A food web for a tropical rain forest: the canopy view from Anolis

TitleA food web for a tropical rain forest: the canopy view from Anolis
Publication TypeThesis
Year of Publication1992
AuthorsDial, R
UniversityStanford University
Accession NumberLUQ.135
Keywordstropical rain forest
Abstract

The trophic stature of Anolis evermanni and A. stratulus is examined in light of a series of experiments and observations conducted at canopy level in a Caribbean rain forest (Puerto Rico). Trade winds are shown to play an important role as a physical transport process in rain forest canopy in the Caribbean. The supply of flying insects to Anolis communities within the forest canopy is determined by a physical transport process in a manner analogous to the way marine intertidal communities are provisioned by water currents. The result is a one-way predator-prey interaction that may enhance species co-existence. A six-month removal experiment performed at canopy level quantified the predatory role of insectivorous Anolis lizards there. Counts were made of aerial-web spiders, leaf-dwelling arthropods, and flying insects caught in sticky-traps. An index of dispersal ability was measured using cylindrical sticky-traps suspended over forest gaps. Initial densities of arboreal anoles correlated positively and significantly with flying insects caught in sticky-traps, but not with leaf-sampled arthropod abundances. Removal and exclusion of anoles from individual tree crowns of Dacryodes excelsa using trunk collars revealed strong responses in abundances of several arthropod groups, particularly those greater than 2 mm long, not cryptically colored and poorly dispersing. The effect on herbivores cascaded to plants. Prevalence of defoliation was higher in anole-removal crowns than in controls. Percentage of leaflets damaged was positively correlated with leaf-dwelling orthopteran abundance, suggesting a three-trophic-level effect of lizards on plants. The effect of lizards on small predators cascaded to the smallest prey lengths with a weak, statistical significance. The two-species guild, A. evermanni and A. stratulus, is investigated. The high degree of overlap in structural niche, solar climatic niche, limiting prey depression, and the observation of interspecific aggression suggests strong present-day competition between the two anole species. This competition is suggested to result in crown-by-crown competitive exclusion. The biology of a flesh fly (Diptera: Sarcophagidae) that lethally parasitizes anoline hosts is described. The implication of the infection on the occurrence of body spots in A. stratulus is discussed.

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