Browsing by Subject "Habitat (Ecology)"
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Item Dispersal-diversity relationships and ecosystem functioning in pond metacommunities(2008-08) Howeth, Jennifer Gail, 1979-; Leibold, Mathew A.Insights gained from metapopulation and metacommunity biology indicate that the connectivity of subpopulations and communities by species dispersal can profoundly impact population dynamics, community structure, and ecosystem attributes. Recent advancements in metacommunity theory further suggest that the rate of species dispersal among local communities can be important in altering local and regional species richness and ecosystem functioning. The role of species dispersal rates relative to patch-type heterogeneity and associated intrinsic community structuring mechanisms (competition, predation) in affecting diversity of multi-trophic communities, however, remains unknown. Here, I address the relative influence of regional and local processes in altering species richness and ecosystem functioning at multiple spatial scales in freshwater pond metacommunities. In a series of experiments, I employed pond mesocosm metacommunities to manipulate planktonic species dispersal rates and the incidence of top predators which differed in prey selectivity. The consequences of dispersal and predation to zooplankton species richness, trophic structure, ecosystem stability, and prey traits were evaluated. Generally, my findings support predictions from metacommunity models, and demonstrate that dispersal strongly affects community and ecosystem-level properties. In accord with dispersal-diversity theory, dispersal rate affected species richness and ecosystem stability at multiple spatial scales. The presence, but not the rate, of dispersal had strong effects on the partitioning of biomass amongst producers, grazers, and top predators. The relative influence of predation on local and metacommunity structure varied across experiments and largely depended upon predator identity and the degree of feeding specialization. The research presented herein is some of the first work to evaluate how species dispersal rates can affect dispersal-diversity relationships, diversity-stability relationships, trophic structure, and the distribution of prey traits in metacommunities. In addition to advancing ecological theory, the results have important implications for conservation as fragmented landscapes become increasingly prevalent, and local and regional biotas modified. Ultimately, it proves critical to identify drivers of local and regional species richness in order to maintain biotic integrity at the global scale.Item Ecotoxicology of Morelet's crocodile in Belize(Texas Tech University, 2003-08) Rainwater, Thomas RobertOver the last two decades, population declines and reproductive impairment have been observed in American alligators (Alligator mississppiensis) inhabiting Lake Apopka, a highly contaminated lake in Florida, USA. Juvenile alligators from the lake have exhibited altered sex-steroid hormone concentrations, abnormal gonadal morphology, and reduced phallus size compared to alligators from a reference lake. No direct cause-effect relationship has been established between these reproductive and endocrine anomalies and environmental contaminants, but results of laboratory and field investigations suggest the potential for contaminant-induced endocrine disruption at various levels of organization in these animals. Although various environmental contaminants considered to be endocrine disrupters have been found in eggs and tissues of crocodilians worldwide, no studies have yet investigated endpoints of endocrine disruption in wild crocodilians outside of Florida. The primary objective of this study was to address this data gap by examining ecotoxicological endpoints in another crocodilian species living in habitats contaminated with endocrine-disrupting chemicals (EDCs), and where appropriate, compare results from this study with those observed for alligators in Florida. During a pilot study in 1995, multiple organochlorine (OC) pesticides considered to be EDCs were found in eggs of Morelet's crocodiles (Crocodylus moreletii) from three localities in northern Belize. Based on these findings and previous data from Florida showing egg contamination, population declines, and reproductive abnormalities in alligators exposed to many of the same chemicals, a multi-year study was initiated to examine various endpoints of contaminant exposure and response in Morelet's crocodiles living on contaminated and reference sites in northern Belize. Gold Button Lagoon, a man-made lagoon from which contaminated crocodile eggs were collected in 1995, was selected as the contaminated site for this study, while New River Watershed, a more remote site with fewer anthropogenic