EEB Seminar: September 26th

This week, we welcome our own Regan Cross and Matt Macpherson.

Abstract:  Populations of many snake species around the globe are in decline as a result of anthropogenic threats such as road mortality. To reduce road mortality, wildlife barrier fencing is often used, albeit with varying levels of success. Given how adept gray ratsnakes (Pantherophis spiloides) are at climbing and the relatively large size they reach, this Threatened species serves as a good system for testing mitigation fencing as they can act as an umbrella species for other, smaller Ontario snakes. In this experiment, the exclusion potential and behavioural response of gray ratsnakes to different types of barrier fencing were assessed. We expect fencing material, height, and/or shape to determine an individual’s success in climbing over it. Gray ratsnakes were tested in circular testing arenas 2m in diameter, and constructed of eight different combinations of fencing materials, heights, and shapes based on the recommendations of the OMNRF’s best management practices for reptiles and amphibians. The behavioural responses, such as success in climbing over the fencing, number of climbing attempts made, and time taken to escape were video-recorded for each snake. Morphometrics and ground temperature were also recorded, as these factors can also affect a snake’s climbing ability. For each of the fencing combinations a minimum of 10 trials were performed (88 trials in total). Preliminary results show that the snakes had the most success escaping from the 0.6 m tall vinyl sheet fencing with a lip (100% escaped), and the most difficulty escaping from the 1 m tall hardware cloth fencing with a lip (only 6.7% escaped). Our study will inform the use of barrier fencing to reduce snake road mortality, thus helping to conserve snake populations at risk and apportioning limited resources for conservation more effectively.

Abstract: Species should be able to continuously adapt to conditions at their geographic range edges and disperse into the habitat beyond, yet most do not. Experimental planting of species within and beyond their range directly tests the mechanisms causing stable range limits, however experimental populations are rarely followed for more than one generation, providing little insight into long-term demography and potential for local adaptation beyond the range. In 2005, we transplanted eight source populations of the Pacific coastal dune plant Camissoniopsis cheiranthifolia into four sites within and one site beyond its northern range limit. Fitness of beyond-range individuals was comparable to within-range populations, suggesting that the northern range edge is limited by dispersal rather than niche constraints. Compared to sites within the range, the beyond-range population experienced high seedling recruitment in the two seasons following the transplant. Approximately 12 generations after planting, beyond-range individuals remained as abundant and reproductively successful as within-range individuals, providing compelling support for a role of dispersal in limiting the northern range edge for this species. Long-term experiments such as this provide robust conclusions in the face of environmental stochasticity, and allow for a better understanding of how species respond to novel habitats.