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Food availability influences postmetamorphic growth in two spadefoot toad species (genus Pelobates)

Abstract:

Understanding how major life history traits such as body size and mass and growth change in response to resource availability is crucial in explaining life history trade-offs. We conducted a laboratory experiment with three (high, medium and low) feeding intensity treatments using metamorphs of two spadefoot toads species, Pelobates syriacus and P. fuscus, from syntopic populations. We tested how total food consumption, final body size and mass, body mass increase, body mass and length growth rates and growth efficiency are influenced by food availability. The responses to food availability differed significantly between the species with respect to the total food consumption, body mass increase, body mass growth rate and growth efficiency (i.e. the ratio between total amount of food consumed during the experiment divided by the increase in body mass). P. syriacus metamorphs had higher growth rates and growth efficiency than P. fuscus juveniles. Also, P. syriacus juveniles responded to differences in food level by increasing growth efficiency with decreasing food levels. Overall P. syriacus seems better adapted to shortages in food availability than P. fuscus. Our results clearly indicate that the differences in body size between the two species originate between metamorphosis and sexual maturity.