Physical barriers are known to limit species' ranges, but, in the absence of physical barriers, what prevents adaptation and expansion at the periphery? Genetic influence from central populations may prevent adaptation to ecological barriers by swamping peripheral populations with suboptimal genes. If this is the case, then isolation may enable local adaptation and further range expansion. Barriers such as rivers provide ideal tests of the influence of gene flow and may explain differences in range sizes. This study investigates northern range limitations and phylogeography of the Northern Two-lined ( Eurycea bislineata) and Northern Dusky (Desmognathus fuscus ) stream salamanders. Phylogeographic patterns of populations throughout Quebec and Labrador were investigated by sequencing portions of cytochrome b and 12S rRNA mitochondrial DNA genes. Interpopulation divergence was low for both species, however, unique genetic haplotypes and morphological variation on the north shore of the St. Lawrence indicate that the river is acting as a barrier to gene flow.

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 2001. / Document électronique également accessible en format PDF. CaQCU

Universiẗat, Diss., 2001--Bremen.

Coexistence among ecologically similar species is often facilitated through temporal or spatial partitioning mechanisms that reduce or eliminate direct interaction. However, in many communities exhibiting guild structure, wherein potential competitors may also prey on one another, sympatric relationships persist despite species' similar life history strategies, spatial and temporal restrictions imposed by ephemeral habitats, and resource limitations that promote competition and predation. To identify the ecological roles of species-specific behavioral patterns within aquatic guilds, I quantified larval intraspecific agonistic behavior among two species of intraguild (IG) predators, Ambystoma opacum and A. tigrinum, and their shared intraguild prey, A. maculatum. All species exhibited similar ontogenetic patterns of aggression, characterized by peaks of aggression early in development and subsequent gradual decreases through metamorphosis. However, the intensity of aggression varied considerably among guild species through development, as did behavioral responses to varying levels of ambient water temperature, invertebrate prey density, and presence of predatory odonate naiads. The observed patterns suggest that guild species, despite morphological and physiological similarities, exhibit unique behavioral responses through ontogeny and in response to habitat variables, suggesting that temporally staggered breeding phenologies have contributed to behavioral divergence among these sympatric congeners. However, in situ observations of larval behavior, although largely in agreement with laboratory results on timing of increased aggression, indicated that IG predators exhibited pond-level species partitioning and do not necessarily co-occur despite being regarded as sympatric. These results, taken together with observed species-specific impacts of IG predators on IG prey, suggest that ecologically similar IG predators exert widely differing predatory pressure on shared prey, and that similarities among guild species may ultimately result in habitat partitioning across local scales.

