Grant M. Connette

Ecological resistance surfaces predict fine‐scale genetic differentiation in a terrestrial woodland salamander

Landscape genetics has seen tremendous advances since its introduction, but parameterization and optimization of resistance surfaces still poses significant challenges. Despite increased availability and resolution of spatial data, few studies have integrated empirical data to directly represent ecological processes as genetic resistance surfaces. In our study, we determine the landscape and ecological factors affecting gene flow in the western slimy salamander (Plethodon albagula). We used field data to derive resistance surfaces representing salamander abundance and rate of water loss through combinations of canopy cover, topographic wetness, topographic position, solar exposure and distance from ravine. These ecologically explicit composite surfaces directly represent an ecological process or physiological limitation of our organism. Using generalized linear mixed‐effects models, we optimized resistance surfaces using a nonlinear optimization algorithm to minimize model AIC. We found clear support for the resistance surface representing the rate of water loss experienced by adult salamanders in the summer. Resistance was lowest at intermediate levels of water loss and higher when the rate of water loss was predicted to be low or high. This pattern may arise from the compensatory movement behaviour of salamanders through suboptimal habitat, but also reflects the physiological limitations of salamanders and their sensitivity to extreme environmental conditions. Our study demonstrates that composite representations of ecologically explicit processes can provide novel insight and can better explain genetic differentiation than ecologically implicit landscape resistance surfaces. Additionally, our study underscores the fact that spatial estimates of habitat suitability or abundance may not serve as adequate proxies for describing gene flow, as predicted abundance was a poor predictor of genetic differentiation.

Life History as a Predictor of Salamander Recovery Rate from Timber Harvest in Southern Appalachian Forests, U.S.A

Forest management often represents a balance between social, economic, and ecological objectives. In the eastern United States, numerous studies have established that terrestrial salamander populations initially decline in abundance following timber harvest, yet the large-scale and long-term consequences are relatively unknown. We used count data from terrestrial survey points to examine the relation between salamander abundance and historic timber harvest while accounting for imperfect detection of individuals. Overall, stream- and terrestrial-breeding salamanders appeared to differ by magnitude of population decline, rate of population recovery, and extent of recolonization from surrounding forest. Specifically, estimated abundance of both species groups was positively associated with stand age and recovery rates were predicted to increase over time for red-legged salamanders (Plethodon shermani) and decrease in stream-breeding species. Abundance of stream-breeding salamanders was predicted to reach a peak by 100 years after timber harvest, and the population growth rate of red-legged salamanders was predicted to undergo a significant increase 100 years after harvest. Estimated abundance of stream-breeding salamanders in young forest stands was also negatively associated with the distance to adjacent forest, a result that suggests immigration has a role in the recovery of these species. Our results indicate that salamander abundance in young forest stands may be only modestly lower than in more mature forest but that full recovery from timber harvest may take a substantial amount of time and that species life history may affect patterns of recovery. Historia de Vida como un Vaticinador de la Tasa de Recuperación de una Salamandra a la Colecta de Madera en los Bosques del Sur de los Apalaches, E.U.A.

Climate change and shrinking salamanders: alternative mechanisms for changes in plethodontid salamander body size

An increasing number of studies have demonstrated relationships between climate trends and body size change of organisms. In many cases, climate might be expected to influence body size by altering thermoregulation, energetics or food availability. However, observed body size change can result from a variety of ecological processes (e.g. growth, selection, population dynamics) or imperfect observation of biological systems. We used two extensive datasets to evaluate alternative mechanisms for recently reported changes in the observed body size of plethodontid salamanders. We found that mean adult body size of salamanders can be highly sensitive to survey conditions, particularly rainfall. This systematic bias in the detection of larger or smaller individuals could result in a signature of body size change in relation to reported climate trends when it is simply observation error. We also identify considerable variability in body size distributions among years and find that individual growth rates can be strongly influenced by weather. Finally, our study demonstrates that measures of mean adult body size can be highly variable among surveys and that large sample sizes may be required to make reliable inferences. Identifying the effects of climate change is a critical area of research in ecology and conservation. Researchers should be aware that observed changes in certain organisms can result from multiple ecological processes or systematic bias due to nonrandom sampling of populations.

