Primary Drivers of Reptile Overwintering Habitat Suitability: Integrating Wetland Ecohydrology and Spatial Complexity

Identifying ecosystems resilient to climate and land-use changes is recognized as essential for conservation strategies. However, wetland ecosystems may respond differently to stressors depending on their successional state and the strength of ecohydrological feedbacks resulting in fluctuations in habitat availability and suitability. Long-term habitat suitability is necessary for the persistence of wetland-dependent species and a key characteristic of climatic refugia. In the present article, we review and synthesize biogeochemical, thermal, ecological, and hydrological feedbacks and interactions that operate within wetlands and, consequently, regulate overwintering suitability for many freshwater turtles and snakes. We propose that understanding the breadth and interconnected nature of processes controlling temperature, dissolved oxygen, and water table position are vital for the conservation of northern reptile populations that depend on wetlands to survive winter conditions. Finally, we suggest that our integrated framework can guide future research and the management of wetland ecosystems in an era of unprecedented change.

Colonization and usage of an artificial urban wetland complex by freshwater turtles

Conservation authorities invest heavily in the restoration and/or creation of wetlands to counteract the destruction of habitat caused by urbanization. Monitoring the colonization of these new wetlands is critical to an adaptive management process. We conducted a turtle mark-recapture survey in a 250 ha artificially created wetland complex in a large North American city (Toronto, Ontario). We found that two of Ontario’s eight native turtle species (Snapping turtle (SN), Chelydra serpentina, and Midland Painted (MP) turtle, Chrysemys picta marginata) were abundant and both were confirmed nesting. The Blanding’s turtle (Emydoidea blandingii) was present but not well established. Species richness and turtle density were not equally distributed throughout the wetland complex. We noted SN almost exclusively populated one water body, while other areas of the wetland had a varying representation of both species. The sex ratios of both SN and MP turtles were 1:1. We tracked the movement of Snapping and Blanding’s turtles and found that most turtles explored at least two water bodies in the park, that females explored more water bodies than males, and that 95% of turtles showed fidelity to individual overwintering wetlands. We performed DNA analysis of two Blanding’s turtles found in the created wetlands and could not assign these turtles to any known profiled populations. The genetic data suggest that the turtles probably belong to a remnant local population. We discuss the implications of our results for connectivity of artificial wetlands and the importance of the whole wetland complex to this turtle assemblage.

Postbreeding movement patterns and habitat use of adult Wood Frogs (Lithobates sylvaticus) at urban wetlands

Habitat loss and degradation linked to urbanization threaten amphibian populations globally, yet studies examining amphibian behaviour and habitat use in cities are rare. Through the use of radiotelemetry, we examined the postbreeding (May–October) movement behaviour and habitat use of adult Wood Frogs (Lithobates sylvaticus (LeConte, 1825)) at natural and constructed urban wetlands in Edmonton, Alberta, located in the semiarid, aspen parkland of Canada. Movement from breeding wetlands was limited, with most tracked individuals remaining within 25 m of ponds in grassy riparian areas. Long-distance migratory movements were rare and only occurred at natural sites with relatively high proportions of forested land surrounding wetlands. In general, tracked frogs showed a preference for habitat close to water that provided shelter from desiccation and predation (e.g., unmowed grass and stands of shrubs). Our findings have implications for the management of wetlands and conservation of amphibian populations in urban environments.

Turning the threat into a solution: using roadways to survey cryptic species and to identify locations for conservation

Freshwater turtles are one of the most imperilled groups of vertebrates globally, and roads have been associated with their decline. Although roads are typically viewed as an imminent threat to population persistence, because of direct mortality and increased landscape fragmentation, we argue that they are an important sampling tool for collecting a wide variety of data that can inform conservation efforts. Road surveys can yield important presence data when conducting species inventories, particularly for cryptic species, and can also indicate where to implement road mitigation measures. Our research examined three road survey methods from two previous studies (walking versus bicycling and walking versus driving) to test their relative effectiveness at locating turtles. We found that walking surveys yielded the highest number of turtles per kilometre; however, bicycling and driving surveys also presented advantages (specifically, the ability to survey longer lengths of road more quickly). We recommend using walking surveys in areas of specific interest (e.g. to investigate suitable habitat for imperilled species or to investigate the presence of cryptic species), and bicycling or driving surveys between sections of specific interest. Road survey methods could be used in addition to more traditional sampling approaches (e.g. trapping and visual surveys), and do not need to be restricted to areas where roadwork projects are in progress or being planned. Road surveys could also be used during general environmental assessments and ecological research, to effectively incorporate turtle presence data into conservation efforts.

