To invade on a larger landscape scale, exotic species must establish reproducing populations within their introduced habitat. In many cases, exotic species successfully exploit unique, well delineated habitats with a particular range of environmental conditions that do not vary substantially. Such habitat stability allows for an increased likelihood of reproductive success. The island apple snail, Pomacea insularum, however, must confront a number of obstacles to survive in both aquatic and terrestrial habitats. Usually occupying cryptic benthic habitats, female apple snails crawl out of the water to deposit large, bright pink egg clutches on emergent objects. These clutches must then dry in the terrestrial, or riparian, environment before yielding hatchlings that drop back down into the water. Collectively, our work examines the implications of “living on the edge” where eggs clutches, and subsequently hatchlings, may face multiple stresses including predation by riparian predators, inundation, nutrient pollution and consumption by aquatic predators including adult apple snails. We tested the predatory potential of red-eared slider turtles (Trachemys scripta elegans) to consume eggs and hatchlings. We also examined the hatching efficiency, growth and survival of 9-day old clutches subjected to eight hours of inundation stress (none, low and high intensity) followed by excess nutrients (N, P & N+P). Our investigations also included examining the likelihood of egg or hatchling consumption by adult snails.
Clutches laid by P. insularum routinely hatch with an efficiency ranging between 60 and 80%. This translates into an average of 1200-1600 hatchlings emerging from each clutch laid by an invasive female. Both small (i.e. baby) and large (i.e. adult) red-eared sliders consumed nearly 100% of apple snail eggs when offered in the water. However, baby sliders failed to show interest in clutches above the surface. In contrast, adult sliders partially consumed (~50%) clutches dangled from a string. Alarmingly, inundation stress did not significantly reduce hatching efficiency of 9-day old clutches. However, exposure to high levels of nutrients decreased growth and resulted in lower survival of 1-week old hatchlings compared to controls. Such susceptibility of hatchlings to nutrient levels suggests a noticeable immediate mortality. We found that adult snails consumed about 10% of available hatchlings. Connected together, our results point to the particular challenge of living on the edge where dual habitats of riparian vegetation and aquatic environments may ultimately work together to limit reproductive success of P. insularum. We recommend more work to quantify hatchling survivorship and dispersal.