Successful use of a passive integrated transponder (PIT) system for below-ground detection of plethodontid salamanders

Abstract Context. Passive integrated transponder (PIT) technology allows for permanent and unambiguous marking of animals and has recently been adapted for locating tagged individuals in the field with portable detection systems. Aims. We seek to assess the effects of PIT tagging on the growth and survival of plethodontid salamanders in the laboratory and to evaluate the effectiveness of this method for subterranean detection of salamanders in the field. Methods. In a laboratory experiment, we assigned 36 Plethodon shermani to either a PIT tag or control group and compared survival and growth rates over the course of 9 weeks. For the field study, we implanted six Plethodon metcalfi with PIT tags and conducted surveys so as to determine their below-ground positions with a portable detector. Key results. We found no effect of PIT tagging on either growth or survival in the laboratory. In the field, PIT telemetry resulted in an overall detection efficiency of 44%, with nighttime surveys yielding a greater detection efficiency than daytime surveys. This technique provided a significant improvement over traditional hand-capture because detected salamanders were rarely visible on the ground surface. Key conclusions. Our study indicates that even these relatively small-bodied salamanders (range: 2.14–5.18 g) are capable of bearing PIT tag implants and confirms the results of previous studies that found no effect of PIT tagging on the health or survival of amphibians. This study further demonstrates that the use of a portable PIT detector can be an effective method for locating below-ground salamanders. Implications. Because of the small size and long lifespan of PIT tags, we believe portable PIT detectors can provide researchers with an unprecedented level of detail for studies of the movement behaviour, spatial ecology and management of species that are small or otherwise challenging to detect and monitor with other techniques.

Context-dependent movement behavior of woodland salamanders (Plethodon) in two habitat types.

Animal movement is critical to the maintenance of functional connectivity at the landscape scale and can play a key role in population persistence and metapopulation dynamics. The permeability of habitat to animal movement may vary as a result of either differential mortality, physical resistance, or simply the behavioral responses of organisms to perceived habitat quality. Understanding how and when animal movement behavior varies among habitat types is critical for identifying barriers to dispersal and predicting species distributions in relation to landscape features. We conducted an experimental translocation study and compared the movement success and behavioral strategies of plethodontid salamanders in both forest and open-canopy habitat. We found that individuals in closed-canopy forest oriented more strongly towards their home ranges and moved significantly farther on their release night. In spite of the clear differences in movement paths, the ultimate movement success of homing salamanders did not appear to vary with habitat type. Our study contributes to a growing body of literature suggesting the importance of recognizing the context dependence of animal movement behavior. Because the movement rates of displaced salamanders were significantly reduced in open-canopy, dispersal rates of plethodontid salamanders in open-canopy habitat are likely lower than in control forest. Further mechanistic studies focusing on habitat-specific movement behavior and survival costs will be valuable for effectively identifying and mitigating barriers to animal movement.

Effects of fine‐scale forest habitat quality on movement and settling decisions in juvenile pond‐breeding salamanders

A better understanding of how individuals respond to variation in habitat quality while moving through heterogeneous habitats is needed to predict ecological phenomena at larger scales, such as local population and metapopulation dynamics. We sought to identify how fine-scale habitat quality affects the decisions of juvenile pond-breeding salamanders (Ambystoma maculatum and A. annulatum) to cease dispersive movements away from their natal pond, select a refuge, and settle. Because of the acute susceptibility of juvenile amphibians to evaporative water loss in terrestrial habitats, we predicted that they possess mechanisms for adjusting their behavior in response to variations in fine-scale habitat quality. We used experimental field enclosures to isolate the effects of habitat quality on settling behavior and employed generalized linear mixed models to examine how manipulations in canopy cover (closed or open) and microhabitat (control, compacted soils, high coarse woody debris, high burrow density), along with environmental variables (rainfall and air temperature), affect the individuals probability of settling. Our results indicated that A. maculatum and A. annulatum had a 10% and 30% decreased probability of settling in open-canopy clearcut habitat, respectively, compared to closed-canopy forest habitat. In addition, A. annulatum were 24% less likely to settle in compacted soil treatments. Although the settlement probability of A. annulatum did not depend on refuge availability, A. maculatum were 18% and 25% more likely to settle under conditions of high burrow density and high coarse woody debris, respectively. These findings make a unique contribution to our understanding of amphibian movement ecology by demonstrating how the interplay of external factors and individual behavior produce observed patterns of movement and habitat selection.

