Habitat Selection, the Included Niche, and Coexistence in Plant-Specialist Frogs from Madagascar

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Classic niche partitioning suggests that coexistence among asymmetric competitors is facilitated by differential resource use. Coexistence is also possible, however, when a species only has access to resources that are shared with a competitor, providing it is the superior competitor on that resource (the 'included niche'). To test predictions of these two coexistence mechanisms, we studied habitat selection of two closely related sympatric plant-specialist frogs from Madagascar (Guibemantis bicalcaratus and Guibemantis punctatus). Both species live and breed only in the water-filled leaf axils of Pandanus plants, and previous experiments with their tadpoles demonstrated asymmetric competition. In a 3-yr field study, we: (1) monitored the biotic and abiotic conditions of 348 plants; (2) surveyed these plants for frogs; (3) undertook a mark-recapture study; and (4) conducted an experiment where we manipulated the amount of detritus in plants. We identified several differences in the conditions of the habitats selected by both species (e.g., plant height, canopy cover over the plant, abundance of heterospecifics). Co-occurrence was nevertheless common, and G. punctatus persisted almost exclusively in plants it shared with G. bicalcaratus. As predicted by theory, G. punctatus was the superior competitor, at least in the tadpole stage. The inferior competitor (G. bicalcaratus) had access to exclusive resources not available to G. punctatus, by virtue of a faster developmental rate that permitted reproduction in lower quality plants. While there was some evidence of weak niche partitioning, we conclude that coexistence in these plant-specialist frogs is primarily via an included niche mechanism. Abstract in French is available at http://www.blackwell-synergy.com/loi/btp. © 2010 The Author(s). Journal compilation © 2010 by The Association for Tropical Biology and Conservation.


Coexistence mechanisms, Developmental constraints, Guibemantis, Niche partitioning, Pandanus, Patch quality, Phytotelmata, Spatial isolation

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