptual model of how interviewees talked about factors influencing binational collaboration. Issues were classified in five thematic clusters: project, organization, people, resources, culture/history. The survey was used to conduct a needs assessment, measuring respondents' attitudes about the relative priority of issues identified in the conceptual model. High priority needs were identified from each thematic cluster: (a) equitable participation in project design and implementation, (b) continuity of personnel, (c) coordination of federal, state and local efforts, (d) increased funding, managed with accountability, and (e) exchange visits to facilitate understanding of diverse perspectives. Responses to almost half the survey items indicated accord among the sample of respondents, providing a basis for shared common ground. The nature of discord was within the range of "manageable", with no clear polarization of attitudes measured. This exploratory data analysis suggested that the structure of the conceptual model developed from the Mexican wolf case study was generally a valid basis for future deductive analysis and reflection by practitioners. For 82% of 22 statements of need, priorities of participants in the Mexican wolf recovery efforts did not differ significantly from other respondents. Nationality (of respondents) significantly affected priority rankings for only 18% of the need statements. Significant effects of five demographic variables indicated that interactive effects should be examined in future multivariate analyses to determine how respondents' attitudes on issues related to priority rankings. Recommendations were provided for a more efficient and effective approach to collaborative problem-solving, engaging reflective practitioners from the private and public sectors in principled negotiation processes to better understand diverse perspectives.Item Brown-headed cowbird parasitism on endangered species: relationships with neighboring avian species(2009-05-15) Farrell, Shannon LeighBrown-headed cowbird (Molothrus ater) parasitism on the endangered black-capped vireo (Vireo atricapilla) is a management concern. Management for black-capped vireos in east-central Texas has focused on habitat restoration through vegetation modification. Loss of productivity due to parasitism, however, may limit the potential habitat restoration in restoring black-capped vireo populations. I investigated the relationships between frequency of parasitism on black-capped and white-eyed (V. griseus) vireos and characteristics of the neighboring avian assemblage to identify avian characteristics useful for predicting expected frequency of parasitism. I located and monitored vireo nests in March?July 2006 to determine frequency of cowbird parasitism on the 2 vireo species on 6 study sites on private land in east-central Texas. I conducted 100-m-radius circular-plot point count surveys on study sites from 1 April? 31 June 2006 to identify neighboring avian assemblages. All black-capped vireo nests (n = 20) and 81% of white-eyed vireo nests (n = 27) were parasitized. Species richness, species evenness, cumulative bird abundance, and cowbird host abundance did not differ significantly among study sites. Parasitism frequency was positively correlated with the number of cowbirds detected (r2 = 0.673, P= 0.045). Parasitism frequency was negatively correlated with abundance (r2 = 0.687, P = 0.042) and proportion of (r2 = 0.692, P = 0.040) of black-and-white warblers (Mniotilta varia), known cowbird hosts. I did not find a relationship between parasitism frequency and abundance of other cowbird hosts. The relationship between black-andwhite warbler abundance and parasitism frequency may reflect an interaction between parasitism and the vegetation characteristics associated with black-and-white warblers, suggesting the need for future study of the relationships between parasitism frequency and vegetation characteristics in the study region. The frequency of parasitism I observed suggests that cowbird control may be an important management tool if management objectives in the study region continue to include recovery of black-capped vireo populations. Number of cowbirds may be a reasonable predictor of expected parasitism frequency in an area, which may be useful to land managers in selecting areas for implementation of cowbird control.Item Conservation of Antillean manatees in the Drowned Cayes area of Belize(2009-05-15) Sullivan, Caryn SelfThe purpose of this study was to determine how manatees use Swallow Caye, Drowned Cayes, and Gallows Reef, three distinct habitat types within the Belize Barrier Reef lagoon system near Belize City. Data were collected using boat-based point scan methods with the assistance of volunteers. Presence/absence and photo ID methods ensured consistency of data collection despite a changing pool of volunteer researchers. Results confirmed the mangrove and seagrass ecosystem between the Belize Barrier Reef and Belize City as important manatee habitat. Inconsistent with the prevailing "seasonal distribution hypothesis" for manatees in Belize, the probability of encountering