POPULATION VIABILITY AND CONNECTIVITY OF THE FEDERALLY THREATENED EASTERN INDIGO SNAKE IN CENTRAL PENINSULAR FLORIDA

Understanding the factors influencing the likelihood of persistence of real-world populations requires both an accurate understanding of the traits and behaviors of individuals within those populations (e.g., movement, habitat selection, survival, fecundity, dispersal) but also an understanding of how those traits and behaviors are influenced by landscape features. The federally threatened eastern indigo snake (EIS, Drymarchon couperi) has declined throughout its range primarily due to anthropogenically-induced habitat loss and fragmentation making spatially-explicit assessments of population viability and connectivity essential for understanding its current status and directing future conservation efforts. The primary goal of my dissertation was to understand how landscape features influence EIS population viability and connectivity in central peninsular Florida. I accomplished this through four components. First, I evaluated EIS movement patterns and space use including daily movement distance, home range size, within-individual home range overlap, and among-individual home range overlap and how these patterns varied by sex and season. Second, I conducted a multi-level, multi-scale habitat selection analysis to create spatially-explicit estimates of EIS habitat selection. Third, using the aforementioned data and previously published data, I developed an agent-based model for simulating EIS movement, survival, reproduction, and dispersal in central Florida. I used this model to determine how landscape features and conservation lands influence EIS occupancy across our study landscape. Finally, I used landscape genetics to determine how landscape features influenced genetic connectivity and to estimate resistance surfaces with which to model potential corridors. I found that male EIS maintain larger home ranges than females and move extensively during the breeding season in search of females. While seasonal home ranges within an individual strongly overlapped, individuals avoided home ranges of same-sex conspecifics. EIS selected home ranges and within-home range locations in areas of undeveloped upland habitat with high habitat heterogeneity and generally avoided urban. While EIS did not avoid roads, they rarely crossed primary and secondary roads. I used observed patterns of movement and habitat selection to calibrate my ABM. My ABM simulated larger male home ranges and smaller home ranges and lower survival in urbanized landscapes although simulated effect sizes were weaker than observed effect sizes. My model was unable to simulate observed patterns of within-individual home range overlap but accurately simulated survival in developed and undeveloped landscapes. EIS occupancy after a 15 year simulation was 56% and occupancy was most strongly affected, negatively, by urbanization. While the presence of conservation lands was not a strong driver of EIS occupancy, EIS occupancy was more consistently higher on conservation lands. EIS gene flow was most strongly associated with undeveloped uplands, urbanization, and habitat edge at the broadest scales we evaluated. Potential corridors were widespread in the southern half of our study area with substantial areas of potential habitat and corridor occurring outside of the existing conservation network. This work indicates that the LWR contains extensive areas capable of supporting EIS although increasing urbanization may have a negative impact on future persistence of EIS

Forecasting Seasonal Habitat Connectivity in a Developing Landscape

Connectivity and wildlife corridors are often key components to successful conservation and management plans. Connectivity for wildlife is typically modeled in a static environment that reflects a single snapshot in time. However, it has been shown that, when compared with dynamic connectivity models, static models can underestimate connectivity and mask important population processes. Therefore, including dynamism in connectivity models is important if the goal is to predict functional connectivity. We incorporated four levels of dynamism (individual, daily, seasonal, and interannual) into an individual-based movement model for black bears (Ursus americanus) in Massachusetts, USA. We used future development projections to model movement into the year 2050. We summarized habitat connectivity over the 32-year simulation period as the number of simulated movement paths crossing each pixel in our study area. Our results predict black bears will further colonize the expanding part of their range in the state and move beyond this range towards the greater Boston metropolitan area. This information is useful to managers for predicting and addressing human–wildlife conflict and in targeting public education campaigns on bear awareness. Including dynamism in connectivity models can produce more realistic models and, when future projections are incorporated, can ensure the identification of areas that offer long-term functional connectivity for wildlife

The Influence of Sex and Season on Conspecific Spatial Overlap in a Large, Actively-Foraging Colubrid Snake

