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UBC Theses and Dissertations

Effects of forest cover and food limitation on the growth and survival of juvenile and adult Northwestern salamanders (Ambystoma gracile Baird) Hilton, Alana


Forest harvesting alters microclimate and structure, which may affect amphibians directly, as well as affect the abundance, diversity and/or availability of amphibian prey. As a result, the foraging efficiency of amphibians in harvested areas may be reduced, lowering body condition, and perhaps survival. I experimentally tested the hypotheses that: 1) body condition would be lower in clearcuts than forested sites; and 2) salamanders would be food limited in clearcuts but not in forest, and food addition to clearcut enclosures would improve body condition, while food addition to forest enclosures would have no effect. We used 24 large-scale field enclosures in a randomized split-plot block design (3 blocks) with forest type (1 clearcut and 1 forest site in each block) and food level (supplemental mealworms, ambient) as factors to examine the effects on growth and survival of adult and juvenile northwestern salamanders. In trial one, which started in October 2003, each of the 24 enclosures received 14 marked and measured juveniles. Juveniles were recaptured and remeasured in April/May 2004. In trial two, each of the enclosures received 7 marked and measured adult salamanders in May 2004, and adults were recaptured and remeasured in October/November 2004. Mealworms were added weekly to half the enclosures at each site. We used an analysis of variance to test for differences between clearcut and forest, supplemental food and ambient food, and any interactions on the weight change of animals and on the proportional survival for each enclosure. We found no significant effect of forest type or food level on growth of juveniles or adults, or on proportion of juveniles recaptured at the end of the experiment. However, for adults, there was a significant effect of forest type on the proportion recaptured (p < 0.001), with fewer animals recaptured in clearcut enclosures. These results indicate that clearcuts may provide unsuitable habitat for salamanders during summer in the Pacific Northwest, but not during winter.

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