manatees at Swallow Caye and in the Drowned Cayes was equal between dry and wet seasons. However, manatees were only observed at Gallows Reef during the wet season. Swallow Caye had the highest probability of encountering manatees, confirming traditional knowledge held by local tour operators, which led to the establishment of Swallow Caye Wildlife Sanctuary in 2002. In contrast to previous studies, my data suggest that at least 44% of the manatee population carry scars from non-lethal boat strikes. The proportion of scarred animals did not vary as a function of habitat type, season, or year. The probability of encountering manatees did not change between years, despite an exponential increase in cruise ship tourism. Marine Protected Areas (MPAs) and wildlife protection laws indicate that Belize is working to meet obligations under international agreements. However, there is still cause for concern. Manatees do not remain inside designated refuge boundaries; governmental agencies depend on co-management agreements with local non-governmental organizations for enforcement of rules inside MPAs; regulations governing human behavior outside MPAs are lacking; funds for monitoring and evaluation of MPAs are lacking. Manatee conservation strategies should be integrated into a system of riverine, coastal, and marine protected areas supported by additional tactics such as required manatee training for boat captains, slow zones at hot spots outside MPAs, and continued educational outreach. With few modifications and increased enforcement and monitoring, the Belize model for manatee conservation could lead to a shared "triumph on the commons" for the manatees and the user groups that shared their habitat.Item Development of a Decision Support Geographic Information System for land restoration programs in the Leon, Lampasas, and Bosque River Watersheds(Texas A&M University, 2006-10-30) Jones, Jason SamuelAshe Juniper encroachment onto privately owned rangelands in Central Texas has resulted in significant degradation of the ecological condition of these lands, and a subsequent public concern for the hydrologic function, wildlife habitat, and livestock production these historically predominant grasslands provide. The result has been an interest and public investment in land restoration programs such as the removal and management of brush via landowner cost-share. Implementation of a publicly funded land restoration program requires the allocation of millions of dollars of public funds on private lands over large geographic areas that represent hundreds of landowners with varying property management objectives, tract sizes, ecological conditions, and geologic characteristics. This study describes the development, accuracy, and application of a decision support geographic information system (DSGIS) for land restoration programs in the Leon, Lampasas, and Bosque River watersheds in the Brazos River basin of Central Texas. The spatially referenced data layers and associated database within the DSGIS provide the capability to assemble site specific information including vegetation cover, endangered species habitat, landowners, ecological sites, elevation and slope, hydrologic characteristics, and political boundaries to support policy and implementation decisions for Ashe Juniper (Juniperus ashei) brush control and management and goldencheeked warbler (Dendroica chrysoparia) habitat restoration programs. The goldencheeked warbler is a federally listed endangered species with a breeding range limited to the oak-juniper woodlands of Central Texas. The data layers were developed with the support of ongoing research from the Leon River Restoration Project (LRRP) in Coryell and Hamilton counties. One hundred and eighty-eight (188) sub-watersheds were delineated within the project area and prioritized for implementation of an Ashe Juniper brush control program and a golden-cheeked warbler habitat restoration program. Costs associated with the clearing and stacking of Ashe Juniper were estimated for selected subwatersheds based on projected landowner participation and an analysis of actual costs from the LRRP. Sub-watersheds were targeted for the implementation of an Ashe Juniper brush control and golden-cheeked warbler habitat management program in Bosque, Coryell, Lampasas, Bell, and Burnet counties. Detailed tables were also developed to document the density and quantity of pertinent layer attributes within each of the 188 sub-watersheds.Item Ecology of Wintering Black-capped Vireos in Mexico(2013-11-06) Powell, Robert AndrewThe black-capped vireo (Vireo atricapilla) is an endangered Neotropical migratory songbird that has received considerable attention in its breeding range, but relatively little attention in its winter range in Mexico. To address information needs regarding winter ecology of the black-capped vireo, I conducted research in Mexico focused on investigations of the winter distribution, habitat use, and migratory linkages between breeding and wintering sites. Over 3 winter periods in 2002?2004, I identified and described the geographic distribution for the black-capped vireo at