Gabriel Blouin-Demers

THERMAL ECOLOGY OF BLACK RAT SNAKES (ELAPHE OBSOLETA) IN A THERMALLY CHALLENGING ENVIRONMENT

A general model in thermal ecology predicts that ectotherms should stop thermoregulating when the costs outweigh the benefits. Support for this model comes from studies of warm-temperate species, but the extent to which the model can be extrapolated to species living in climatic extremes is unknown, because of the lack of information regarding the thermoregulatory behavior of such species. We tested the applicability of this cost-benefit model using data for black rat snakes (Elaphe obsolete obsoleta) studied at the northern extreme of their range in Ontario. During 1997-1999, we used automated temperature-sensitive radiotelemetry to collect -150000 body temperatures from 53 free- ranging rat snakes. Simultaneously, we used physical models of snakes to measure the environmental operative temperatures available to black rat snakes, and we determined their preferred body temperature range in a laboratory thermal gradient. The mostly forested habitats inhabited by rat snakes in Ontario were more thermally challenging than the habitats of other species studied to date. The preferred body temperature ranges of male, nongravid female, and gravid female black rat snakes were not significantly different (preferred body temperature averaged across all individuals, 28. 1C). However, free-ranging gravid females tended to maintain higher body temperatures in order to thermoregulate more effectively as well as exploit their thermal environment more than males and nongravid females. This difference was most pronounced during the day and prior to egg laying, and constituted the first documentation of such a phenomenon in an oviparous snake. Black rat snakes had indices of thermoregulation effectiveness similar to other species but tended to exploit opportunities for thermoregulation less. Overall, our data provided support that was at best ambiguous for the current cost-benefit thermoregulation model, suggesting that this model may generally be less applicable to species inhabiting climatic extremes. We propose that, for species in extreme climates, the costs associated with thermoconformity may be more important than previously recognized. We identified several problems associated with the index of thermoregulation effectiveness used by previous researchers, and we propose a mathematically simpler alternative that circumvents these problems. We also make rec- ommendations regarding the future use of the various indices of thermoregulation developed in recent years.

HABITAT USE BY BLACK RAT SNAKES (ELAPHE OBSOLETA OBSOLETA) IN FRAGMENTED FORESTS

Declining nest success of forest birds in fragmented habitat has been attri- buted to increased nest predation. Better understanding of this problem and potential so- lutions to it require information on why nest predators are attracted to habitat edges. Toward this end we investigated habitat use by black rat snakes (Elaphe obsoleta obsoleta), an important avian-nest predator in eastern deciduous forests. We radio-tracked 52 black rat snakes for periods of 3-41 mo from 1996 to 1999. All black rat snakes exhibited a strong preference for edge habitats. Consistent with edges being used because they facilitate thermoregulation, gravid females associated more strongly with edges than did males and nongravid females, and sites used by snakes when shedding were significantly associated with habitat edges. Gravid females lost an average of >20% of their body mass, while nongravid females and males did not lose mass, suggesting that edges were not used because they offered high success in foraging. Similarly, an increase in use of edge habitat through the season by all rat snakes was inconsistent with the snakes being attracted principally to hunt: avian prey would have been more abundant in spring when birds were breeding, and the density of small mammals in edges did not vary seasonally. Also, snakes moved longer distances and were found traveling.more often when located in forests. Because our results collectively are most consistent with the hypothesis that rat snakes use edges for ther- moregulatory reasons, the negative impact of the snakes on nesting birds may be coinci- dental; the snakes primarily use edges for reasons other than foraging but opportunistically exploit prey they encounter there. Rat snakes appeared to respond to the edge structure rather than to how the edge was created (natural vs. artificial). Thus, fragmentation of forests by humans has created habitat structurally similar to that preferred by rat snakes in their natural habitat, thereby inadvertently increasing contact between the snakes and nesting birds.

Kernels are not Accurate Estimators of Home-Range Size For Herpetofauna

Abstract Kernel home-range estimators are becoming more widely used to determine the home-range size for herpetofauna, despite the problems associated with selecting the appropriate smoothing factor. We used simulations to demonstrate the inconsistency of kernel estimators at determining the home-range size of random distributions. Furthermore, we used the positions of ten adult male Lampropeltis triangulum radio-tracked over two full active seasons (2003 and 2004) to demonstrate that the size of the home range increases significantly with an increase in the smoothing factor. The degree of increase, however, was not consistent between individuals. In addition, using least-squares cross-validation to select the smoothing factor produced a wide range of values for different individuals. Because of these inconsistencies, we suggest using the minimum convex polygon (MCP) method to calculate home-range size in studies of herpetofauna. When studying habitat use, however, we suggest using the MCP as the area of the home range and adjusting the smoothing factor until the area of the 95% kernel equals the area of the MCP. This provides an objective method for selecting the smoothing factor.