inputs than Gold Button Lagoon, was selected as the reference site. Three primary endpoints of endocrine disruption were evaluated in this study. First, vitellogenin induction was examined as an endpoint of exposure to exogenous estrogens or estrogen-mimicking contaminants. Vitellogenin is an egg-yolk precursor protein expressed in all oviparous and ovoviviparous vertebrates. Male and juvenile females normally have no detectable concentration of vitellogenin in their blood but can produce it following stimulation by an exogenous estrogen, such as an EDC. Thus, the presence of vitellogenin in the blood of male or juvenile female crocodiles can serve as an indicator of exposure to an estrogen-mimicking EDC. Of 358 males and juvenile females sampled in this study, no vitellogenin induction was observed, suggesting these animals were likely not exposed to estrogenic xenobiotics. However, many of the animals sampled were later found to contain OC pesticides in their caudal scutes, confirming they had in fact been exposed to OCs (and EDCs). These data suggest the lack of a vitellogenic response should not necessarily be interpreted as an indication that no exposure or other contaminant-induced biological response has occurred. Second, plasma sex-steroid hormone concentrations were examined as an endpoint of response to EDC exposure in crocodiles from the two study sites. The selection of this endpoint was based on numerous studies reporting altered concentrations of estradiol-17P (E2) and testosterone (T) in alligators from Lake Apopka and other contaminated lakes in Florida. In the present study, few inter-site differences in plasma hormone concentrations were noted. No significant differences in plasma E2 concentrations were detected between sites. However, juvenile males and females from the contaminated site exhibited significantly reduced plasma T concentrations compared to juvenile males and females from the reference site, respectively. This finding was consistent with results from previous studies on alligators in Florida. No other inter-site differences in hormone concentrations were observed. Relationships between body size and hormone concentrations were variable and showed no clear pattern. Third, male phallus size was examined as a second endpoint of response to EDC exposure in crocodiles from the two study sites. Concurrent with reductions in plasma T concentrations, male alligators from Lake Apopka and other contaminated lakes in Florida have exhibited smaller phallus size compared to animals from a reference lake. Researchers speculate that abnormal hormone concentrations during early life stages may affect anatomical structures dependent on these hormones for proper growth and development (i.e., genitalia). p,p '-DDE, a known anti-androgen, has been detected in alligator eggs and serum from Lake Apopka and was also detected in eggs and scutes of Morelet's crocodiles from the two Belize study sites. Thus, in the present study, male crocodile phallus size and plasma T concentrations were examined as endpoints of response to p,p '-DDE exposure as well as exposure to other contaminants. No differences in mean phallus size were observed between sites, whereas mean plasma T concentrations in juveniles from Gold Button Lagoon were significantly reduced compared with those from New River Watershed. It was discovered late in the study that New River Watershed exhibited a contaminant profile similar to that observed at Gold Button Lagoon, with multiple OCs detected at similar concentrations in sediments, crocodile eggs, and crocodile caudal scutes at both sites. With the lack of a suitable reference site, it is thus unclear if steroid hormone concentrations and male phallus size observed in this study are within the normal range exhibited by Morelet's crocodiles living in non-contaminated habitats or if they are altered in some way (e.g., increased, reduced). In addition, it is also unclear if inter-site differences in plasma T are the result of exposure to EDCs, natural variation, one or more undetermined factors (e.g., stress), or a combination of these factors. In general, the results of this study indicate few or no effects of EDC exposure on Morelet's crocodiles inhabiting contaminated wetlands in northern Belize. However, multiple uncertainties encountered in this study make inter-site and inter-study (crocodile to alligator) comparisons difficult and some results equivocal. Thus, the potential effects of EDCs and other contaminants on crocodiles inhabiting these sites should not be assumed to be negligible. Long-term studies are essential to adequately assess the effects of EDCs on crocodilian populations, as these animals are long-lived and many contaminant-induced effects are organizational in nature, occurring during embryonic development but not