<p> Agrochemical exposure is one of the factors that contributes to worldwide amphibian declines. Most studies that examine agrochemicals and amphibian declines focus on toxicity. However, declines are more likely caused by the sub-lethal effects of agrochemical exposure. Past emphases on the lethal effects of agrochemical exposure have overshadowed the contribution of decreased recruitment in amphibian declines. Additionally, studies that examine agrochemicals and reproductive function tend to focus on the effects of single chemical exposures instead of the effects of ecologically relevant mixtures. To address these issues, this dissertation examined the effects of ecologically relevant agrochemical exposures on the stress response and the reproductive endocrinology, morphology, and behaviors of male amphibians in the laboratory and the wild. </p><p> Chapter 1 provides a general review of the factors implicated in amphibian declines and provides an overview of the previous research conducted on the effects of agrochemical exposure on recruitment. </p><p> Chapter 2 is a field study that examined whether agricultural run-off alters the stress response and reproductive function of male bullfrogs (<i> Lithobates catesbeianus</i>). Bullfrogs were collected upstream and downstream of agricultural activity across three California river systems (Salinas, Sacramento and San Joaquin). Size, primary and secondary sex traits, sperm count, and corticosterone and testosterone levels were examined. Overall, bullfrogs living downstream of agricultural activity (i.e. exposure to agricultural run-off) were small and had elevated testosterone and corticosterone levels. In addition, downstream males from the Salinas and San Joaquin Rivers were also small in size and had elevated testosterone levels. However, only downstream males of the San Joaquin River had elevated corticosterone and exaggerated secondary sex traits. Together, these data suggest that living downstream of agriculture can alter size, hormone levels, and the expression of sexually dimorphic sex traits. Such changes to the reproductive endocrinology and morphology of male amphibians can be detrimental to the reproductive health and long-term reproductive success of amphibian populations. </p><p> In Chapter 3, I examined corticosterone, testosterone, and the reproductive clasping behaviors of adult male African clawed frogs (Xenopus laevis) exposed to field collected and simulated agricultural run-off. This experiment implemented a novel eco-relevant experimental design to mimic real-life agrochemical exposures. Male frogs were exposed to field water collected downstream (agricultural run-off) and upstream (negative control) of agricultural activity along the Salinas River, CA. In addition, a pesticide mixture containing the top agrochemicals used in the Monterey County was included to simulate agricultural run-off. Mating behavior was suppressed in males exposed to simulated agricultural run-off but enhanced in males exposed to field collected agricultural run-off. In addition, testosterone levels of clasping males were elevated in comparison to controls. Males immersed in simulated agricultural run-off had significantly lower testosterone levels than control males in 2010. These data suggest that agrochemical exposure (both field collected and simulated) can alter reproductive hormones and clasping behaviors. Altered sex hormones and behaviors in male amphibians may play a role in amphibian declines. </p><p> Lastly, this dissertation is summarized in Chapter 4. The applicability of this dissertation as a model for amphibian declines and other reproductive related human health concerns are also introduced.</p>

<p> West Texas, especially the Trans-Pecos region, mainly consists of desert shrubs and grasslands with patches of higher elevation (1,500 &ndash; 2,000 m) mountain ranges. Black bears (<i>Ursus americanus</i>) were extirpated from this area by the 1940s because of predator control and over hunting. In the 1980s, black bears returned to west Texas in a natural recolonization movement from Mexico, where they had survived. The black bear populations of the Trans-Pecos region and northern Mexico fit a mainland-island metapopulation model. Based on previously published research on this recolonization event, I identified several likely habitat recolonization sites and corridor routes for use in predicting possible black bear dispersal throughout the area. Then, using these corridor and recolonization scenarios, I produced a black bear metapopulation model for the Trans-Pecos region.</p><p> The possible habitat recolonization site map was created by combining 2 habitat suitability index (HSI) maps and using these HSI maps to define 'core' and 'useable' black bear habitat within the Trans-Pecos region. Using these locations, along with dispersal probabilities and black bear demographic parameters, I created a corridor dispersal map of the area using the program Circuitscape.</p><p> The metapopulation model was created using STELLA modeling software. Each recolonization location in the Trans-Pecos region (Big Bend National Park, Black Gap Wildlife Management Area, and the Davis Mountains) has its own black bear subpopulation. The metapopulation model is a stochastic compartment model based on a yearly time step (&Delta;<i>t</i> = 1 yr). This model was tested for the effects of: carrying capacity per site, immigration rates from Mexico, rates of dispersal from Black Gap Wildlife Management Area to the Davis Mountains, and the recovery time for the area after complete extirpation from the Trans-Pecos. This information will help local biologists conserve and manage these returning black bears in the Trans-Pecos region. </p>

