Although predation is generally seen as one of the key factors determining the abundance and composition of insect herbivore communities in tropical rain forests, quantitative estimates of predation pressure in rain-forest habitats remain rare. We compared incidence of attacks of different natural enemies on semi-concealed and exposed caterpillars (Lepidoptera) in lowland and montane tropical rain forests, using plasticine models of caterpillars. We recorded attacks on caterpillars in four habitats: primary forest, secondary forest and forest fragment in lowlands (200 m asl), and montane primary forest (1700 m asl). We used 300 exposed and 300 semi-concealed caterpillars daily, and conducted the experiment for 6 d in every habitat. Daily incidence of attacks was higher on exposed caterpillars (4.95%) than on semi-concealed (leaf-rolling) caterpillars (2.99%). Attack pressure of natural enemies differed also among habitats. In the lowlands, continuous primary and secondary forests had similar daily incidence of attacks (2.39% and 2.36%) which was however lower than that found in a primary forest fragment (4.62%). This difference was caused by higher incidence of attacks by birds, ants and wasps in the forest fragment. The most important predators were birds in montane rain forests (61.9% of identified attacks), but insect predators, mostly ants, in the lowlands (58.3% of identified attacks). These results suggest that rapid decrease in the abundance of ants with altitude may be compensated by increased importance of birds as predators in montane forests. Further, it suggests that small rain-forest fragments may suffer from disproportionately high pressure from natural enemies, with potentially serious consequences for survival of their herbivorous communities.
Accurate recognition of a predator is the necessary precondition for adequate antipredatory behaviour. We used feeder experiments to examine whether birds adopt the appropriate antipredatory response according to the level of threat posed by predators. The results support the idea that the tits made a decision on the threat level. The tits distinguished among equally sized obligatory predators (sparrowhawk, kestrel), an occasional predator (jay) and a harmless bird of similar size (pigeon) and a smaller harmless bird (thrush). The presence of both birds of prey was associated with a considerable reduction in the number of feeder visits when compared with the harmless birds. The number of visits to the feeder that had a dummy jay positioned on it did not significantly differ for harmless birds or for predators. Different sizes of harmless birds did not influence the tits' behaviour. The increasing risk lowered not only the number of visits to the feeder but also the success of the visit, pecking rate, and the direction of arrival to the feeder. Generally, birds assessed the risk during food searching, evaluated the situation, and adapted their behaviour accordingly.
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