Hossie, Thomas J

Amphibian biodiversity is in global decline, driven primarily by habitat loss and fragmentation arising from landcover alteration. For pond-breeding amphibians, larval abundance should be governed by aquatic breeding site quality, surrounding terrestrial habitat characteristics, and proximity to neighbouring populations. If safeguarding salamander populations is a priority, conservation efforts will benefit from understanding the relative importance of each feature on salamander populations. I sought to identify the factors associated with relative abundance of Ambystoma salamander larvae across habitat patches on Pelee Island, Ontario, Canada. Larval density and a suite of environmental variables were measured at 34 breeding sites across the island. Using spatial analysis, I also determined landcover features surrounding the breeding site, including, terrestrial habitat type, terrestrial patch size, and indices of isolation (e.g., nearest neighbour distance, proximity index). The relative abundance of Ambystoma larvae was best predicted by additive effects of breeding site quality (e.g., canopy cover, submergent vegetation, and cooler water temperature) and size of surrounding terrestrial habitat patches. I did not detect any influence of agricultural land cover within 300 m of the breeding sites on larval count, implying that Ambystoma can persist within agriculture-dominated landscapes provided that high breeding habitat quality is maintained, and ponds are embedded within large forest patches. Further, I failed to detect any impact of breeding site isolation on larval numbers, indicating that local habitat quality and terrestrial patch size more strongly determine larval abundance than patch connectivity. My research highlights the critical importance of conserving high-quality aquatic breeding habitats and maintaining large contiguous patches of terrestrial habitat for amphibian

Author Keywords: Amphibian, Anthropogenic impacts, Biodiversity conservation, Habitat fragmentation, Habitat suitability, Salamanders

Calcium (Ca) limitation and sodium chloride (NaCl) toxicity tolerance are potential controllers of Daphnia populations. D. pulicaria neonates collected from 14 Kawartha Highland lakes were exposed to 6 Ca concentrations (0.5-5.0 mg Ca L-1) over 6 days. We did not find differences in maximum mass-specific growth rate or half-maximum thresholds between source lakes. Growth rates were reduced <1.5 mg Ca L-1, and there was a significant interaction between Ca and source lake lineage. We also compared log-logistic NaCl dosage models estimating 48-hour lethal concentration (LC)10, LC25, and LC50 by exposing 9 clones to 10 concentrations, 18-2700 mg Cl L-1. Survivorship decreased >1500 mg NaCl L-1, and there were differences between lake lineage LC50 estimations. This suggests our D. pulicaria genotypes may not have experienced extreme enough selection pressure from either stressor to develop local adaptation, but allele variability between lakes may explain differences in NaCl toxicity and Ca limitation responses.

Author Keywords: Calcium, Daphnia, Mass Specific Growth Rate, Sodium Chloride, Toxicity, Zooplankton