PARENT SESSION
Oral Session #36: Animal Community Ecology.
Presiding: S. Simonson
Tuesday, August 6. 8:00 AM to 11:30 AM. Mesquite Room, Radisson.
Performance tradeoffs along resource quality/quantity gradients in anuran larvae.
Schiesari, Luis*,1, Werner, Earl1, 1 University of Michigan, Ann Arbor, MI
ABSTRACT- The differential ability of organisms to acquire and utilize resources contributes to species compositional changes along productivity gradients. We tested the hypothesis that these changes may arise from a tradeoff maximizing performance under conditions of either high or low resource quality/quantity. We demonstrated this tradeoff in anuran larvae segregating along a pond canopy-cover gradient. Leopard frogs (Rana pipiens) inhabit productive (open-canopy) ponds whereas wood frogs (Rana sylvatica) inhabit both open-canopy and closed-canopy (unproductive) ponds. In laboratory experiments, leopard frogs grew faster than wood frogs under high quality/quantity artificial and natural (periphyton, phytoplankton) foods. Conversely, wood frogs grew faster than leopard frogs under low quality/quantity artificial and natural (detritus) foods. Testing this tradeoff's consequences to species distribution patterns requires translation of individual performance into demographic parameters. A field experiment transplanting both species to cages in open and closed-canopy ponds showed that the relationship between mortality and growth is null for wood frogs but steeply negative for leopard frogs. Leopard frogs exhibit fast growth in open-canopy ponds, but slow growth and high mortality in closed-canopy ponds. In conclusion, we found support for a growth tradeoff at resource abundance vs. scarcity. In addition, we found support for a second tradeoff of possibly greater ecological implications, that between growth at resource abundance vs. survival at resource scarcity. Together these two tradeoffs have the potential to generate patterns of species habitat segregation across productivity gradients.
KEY WORDS: tradeoff, productivity gradients, power-efficiency hypothesis, Anura