Browsing by Author "Caruso, Nicholas M."

Now showing 1 - 6 of 6
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    Assessing Changes in Bog Turtle (Glyptemys muhlenbergii) Population Abundance and Factors Influencing Nest Predation in Virginia
    Holden, Michael Thomas (Virginia Tech, 2021-06-10)
    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.
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    Forecasting the flooding dynamics of flatwoods salamander breeding wetlands under future climate change scenarios
    Chandler, Houston C.; Caruso, Nicholas M.; McLaughlin, Daniel L.; Jiao, Yan; Brooks, George C.; Haas, Carola A. (PeerJ, 2023-09-19)
    Ephemeral wetlands are globally important systems that are regulated by regular cycles of wetting and drying, which are primarily controlled by responses to relatively short-term weather events (e.g., precipitation and evapotranspiration). Climate change is predicted to have significant effects on many ephemeral wetland systems and the organisms that depend on them through altered filling or drying dates that impact hydroperiod. To examine the potential effects of climate change on pine flatwoods wetlands in the southeastern United States, we created statistical models describing wetland hydrologic regime using an approximately 8-year history of water level monitoring and a variety of climate data inputs. We then assessed how hydrology may change in the future by projecting models forward (2025–2100) under six future climate scenarios (three climate models each with two emission scenarios). We used the model results to assess future breeding conditions for the imperiled Reticulated Flatwoods Salamander (Ambystoma bishopi), which breeds in many of the study wetlands. We found that models generally fit the data well and had good predictability across both training and testing data. Across all models and climate scenarios, there was substantial variation in the predicted suitability for flatwoods salamander reproduction. However, wetlands with longer hydroperiods tended to have fewer model iterations that predicted at least five consecutive years of reproductive failure (an important metric for population persistence). Understanding potential future risk to flatwoods salamander populations can be used to guide conservation and management actions for this imperiled species.
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    Gender Differences in Grant Submissions across Science and Engineering Fields at the NSF
    Rissler, Leslie J.; Hale, Katherine L.; Joffe, Nina R.; Caruso, Nicholas M. (2020-09)
    There has been great growth in women's participation in the US academic doctoral workforce, but underrepresentation remains in all science and engineering fields, especially at high academic ranks. We obtained estimates of the numbers of professorial women and men in fields likely to seek funding from the National Science Foundation and aligned those numbers with each of six research directorates to investigate temporal trends in submission patterns. We found that women are as likely to be funded as men, but the percentage of women submitting proposals was less than expected in every field but engineering. Women are as likely as men to be employed at the most research active institutions, but women are less likely than men to self-report research as their primary work activity in almost all fields but engineering. This work imbalance ultimately limits the diversity of basic science research ideas in science and engineering.
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    The influence of silvicultural manipulations on plethodontid salamanders
    Engler, Victoria Margaret (Virginia Tech, 2024-05-20)
    Habitat alteration (i.e. degradation, fragmentation, and destruction) is the primary driver of amphibian decline and extinction. Despite their ecological importance and threatened status, very little long-term research has been conducted on how methods of forest management impact salamanders. In this research, I examine how experimental silviculture impacts plethodontid salamander relative abundance and count, and I compare three different body condition indices. Chapter 1 focuses on plethodontid salamander relative abundance 30 years after experimental treatments (including clearcut and shelterwood harvests, understory herbicide, uneven-aged management, and an untreated control) were first applied. I found that plethodontid salamander populations in all silvicultural treatments without stand re-entry have reached pre-harvest relative abundance levels. Chapter 2 describes how artificial tip-up mounds that could be used to mimic old-growth forest characteristics impact plethodontid salamander count. Salamander count significantly declined in treatment units with artificial tip-up mounds but this could be an artifact of the heavy disturbance required for installation. Chapter 3 compares three different body condition indices for plethodontid salamanders. I found that bioelectrical impedance analysis (BIA) is likely not suitable for use with plethodontid salamanders and mass divided by snout-to-vent-length is likely a superior estimate to tail width divided by snout-to-vent-length. These findings further our understanding of how different forest management practices affect salamander populations and provide guidance for evaluating body condition.
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    Interacting effects of temperature and food on early growth of two plethodontid salamanders
    Holguin, Charlie (Virginia Tech, 2023-09-19)
    An amphibian's life history includes patterns such as growth, development, and reproduction. These life history traits are essential to the fundamental understanding of population dynamics. Despite the importance of life history traits, key knowledge gaps still exist, hindering key information on birth/death rates, age/size at sexual maturity, size at metamorphosis, and clutch sizes for amphibians. Moreover, these life patterns can vary due to environmental conditions such as temperature and food availability, further emphasizing the importance of knowledge of species demographics. In this study, I aimed to investigate the growth of young-of-the-year and juvenile plethodontid salamanders with different life cycles, Plethodon cinereus (direct development) and Eurycea cirrigera (metamorphosis). Specifically, I was interested in examining the response of growth trajectories to different temperatures and food availability. I hypothesized that salamanders in the high-temperature treatment will grow faster initially but will be smaller at the conclusion of the experiment, while salamanders in the low-temperature treatment will grow slower initially but will be larger at the end of the experiment. To investigate the interaction between body size and environmental conditions, I exposed both species of salamanders to a factorial design, with two food treatments crossed with two temperature treatments. To analyze the data, I used a generalized additive mixed model (GAMM). The study revealed distinct growth patterns for both species of salamanders. P. cinereus experienced linear growth throughout the duration of the study, whereas E. cirrigera displayed non-linear growth (Throughout the experiment, salamander experienced a decrease in total length and mass). The results of the GAMM did not support my hypothesis for P. cinereus. However, the GAMM results did provide support for my hypothesis in the case of E. cirrigera under high food availability treatment. Furthermore, salamanders with limited food availability in both experiments grew at a slower rate. Forecasting the impacts of climate change on salamander populations is complex and will require the understanding of habitat quality and climate factors.
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    Niche partitioning and the storage effect facilitate coexistence in an amphibian community
    Brooks, George C.; Caruso, Nicholas M.; Chandler, Houston C.; Haas, Carola A. (Wiley, 2023-10-18)
    Virtually all natural community assemblages are dominated by a handful of common species. Dominant species can exert negative impacts on biodiversity through competitive exclusion, and thus there is a strong incentive to understand imbalances in community composition, changes in dominance hierarchies through time, and mechanisms of coexistence. Pond-breeding amphibians that utilize ephemeral wetlands provide an excellent opportunity to evaluate theoretical predictions of community composition in stochastic environments. One of the most striking features of pond-breeding amphibians is the marked stochastic fluctuations in abundance across years. Given strong theoretical and empirical links between evenness and biomass, one would expect community evenness to change from year to year. Moreover, if different species exhibit different boom-and-bust reproductive cycles, then a storage effect may help to explain why one species does not outcompete all others. Here, we explore the interplay between biotic and abiotic conditions in shaping amphibian communities at two ephemeral wetlands on Eglin Air Force Base, Florida. We document consistent community composition over 6 years of monitoring, resulting from a lack of species turnover and similar responses of all community members to environmental conditions. The similar dynamics of species argues against a storage effect as the sole mechanism for coexistence and instead points to niche partitioning as a more important factor. In support of this conclusion, we show that the degree of synchrony in breeding migrations only correlates with environmental conditions within species, not between species. The lack of pattern seen between species implies that individuals are somewhat constrained in the timing of breeding migrations, perhaps owing in part to competition with other community members. We hope that our work reinvigorates interest in amphibian communities and highlights ephemeral wetlands as model systems to study community dynamics in stochastic environments.