Vertical distribution
To corroborate whether our study tadpoles dwell mostly on the pond surface, we tested for differential use of the water column. We used 12 transparent plastic columns of 70 cm high and 50 cm diameter, marked every 5 cm depth. The columns were filled with water from the same pond in which the tadpoles were captured. During a single assay, seven tadpoles were added to each of the 12 columns. For the acclimation period, we placed the columns in a quiet place all night. The next day we noted the position of tadpoles along the water column. These observations were repeated every 2 h, between 06:00 – 18:00 h. ForP. bicolor , we used three size groups of tadpoles: small (stage 25-27), medium (stage 28-32), and large (stage 33-39) (Gosner 1960). Due to constraints in the availability of tadpoles, we used only large tadpoles of P. vaillanti and could not conduct a similar experiment with C. tomopterna .