study sites across 8 states in western Mexico and determined if differential migration occurs among different classes of individuals. I documented winter occupancy in the 5 most northern Mexican states surveyed (Sinaloa, Durango, Nayarit, Jalisco, and Colima), and identified a strong association between sex/age class and winter latitude with adult males occupying habitat at more northern latitudes relative to females and juveniles. During two winters in 2003-2004, I conducted field research at study sites in Mexico to evaluate patterns of winter habitat use by black-capped vireos and determine which habitat characteristics may influence vireo use of winter patches. Winter habitat use by black-capped vireos was best predicted by increasing values of slope and foliage cover, and by decreasing values of canopy cover and tree diameter. Vireo use plots characterized as thorn forest had greater foliage density, greater shrub density, less canopy cover, and smaller tree diameter than plots classified as tropical deciduous or semi-deciduous forest, suggesting that thorn forests may be most suitable for vireo occupancy during the winter months. I also used stable carbon, hydrogen, and nitrogen isotopes in black-capped vireo feathers obtained across 3 states in the breeding range and 8 states in the wintering range to determine if vireo feathers collected on the wintering grounds could be used to assess breeding origins and to determine if a relationship exists between breeding and wintering latitudes such as chain or leapfrog migration. Feathers collected at both breeding and wintering sites displayed considerable variability in isotopic composition for all 3 isotopes analyzed, and thus did not provide sufficient information to establish migratory linkages between breeding and wintering sites.Item Empowering All Who Dwell Here: Natural Resource Management and Public Participation(2014-08-01) Bernacchi, Leigh AlexisI studied the potential for community-based planning in the winter habitat of the federally-endangered whooping crane (Grus americana) to better understand the relationships, barriers and opportunities to conservation and public participation. Rooted in the literature of public participation in natural resource management, I describe my project within this larger discourse. I seek to address the issue of local public resource management and the ways in which it is or is not represented in public processes. I submit constructive ameliorations for improved democratic engagement, resource and wildlife conservation. My methods are qualitative: 35 local and regional individuals interested in crane conservation were interviewed, transcribed, and coded in NVivo Qualitative Analysis software from QSR International to conduct a content analysis. I employed theoretical and pragmatic constructions to provide constraints and perspectives on the same dataset. I apply a ritual communication perspective to the communication among birdwatchers and with birds. Though a wide-ranging topic, I describe the key aspects of birding, and how competition and cooperation are the two sides of birding?s social relations. I propose that wildlife managers could pay attention to these relationships to better represent interests in birds in management. I examine how wildlife managers are tasked with engaging the public for natural resource management and planning, and I propose that including a responsive public can improve the plan and conservation. I found that the public was amenable to working with wildlife managers due to whooping the crane?s iconic nature and economic value, and the public was responsive to agency intervention when they were dependent on their knowledge and standing for navigating the dynamic complexity of managing the species and ecosystem. By recognizing a responsive public, wildlife managers can expand public participation to include more public perspectives. From a public understanding of science perspective, I explore the dominant scientific narratives associated with whooping crane conservation. I examine these narratives for their ability to empower and to constrain public participation in various management schemes. I argue that production of a reductive scientific narrative reproduces an equally reductive public discourse that limits possibilities for public participation.Item Evaluating sustainability of endangered species via simulation: a case study of the Attwater's prairie chicken (Tympanuchus cupido attwateri)(2009-05-15) Defex Cuervo, Tulia InesOnce abundant in the Texas and Louisiana coastal prairie, currently the Attwater?s Prairie Chicken (Tympanuchus cupido attwateri, APC) is close to extinction. Efforts to increase the size of the remaining populations at the Attwater Prairie Chicken National Wildlife Refuge (APCNWR) and the Galveston Bay Prairie Preserve (GBPP) with releases of captive-reared individuals are part of the APC captive- breeding initiative. However, after a decade of yearly releases, the populations are not reaching viable sizes. I analyzed post-release survival data of individuals released at the APCNWR from 1996 to 2005. Results suggest that age