For many animals, rapid movements place high power demands on underlying muscles. Storage of muscle energy in elastic structures and the subsequent rapid release of that energy can effectively amplify muscle power. Elastic recoil can also confer thermal robustness to performance in behaviors occurring at variable temperatures. Muscle contractile performance tends to decrease at lower temperatures, but elastic recoil is less affected by temperature. Here I examine the impacts of temperature and scale in systems using elastic recoil and I explore possible interactive effects on movement performance. I explored the role that muscle contractile properties play in the differences in performance and thermal robustness between elastic and non-elastic systems by examining muscles from two species of plethodontid salamanders with elastically powered tongue projection and one with non-elastic tongue projection. These salamanders use tongue projection to capture prey and in species with elastic mechanisms, tongue projection is characterized by higher mechanical power output and thermal robustness compared to tongue projection of closely-related genera with non-elastic mechanisms. In vitro and in situ muscle experiments reveal that species differ in their muscle contractile properties, but these patterns do not predict the performance differences between elastic and non-elastic tongue projection. Overall, salamander tongue muscles are like other vertebrate muscles in contractile performance and thermal sensitivity. I conclude that changes in the tongue-projection mechanism, specifically the elaboration of elastic structures, are responsible for high performance and thermal robustness in species with elastic tongue projection. This suggests that the evolution of high-performance and thermally robust elastic-recoil mechanisms can occur via relatively simple changes to morphology, while muscle contractile properties remain relatively unchanged. The efficacy of elastic recoil in the face of changing temperature depends on the mechanical work done by muscle contraction being unaffected by temperature. In vitro stimulation of Cuban tree frog (Osteopilus septentrionalis) plantaris muscles reveals that interactions between force and temperature affect the mechanical work of muscle. At low temperatures (9 – 17°C), muscle work depends on temperature when shortening at any force, and temperature effects are greater at higher forces. At warmer temperatures (13 – 21°C), muscle work depends on temperature when shortening with intermediate and high forces (≥ 30% peak isometric tetanic force). Shortening velocity is most strongly affected by temperature at low temperatures and high forces. Power is also most strongly affected at low temperature intervals but this effect is minimized at intermediate forces. Effects of temperature on muscle force explain these interactions; force production decreases at lower temperatures, increasing the challenge of moving a constant force relative to the muscle’s capacity. These results suggest that animal performance that requires muscles to do work with low forces relative to a muscle’s maximum force production will be robust to temperature changes, and this effect should be true whether muscle acts directly or through elastic-recoil mechanisms and whether force is prescribed (i.e. internal) or variable (i.e. external). Conversely, performance requiring muscles to shorten with relatively large forces is expected to be more sensitive to temperature changes. How muscle work and power scale determines, in part, the scaling of movement performance. Muscle-mass-specific work is predicted to remain constant across a range of scales, assuming geometric similarity, while muscle-mass-specific power is expected to decrease with increasing scale. I tested these predictions by examining muscle morphology and contractile properties of plantaris muscles from frogs ranging in mass from 1.28 to 20.60 g. Scaling of muscle work and power was examined using both linear regression on log10-transformed data (LR) and non-linear regressions on untransformed data (NLR). In LR, muscle-mass-specific work decreased with increasing scale, but this is counteracted by a positive allometry of muscle mass to predict constant movement performance at all scales. These relationships were non-significant in NLR, though scaling with geometric similarity also predicts constant jump performance across scales. Both intrinsic shortening velocity and muscle-mass-specific power were positively allometric in both types of analysis. However, these differences between methods are caused not by large changes in scaling slopes, but by changing levels of statistical significance using corrections for multiple tests. The dependence of these conclusions on the method of regression, largely because of the setting and adjusting of an arbitrary alpha, demonstrates the importance of careful consideration of statistical methods when analyzing patterns of scaling. Nonetheless, scale accounts for little variation in contractile properties over the range of scales examined, indicating that other sources of intraspecific variation may be more important in determining muscle performance and its effects on movement. Elastic recoil used for power amplification is most often found in smaller animals, suggesting that performance in larger animals using less elastic recoil would be affected more by changing temperatures. To examine the interaction between scale and temperature on performance, I recorded jumps from 1-34 g Cuban tree frogs (Osteopilus septentrionalis) at 10, 20, and 30°C and compared jump performance to predictions based on the effects of temperature and scaling on muscle properties. High muscle-mass-specific power requirements from measured jumps indicate that frogs use elastic recoil at all scales to achieve performance that would be impossible using only muscle, and elastic recoil allows small frogs to achieve the same level of performance as large frogs. Performance that is greater at all temperatures than predictions from models using only muscle power could result from some combination of elastic recoil and power directly from muscle. The relative contributions of muscle power and elastic recoil cannot be discerned by examining temperature effects on performance because these effects are predicted to be so similar. Predicted performance from models of elastic recoil is significantly affected by changing temperature at all scales with temperature coefficient (Q10) values similar to predictions for muscle-powered jumping. Measured Q10 values are similar to those from both predictive models and there is no interaction between temperature and scale. Therefore, elastic recoil allows for jump performance that could not be achieved by muscle power alone at all temperatures and scales, but performance predictions from elastic recoil are not more thermally robust than predictions for muscle-powered jumping.

