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Effects of Reduced Perch‐Height Separation on Competition between Two Anolis Lizards

Rummel, John D., Roughgarden, Jonathan
Ecology 1985 v.66 no.2 pp. 430-444
Anolis, egg production, field experimentation, food intake, interspecific competition, lizards, microclimate, predation, Netherlands Antilles
Some effects of the presence of Anolis bimaculatus (snout—vent length [SVL] 85 mm) on A. wattsi (SVL 49 mm) were assessed in a field experiment on the island of St. Eustatius, Netherlands Antilles. A. wattsi normally perches below 0.5 m. A. bimaculatus above 1.5 m. The effects of reducing this perch—height separation on the interaction of these species was studied in enclosures experimentally modified to contain A. wattsi alone, A. wattsi with A. bimaculatus and a normal range of available perch positions, or A. wattsi with A. bimaculatus but no available perch positions above 1.5 m in height. The presence of A. bimaculatus at normal perch heights caused A. wattsi to use perch positions with hotter microclimates and to be active at different times of day than when A. bimaculatus was absent, but A. bimaculatus did not affect the growth, egg production, or prey selection of A. wattsi during this study. Effects of perch—lowered A. bimaculatus on A. wattsi were identical, but the A. bimaculatus themselves had lower growth rates, egg production, and food intake when compared to those with access to the normal range of perches. The absence of a strong effect on A. wattsi is consistent with the results of a previous reciprocal experiment; this further establishes that there is an inverse relationship between interspecific competition and resource partitioning. The effect of A. bimaculatus on A. wattsi was, however, greater than that of A. wattsi on A. bimaculatus, which supports the hypothesis that the competitive relationship between these two species is asymmetric. Our finding that the perch lowering did not increase the effect of A. bimaculatus on A. wattsi suggests that perch height is not an axis of niche separation important to the competition between these two species.