<p> Weathervane scallops (<i>Patinopecten caurinus</i> [Gould, 1850]) off Alaska are commercially harvested in areas that contain commercially important groundfish and crabs. Using observer bycatch data collected during 1996-2012, we analyzed spatial and temporal patterns in community composition on weathervane scallop beds and explored whether observed patterns related to environmental variables (sediment, depth, bottom water temperature, and freshwater discharge) and anthropogenic variables (trawling and dredging effort). Significant (P&lt;0.05) differences in community structure were observed at the scale of state fishery registration districts, as well as among individual scallop beds. Spatial differences were most strongly correlated with sediment, depth, and dredging effort. Sequential changes over time were also detected, as was a split between 1996-1999 and 2000-2012. Temporal changes were weakly yet significantly correlated with freshwater discharge and dredging effort. We also conducted a socioeconomic assessment of the commercial weathervane scallop fishery, structured within the framework of a SWOT (strengths, weaknesses, opportunities, threats) analysis. Specifically, we focused on five categories: social, technological, economic, environmental, and regulatory. Whereas the data-poor status of the stock appears to be the fishery's biggest weakness, the largest strengths are conservative management, industry self-regulation, and the fishery's small footprint. Impending threats include stock declines, effects of dredging, and changes in the structure of the fishery. These analyses provide a baseline of benthic community composition on weathervane scallop beds, as well as socioeconomic information to contribute to the environmental, economic, and social sustainability of the Alaska scallop fishery.</p>

<p> This study assessed the occurrence and impacts of maternal metal transfer in live-bearing fish. The occurrence was investigated in two different species (<i>Gambusia affinis</i>and <i>Heterandria formosa</i>), while the impacts were studied only in <i>G. affinis.</i> Occurrence and impacts were addressed by exposing gravid females for 10 days to 0.15 &mu;M of copper or cadmium, transferring the fish to clean water, monitoring their reproduction and collecting newborn offspring for further analyses of their health and reproductive success. </p><p> Maternal transfer of copper and cadmium occured in both study species. Metal levels decreased in subsequent broods and in broods born later after a female's exposure. Metal exposure impacted the reproductive success of exposed-females; effects included smaller broods and more broods were aborted broods or contained dead offspring. Many effects remained for second broods developing well after the exposure. </p><p> The maternal metal exposure also impacted the offspring's health. Newborn offspring were smaller at birth, had reduced calcium levels, had a lowered metal tolerance, and had cellular membrane damage. When these offspring grew up, they had an increased rate of malformations, a smaller size at sexual maturity, increased gestation time and fewer broods. In spite of the impacts on life history parameters found in the laboratory, effects on population dynamics were very limited for greenhouse mesocosm populations established with the offspring of exposed females. </p><p> Effects for the essential metal (copper) and the nonessential metal (cadmium) were generally similar. A few effects, like those on body size, were evident for copper but not for cadmium. However, several of the more severe impacts, like the increase in malformations and reductions in the number of broods, were greatest for the offspring of the cadmium-exposed females. </p><p> This is the first report demonstrating negative impacts resulting from a short-term maternal metal exposure in live-bearing fishes. Effects were evident not just for reproduction of exposed-females but also for their offspring's health and reproduction. The latter continued beyond the offspring that were developing during exposure. This study demonstrated that the internal development in live-bearing fish may not spare the developing young from impacts caused by a metal-contaminated environment.</p>

<p> Anthropogenic lead releases into the environment often end up in aquatic sediments. Ecotoxicologists have historically studied biological effects of toxicants, such as lead, using individuals or populations as models in laboratory settings. It has recently been suggested that because such bottom-up approaches can be difficult to extrapolate to actual effects of contaminants in the field, more research should take a top-down perspective. My project therefore aimed to investigate sediment lead effects at the community level, as well as on ecosystem function. Studies were conducted in a lake with a gradient of low-level sediment lead contamination. An assessment of benthic macroinvertebrate communities at fifty points in the lake revealed a negative correlation between sediment lead concentration and community abundance and diversity. Leaf-litter bags were deployed at thirty of the same points and decomposition rate was assessed after thirty days. Analyses indicated that decomposition rate decreased with increasing sediment lead concentration. Acute lead bioassays, using benthic macroinvertebrates collected from different areas of the lake, revealed that communities from the contaminated area were more tolerant to lead than were communities from uncontaminated areas. The pattern of increased community tolerance as a result of chronic exposure to low-level sediment lead was confirmed with macrobenthic communities that had been pre-exposed to environmentally-relevant lead concentrations for eighteen months in sediment mesocosms. Communities exposed to elevated lead levels had an increased tolerance when exposed to lethal lead levels. This was supported by the observed reduction in abundance and diversity that correlated with an increase in benthic macroinvertebrate community tolerance to lead. Additionally, reductions in leaf-litter decomposition, a vital ecosystem function in lentic systems, were also correlated with reductions in benthic macroinvertebrate abundances. Overall, the low-levels of sediment lead in the lake system appeared to have adverse effects on both structural and functional aspects of ecological integrity. Because sediment concentrations in the lake system were largely below widely accepted guidelines that are considered to be protective of benthic macroinvertebrates, my results have implications for risk-assessment in lentic systems contaminated with lead.</p>

