Habitat size thresholds for predators: why damselflies only occur in large bromeliads

Predators are often more sensitive to habitat size than their prey, and frequently occur in only the largest habitats. Four explanations have been proposed for this pattern: (1) small habitats do not have enough energy to support higher trophic levels; (2) small habitats are less likely to contain particular prey required by specialist predators; (3) small habitats are risky for predators with slow life histories or large body sizes; (4) small habitats are numerically unlikely to be colonized by regionally rare species, such as predators. We critically examine these four hypotheses in relation to the predatory damselfly larva, Mecistogaster modesta Selys. (Pseudostigmatidae), which occurs almost exclusively in bromeliads > 100ml in capacity. We synthesize multiple years of survey data and three manipulative experiments from the Área de Conservación Guanacaste, Costa Rica to conclude that damselflies do not occur in small bromeliads due to their higher risk of desiccation – not becaus...