We investigated how competition and predation alter prey phenotypic traits (morphology and behavior) using a system of sympatric tadpoles Rhacophorus schlegelli (RS) and Pelophylax nigromaculatus (PN) and non-lethal dragonfly larva, in a 2x2 factorial laboratory experiment (presence or absence of predator, presence or absence of competitor). The two species competed asymmetrically with RS being the superior competitor; the presence of predator strengthened this interaction. The presence of predator increased PN growth rate, which might be mediated by its long gut. Preys differentially invested in phenotype depending on their competitive ability. In the absence of predator, the superior competitor exhibited a longer tail while the inferior one reduced its muscle area and activity level but increased gut length; In the presence of predator, the inferior competitor amplified its antipredator defense (higher tail area and higher reduction in activity), expressed a long gut and further reduced its tail muscle area. Flexible alimentary tract and tail musculature appear to be strategies to accommodate the amplification of defense structure. We provided a new perspective to appreciate the mechanism through which costs of inducible defenses are offset in anuran larvae.