at release or date of release had little influence on survival of captive-breed APC. At two weeks post-release, survival estimates (SE) were 0.76 (0.03) for females and 0.82 (0.04) for males. Approximately 50% of the females and 33% of the males died within the first 60 days post-release. Survivorship during the breeding season showed that male survival (0.36) was higher than female survival (0.23). Survivorship from the median release date to beginning of the breeding season was 52% for males and 39% for females. Mean female survival was 155 days, while median survival was 94 days. For males, mean survival was 135 days and the median was 81 days. Results from a stochastic simulation model, which was developed based on the survival analysis of APC on the APCNWR, confirmed that releasing individuals closer to the beginning of the breeding season and sex ratio at release had little effect on population growth. Regardless of the number of individuals released annually, population sizes immediately prior to the release dates were only 11?12% of the population sizes immediately after the release dates. At current mortality rates, simulated APC populations could not sustain themselves even if reproductive parameters were increased to the maximum rates reported for APC, or to the maximum rates reported for the closely related Greater prairie chicken. Based on these results, the APC may face extinction within the next decade unless conservation efforts succeed on increasing reproductive success and greatly reducing mortality rates.Item Genetic relationships among Spiranthes parksii and congeneric species(Texas A&M University, 2007-04-25) Walters, CatherineUsing four AFLP markers and seven polymorphic microsatellite loci, we examined the genetic structure of the rare and endangered Spiranthes parksii Correll (Orchidaceae). Spiranthes parksii is not distinguishable from sympatric S. cernua (L.) Rich based on these data, though low levels of polymorphisms exist within both. These low levels of genetic diversity are likely a result of high levels of agamospermic reproduction through adventitious embryony. These results suggest that both S. parksii, as well as the sympatric, open flower form of S. cernua, are products of the more widely distributed S. cernua complex. Further, another local form of S. cernua, distinguished by its tendency to produce closed flowers is genetically distinct from both S. parksii, as well as the openflower form of S. cernua, as shown by AFLPs and microsatellite loci. This is the first known set of microsatellite primers developed specifically for use in Spiranthes. The application of these markers may be used to address other unresolved relationships among species of Spiranthes, many of which are also endangered or have populations in decline.Item Habitat relationships of seven breeding bird species in the Leon River Watershed investigated at local scales(Texas A&M University, 2005-02-17) Juarez Berrios, Edwin AlfredoOver the past 100?150 years Texas rangelands have dramatically changed from native open savannahs to dense woodlands. On the Edwards plateau, a major management concern is the increasing encroachment of Ashe juniper (Juniperus ashei). Preceding an anticipated brush management program, I investigated the presence, co-occurrence, and habitat relationships of 7 breeding bird species in the Leon River Watershed in central Texas, USA: black-capped vireo (Vireo atricapillus), golden-cheeked warbler (Dendroica chrysoparia), northern bobwhite (Colinus virginianus), white-eyed vireo (Vireo griseus), Bell?s vireo (Vireo bellii), painted bunting (Passerina ciris), and brown-headed cowbird (Molothrus ater). Vegetation characteristics were compared between sites occupied by each species and unoccupied sites using univariate analysis. Models for predicting species site occupancy were developed (using logistic regression) based on habitat characteristics correlated with the presence of each species. Two species of special concern, the endangered black-capped vireo and golden-cheeked warbler occupied 5.6% of sites and 13.8% of sites respectively, while the brood parasite brown-headed cowbird was the most widespread, occupying 86.8% of sites. Species co-occurrence patterns revealed significant associations between the golden-cheeked warbler and each of 5 other species. For most species, variables included in habitat models could be explained by knowledge of species known habitat associations. For example, the black-capped vireo was positively associated with increasing low-growing (<1.5 m) hardwood cover and with Low Stony Hill ecological sites. The golden-cheeked warbler was positively associated with increasing density of larger juniper trees, increasing variability in vertical vegetation structure, and decreasing midstory canopy of deciduous nonoaks (e.g., cedar elm [Ulmus crasifolia]). It also preferred Low Stony Hill and Steep Adobe ecological sites. Site occupancy seemed to be driven by variables that describe overall vegetation structure. In particular, cover of low-growing non-juniper vegetation and juniper tree density appeared to be important in determining