Patterns of intraspecific aggression inferred from injuries in an aquatic turtle with male-biased size dimorphism

Patterns of sexual size dimorphism (SSD) in turtles are correlated with ecological mode, and it has been hypothesized that mating systems are also shaped by ecological mode. Male combat and coercive mating are competing explanations for male-biased SSD, but are difficult to assess empirically in aquatic species with cryptic behaviour. We quantified SSD and compiled observations of putative combat wounds collected from over 500 captures of Snapping Turtles (Chelydra serpentina (L., 1758)) in Algonquin Provincial Park, Ontario, to test hypotheses of mate competition and coercion. We found that both sex and body size were important predictors of risk of wounding, consistent with the hypothesis that male–male sexual competition is the primary driver of intraspecific aggression. Low wounding rates among females suggests that resource competition and coercive mating are not important causes of injuries. The risk of wounding increased monotonically with body size in adult males but not in adult females, and small males were less likely to be injured, suggesting that they employ a risk-averse strategy by avoiding direct competition for mates. There was no evidence of asymptotic or decreasing wounding probability in the largest males, which is consistent with the hypothesis that large males compete most intensively to monopolize mates.

Ecological specialisation in habitat selection within a macropodid herbivore guild

Specialist species show stronger resource selection, narrower niches and lower niche overlap than generalist species. We examined ecological specialisation with respect to habitat selection in a macropodid community comprising the western grey kangaroo Macropus fuliginosus, red-necked wallaby M. rufogriseus and swamp wallaby Wallabia bicolor in the Grampians National Park, Victoria, Australia. We used radio tracking to quantify habitat selection. We predicted that because the fitness benefits of generalisation and specialisation differ, there would be a mix of generalised and specialised species in our community. As all three macropodid species show marked sexual dimorphism, we also expected that they would show sex-based specialisation. Finally, because many large herbivores select different habitats for foraging and resting, we predicted that our species would specialise on a subset of their overall selected habitat based on activity period (diurnal or nocturnal). All three species specialised on the available resources to some degree. Western grey kangaroos were specialists, at least during the active period. Niche data for the two wallaby species were harder to interpret so we could not determine their degree of specialisation. Within species, we found no evidence of sex-based specialisation. However, we found clear evidence of specialisation by activity period in western grey kangaroos and red-necked wallabies, but not in swamp wallabies. The strength of behavioural decisions made during the active period in influencing specialisation points to the likelihood that bottom-up processes regulate this community.

Diet specialization in a generalist population: the case of breeding great tits Parus major in the Mediterranean area

The analysis of diet specialization provides key information on how different individuals deal with similar food and habitat constraints within populations. Characterizing parental diet specialization at the moment of breeding, and the consistency of these preferences under different levels of effort, may help us to understand why parents exploit alternative resources. We investigated these questions in a species commonly considered a generalist: a breeding population of Mediterranean great tits Parus major. Our aim was to determine whether they are specialists or generalists at the pair level, and the consistency of this behaviour under different levels of effort. Using proportional similarity and mean pairwise overlap indices, we found that parents showed great variability in prey selection between territories. That is, they displayed a small niche overlap. Interestingly, the most specialized breeding pairs showed a tendency to have larger broods. Additionally, we experimentally manipulated brood size and found that parents showed high short-term consistency in their foraging behaviour. They precisely adjusted the number of provisioning trips to the number of nestlings, while they were unable to modify prey proportions or prey size after brood size was changed. We can therefore characterize their foraging strategies as highly consistent. Our results suggest that although the great tit may be considered a generalist at the species or population level, there was a tendency for trophic specialization among breeding pairs. This high inter- and intrapopulation plasticity could account for their great success and wide distribution.