Identification of Polymorphic Loci in Ambystoma annulatum and Review of Cross-species Microsatellite Use in the Genus Ambystoma

We screened 74 published microsatellite primers in Ambystoma annulatum, a species for which no microsatellite markers have been developed. Overall, we had a moderate success rate, identifying 11 polymorphic microsatellites previously developed in four different species of Ambystoma. We also conducted a review of the literature, collecting all published cross-species applications of microsatellite markers within the genus Ambystoma. From this, we identified 20 loci that have amplified in three or more species. Our synthesis of microsatellite use within the genus Ambystoma should prove valuable to future molecular research, especially in species without developed markers and for studies in species that may already have microsatellites, but are being conducted far from the region where individuals were collected for original development of species-specific loci.

A multistate mark–recapture approach to estimating survival of PIT‐tagged salamanders following timber harvest

Summary Survival is a critical component of individual fitness, population dynamics and the landscape ecology of organisms. Survival in animal populations is frequently estimated from capture–mark–recapture studies, yet these estimates are biased low when the permanent emigration of individuals is confounded with mortality. This systematic bias can limit the value of demographic information available for conservation and management efforts. We developed a novel multistate mark–recapture model for survival estimation in fossorial organisms that incorporates auxiliary passive integrated transponder (PIT-tag) detection data to account for the possibility of permanent emigration from our study area as well as the imperfect detection of individuals. Our study provides a direct comparison of mortality, emigration and reduced ground surface activity as explanations for declines in terrestrial salamander counts which are commonly reported following timber harvest. Reduced ground surface activity was not supported as a likely cause for reduced counts of plethodontid salamanders after timber harvest. Instead, ground surface activity was predicted to be considerably higher after timber harvest, suggesting that surface counts would under-represent the extent of population losses relative to control areas. Controlling for multiple causes for non-detection of salamanders, we found evidence that survival probability was reduced while permanent emigration rates may also be elevated in the initial months after timber harvest. However, a substantial majority of salamanders were known to survive the process of initial forest stand entry and timber removal. Synthesis and applications. Our analysis of passive integrated transponder (PIT-tag) detection data with a novel multistate mark–recapture model indicated that mortality and emigration are both potential causes for short-term reductions in salamander abundance following timber harvest. We suggest that salamander mortality is likely tied to habitat or microclimate conditions in early successional timber cuts, rather than the physical process of timber removal.

Influence of Abiotic Factors on Activity in a Larval Stream Salamander Assemblage

Abstract Larval stream salamanders are the numerically dominant predators in many headwater stream systems. Nonetheless, little is known about their activity patterns or the extent to which their movements are influenced by prevailing environmental conditions. In this study, we used capture rates from passive trapping as an index of activity level and sought to identify the environmental variables most responsible for fluctuations in larval stream salamander activity. Over the course of two months, we captured stream salamanders in aquatic funnel traps during both day- and night-trapping sessions at a first-order stream in the North Carolina Piedmont. Using an information-theoretic approach, we constructed models to elucidate the effects of (1) water temperature, (2) cloud cover, (3) days since last rainfall, and (4) time of day on larval salamander activity. We found that the model incorporating time of day and cloud cover was the best predictor of larval salamander activity. In our study, larval salamander activity was highest at night and also demonstrated a weak positive correlation with increasing cloud cover. Using model-averaging, we further determined that our time of day and cloud cover variables demonstrated a significant correlation with observed activity levels. This pattern of peak activity under low light conditions could be a behavioral adaptation that limits predation risk for larval salamanders.

Relationship between Diet and Microhabitat Use of Red-legged Salamanders (Plethodon shermani) in Southwestern North Carolina

The selection of a foraging habitat may be driven by food availability or by the cost associated with the use of that habitat. This basic tradeoff can lead individuals in the same population to occupy different habitats in response to perceived risk levels. In the southeastern United States, plethodontid salamanders are often observed climbing vegetation, which represents a potential foraging habitat. We examined whether diet composition of the Red-legged Salamander, Plethodon shermani, differed between salamanders found on vegetation and on the ground surface. Contrary to the results of a previous study, we found that the overall number and mass of prey items did not differ between salamanders in these two microhabitats. Furthermore, we found no evidence that the relative use of different prey categories varied in relation to a salamanders selected microhabitat. Although salamanders of all body sizes had consumed a diverse range of prey items, we found evidence of an ontogenetic shift in prey utilization, with smaller salamanders consuming a significantly greater number of prey items than larger salamanders while there was no relationship between body size and mass of prey consumed.