Understanding habitat requirements of species is fundamental for their conservation. Comparing habitat variables measured at locations where animals are found to random locations is one method of understanding how a species uses its habitat non-randomly. Northwestern gartersnakes (Thamnophis ordinoides) are common in parks in Victoria, but their specific habitat requirements are poorly understood. Victoria’s parks vary in habitat composition from mature Douglas-fir forest to Garry Oak meadow, with open grassy areas, to parking lots and patches of dense invasive shrubs. Based on previous studies and thermoregulatory needs of snakes, I predicted that substrate temperature and distance to edge would be of greatest importance in determining where snakes would be found. From May to September, 2012 I captured 124 northwestern gartersnakes by hand on random transects and habitat edge surveys. At capture locations and randomly chosen points nearby I measured the composition and structure of vegetation, as well as abiotic factors such as substrate temperature, aspect and slope. Also, I used air photos and GIS to determine proportional use of broad habitat types at home range scale. I found differential use of habitat between the sexes in relation to the proportion of herbaceous vegetation and organic litter. Northwestern gartersnakes generally use locations that are warmer than random locations, though individuals that have fed recently have a greater thermophilic response than snakes that have not. Overall, at small scale, distance to edge was the most important variable measured. At large scale, estimated home ranges contained more open ground as northwestern gartersnake snout-vent-length (SVL) increased (presumably because they had fewer potential predators and could more afford to use open habitats). These results support my hypothesis that warm locations that are close to habitat edges are important habitat for northwestern gartersnakes. The parks at which I conducted surveys appear to have large populations of northwestern gartersnakes with abundant habitat. However, the fact that habitat is used does not necessarily indicate that it is of high quality, and further research is required to determine if these populations are stable, increasing, or decreasing. / Graduate / 0329 / grahamdm@uvic.ca
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/5081 |
| Date | 13 December 2013 |
| Creators | Dixon-MacCallum, Graham |
| Contributors | Gregory, Patrick T. |
| Source Sets | University of Victoria |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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