site occupancy for several species. Although the models constructed were not very robust, resource managers can still benefit from such models because they provide a preliminary examination of important controlling variables. Managing rangelands to maintain or restore a mosaic of juniper patches and open shrublands are likely to help meet the habitat requirements of these bird communities.Item Metapopulation Ecology and Recovery of the Endangered Lower Keys Marsh Rabbit(2011-02-22) Schmidt, Paige McGeeThe Lower Keys marsh rabbit (LKMR, Sylvilagus palustris hefneri), a subspecies of marsh rabbit endemic to the Lower Keys, Florida, is threatened with extinction due to extensive coastal development of salt marsh habitats. LKMR recovery is limited by habitat loss and degradation from brush encroachment, predation by freeroaming cats (Felis catus) and raccoons (Procyon lotor), sea-level rise, and hurricanes. This study sought to determine local and landscape factors that influence LKMR metapopulation ecology and dynamics and to evaluate strategies for their recovery. I evaluated the influence of patch and landscape characteristics on LKMR densities, extinction, and colonization rates following Hurricane Wilma, and the response of LKMRs and salt marsh habitats to prescribed fire. I used estimates of population change based on annual monitoring data to validate vital rates, constructed a spatially explicit demographic model to evaluate various levels and spatial configurations of recovery scenarios implemented throughout the LKMRs range, and validated expected changes in parameter estimates using measures of habitat degradation and raccoon activity from known LKMR populations. I found LKMR densities were higher in patches with greater numbers of bunchgrasses and forbs and less edge and lower in patches with higher measures of raccoon activity. In response to a hurricane, I found the distance between LKMR patches and the coast had a negative influence on extinction probability; the distance between an extirpated and occupied LKMR patch had a negative influence on colonization probability and patch size had a positive influence. Adult LKMRs increased as woody cover <0.5 m decreased, herbaceous cover <0.5 m increased, and food availability increased in at least one site following prescribed fire. Model results indicated habitat management actions that improve carrying capacity of local rabbit populations and juvenile survival and control raccoon populations to increase rabbit reproductive rates are effective population recovery strategies. In total, my results provide a conservation planning tool that can be used to select recovery strategies and locations that will maximize benefits to LKMRs, thus improving their viability and recovery.Item Modeling an endangered species in an urban landscape: fountain darter (Etheostoma fonticola) survival in the Upper San Marcos River, Hays County, Texas(2010-07-14) Wilkins, Leann I.To accommodate for human population growth along the Texas I-35 corridor, land is becoming increasingly urban and decreasingly pervious, modifying the infiltration and runoff rates in the Edwards Aquifer, especially to its spring fed Upper San Marcos River (USMR). Contaminants like heavy metals and organic chemicals can accumulate on impervious surfaces and with runoff, enter into the USMR at potentially harmful levels. The objective of this study was to determine how the population of an endangered Edwards Aquifer species, the fountain darter (Etheostoma fonticola), might respond to potential water quality changes associated with urbanization. I developed a stochastic, sex and stage-structured population dynamics simulation model that represents the relationships between urbanization, springflow variations, contamination levels, and natural history of the fountain darter. Future fountain darter population trends (2008-2040) were simulated under 10 treatments of nine scenarios. A simulation scenario (n=50) corresponded to one of three variations of springflow (random, high and low flow) and one of three variations in percentage of runoff entering the river (100, 50 or 30). The 10 treatments were variations on water quality: uncontaminated (1), contaminated by Cu (2), Zn (3), Cd (4), Cr (5), polycyclic aromatic hydrocarbons (PAH) (7), bifenthrin (8), carbaryl (9) and dicamba (10) and an additive affect of Cu, Cr, Cd, and Zn (6). Simulating ideal conditions, the average darter population from 2008-2040 was 54155+2969 (mean+SE) individuals. Contaminant treatments that caused a significant (p<0.001) decline in the population by 2040 under 100% runoff conditions were the all metal (650 plus/minus 640), Cu (3141 plus/minus 265), PAH (4621 plus/minus 475), Zn (6169 plus/minus 5406), and Cd (27987 plus/minus 6751) scenarios. With 50% runoff, the all metals (15740 plus/minus 5455), Cu (16815 plus/minus 6263), PAH (19675 plus/minus 995), and Zn (15585 plus/minus 3097) treatments simulated significantly lower populations (p less than 0.001). At 30% runoff, Cu (23976 plus/minus 6787), the all metal (25853 plus/minus 7404) and PAH (28167 plus/minus 1194) treatments decreased the