Understanding the factors influencing the degree of spatial overlap among conspecifics is important for understanding multiple ecological processes. Compared to terrestrial carnivores, relatively little is known about the factors influencing conspecific spatial overlap in snakes, although across snake taxa there appears to be substantial variation in conspecific spatial overlap. In this study, we described conspecific spatial overlap of eastern indigo snakes (Drymarchon couperi) in peninsular Florida and examined how conspecific spatial overlap varied by sex and season (breeding season vs. non-breeding season). We calculated multiple indices of spatial overlap using 6- and 3-month utilization distributions (UD) of dyads of simultaneously adjacent telemetered snakes. We also measured conspecific UD density values at each telemetry fix and modeled the distribution of those values as a function of overlap type, sex, and season using generalized Pareto distributions. Home range overlap between males and females was significantly greater than overlap between individuals of the same sex and male home ranges often completely contained female home ranges. Male home ranges overlapped little during both seasons, whereas females had higher levels of overlap during the non-breeding season. The spatial patterns observed in our study are consistent with those seen in many mammalian carnivores, in which low male-male overlap and high inter-sexual overlap provides males with greater access to females. We encourage additional research on the influence of prey availability on conspecific spatial overlap in snakes as well as the behavioral mechanisms responsible for maintaining the low levels of overlap we observed

The effects of estradiol-17β on the sex reversal, survival, and growth of green sunfish Lepomis cyanellus

The feminization of green sunfish Lepomis cyanellus could expand their utility as a game fish or aquacultured species by preventing overcrowding and precocious reproduction in stocked systems. Feminization of green sunfish could also help elucidate information on their sex determination system. We report the feminization of green sunfish cohorts via oral administration of estradiol-17β (E2) during early development. A low-dose (100 E2 mg per kg of diet) and a high-dose (150 E2 mg per kg of diet) experimental E2 treatment were fed to juvenile green sunfish from 30 to 90 days post-hatch. Fish were subsequently evaluated for any treatment effect on gonadal development, survival, and growth. Both E2 treatments resulted in 100% feminization, with no morphological or histological differences detected between E2 treated ovaries and those from a control group. The control group was composed mostly of males (82.61%). Overall, there was no effect of E2 on survival (P = 0.310) and growth rate data suggested no statistical differences (P = 0.0805). However, the growth rate of the high-dose group increased slightly higher after the treatment ended than the other treatments (P = 0.042), suggesting that E2 might suppress growth in green sunfish. In addition, the control group did not exhibit a higher survival rate after the treatment period ended (P = 0.266), whereas both E2 treated groups did (P = 0.0003–0.0050). We found that the low dose, 100 E2 mg per kg of diet, was sufficient for fully feminizing green sunfish if administered during development from 30 to 90 days post-hatch and E2 dosages may result in deleterious effects on green sunfish’s health and growth

Dcouperi_home_range_overlap_metrics.csv

Data used in the analyses of conspecific spatial overlap of Drymarchon couperi (eastern indigo snake). Multiple metrics of spatial overlap between simultaneously adjacent dyads of radio-telemetered snakes using 95% and 50% fixed kernel utilization distributions (UD) are provided as well as the sex of the individuals in the dyad, the season and year of the dyad, and the study area in which the dyad was collected. Additionally, the criteria used to determine if the UD were accurately estimated are provided. Additional details are provided within this dataset and in the text of Bauder et al. (2016).<br

Dcouperi_radiotelemetry_summary_stats.csv

Information on fixed kernel utilization distributions (UD) estimated for individual radio-telemetered Drymarchon couperi (eastern indigo snakes) used in the analyses described and reported in Bauder et al. (2016). Data on each UD's season, year, number of telemetry fixes, number of days tracked, and home range size are provided. Additionally, the sex, size, and study area of individual D. couperi are provided. Additional details are provided within the dataset and the text of Bauder et al. (2016).<br

Dcouperi_conspecific_UD_density_values.csv

Data used in the analyses titled "Individual use of conspecific space" within Bauder et al. (2016). Data values are the probability density values from simultaneously adjacent conspecific utilization distributions (UD) at a particular snake's radio telemetry location. Higher values indicate a location was in an area more intensely used by a conspecific. The individual identification and sex of each radio-telemetered snake are provided as well as the season in which the UD was estimated and whether the neighboring conspecifics were of the same or opposite sex. Additional details are provided within this dataset and in the text of Bauder et al. (2016). <br

