Mangrove Species Distribution and Propagule Predation in Belize: An Exception to the Dominance-Predation Hypothesis

Abstract

Predation on mangrove propagules was studied to assess its impact on the intertidal distribution of Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa. Field experiments conducted on a mangrove island range (Twin Cays) in Belize showed that rates of predation (percent of propagules rendered nonviable in 9 days) just after peak dispersal (December) were highest for A. germinans (60 ? 8%) and significantly lower for R. mangle (18 ? 5%) and L. racemosa (28 ? 9%), which were not significantly different. Rates varied seasonally, however, with highest losses of propagules at the beginning of dispersal (July). Major predators were the mangrove crabs, Goniopsis cruentata and Ucides cordatus. The high predation rate on A. germinans propagules was attributed to a relatively small size (facilitating burial in crab burrows), a higher nutritive content, and lower amounts of defensive chemicals such as tannins. Interspecific differences in predation rates, however, could not explain the relative dominance and spatial distribution of two of the three species that comprise this intertidal community. Comparison of predation rates in forest locations dominated by either R. mangle or A. germinans demonstrated that consumption of R. mangle propagules was highest in areas where it dominated the canopy and lowest where A. germinans was dominant. Predation also could not account for the infrequent occurrence of L. racemosa trees at Twin Cays, since rates of propagule consumption were not different from that of R. mangle and significantly less than that of A. germinans. High densities of L. racemosa seedlings further suggested that predators were not preventing this species' establishment here. Only the predation pattern for A. germinans was consistent with intertidal dominance of trees. The results indicate that differential predation plays a less important role in the zonation of these island mangrove forests than has been reported for other geographic regions.