population significantly (p less than 0.001). Over all scenarios, copper, zinc and PAHs caused >50% decline in the population. Assuming 100% or 50% of all San Marcos sub-basin runoff is directly entering USMR, there could currently be levels of Cu, Zn, and PAHs higher than what darters can withstand.Item Modeling aspects of the ecological and evolutionary dynamics of the endangered Houston toad(2009-05-15) Swannack, Todd MichaelThe goal of my dissertation was to describe the dynamics of a group of Houston toads located at the Griffith League Ranch (GLR), Bastrop County, Texas. My research included using statistical modeling to predict activity and abundance, mark-recapture techniques to estimate survivorship, and simulation modeling to explore the impacts of the difference in age at first reproduction and to project the future dynamics of the population at the GLR. From 2001 ? 2005, 225 individual Houston toads (199 M : 26 F) were captured using two methods: breeding pond surveys and drift fences. Houston toads were neither caught equally among capture methods, nor across years. Toad activity was mostly confined within their breeding season, and activity was not continuous. A logistic regression indicated activity depended on time of year, mean precipitation, mean minimum daily temperature, and mean percent lunation as well as two-way interactions with moon-phase and other variables. Abundance depended on time of year, current precipitation, minimum temperature, and two-way interactions between time of year and the other two variables. Twenty-one of the 199 males (10.5%) and no females were recaptured among years. The probability of male survival was estimated using program MARK. Eight of 16 candidate models were supported and all but one contained precipitation as a covariate, indicating precipitation is important for Houston toad survival. Survivorship estimates varied from 0.1 to 0.41. The sex ratio was significantly male-biased. The odds of catching females in traps were 3.5 greater than capturing females in a pond, while the odds of capturing males in a trap were 0.28 compared to ponds. Results from a simulation model indicated the sex ratio is biased because of the difference in maturation times between males and females, coupled with high juvenile mortality. Results from an individual-based, spatially-explicit, stochastic simulation model, indicated a relatively low probability (~ 0.013) of B. houstonensis going extinct at the GLR within the next 10 years. Emergent properties of the model were similar to results observed in the field or reported in the literature. The model also identified that dispersal of Houston toads should be a future research priority.Item Mycorrhizal Associations, Life History, and Habitat Characteristics of the Endangered Terrestrial Orchid Spiranthes parksii Correll and Sympatric Congener Spiranthes cernua: Implications for Conservation(2013-12-10) Ariza, Martha CSpiranthes parksii Correll is a federally listed endangered terrestrial orchid endemic of Texas. The species exhibit a very limited geographic distribution and most remaining populations are threatened by habitat loss and fragmentation. Development of in situ and ex situ conservation strategies is fundamental for the protection and re-introduction of the species in their natural habitat. In this dissertation the life history, symbiotic mycorrhizal fungal associations, and habitat characteristics of S. parksii and sympatric congener Spiranthes cernua were investigated by the use of in situ, and ex situ methods. The central research objective was to investigate the orchid-fungal relationship and its distribution in natural habitats and to provide critical information for conservation of the species. Population dynamics and reproductive phenology of both species were studied from 2007 to 2013. Demographic parameters, cost of reproduction, and response to environmental conditions were analyzed. Results indicate that probability of flowering is strongly influenced by vegetative size and environmental conditions in the year preceding a flowering event. Reproductive effort resulted in a decrease in plant size, reducing the probability of flowering subsequently. Environmental conditions explained ?70% of the annual variation in the proportion of flowering plants and inflorescence characteristics. Mycorrhizal fungi associations and belowground phenology of both species were studied for three growing seasons. Data suggest that both species form generalist mycorrhizal associations with fungi tentatively classified, as Epulorrhiza sp., and Ceratobasidium sp. Both orchids sustain mycorrhizal colonization throughout their life cycle. However, seasonal changes in mycorrhization reveled a distinctive annual cycle of infection and digestion of fungal hyphae. Seed viability, in situ germination, seedling development, and mycorrhization were examined in situ by using orchid seed baits. Results suggest that S. parksii seeds are short-lived and germination is constrained by rapid reduction in seed viability, prevailing environmental conditions, and distribution of compatible mycorrhizal fungi. Data indicates