RESUMEN
Many prey species face trade-offs in the timing of life history switch points like hatching and metamorphosis. Costs associated with transitioning early depend on the biotic and abiotic conditions found in the subsequent life stage. The red-eyed treefrog, Agalychnis callidryas, faces risks from predators in multiple, successive life stages, and can hatch early in response to mortality threats at the egg stage. Here we tested how the consequences of life history plasticity, specifically early hatching in response to terrestrial egg predators, depend on the assemblage of aquatic larval predators. We predicted that diverse predator assemblages would impose lower total predation pressure than the most effective single predator species and might thereby reduce the costs of hatching early. We then conducted a mesocosm experiment where we crossed hatchling phenotype (early vs. normal hatching) with five larval-predator environments (no predators, either waterbugs, dragonflies, or mosquitofish singly, or all three predator species together). The consequences of hatching early varied across predator treatments, and tended to disappear through time in some predation treatments, notably the waterbug and diverse predator assemblages. We demonstrate that the fitness costs of life history plasticity in an early life stage depend critically on the predator community composition in the next stage.
Asunto(s)
Conducta Animal , Conducta Predatoria , Ranidae/fisiología , Animales , Ambiente , Larva , Estadios del Ciclo de Vida , Metamorfosis Biológica/fisiología , FenotipoRESUMEN
Incidental task structure is consistent, potentially beneficial, information that is not necessary for successful task performance (i.e., is seemingly unrelated to the task). The authors investigated whether incidental task structure was differentially beneficial to younger and older adults. Across three experiments, 122 participants searched for targets among stimuli laid upon different patterns, such that certain patterns correlated with target location at varying degrees of consistency. An age-related difference was identified in the ability to learn an incidental structure under certain conditions and a strategy explanation for the difference was investigated. When older adults' were encouraged to orient at least some degree of attention toward the predictive information, learning occurred. Older adults are capable of learning incidental, environmental information but their learning was not identical to younger adults'. Younger adults showed performance benefits when provided with incidental task structure, but older adults may need to be made explicitly aware before it is useful.