appearing until later in life.Item Microsite and habitat boundary influences on small mammal capture, diversity, and movements(Texas Tech University, 1997-08) Root, J. JeffreyHabitat, habitat edges, and microhabitat are important components for theories and concepts of community ecology. However, their effects have not been examined in many locations. Replicated studies in different ecosystems are necessary to determine the generality of the effects of these habitat variables. The effects of trap-site disturbance and microhabitat on small mammal capture rates were examined in the Tularosa Basin of south-central New Mexico during 7-14 April, 1996. The study was conducted in a mixed desert scrub habitat characteristic of the Chihuahuan Desert. Small mammals were live-trapped on 32 study plots. Soil disturbance and microhabitat treatments were assigned to study plots in a completely randomized factorial design to test the hypothesis that trap-site disturbance can influence small mammal captures between microhabitats. Thirteen species of small mammals were captured, including four species of Heteromyidae, eight species of Muridae, and one species of Sciuridae. Peromyscus eremicus was captured more frequently at undisturbed sites (P=0.004) and was recaptured more frequently under shrubs j[P=0.048). Neotoma micropus was captured less frequently at undisturbed sites in the open (P=0.035). No other species were affected by microhabitat, trap-site disturbance, or interactions (P>0.05). These results provide limited support to the hypothesis that trap-site disturbance can influence small mammal captures between microhabitats.Item Relationship of lesser prairie-chicken density to landscape characteristics in Texas(2012-05) Timmer, Jennifer; Boal, Clint W.; Butler, Matthew J.; Ballard, Warren B.; Whitlaw, Heather A.Ground-based lek surveys have traditionally been used to index trends in prairie grouse populations (Centrocercus and Tympanuchus spp.). However, indices of abundance or density can be fundamentally flawed and techniques that account for incomplete detection should be used. Distance sampling is a common technique used to estimate the density and abundance of animal populations and has been used with aerial surveys to monitor avian populations. With an increase in renewable energy development in native prairies and sagebrush steppe, there is a greater need to effectively monitor prairie grouse populations. One such species, the lesser prairie-chicken (LPC; T. pallidicinctus), has faced significant population declines and is thus, a species of conservation concern. In addition, much of the current and proposed wind energy development in the Great Plains overlaps some of the extant LPC distribution and few peer-reviewed studies have been conducted to investigate this potential threat to LPCs. Hierarchical distance sampling models can relate LPC lek density to landscape features and help predict the potential impact from wind and other energy development on lek density. Thus, the main objectives of our study were to estimate lek density in the LPC range in Texas and model anthropogenic and landscape features associated with lek density. We accomplished this by flying helicopter lek surveys for 2 field seasons and employing a line-transect method developed at Texas Tech University. We inventoried 208, 7.2 km × 7.2 km survey blocks and detected 71 new leks, 25 known leks, and observed 5 detections outside the current LPC range. We estimated 2.0 leks/100 km2 (90% CI = 1.5–2.8 leks/100 km2) and 12.3 LPCs/100 km2 (90% CI = 8.5– 17.9 LPCs/100 km2) for our sampling frame. Our state-wide abundance estimates were Texas Tech University, Jennifer M. Timmer, May 2012 vii 301.9 leks (90% CI = 219.4–415.4 leks) and 1,822.4 LPCs (90% CI = 1,253.7–2,649.1 LPCs). Our best model indicated lek size and lek type (wi = 0.360) influenced lek detectability. Lek detectability was greater for larger leks and natural leks rather than man-made leks. We used hierarchical distance sampling to build spatially-explicit models of lek density and landscape features. The 2 most competitive models included percent shrubland + transmission line (>69kv) density and only percent shrubland (AIC= 943.817, wi = 0.486; AIC = 945.098, wi = 0.256, respectively). We model-averaged our most competitive models and estimated the number of leks in our sampling frame at 245.7 leks (cv = 0.137). Lek density peaked at lower levels of transmission line density and where ≈60% of the landscape was composed of shrubland patches (shrubs <5 m tall comprising ≥20% of the total vegetation). Our state-wide survey efforts provide wildlife managers and biologists with population estimates, new lek locations, and identified spatially-explicit predictions of lek density. Our spatially-explicit models predicted lek density based on