Niche Differentiation in Tank and Atmospheric Epiphytic Bromeliads of a Seasonally Dry Forest

Factors influencing the niche differentiation of epiphytes have been determined for the epiphytic bromeliads that coexist in the seasonally dry forest of Chamela, Mexico. Over 40 percent of the bromeliad epiphytes were distributed in only 5 percent of the trees. The occurrence of compound leaves in host trees was highly correlated with abundance of epiphytes, as these allow scattered light to penetrate throughout the canopy. The effect of leaf type overrides the effect of bark type, the main factor determining seedling establishment in moist forests. Eight species had the atmospheric life form, while only two species had tanks, formed by overlapping leaf bases and associated to a lower drought tolerance. Distribution in the canopy is counter to that observed in moist forests, since tank species occur in the upper canopy. Tank life forms showed most annual carbon gain during the rainy season, when the newly leafed out trees provide shade to the lower canopy. Atmospheric species had photosynthetic activity for longer into the dry period, possibly supported by dew and fog events. Leaf angles, orientation, trichome, and stomata densities are discussed in relation to water and light use among the species with contrasting ecological strategies.