THE COST–BENEFIT MODEL OF THERMOREGULATION DOES NOT PREDICT LIZARD THERMOREGULATORY BEHAVIOR

Physiological processes are optimized within a narrow range of body temperatures. Reptiles engage in behavioral thermoregulation to achieve the optimal body temperature range. Interestingly, however, thermoregulatory effort varies over time and across species. The cost–benefit model of thermoregulation of R. B. Huey and M. Slatkin is the only conceptual framework that attempts to explain the observed variation. The model postulates that reptiles should engage in thermoregulation when the costs incurred do not outweigh the benefits. The main cost is the thermal quality of the environment: thermoregulation is more costly in habitats of low thermal quality. We used thermal quality of the habitat, measured by the deviations of operative temperatures from the preferred body temperature range, as an indicator of costs and two quantitative indices of thermoregulation as indices of thermoregulatory investment. Regressions of the indices of thermoregulation on thermal quality of the habitat produced no pattern or ...

Thermal quality influences effectiveness of thermoregulation, habitat use, and behaviour in milk snakes

We investigated the link between thermal quality and the effectiveness of thermoregulation in milk snakes in a thermally challenging environment. We defined thermoregulatory effectiveness as the extent to which an individual maintains its body temperature (Tb) closer to the preferred range (Tset) than allowed by the thermal quality of its environment. We defined thermal quality as the magnitude of the difference between operative environmental temperatures (Te) and Tset. Because ectotherms regulate body temperatures through choice of habitat and behavioural adjustments, we also examined the link between thermoregulation, habitat use and behaviour. During 2003–2004, we located 25 individuals 890 times, and recorded their Tb. Thermal quality was lower in the spring and fall than in the summer, and was lower in forests than in open habitats. Milk snakes thermoregulated more effectively in the spring than in the summer and fall, and more effectively in the forest than in open habitats. Milk snakes had a strong preference for open habitats in all seasons, which was likely to facilitate behavioural thermoregulation. The preference for open habitats was equally strong in all seasons and, therefore, the higher effectiveness of thermoregulation was not a result of altered habitat use. Instead, milk snakes modified their behaviour and were seen basking more and moved less in the spring than in the summer.

Thermorégulation and habitat selection in wood turtles Glyptemys insculpta: chasing the sun slowly

1. It is widely accepted that reptiles are able to regulate behaviourally their body temperature (T(b)), but this generalization is primarily based on studies of lizards and snakes in the temperate zone. Because the precision of T(b) regulation may vary considerably between taxa and over geographical ranges, studies of semi-terrestrial turtles in climatic extremes are relevant to the understanding of reptilian thermoregulation. 2. We studied thermoregulation in 21 free-ranging wood turtles (Glyptemys insculpta) at the northern limit of their range in Québec, using miniature data loggers to measure their internal T(b) and external temperature (T(ext)) continuously. We simultaneously recorded the available operative environmental temperature (T(e)) using 23 physical models randomly moved within each habitat type, and we located turtles using radiotelemetry. 3. The habitat used by wood turtles was thermally constraining and the target temperature (T(set)) was only achievable by basking during a short 5-h time window on sunny days. Wood turtles did show thermoregulatory abilities, as determined by the difference between turtle T(b) distribution and the null distribution of T(e) that resulted in T(b) closer to T(set). Although most individuals regulated their T(b) between 09.00 h and 16.00 h on sunny days, regulation was imprecise, as indicated by an index of thermoregulation precision (| T(b) - T(set) |). 4. The comparison of habitat use to availability indicated selection of open habitats. The hourly mean shuttling index (| T(ext) - T(b) |) suggested that turtles used sun/shade shuttling from 09.00 to 16.00 h to elevate their T(b) above mean T(e). 5. Based on laboratory respirometry data, turtles increased their metabolic rate by 20-26% over thermoconformity, and thus likely increased their energy gain which is assumed to be constrained by processing rate at climatic extremes.

Habitat distribution influences dispersal and fine-scale genetic population structure of eastern foxsnakes (Mintonius gloydi) across a fragmented landscape.

