托福口语 Task 4

Today we're going to talk about a fascinating concept in biology: behavioral adaptation through environmental cues. Specifically, I want to discuss how some animals change their behavior based on the presence of predators, even when those predators are not immediately threatening. This is called 'predator-induced behavioral plasticity.' Let me give you two examples. First, consider the Trinidadian guppy. In streams where pike cichlids, their predators, are present, guppies mature earlier and produce more offspring, but they also grow slower and have shorter lifespans. This is a trade-off: they invest in reproduction early because the risk of being eaten is high. Second, think about the wood frog tadpole. When dragonfly larvae, which prey on tadpoles, are in the same pond, the tadpoles develop deeper tail fins and smaller bodies. This makes them faster swimmers, helping them escape. Interestingly, these changes only occur when the tadpoles detect chemical cues from the dragonflies in the water. If the dragonflies are absent, they develop normally. So, in both cases, the animals adjust their life history or morphology in response to the threat level in their environment, maximizing their chances of survival and reproduction.