percent shrubland and transmission line density, which can be used to predict how lek density may change in response to transmission line development and changes in habitat conditions. This copy has been corrected.Item Use of Broad-scale data to assess changes of scaled quail populations in Texas(Texas Tech University, 2000-08) Leyva-Espinosa, Raquel IreneScaled quail {Callipepla squamata) is an upland species that has declined in areas of historical distribution in Texas. Potential causes for the present decline have been attributed to precipitation and changes in landscape characteristics. The effects of long-term landscape modification, precipitation variation, and scaled quail populations were evaluated using a Geographic Information System (GIS). Three databases were included in the construction of the GIS. The first database included records for precipitation for the state of Texas from 1968 through 1997. The second database consisted of Multispectral Scanner (MSS) satellite images for the state of Texas obtained during 1973, 1986, and 1991 to determine land use and land cover changes. Finally, the third database consisted of annual records for scaled quail population in Texas from 1968 through 1997. The objective of this project was to evaluate the use of broad-scale data to describe local reduction of scaled quail densities in Texas due to (1) changes in suitable habitat; (2) temporal precipitation variation; and (3) the combined effect of long-term habitat modifications and temporal climatic variation. The temporal distribution of precipitation was studied for two main rainy seasons, corresponding to the months of April-June (first rainy season) and July-September (second rainy season). Temporal precipitation variability and scaled quail population trends were analyzed using cross-spectral analysis for time series to determine whether or not these series were correlated. Scaled quail data were obtained from Breeding Bird Survey records for the 1968-1997 period. Long-linear models were used to determine scaled quail population trends at individual Breeding Bird Survey routes, ecoregions, and the area of scaled quail distribution in Texas. Two ecoregions were not included in the analysis due to the lack of data. A landscape gradient including rangelands, cultivated lands, water bodies, and urban areas was created to determine changes in suitable habitat during 1973, 1986, and 1991. Scaled quail population densities were compared at state, ecoregion, and Breeding Bird Survey route. Analysis of the temporal distribution of climatic parameters suggested the presence of annual trends plus lag-times that varied from 2 to 11 years; however, most sites presented periods ranging between 2 to 3 years. The use of cross-spectral analysis suggested that scaled quail populations in the Basin and Range and the Rolling Plains ecoregions were cross-correlated with precipitation. The Rio Grande Plain and the Texas High Plains ecoregions did not present strong correlations between scaled quail and either rainy season. Multiple regression indicated that changes in precipitation explained changes in scaled quail for ecoregions were the species is distributed; however, only the Basin and Range ecoregion presented statistically significant slopes. The combined effect of precipitation and vegetation did not explain changes in scaled quail populations in the Texas High Plains ecoregion. The combination of vegetation and precipitation influenced scaled quail only in the Rolling Plains but the slopes were not statistically significant. The lack of complete scaled quail records presented a big problem in the analysis of the population trends for the complete distributional range of the species. However, it provided a potential tool to determine changes at the ecoregion level. To develop state- wide management plans for scaled quail populations in Texas, the first step was to develop complete data sets. Scaled quail populations generally have declined in the past 3 decades. This negative trend may have been influenced by the combination of the temporal and spatial distribution of climatic parameters and habitat modification, however the lack of a strong data set may weaken results making them inconclusive and contradictory. The methodology used in this research provided alternatives to handle missing values and the presence of potential lag-effects in the data. These techniques in combination with more complete databases may provide, in the future better estimations of the relationships between scaled quail and long-term habitat modifications at different scales. Also the use of GIS allowed the integration of large databases to aid in the analysis of potential causes for scaled quail decline in the state of Texas. This approach may also provide the tools for management of other species.