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Prescribed fire has increased as a forest management practice in southern Appalachia, but investigations into the effects of this silvicultural treatment on non-game wildlife inhabiting the region is limited. This study investigated the effects of prescribed fire on millipede and salamander populations. Seventeen sites within the Cherokee National Forest in east Tennessee that were treated once with prescribed fire between 1998 and 2002 were examined in the spring of 2002. Each burned plot was paired with an adjacent unburned plot. The number of individual millipedes and salamanders collected from burned plots was compared to the corresponding control plot. Millipedes declined in numbers following treatment with prescribed fire. The number of salamanders collected was insufficient to permit analyses comparing the number of salamanders found in burned and control sites. No difference between burned and control plots was detected in the species comprising the millipede communities.

In the Southern Appalachians, there are growing concerns about Spotted Salamanders (Ambystoma maculatum) due to habitat destruction and the uncertain future of their forested riparian habitat. In this study, I establish baseline data of a population of Spotted Salamanders so future monitoring of this population can be performed. The study site is located in northeastern Tennessee, just east of the city of Bristol. It is a vernal pond at the Osceola Island Recreation Area one mile below the South Holston Dam on Holston View Dam road. A drift fence was established completely around the perimeter of the vernal pond to capture Spotted Salamanders entering and exiting the study pond. Individual Spotted Salamanders were identified using spot pattern recognition. An estimated population size of 2,449 Spotted Salamanders was determined to utilized the pond for breeding for the spring of 2003.

In forested ecosystems, salamanders occupy important ecological roles as predator, prey and as potential regulators of ecological processes. The effects of forest management, particularly clearcut harvesting, on salamanders have been well documented; removal of overstory trees negatively affects abundances of salamanders. However, the length of time that salamander populations remain depressed following forest harvesting and factors limiting population recovery have been a source of controversy in the literature and are the goal of this dissertation. As part of the Southern Appalachian Silviculture and Biodiversity (SASAB) project (Chapter 1), a long-term replicated field experiment designed to evaluate a range of silvicultural treatments on biodiversity, I evaluated specific hypotheses related to salamander populations, their prey, and their habitat. First, I examined long-term trends in salamander abundances across a range of silvicultural treatments to determine whether negative effects of forest harvesting persisted for 13-years after harvest (Chapter 2) and to document the effects of multiple harvests on salamanders (Chapter 3). The relative abundances of terrestrial salamanders were quantified in six silvicultural treatments and an unharvested control and on six replicated field sites with night-time, area-constrained searches. Across 13-years of post-harvest data, terrestrial salamander abundances generally were lower in silvicultural treatments with some disturbance to the canopy (group selection harvest through silvicultural clearcut). Further, a comparison of demography of common species of salamanders suggested that differences in habitat quality existed between harvested and unharvested experimental units (EUs). A second harvest in the shelterwood plots to remove overwood had a cumulative negative effect on salamanders at one of two sites studied. Additionally, I conducted a sensitivity and elasticity analysis for eastern red-backed salamanders (Plethodon cinereus) and modeled population growth to evaluate the contribution of demographic parameters to population recovery. These analyses indicated that adult survival was the parameter with the greatest influence on the population growth rate and that >60 years would be required for recovery of salamander populations to preharvest levels even if habitat conditions were restored to preharvest conditions immediately. Next, I quantified the bioenergetics of salamanders across a disturbance gradient to evaluate whether changes to (1) invertebrate prey, (2) energy expenditure for basic maintenance costs, and or (3) an index to body condition could help explain observed changes to abundances or demography of salamanders from forest harvesting (Chapter 4). Although I did not detect a difference in abundances of invertebrates along the disturbance gradient, I determined that salamanders in recently disturbed forest stands expended approximately 33% more energy for basic maintenance costs in an active season and the body condition of salamanders was greater at one of two sites in disturbed EUs. Thus, the bioenergetics of terrestrial salamanders may have been affected by increasing temperatures from silvicultural disturbance and may cause salamanders to allocate less energy to reproduction or growth because of increased maintenance costs. In collaboration with Eric Sucre, Department of Forestry at Virginia Tech, I examined the effects of salamanders on invertebrates and ecosystem processes, specifically leaf litter decomposition. We constructed 12 in situ field mesocosms and I manipulated densities of red-backed salamanders into zero, low, and high density treatments. From June 2006-June 2008, I estimated invertebrate abundances, rates of leaf litter decomposition and food habits of salamanders across treatments. I found that invertebrate abundances were more affected by season than by the density of salamanders and that rates of leaf litter decomposition did not differ among salamander treatments. Salamanders were euryphagic and consumed more (by abundance and volume) herbivorous invertebrates than predators or detritivores. Finally, I modeled habitat relationships of terrestrial salamanders at two spatial scales on the SASAB study sites (Chapter 6). I quantified abundance of salamanders with area-constrained searches during warm rainy nights and measured forest characteristics related to foraging or refugia habitats or that described the overstory and understory of forest stands. At the scale of the 30 m2 transect and the 10 m2 sub-transect, abundance of salamanders was best described by models that incorporated descriptors of canopy cover and woody and herbaceous understory vegetation. Thus, terrestrial salamanders may have responded positively to forest stands with a mature overstory and structurally diverse understory for foraging habitat. Collectively, these data suggest that recovery of salamander populations after forest harvesting will take approximately 60 years, and that life history characteristics (low fecundity, late sexual maturity) and possibly changes to bioenergetics may contribute to the slow recovery. Further, silvicultural practices that retain some canopy trees through a rotation may have a more rapid return of salamander populations to preharvest levels and may encourage development of understory structure for salamander foraging. Although these data fill some gaps in knowledge of relationships between silviculture and terrestrial salamanders, many questions about long-term effects of disturbances on populations and habitats remain. My modeling of recovery of salamander populations depended on estimates of a survival from a congener, and I did not document whether forest harvesting decreases survival of terrestrial salamanders. Lastly, the influence of stochastic events on population dynamics particularly in disturbed stands was not examined in this dissertation. Therefore, future research on the SASAB study sites should continue to track abundances and demography across the disturbance gradient, acquire age-specific estimates of survival, determine whether salamanders exhibit density dependence, develop estimates of entire energy budgets, and use manipulative laboratory experiments to describe the role of plethodontid salamanders in ecosystem functions. / Ph. D.