a small optimal window for recruitment restricted to the first spring after dispersal. Microhabitat characteristics of S. parksii were compared to microsites of sympatric S. cernua, historical S. parksii microsites and vacant microsites currently not supporting either orchid. Vegetation, edaphic, and environmental parameters were evaluated. The study found that microsites currently occupied by S. parksii differ significantly from other types in canopy cover, leaf litter, herbaceous cover, and soil pH. Furthermore, woody encroachment may significantly affect the availability of suitable microsites not only as a result of altered light environments, but also due to changes in community composition, microclimatic, and edaphic conditions.Item Population Status and Evaluation of Landscape Change for the Lower Keys Marsh Rabbit(2011-02-22) Schmidt, Jason AlanWildlife biologists and land managers tasked with the recovery of the endangered Lower Keys marsh rabbit (LKMR; Sylvilagus palustris hefneri) were in need of a current population estimate as well as a method to estimate the LKMR population annually. Habitat loss and fragmentation from population growth and development have threatened the existence of the LKMR. Establishing and understanding long-term habitat availability for the LKMR is important for determining causes of historical population declines as well as designing and implementing successful recovery plans. I conducted a range-wide pellet survey and a mark-recapture study to estimate the LKMR population. I evaluated the fit of 5 models and considered the variation in behavioral response model the best model. I correlated (r2 = 0.913) this model's rabbit abundance estimates to pellet density in 11 patches and generated a range-wide population estimate of 317, a western clade population of 257, an eastern clade population of 25, and translocated LKMR populations of 35 and 0 on Little Pine and Water keys, respectively. This prediction equation provides managers a quick, efficient, and non-invasive method to estimate LKMR abundance from pellet counts. To quantify the amount of habitat loss and fragmentation that occurred over the last 50 years, I systematically delineated and compared potential LKMR habitat using 1959 and 2006 aerial photographs. Additionally, I investigated if other factors could have reduced the amount of suitable habitat available for the LKMR with a comparison of habitat loss and fragmentation on a developed island and an undeveloped island. Range-wide, I found that number of habitat patches increased by 38, total class area decreased by 49.0%, and mean patch size decreased by 44.3%. Mean shape index increased by 4.2% and mean proximity index decreased by 13%. Both the 1959 and 2006 connectance indices were low while the 2006 set decreased 12.1%. I observed the same patterns of habitat loss and fragmentation on both the developed and undeveloped islands as I did in the range-wide landscape analysis. I found that LKMR habitat has declined in area and become more fragmented over the last 50 years. Habitat loss and fragmentation by development have directly endangered the LKMR; however, sea level rise and woody encroachment also could have historically caused habitat loss and fragmentation. Although development in LKMR habitat was halted, sea-level rise and woody encroachment could continue to alter LKMR habitat.Item The Impact of a Forest Pathogen on the Endangered Golden-cheeked Warbler(2012-07-16) Stewart, Laura RoeOak wilt is a fatal disease of oaks caused by the fungus Ceratocystis fagacearum. Loss or degradation of habitat due to the disease may negatively affect the federally endangered golden-cheeked warbler (Setophaga chrysoparia). To assess the impact of oak wilt on golden-cheeked warblers, I investigated its influence on habitat selection and quality. I used remote sensing to estimate the amount of potential golden-cheeked warbler habitat currently affected by oak wilt, to predict the amount of potential habitat likely to be affected in the near future, and to assess the current probability of warbler occupancy in areas affected by oak wilt historically. I also quantified vegetative characteristics to assess overstory vegetation and regeneration in areas affected by the disease. I found proportional occupancy and territory density in unaffected areas to be, respectively, 3.5 and 1.8 times that of affected areas. Pairing success was 27% lower for territories containing oak wilt but fledging success was not affected. I estimated that 6.9% of potential golden-cheeked warbler habitat and 7.7% of the total area within my study region was affected by oak wilt in 2008. By 2018, I predicted that 13.3% of potential golden-cheeked warbler habitat and 16.0% of the study region would be affected by the disease. Using historical imagery, I found that areas affected by oak wilt in the past are less likely to be classified as current potential warbler habitat than areas never affected by the disease. I found no differences between the understory vegetation of affected and unaffected areas but that oaks were more common in the overstory than in the