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 .