We compare diet and feeding behaviour of Snapping Turtles (Chelydra serpentina) and Midland Painted Turtles (Chrysemys picta marginata) in Algonquin Provincial Park, Ontario, Canada. We observed young Chelydra and Chrysemys turtles feeding on insect and amphibian larvae in ephemeral ponds, adult Chrysemys terrestrially foraging on odonate larvae, and adult Chelydra consuming aquatic vegetation and seeds. These and other observations highlight the importance of seasonally available habitat and food for juvenile turtles. We also discuss the evidence for, and importance of, turtles as seed-dispersal agents for aquatic vegetation. Illustrative video recordings accompany our dietary observations.

Organisms with multiple biotic attributes may also have conflicting niche determinants, and we assessed whether the realized niche reflects single or multiple biotic attributes. A group of all-female salamanders found in eastern North America (unisexual salamanders; Ambystoma spp.) embody two potentially competing biotic states: hybridism and obligate reproductive parasitism. In theory, hybrids should occupy areas that are transitional to those used by parental species, parasites must live in syntopy with their hosts, and parasites that engage in ecological competition with hosts should be most successful in habitats that are moderately suitable for hosts. We built niche models for bisexual salamanders (Ambystoma laterale and Ambystoma jeffersonianum), as well as for unisexual Ambystoma that posses nuclear DNA from both of these species. These unisexuals are both phenotypic hybrids and obligate reproductive parasites of the bisexual species. We characterized realized niches predicted for unisexual Ambystoma via a hybrid-framework model (e.g., using environmental predictors) and a parasite-framework model (e.g., using host suitability predictors). Model validation using ancillary data permitted evaluation of which biotic state (hybrid vs. parasite) fit the observed patterns of occupancy. The hybrid model conformed strongly with predictions that the unisexual niche would be transitional between A. laterale and A. jeffersonianum bisexuals. Average annual temperatures and terrestrial salamander species richness (a proxy for competition) were particularly descriptive of parental niches and hybrid occupancy of transitional environments. While the parasite model behaved as expected, model validation did not fully corroborate its utility for determining patterns of occupancy. Instead, model selection revealed that the hybrid model was more descriptive of unisexual occurrence than the parasite model. Despite the fundamental importance of reproductive parasitism to the persistence of unisexual Ambystoma, we suggest that hybridism has greater contribution to the realized niche. When species have competing ecological attributes, one primary biotic state may dominate as a determinant of the realized niche.

The Mudpuppy (Necturus maculosus) is an entirely aquatic salamander whose geographic range is thus defined by immigration routes in watersheds that permit feasible travel. Significant barriers, such as large waterfalls, effectively bar this species from further colonization upstream. We compared the contemporary distribution of Mudpuppies in southern Ontario with varying post-glacial ancient lake maxima and riverine outlet-flow conditions. Topography does not appear to be a range-limiting factor, but the type of river grade (waterfalls versus riffles) does. The distribution of modern records of this species in Ontario aligns closely with maxima from the Nipissing phase occurring 4000-5000 years ago, leading us to suggest that this is when Mudpuppies invaded and proliferated in the Great Lakes Basin.