<p> Male katydids produce mating calls through stridulation to attract potential mates. Calls were recorded in the field and analyzed to compare between two related species that occur in overlapping ranges in the northwestern United States. Distinct differences were found between the two species' calls in both dominant frequency and chirp rate. Also, one species interspersed trills amongst the chirps of the call, while the other species' call did not include trills. These distinct call differences can be used for species identification and can be easier to differentiate than physical characteristics. </p><p> The upper limits of sexual selection can be estimated using upper limits on Bateman gradients, which represent how fecundity increases with additional mates. Upper limits on Bateman gradients are expected to be constrained by various factors such as nutrition. These upper limits were estimated using controlled mating experiments with katydids on high and low protein diets (as adults) by measuring how maximum fecundity (fecundity with ideal mates) increased with each mating. Decreases in both maximum fecundity and the potential for sexual selection were expected in males and females due to protein limitation. This would result from decreased potential fecundity in low protein females and decreased value of nuptial gifts given by low protein males. The results did not support our predictions as strongly as hoped, but a decrease in the upper limits of sexual selection was nearly significant in low protein males, evidenced by reduced fecundity gains from remating. Also, spermatophores (the katydid nuptial gift) had a more complicated effect on fecundity than expected. Spermatophore size differed between males' first and second matings, however, larger spermatophores did not always confer more value to females, particularly in second matings. </p><p> Stable isotope analysis was used to examine the lack of significant effects from differences in dietary protein on the upper limits of sexual selection in the previous experiment. Stable isotope ratios were analyzed for three body tissues to infer diet at different life stages by comparison with isotopic values from the foods. Results showed that animals on the low protein diet may have eaten more food to make up for their protein deficit, which would have confounded nutritional effects in the previous study. Sex differences in nutrient processing were present as would be expected if males and females experience different nutritional requirements for reproduction. Nutrient processing in exoskeleton varied across food treatments in males but not in females. This suggests that males experienced greater protein limitation than females and adjusted their nutrient processing accordingly. Further work is underway to determine how much of each type of food was consumed by individuals in different experimental treatments and during different life stages. </p>

<p>I investigated percent coverage, plant height, species richness, and woody stem density in plant communities in ten study plots during spring and fall (2010&ndash;2012) within 3 different treatments (continual mowings, one fall mowing, and one fall mowing with native wildflower seeds) on Highway 25 right-of-way in Oktibbeha and Winston counties, Mississippi. I recorded 277 plant species including native and non-native forbs, legumes, grasses, rushes/sedges, and woody plants. Non-native agronomic grasses exhibited greatest coverage greater than 90 percent occurring in all treatments. Percent coverage of plants less than 0.46m height category exceeded 100 while, greater than 0.46m plant height categories averaged 55 percent. Woody stem density ranged from 7,772 year 1 to 10,025 stems/hectare year 2. I detected no significant differences in plant height or woody stems among treatments. One mowing per year retained agronomic plant cover for erosion control and annual cost savings up to 75 percent for roadside maintenance. </p>