Effects of translocation on survival of nuisance bears

Effective mitigation of human–wildlife conflict should aim to reduce conflicts while also minimizing wildlife mortality. Translocation is often used to mitigate human–wildlife conflict but translocated individuals may have reduced survival, which could negatively affect population growth and social acceptance of translocation as a management tool. Yet, non-translocated nuisance individuals may also have low survival due to inherent risks associated with nuisance behavior. We used a 38-year dataset of 1233 marked and translocated nuisance American black bears (Ursus americanus) as a model system with which to evaluate the impacts of translocation on nuisance bear survival. We used multi-state mark-recapture models to estimate annual harvest and non-harvest mortality rates and tested for effects of translocation distance and harvest rate on recapture and both mortality rates. Recapture probability increased with translocation distance but 75% of translocated bears were translocated ≤75 km and recapture probabilities were \u3c0.05 across these distances. Survival was 0.43 for adult males, 0.56 for adult females, and 0.38–0.40 for yearlings. However, increasing translocation distance reduced both harvest and non-harvest mortality (β = −0.0044, 95% CI = −0.0081 to −0.0006 and β = −0.0020, 95% CI = −0.0051 to 0.0011, respectively) showing that increasing translocation distance does not negatively impact survival. Our survival estimates were generally lower than those reported for non-nuisance American black bear populations (0.67–0.83), which likely reflects risks associated with nuisance behavior, such as proximity to human dwellings, agriculture, or roads which in turn may increase harvest and/or road mortality. Our results show that translocation is a useful approach for mitigating human–bear conflict that does not always negatively affect survival. Lower survival of nuisance bears suggests that biologists should focus efforts on reducing the incidences of human–wildlife conflicts (e.g., removing anthropogenic food sources)

Relationships of catch-per-unit-effort metrics with abundance vary depending on sampling method and population trajectory.

Catch-per-unit-effort (CPUE) is often used to monitor wildlife populations and to develop statistical population models. Animals caught and released are often not included in CPUE metrics and their inclusion may create more accurate indices of abundance. We used 21 years of detailed harvest records for bobcat (Lynx rufus) in Wisconsin, U.S.A., to calculate CPUE and 'actual CPUE' (ACPUE; including animals caught and released) from bobcat hunters and trappers. We calibrated these metrics to an independent estimate of bobcat abundance and attempted to create simple but effective models to estimate CPUE and ACPUE using harvest success data (i.e., bobcats harvested/available permits). CPUE showed virtually no relationship with bobcat abundance across all years, but both CPUE and ACPUE had stronger, non-linear, and negative relationships with abundance during the periods when the population was decreasing. Annual harvest success strongly predicted composite ACPUE and CPUE from hunters and trappers and hunter ACPUE and CPUE but was a poorer predictor of trapper ACPUE and CPUE. The non-linear, and sometimes weak, relationships with bobcat abundance likely reflect the increasing selectivity of bobcat hunters for trophy animals. Studies calibrating per-unit-effort metrics against abundance should account for population trajectories and different harvest methods (e.g., hunting and trapping). Our results also highlight the potential for estimating per-unit-effort metrics from relatively simple and inexpensive data sources and we encourage additional research into the use of per-unit-effort metrics for population estimation

Native fish abundance and habitat selection changes in the presence of nonnative piscivores

We compared abundance patterns and developed resource selection models for imperilled native southwestern (USA) fishes in the presence and absence of Black Bass (Micropterus spp.) to evaluate how fishes alter their selection for habitats when sympatric with a nonnative piscivore. We collected data using snorkel surveys and in-stream habitat sampling in Fossil Creek (AZ), upstream (native fish only) and downstream (native and nonnative fish) of a fish barrier. The abundance of all Roundtail Chub (Gila robusta), small (≤127 mm total length [TL]; vulnerable to predation) Sonora Sucker (Catostomus insignis) and Speckled Dace (Rhinichthys osculus) was significantly reduced, but the abundance of both small and large (>127 mm TL; invulnerable to predation) Desert Sucker (Catostomus clarkii) was similar in sampling reaches with and without Black Bass. When sympatric with Black Bass, small Roundtail Chub increased their selection for riffles by 2.57 times and small Desert Sucker reduce their selection for pools by 6.90 times while also selecting for faster flow velocity and finer substrates in lotic mesohabitats. Large native fishes altered selection least, notwithstanding an increased selection for canopy cover in sampling reaches with Black Bass. Observed shifts in resource selection are consistent with predator avoidance strategies. Our study highlights the behavioural consequences of nonnative piscivores on native fish communities and stresses the importance of maintaining lotic mesohabitats as potential refugia for vulnerable native fishes when nonnative piscivores are present.U.S. Forest Service12 month embargo; first published 13 August 2023This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]