PARENT SESSION
Contributed Oral Session 108: Aquatic Trophic Systems II
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 524 C, Level 5, Palais des congrès de Montréal
Indirect effects of ultraviolet radiation stress on ephemeral pond communities: who can take the heat?
Garcia, Tiffany*,1, Blaustein, Andrew1, 1 Oregon State University, Corvallis, Oregon
ABSTRACT- Indirect effects of UV-B radiation are poorly understood in most ecosystems, especially in habitats where amphibians are abundant. The Red-legged Frog (Rana aurora) and the Pacific Treefrog (Hyla regilla) are two anuran species which sympatrically inhabit ephemeral ponds along the central Oregon coastline but differ in competitive ability and the degree to which their larval stages are affected by ambient levels of UV-B radiation. Direct impacts of UV-B on amphibian larvae, (i.e. changes in density, distribution and behavior) can lead to indirect impacts on other members of the community, including competing amphibian species and their invertebrate predators. In habitats where multiple anuran species with differential sensitivity to UV-B co-occur, UV-B stress has allowed the more resistant species to occupy the shallow, warmer areas of the pond, relegating the colder waters to less competitive anuran species and their predators. Hyla regilla are inferior competitors relative to R. aurora when UV-B radiation is excluded, but out-compete R. aurora larvae in a UV-B present environment. Tolerance of UV-B stress allows H. regilla larvae to occupy the warmer, shallow areas of the pond, resulting in faster larval growth and development rates. Laboratory experiments show strong UV-B avoidance behaviors, such as refuge use and depth choice, in R. aurora larvae, while H. regilla larvae responded with only an increase in refuge use. UV-B impacts on amphibian behavior also indirectly affect the distribution of invertebrate predators. In a field experiment measuring predator abundance at different depth profiles in UV present and UV excluded enclosures, we found predators occupied water depths consistent with the presence of their preferred food item, regardless of UV presence. Anuran and invertebrate predator distribution throughout the pond is directly and indirectly dependent on which species can occupy high UV exposed areas.
Key words: indirect effects, amphibian larvae, ultraviolet radiation, competition