<p> During the 1970s to the 1990s, Steller sea lions (<i>Eumetopias jubatus</i>) in Alaska declined severely, resulting in the western stock's listing as endangered under the United States Endangered Species Act. The localized depletion of their main food source around rookeries and haul out sites was the primary cause of their depletion. The western stock has still not recovered to historical levels. Therefore, scientists have continued to study Steller sea lions diet and foraging habits. One approach has been through stable isotope analysis of their various tissues. Analysis of their vibrissae, or whiskers, provides an exact record of an individual's diet from birth to the present. However, scientists so far have only measured stable isotope values of a single vibrissa from an individual, assuming no significant difference among vibrissae within or between cheeks. They have not accounted for the possibility of variable stable isotope accumulation in an individual's different vibrissae. In this study, I tested the assumption of no significant individual variability among vibrissae by examining the &delta;¹³C and &delta;¹⁵N values in all of the vibrissae on five Steller sea lion pups recovered in Alaska. &delta;¹⁵N values did not differ between vibrissae on a cheek or between vibrissae from left and right cheeks. The &delta;¹³C values did not differ between vibrissae within cheeks; however, &delta;¹³C values were significantly different between the left and right cheeks of Lowrie Island Pup and PWS 29 Pup. This between cheek variation is most likely due to small sample size rather than different stable isotope incorporation. The lack of &delta;¹⁵N value variation within or between cheeks, as well as the lack of &delta;¹³C variation within cheeks, supports the assumption that stable isotope accumulation is similar between all vibrissae and validates sampling protocols of previous studies collecting just the longest, thick vibrissa from a Steller sea lion. More studies similar to this one are needed to verify these findings and to look at variability in stable isotope incorporation of juvenile and adult Steller sea lion vibrissae as well as other mammal species.</p>

<p> Since the 1970s halibut size-at-age has decreased in southcentral Alaska; the mechanisms causing decreased size-at-age are unknown. The objectives of this study were to 1) compare size-at-age of port-sampled fish in Homer to survey samples from Gulf of Alaska; 2) assess stable isotope values (&delta;¹³C, &delta;¹⁵N) of halibut by sex, size, location and date; 3) determine mean stable isotope values for prey; and 4) identify prey associated with smaller and larger size-at-age. We used port-sampled halibut from the Homer sport fishery due to the quantity of available carcasses. Port-sampled fish were generally larger than survey sampled fish from the same region. Halibut had a wide range of stable isotope values that varied with all factors. Prey isotope values were wide and overlapping, allowing for distinctions among teleost, cephalopods, crustaceans and amphipods. Older and younger fish of the same size and sex had different proportions of prey assimilated into their muscle.</p>

Anadromous Pacific salmon (Oncorhynchus spp.) return annually from marine ecosystems to their natal freshwater habitat to spawn and die. Runs of spawning salmon provide an important source of nutrients and energy to watersheds. However, in coastal systems, substantial amounts of salmon-derived nutrients can be exported back to estuaries. Human land use, including agriculture and urban development, also contribute substantial nutrients to coastal ecosystems, and have the potential to confound results from salmon-derived nutrient studies. This thesis examines the influences of spawning salmon and human land use on stream nutrient and particulate dynamics, including export to estuaries. It also investigates the use of the stable isotope composition (δ13C and δ15N) of estuarine clams, the varnish clam (Nuttalia obscurata: Reeve, 1857) and the manila clam (Tapes philippinarum), and their food sources, as indices of the freshwater export of salmon-derived nutrients to estuaries. Samples were collected from three nearby river-estuary systems along Southeast Vancouver Island, British Columbia. Study systems had either a large number of returning salmon and little human land use (Goldstream), few returning salmon and extensive human land use (Shawnigan), or few returning salmon and little human land use (Holland). In Goldstream River, high abundance of salmon carcasses increased concentrations of total nitrogen and total phosphorus stream water below a barrier to upstream salmon migration. Carcasses also contributed substantial amounts of organic matter to the stream, as indicated by high δ13C and δ15N, and corresponding low C:N ratios in suspended particulate organic matter. My calculations indicate that between 51-77% of the phosphorus transported upstream by migrating salmon, was exported back to the estuary. Human land use also increased downstream nutrient concentrations and raised baseline δ15N in stream ecosystems, which is cause for concern and caution for salmon-derived nutrient studies in land use-affected watersheds, or in the reverse situation, for anthropogenic nutrient studies in watersheds that support runs of anadromous salmon. The high δ15N of anthropogenic nitrogen was not evident in the Shawnigan Estuary. In the Goldstream Estuary salmon-derived nutrients appeared to increase the δ15N of clams, and both the δ13C and δ15N of sedimentary organic matter (SOM), with more enrichment in the high intertidal zone near the river mouth, than in the mid-intertidal zone. The stable isotope composition of clams and SOM was relatively constant across the period of salmon spawning and carcass decay, indicating that they may reflect a legacy salmon-derived nutrient input into estuaries. This study demonstrates that substantial amounts of salmon-derived nutrients are exported back downstream to the Goldstream Estuary where they appear to become integrated into the estuarine food web. Data from a series of estuaries receiving a range of nutrients inputs from salmon is needed to confirm indices of salmon-derived nutrients in estuaries. There is also need for more extensive examination regarding the downstream effects of salmon-derived nutrients in areas such as estuarine productivity, community composition, and positive feedback mechanisms that influence salmon populations. This last area of research is of particular importance considering the high number of salmon stocks at risk in B.C.