Effects of habitat and predators on caterpillar predation in a tropical rainforest

Background/Question/Methods

Primary consumers in tropical rainforests can defoliate almost half of the leaf area, leading us to question how such rainforests retain their foliage. One such primary consumer is the caterpillar. In an experiment at La Selva Biological Station, situated in wet tropical forest of Costa Rica, we conducted an experiment designed to examine relationships between predation on caterpillars and how their habitat preferences might limit their densities. We constructed model caterpillars of plasticine and placed them in four different habitats, with n = 18 caterpillars per habitat. The habitats consisted of two locations, interior or edge of the forest, with two substrate types, leaf or tree trunk, in each location. After three days we collected the model caterpillars and compared predation rates in relation to habitat and predator type, with predator types categorized as bird, arthropod or mammal. We compared predation among the four habitats and by predator type using student t-tests.

Results/Conclusions

Percent predation did not differ between the edge and interior of forests (P = 0.61) or between models placed on trees or leaves (P = 0.57). This conclusion allowed us to infer that predators can readily locate and consume caterpillar prey, a primary consumer. However, birds did preferentially prey on models on the forest edge compared with those in the interior (P = 0.005). The edge may have allowed more exposure of and access to the models. Overall, the greatest predation, 64%, was by arthropods, likely due to the proportionally higher abundance of arthropods in tropical forest habitats relative to other predator types. Of the 72 model caterpillars placed, we recorded 42 predation events. This means that while primary consumers may be defoliating the forest at a fast rate, only 40% of caterpillars are surviving, leaving the forest with an abundance of leaves.