Abstract. Habitat isolation is well known to alter patterns of species' abundance, richness, and the ratios of predators : prey. Less clear, however, is how isolation alters interactions within food webs. Here, we present the results from an experiment performed in artificial ponds (mesocosms) manipulating habitat isolation crossed with a predator reduction treatment to disentangle how isolation mediates the top-down effect of predators. The strength of the trophic cascade, from predators, through herbivores, to producers, was considerably stronger in connected than in isolated habitats. We further found that the overall richness of both predator and herbivore species declined strongly with isolation. Experimental predator reductions suggest that the mechanism underlying the herbivore response was likely mediated by a keystone predator effect; when predators were reduced, herbivore richness was lower, and there was no discernable effect of isolation on herbivore richness. Finally, we found that the composition of predators in more isolated habitats consisted of species that were smaller and likely less effective predators than species that persisted in less isolated habitats. In all, our experiment showed that habitat isolation can alter the structure of communities by a combination of direct effects of the species in question, as well as effects mediated through their interactions in the food web.

The ability of prey to respond to novel predator cues may depend on the generality or specificity of the response to predator cues. We used laboratory behavioral experiments to examine the ability of tadpoles of three species of anurans (American toad, Bufo americanus; bullfrog, Rana catesbeiana; and green frog, R. clamitans) to respond to the presence of two native potential predators (bluegill, Lepomis macrochirus; and largemouth bass, Micropterus salmoides) and one non‐native potential predator (goldfish, Carassius auratus). We also examined the effect of tadpole size on the behavioral responses of American toads and green frogs to predator cues. All three species of tadpoles responded to the presence of predator cues, although the specific responses varied among species. American toads and green frogs reduced activity in the presence of at least some fish cues, but bullfrog tadpoles did not change their activity. Bullfrogs decreased use of vegetation in the presence of some predator cues, whereas American toads and green frogs did not. American toads only responded to the presence of bluegill cues but not the other fish predator cues, whereas bullfrogs and green frogs responded more generally to the fish predators. In both American toads and green frogs, tadpole size affected behavior. For American toads, activity increased, as did the use of the vegetated side of the aquarium, in larger tadpoles. Not only did size affect American toad behavior, but it also influenced the responses of the tadpoles to predator cues. For green frogs, activity decreased in larger tadpoles. Our results suggest that behavioral responses of tadpoles to predator cues can be influenced by both the identity of the predator and the prey, as well as the size of the potential prey.

No abstract

Recent surveys of aquatic habitats suggest that organic wastewater contaminants (OWCs) may be common in aquatic ecosystems. However, relatively little is known about the impacts of OWCs on amphibians. We studied the lethal and sublethal effects of three OWCs (acetaminophen, caffeine, and triclosan) on American toad (Bufo americanus) tadpoles. High concentrations of triclosan increased activity, whereas acetaminophen had a significant effect on activity but there was no discernable pattern or trend with concentration. Caffeine did not affect activity in B. americanus tadpoles. None of the OWCs we studied had a significant effect on growth. Caffeine had no effect on survivorship. Higher concentrations of acetaminophen increased mortality. Intermediate concentrations of triclosan had a negative effect on survivorship, but the highest concentration apparently had a positive effect on survivorship. Our results suggest that there is variation in the toxicity of the three OWCs we studied.

Species distribution models (SDMs) have become an important tool for ecologists by providing the ability to predict the distributions of organisms based on species niche parameters and available habitat across broad geographic areas. However, investigation of the appropriate extent of environmental data needed to make accurate predictions has received limited attention. We investigate whether SDMs developed with regional climate and species locality data (i.e., within Missouri, USA) produce more accurate predictions of species occurrences than models developed with data from across an entire species range. To test the accuracy of the model predictions, field surveys were performed in 2007 and 2008 at 103 study ponds for eight amphibian study species. Models developed using data from across the entire species range did not accurately predict the occurrences of any study species. However, models developed using data only from Missouri produced accurate predictions for four study species, all of which are near the edge of their geographic ranges within the study area. These results suggest that species distribution modeling with regionally focused data may be preferable for local ecological and conservation purposes, and that climate factors may be more important for determining species distributions at the edge of their geographic ranges.