Shifts in life history as a response to predation in western toads (Bufo boreas)

Larval western toads (Bufo boreas) are known to exhibit antipredator behavi or in response to both chemical alarm cues released from injured conspecifi cs and chemical cues of predatory invertebrates. In this study, we tested w hether long-term exposure to predator and alarm cues resulted in an adaptiv e shift in life history characteristics of the toads. We raised groups of t adpoles in the presence of: (I)predatory backswimmers (Notonecta spp.) that were fed toad tadpoles, (2) nonpredatory water boatman (Corixidae), and (3 ) chemical alarm cues of injured conspecifics. Tadpoles raised in the prese nce of both chemical alarm cues and cues of predators fed tadpoles metamorp hosed in significantly shorter time than those raised in the presence of th e nonpredator control. Reducing time taken to reach metamorphosis would red uce exposure to aquatic predators. There was no difference among treatments in the size at metamorphosis. Our results suggest that this shift in metam orphic characteristics may represent a facultative alteration in life histo ry.