PARENT SESSION
Oral Session #90: Evolutionary Ecology.
Presiding: R. del Castillo
Thursday, August 8. 1:00 PM to 3:45 PM. Apache Meeting Room, TCC.
Natural selection does not favor habitat choice in a natural population of frogs.
Van Buskirk, Josh*,1, Smith, David2, 1 University of Zurich, Zurich, Switzerland2 Williams College, Williamstown, MA
ABSTRACT- The spatial pattern of variation in individual fitness strongly influences the evolution of habitat choice. We measured growth rate and survival for >1000 broods of Pseudacris triseriata tadpoles inhabiting about 90 ponds in northern Michigan over 16 years, and the data unexpectedly show that selection is not currently acting upon habitat choice of adult frogs. First we partitioned the overall variation in tadpole performance into within-pond and among-pond components. Between 20% and 50% of the variance in most years was among ponds, suggesting substantial opportunity for selection on oviposition site choice within any single year. Next we quantified the spatial distribution of the factors that account for most differences in tadpole growth and survival. Predators were confined to the more permanent ponds, disturbance and desiccation affected ephemeral ponds, and competition for food was most severe in ponds intermediate between these extremes. These factors tended to even out when acting in combination, so that average tadpole survival and growth across all years showed almost no spatial pattern. Thus, ovipositing frogs effectively distribute their eggs to produce an 'ideal free distribution' of fitness, resulting in no net selection on adult habitat choice in this system.
KEY WORDS: habitat selection, tadpoles, predation, ideal free distribution