Effects of resource distribution on the cost of predator avoidance behaviour in tadpoles

Tadpoles reduce activity and increase hiding in the presence of dragonfly larvae. Several studies demonstrate that tadpoles showing this behaviour have slower growth, however, other studies have found no effect or even positive growth in tadpoles exposed to predators. A recent study demonstrated that swimming is an energetically expensive activity for Bufo arabicus tadpoles. Therefore, if food resources are abundant close to refuges, reduced activity may be an advantage and could offset the cost of reduced foraging. I tested this hypothesis by growing B. arabicus tadpoles with food provided either near or away from shelters, in the presence or absence of caged dragonfly larvae. In the presence of dragonfly larvae, tadpoles provided with food close to shelters were significantly larger than those with food further away. Control tadpoles under both food treatments were intermediate in size, although not statistically different from the predator + near food tadpoles. The results indicate that access to resources is the main determinant of growth in B. arabicus tadpoles and that the energetic cost of swimming is a secondary factor.