No description available.

No description available.

No description available.

No description available.

One of the basic questions of concern in mathematical biology is the long-term survival of each species in a set of populations. This question is particularly puzzling for a natural system with omnivory due to the fact that simple mathematical models of omnivory are prone to species extinction. Omnivory is defined as the consumption of resources from more than one trophic level. In this work, we investigate three omnivory models of increasing complexity. We use the notion of permanent coexistence, or permanence, to study the long-term survival of three interacting species governed by a mixture of competition and predation. We show the permanence of our models under certain parameter restrictions and include the biological interpretations of these parameter restrictions. Sensitivity analysis is used to obtain important information about meaningful parameter data collection. Examples are also given that demonstrate the ubiquity of omnivory in natural systems. / Ph. D.

Briery Creek Lake (BCL) has low abundance of young largemouth bass (LMB) compared to Sandy River Reservoir (SRR), which could jeopardize the trophy-LMB management goal in BCL. I assessed factors that may limit recruitment of LMB in BCL: angling, predation, competition, growth, and food availability. Age-0 LMB were monitored from nesting through their first summer with nest surveys, light traps, and electrofishing. Nesting success was higher in BCL (53%) than SRR (31%). Initial light trap catch-per-unit-effort (CPUE) was higher in BCL than SRR but, by July, light trap and electrofishing CPUE was higher in SRR than BCL. LMB nest success, growth, and CPUE did not differ between areas in BCL that were experimentally closed and areas left open to angling. Predation on age-0 LMB did occur in BCL, but was not higher than predation in SRR. Diet overlap between age-0 LMB and bluegill in BCL was >60% during June, indicating potential for competition. Zooplankton samples indicated that density of copepods was similar between reservoirs (2.3/liter); however, the average size of copepods was smaller in BCL (0.42 mm) than SRR (0.71 mm). I examined the activity of trypsin, which digests and converts protein. Trypsin activity was lower in BCL than SRR on 23 and 27 June, indicating that a nutritional deficiency exists for age-0 LMB in BCL. This deficiency was likely caused by the reduced zooplankton size in BCL and led to slower growth of age-0 LMB during June in BCL (0.8 mm/day) than SRR (1.2 mm/day). The fact that age-0 LMB CPUE in BCL dropped lower than SRR by July, despite BCL having a greater nesting success and higher CPUE in early June, indicates that a recruitment bottleneck for LMB occurred in June. Maintaining the trophy LMB fishery in BCL requires management options that consider the factors in June that affect recruitment. I recommend decreasing the presently overabundant aquatic macrophytes in BCL, thus allowing for increased nutrient availability for phytoplankton, the primary food source of zooplankton. This could increase the density and size structure of zooplankton, and thereby increase food availability for age-0 LMB. / Ph. D.

When touched with a contact stimulus, 50% of adult Uloborus glomosus jumped from the web; 33% remained motionless; 13% moved to the edge of the web; and 4% shook the web. In a population of juveniles, 45% moved to the edge of the web; 27% jumped from the web; 24% shook the web; and 4% remained motionless. Adults with either stabilimenta or eggsac chains in their webs showed a tendency to shake their webs in the morning and move to the edge in the evening. Those without web structures jumped from their webs throughout the day. Juveniles with stabilimenta shook their webs in the afternoon; those without stabilimenta shook their webs in the evening. Adults aligned with web structures remained motionless when disturbed. Marked adults observed over the course of 4 weeks moved to the edge of the web or remained motionless when contacted in the mornings and jumped in the afternoons and evenings. During this time, the frequency of the jumping behavior increased. An adult U. glomosus jumped from its web in response to contact by a spider-hunting wasp. Other spiders tested with a contact stimulus and the combined visual and vibratory stimuli produced by a tethered wasp responded only to contact. Females tending their eggsac chains exhibited two types of defensive behaviors when either the parasitoid Arachnopteromalus dasys or spiderlings were placed on their eggsacs. They jerked their webs and swept the eggsacs with their long front legs. / Master of Science

Smith Mountain Lake, Virginia supports a successful put-grow-take striped bass fishery. Empiric analysis of striped bass stocking has shown an inverse relationship between number of fingerling striped bass stocked and survival to age 1. Potential causes for this inverse relationship include largemouth bass predation on fingerling striped bass and mortality resulting from stocking stress. Cage studies performed in 1994 and 1995 quantified percentage of fingerlings lost due to hauling/handling stress. Mean mortalities ranged from 1.78% for Phase I fingerlings in 1994 to 99.5% for Phase II fingerlings (reared in a recirculating aquaculture system for increased size at stocking) in 1994. Mortality rates varied greatly and were probably directly related to length of transport and inadequate thermal tempering prior to stocking. Highest mortality occurred at transport times in excess of six hours and when receiving water was 5° C warmer than transport water. A trial in which Phase I fingerlings were caged without transport or temperature change resulted in no mortality. Predation mortality by largemouth bass was also considered as a source of poor first-year survival of striped bass in Penhook and Waterwheel stocking coves at Smith Mountain Lake. It was necessary to estimate largemouth bass population size, diet composition, and daily consumption (bioenergetic modeling) to determine the total number of striped bass lost to predation. Diet analysis revealed that age-0 striped bass made up a maximum of 2.5% of largemouth bass diets in the month following stocking; adult alewives constituted more than 60% by weight. The estimated number of striped bass lost was only 360 (0.1%) in 1994 and 3062 (1.2%) in 1995. Bioenergetic simulations demonstrated that predation could become significant in the unlikely event that the contribution of striped bass to largemouth diets increased to 10% or more. Based on results from diet analysis and a prey preference laboratory study, alewives appear to buffer predation of age-0 striped bass during the month after stocking. In 1994 and 1995, neither stocking stress associated with the typical Phase I fingerling stocking procedure nor largemouth bass predation resulted in substantial mortality of stocked fingerling striped bass. / Master of Science