Dispersal is a fundamental attribute of species in nature and shapes population dynamics, evolutionary trajectories and genetic variation across spatial and temporal scales. It is increasingly clear that landscape features have large impacts on dispersal patterns. Thus, understanding how individuals and species move through landscapes is essential for predicting impacts of landscape alterations. Information on dispersal patterns, however, is lacking for many taxa, particularly reptiles. Eastern foxsnakes (Mintoinus gloydi) are marsh and prairie specialists that avoid agricultural fields, but they have persisted across a fragmented region in southwestern Ontario and northern Ohio. Here, we combined habitat suitability modelling with population genetic analyses to infer how foxsnakes disperse through a habitat mosaic of natural and altered landscape features. Boundary regions between the eight genetic clusters, identified through assignment tests, were comprised of low suitability habitat (e.g. agricultural fields). Island populations were grouped into a single genetic cluster, and comparatively low FST values between island and mainland populations suggest open water presents less of a barrier than nonsuitable terrestrial habitat. Isolation by resistance and least‐cost path analysis produced similar results with matrices of pairwise individual genetic distance significantly more correlated to matrices of resistance values derived from habitat suitability than models with an undifferentiated landscape. Spatial autocorrelation results matched better with assignment results when incorporating resistance values rather than straight‐line distances. All analyses used in our study produced similar results suggesting that habitat degradation limits dispersal for foxsnakes, which has had a strong effect on the genetic population structure across this region.

Anthropogenic noise affects song structure in red-winged blackbirds (Agelaius phoeniceus)

SUMMARY Anthropogenic noise can mask animal signals that are crucial for communicating information about food, predators and mating opportunities. In response to noise masking, signallers can potentially improve acoustic signal transmission by adjusting the timing, frequency or amplitude of their signals. These changes can be a short-term modification in response to transient noise or a long-term modification in response to chronic noise. An animals ability to adapt to anthropogenic noise can be crucial to its success. In this study, we evaluated the effects of anthropogenic noise on the structure of red-winged blackbird song. First, we manipulated the presence of anthropogenic noise by experimentally broadcasting either silence or low-frequency white noise to subjects inhabiting quiet marshes located away from roadsides. Subjects exhibited increased signal tonality when temporarily exposed to low-frequency white noise, suggesting that red-winged blackbirds can alter their signals rapidly in response to sudden noise. Second, we compared songs produced in quiet marshes located away from roadsides with songs produced during quiet periods at roadside marshes that are normally noisy. This allowed us to test whether birds that are exposed to chronic anthropogenic noise exhibit altered song structure during temporarily quiet periods. Subjects residing in roadside marshes that are normally polluted with anthropogenic noise sang songs with increased tonality during quiet periods. Overall, our results show that anthropogenic noise influences the structure of birdsong. These effects should be considered in conservation and wildlife management.

Comparative demography of black rat snakes (Elaphe obsoleta) in Ontario and Maryland

This study investigated how demographic characteristics of black rat snakes Elaphe obsoleta are affected by the length of the active season, and also used the resulting demographic data to determine the proximate factors responsible for male-biased sexual size dimorphism (SSD) in the species. Demographic data collected from 1981 to 1998 in Ontario (ON; 583 males and 588 females) and from 1942 to 1976 in Maryland (MD; 180 males and 150 females) were used to develop growth models with the von Bertalanffy growth equation. Instantaneous growth rates declined significantly with increasing snout–vent length (SVL) in males and females of each population. The growth models predicted age using SVL satisfactorily, but the accuracy of the model decreased significantly with increasing SVL. As predicted, based on the brevity of their active season (ON [ape ] 135 days, MD [ape ] 190 days), rat snakes of both sexes from Ontario had lower and more variable instantaneous growth rates and matured at a more advanced age (ON [ape ] 9 years, MD [ape ] 4 years) than snakes from Maryland. However, the rapid growth and early maturation in Maryland snakes occurred at the expense of longevity (maximum: ON [ape ] 30 years, MD [ape ] 20 years). Slower growth and later maturation will make rat snakes in Ontario less capable of recovering from population declines. Within each population, males grew faster than females. Survivorship for Ontario snakes did not vary by sex, but increased significantly with increasing SVL. The demographic consequence of sex differences in growth was a male-biased sex ratio among larger snakes. Because SSD is a function of males growing faster than females, SSD in black rat snakes is probably a product of sexual selection, suggesting that large size confers a mating advantage in males.

Freshwater Commercial Bycatch: An Understated Conservation Problem

Bycatch from marine commercial fisheries has been regarded as a global conservation concern for decades. Fortunately, some headway has been made in mitigating bycatch problems in marine fisheries. Freshwater commercial fisheries, however, have been relatively understudied. Although freshwater yields comprise 11% of the global commercial catch, bycatch research focusing on freshwater commercial fisheries represents only about 3% of the total bycatch literature. This paucity of research is particularly alarming given that so many of the worlds threatened species live in freshwater. The limited literature that does exist includes examples of population declines attributed to commercial bycatch (e.g., the Yangtze River dolphin) and illustrates that bycatch is substantial in some systems (e.g., lake trout in Laurentian Great Lakes fisheries). Encouraging results from the marine realm can serve as models for bycatch research and development in freshwater and can lead to measurable gains in the conservation of freshwater ecosystems. We summarize existing work on inland bycatch in an effort to draw attention to this understated and understudied conservation problem.