understory, suggesting that species composition in affected areas may shift in the years following an outbreak of the disease. My results suggest that the presence of oak wilt negatively influences habitat selection and quality for golden-cheeked warblers, likely due to reduced canopy cover in susceptible oak species. Additionally, oak wilt frequently occurs in golden-cheeked warbler habitat and will continue to spread into warbler habitat in the coming years. Future management efforts should address the threat oak wilt poses to golden-cheeked warblers by incorporating applicable preventative measures.Item Understanding Participation in Wildlife Conservation Programs on Private Lands(2010-01-14) Sorice, Michael G.One major lesson derived from the implementation of the Endangered Species Act (ESA) over the past 30 years is that direct regulation is not the only nor the optimal way to protect endangered species on working lands because of an undue burden imposed on private landowners. The role of a voluntary conservation program is to rearrange incentives so that society bears the cost rather than the landowner. Employing a survey research methodology, I used theories of reasoned action and random choice to explore landowners? stated preferences for conservation programs. I found landowners? stated interest in compensation programs to be moderate at best. For those willing to consider programs involving endangered species, associating land management requirements for species conservation with direct benefits to the landowner is important, but perhaps not as important as ensuring that the program provides adequate financial incentives, consideration of the term of the program, and a level of certainty regarding the landowner?s future obligations under the ESA. Landowners are not a homogenous group. I identified two classes of landowners according to preferences for program structure. One group was highly sensitive to program structure, aside from financial incentives, while the other was likely to participate if adequately compensated with financial and technical assistance. These differences related to opinions on endangered species protection and dependence on their land for income. Voluntary incentive programs increasingly are a popular tool to maintain and enhance conservation; however, these programs are only successful insofar as landowners choose to enroll. This research demonstrates that improving recovery efforts on private lands requires program administrators to have a more complete understanding of landowners? views on endangered species and conservation programs in general, as well as their motivations for owning and operating their land. By doing so, programs with broader appeal and greater efficacy can be designed and implemented.Item Updated distribution and reintroduction of the Lower Keys marsh rabbit(Texas A&M University, 2005-02-17) Faulhaber, Craig AlanListed as federally-endangered in 1990, the Lower Keys marsh rabbit (LKMR, Sylvilagus palustris hefneri) exists as a metapopulation in patches of wetland habitat in Florida?s Lower Keys. This study sought to address 2 priority actions identified by the LKMR Recovery Team: (1) monitoring of populations and (2) reintroduction. Monitoring the distribution and status of LKMR populations is critical for targeting future management actions. Informal transects for rabbit fecal pellets were used to survey habitat patches documented in1988?1995 surveys and to identify additional patches of occupied and potential habitat. Next, a buffer was created around patches to help managers account for uncertainty in rabbit movements and to identify groups of patches that might function as local populations. Surveys included 228 patches of occupied and potential habitat, 102 of which were occupied by rabbits. Patches were arranged in 56 occupied and 88 potential populations. Surveys revealed new patches of both occupied and potential habitat. Considering only areas included in 1988?1995 surveys, however, revealed a net decrease in the number of occupied patches. Many of the recently extirpated populations, which tended to occupy the periphery of larger islands or small neighboring islands, were unlikely to be recolonized without human intervention. Reintroduction provides a means of artificially recolonizing potential habitat. Two pilot reintroductions were conducted to evaluate this conservation strategy for the species. The second reintroduction was postponed, but the first effort met all criteria for short-term success, including survival comparable to a control group, fidelity to release sites, and evidence of reproduction. There are a limited number of potential source populations for translocations. Future efforts should consider using in-situ captive breeding to prevent potential long-term impacts to these populations. Few potential release sites exhibited suitable habitat quality and landscape context. Thus, for reintroduction to be more widely-applied for this species, it must be part of a comprehensive management plan involving land acquisition, control of secondary impacts from development, and habitat restoration and enhancement.