PARENT SESSION
Contributed Oral Session 17: Reptiles and Amphibians: Habitat; and Communities
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal
Mechanisms underlying long-term fluctuations in a subalpine population of tiger salamanders.
Wissinger, Scott*,1, 3, Whiteman, Howard 2, 3, 1 Biology Department, Meadville, PA, USA3 Rocky Mountain Biological Laboratory, Crested Butte, CO, USA2 Department of Biological Sciences, Murray, KY, USA
ABSTRACT- Over the past 20 years, the population size of tiger salamanders (Ambystoma tigrinum nebulosum) in an isolated cluster of subalpine wetlands in Colorado has fluctuated from fewer than 100 to more than 5000 individuals. Historical data and anecdotal observations suggest a multi-decadal history of population cycles. For the past 15 years, we have closely monitored recruitment, mortality, and life history trajectories of all life stages in this population (metamorphic adults, paedomorphic adults, multiple year classes of larvae) through an intensive mark-recapture program. Demographic data suggest that fluctuations are partly related to the cyclic production of dominant cohorts that subsequently suppress recruitment. Fluctuations in the abundance of salamanders are correlated with an order-of- magnitude change in the biomass of benthic and planktonic invertebrate prey. We hypothesized that cannibalism and/or resource depression by dominant cohorts suppress recruitment during the decline phase of cycles. Experiments in mesocosms, and dietary data from natural populations provide evidence that cannibalism by paedomorphs on small salamander larvae can explain the low survival of larvae, even in years in which there are initially large hatchling cohorts. In addition to the lethal effect of cannibalism, paedomorphs have several sublethal effects on smaller conspecifics including reduced foraging activity and growth, and increased injury. In separate experiments, we found little evidence to support the hypothesis that paedomorph-induced resource depression has a major effect on the growth and survival of small larvae. Our results are consistent with the hypothesis that the population cycles at our study site are driven mainly by intrinsic mechanisms, and can be explained without invoking climatic or human-induced extrinsic factors. Understanding the mechanisms that underlie natural population cycles in amphibians is critical for distinguishing them from amphibian declines related to anthropogenic causes.
Key words: population cycles, cannibalism, resource depression, amphibian decline