The top piscivore in Byllesby Reservoir, a 98.6 ha hydropower impoundment in southwestern Virginia is the flathead catfish Pylodictis olivaris. The most numerically abundant fish in the reservoir are centrarchids, specifically bluegill Lepomis macrochirus, redbreast sunfish L. auritus, smallmouth bass Micropterus dolomieu, and spotted bass M. punctulatus. A bioenergetics model was used to estimate the number of age-l and older centrarchids consumed annually by the flathead catfish population. These estimates were then compared to estimated abundances of each centrarchid species (age-1 and older) in the impoundment, resulting in an estimate of predation impact. / Master of Science

Across the globe, wildlife populations are facing increasing challenges, with many taxonomic groups significantly declining. Among endangered vertebrates (including birds, non-avian reptiles, fishes, mammals, and amphibians), turtles are one of the most threatened groups with over 60% of the 356 recognized species classified as threatened or worse. Bog turtles (Glyptemys muhlenbergii), are among the most imperiled of North American freshwater turtles. These small, secretive turtles have declined by up to 90% in parts of their range, which consists of the Northern Population and the Southern Population, and spans the eastern U.S. from New York to Georgia. These declines are mainly documented in the northern part of their range, but recent work in North Carolina suggests that turtles in the southern part of their range are similarly declining. Prior to this research, surveys aimed at estimating abundance had not been conducted in Virginia since the late 1990's. The research described here was conducted as part of a state-wide population assessment of bog turtles in Virginia. For my first chapter, I conducted capture-mark-recapture surveys in six wetlands in Floyd County, Virginia during 2019 and 2020, and generated abundance estimates. These wetlands had been surveyed in the same manner in 1997, which provided me the opportunity to compare recent abundance estimates with those generated from the 1997 data. My analyses suggest that turtle abundance across these six sites has declined by approximately 50% since 1997. This decline appears to be driven by, but not wholly attributable to, the alteration and loss of habitat at 2-3 of the 6 sites. Habitat loss is acknowledged as one of the major drivers of population declines throughout the range of the bog turtle, in addition to illegal collection for the international pet trade. Due to the life history traits of this species (long life span and low fecundity), the loss of an individual from any life stage from the population can have detrimental effects. While many turtle populations are not heavily impacted from periods of low reproductive success, numerous subsequent years of complete nesting failure can negatively impact population-level survival. Recent studies have suggested that anthropogenically subsidized nest predators may be playing a role in continued nest failure at certain wetlands. My second chapter investigated the factors associated with anthropogenic footprint (i.e., buildings) and infrastructure that may be driving nest predation by these subsidized predators. In 2019 and 2020, I conducted a field experiment in 35 wetlands which utilized artificial turtle nests to investigate variation in nest predation across Montgomery and Floyd Counties, Virginia. I found that increases in the percent of developed land-use and other metrics of anthropogenic disturbance significantly increased nest predation, while increases in the percent of land-use without roads or buildings significantly decreased nest predation. The findings from these two chapters are consistent with population trends documented in other parts of the bog turtle range, and build upon prior studies to investigate drivers of nest predation. These results provide information that can be used by managers to aid in the conservation of this state endangered species, and suggest further courses of research for future projects. / Master of Science / Across the globe, wildlife populations are facing increasing challenges, with many taxonomic groups significantly declining. Turtles are one of the most threatened groups of vertebrates with over 60% of the 356 species of turtle classified as threatened or endangered. Bog turtles (Glyptemys muhlenbergii), are among the most imperiled of North American freshwater turtles. These small, secretive turtles have declined by up to 90% in parts of their range, which consists of the Northern Population and the Southern Population, and spans the eastern U.S. from New York to Georgia. Prior to this research, no information on population trends was available for Virginia. To address this knowledge gap, I conducted surveys for bog turtles in six wetlands in Floyd County, Virginia during 2019 and 2020, and used the data from those surveys to estimate how many turtles were present in the wetlands. These wetlands had been surveyed in the same manner in 1997, which provided me the opportunity to compare recent estimates with those generated from the 1997 data. My analyses suggest that the total number of bog turtles present across these six sites has declined by approximately 50% since 1997. This decline appears to be caused at least in part by the alteration and loss of habitat at 2 of the 6 sites. Habitat loss is thought to be one of the major drivers of population declines throughout the range of the bog turtle, in addition to illegal collection for the international pet trade. Recent studies have suggested an additional problem, that anthropogenically subsidized nest predators may be playing a role in continued nest failure at certain wetlands. Animals such as raccoons, skunks, and bears can persist in greater numbers around human habitation, as we provide extra food sources such as garbage, bird feeders, deer feeders, etc. I investigated the factors associated with human infrastructure that may be driving nest predation by these subsidized predators. In 2019 and 2020, I conducted a field experiment in 35 wetlands using artificial turtle nests to investigate variation in nest predation across Montgomery and Floyd Counties, Virginia. I found that nest predation was significantly higher in areas with a higher percent of developed land-use. The findings from these two studies are consistent with population trends documented in other parts of the bog turtle range, and build upon prior studies to investigate drivers of nest predation. These results provide information that can be used by managers to aid in the conservation of this endangered species, and suggest further courses of research for future projects.