Effects of hatching timing on red-eyed treefrog tadpoles: relative vulnerability varies among predators but not with hatchling age-structure, growth varies with the presence of more vulnerable tadpoles [poster]
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In Gamboa, Panama, undisturbed red-eyed treefrog embryos typically hatch at age 6 days, but they can hatch as early as 4 days if attacked by egg predators. Early hatchlings are less developed and more vulnerable to predatory shrimp and fish. Here we assess the effect of hatching timing on risk of predation by three common insects, with different foraging styles, that prey on red-eyed treefrog larvae. Further, we examine whether the consequences of hatching early vary with the presence of later-hatched tadpoles. We induced hatching at 4 and 6 days and exposed tadpoles to giant water bugs or aeshnid or libellulid dragonfly larvae over 24 hrs, quantifying tadpole behavior and mortality. We used substitutive designs with three treatments: early hatched, late hatched and mixed hatching ages. In no case did presence of the other age class alter mortality. Hatching age did not affect libelullid predation, which was low in both cases. Early-hatched tadpoles had higher mortality than late hatchlings with water bugs, which move throughout the water column. In contrast, early hatchlings had lower mortality than late hatchlings with aeshnids, which cue strongly on movement. Late-hatched tadpoles were more active than early hatchlings, and movement was reduced in the presence of aeshnids. Combining across this and previously published studies, early hatchlings are more vulnerable than late hatchlings to most (3/5) predators. Variation in relative, age-specific hatchling vulnerability to predators with different foraging styles is consistent with developmental changes in tadpole behavior.
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