In the southeastern United States, ephemeral wetlands in pine flatwoods provide important habitat for amphibians and aquatic invertebrates, but extensive deforestation has destroyed or isolated many wetlands and fire suppression has altered vegetation in others. My goals were to identify how wetland hydroperiods have changed through time and to examine the effects of long-term fire suppression on aquatic communities, including Reticulated Flatwoods Salamanders (Ambystoma bishopi) and Ornate Chorus Frogs (Pseudacris ornata). Chapter 1 used a modeling approach to relate wetland hydroperiods to current climate conditions and to hindcast historic conditions. Over the past 118 years, hydroperiods were often unfavorable for A. bishopi reproduction, and in recent years hydroperiods were shortened by persistent drought. Chapters 2 and 3 focused on identifying the effects of shifting from an open, grass dominated wetland to a wetland with high canopy cover and little herbaceous vegetation. In Chapter 2, I quantified amphibian and invertebrate communities in several wetlands. A. bishopi and P. ornata tended to occupy wetlands with lower canopy cover and higher herbaceous vegetation cover. Aquatic invertebrate abundance was generally higher in wetlands with lower shrub density and lower canopy cover. In Chapter 3, I examined how a reduction in herbaceous vegetation affected tadpoles when a predatory crayfish was present using two experiments. Crayfish were effective predators of both species across all vegetation treatments and often caused nonlethal tail injury. My results suggest that managers should focus on ensuring that wetland basins regularly burn, and wetlands with longer hydroperiods should be a management priority. / Master of Science