Palatability
To know whether tadpoles of the three species were palatable to potential aquatic predators that coexist with them, we conducted a predation experiment. As predators, we used odonate naiads in the families Libellulidae and Aeshnidae obtained from the same ponds as the tadpoles or small ponds nearby; naiads are known to be voracious predators with significant importance for the population dynamics of pond-dwelling organisms (Magnusson & Hero 1991; Cobert 1999). During each assay, a single naiad was kept in a 30 x 40 x 15 cm (W x L x H) plastic container and fasted for 12 h prior to the treatment, which consisted in adding a single tadpole. The survival of both the larvae and the naiad was monitored every hour throughout eight hours. To avoid pseudoreplication (Hurlbert 1984), we used a unique naiad for each tadpole: 18 tadpoles of P. vaillanti , 9 of P. bicolor , and 11 of C. tomopterna . The body size (snout to vent length, SVL) of each tadpole and naiad was measured before initiating each trial.