Christopher L. Higgins and Christopher P. Bloch

The Luquillo Experimental Forest, located in the Caribbean National Forest of Puerto Rico, is part of a network of long-term ecological research programs funded by the National Science Foundation.  The overarching goal of the Luquillo Experimental Forest program is to understand the long-term dynamics of tropical forest ecosystems that experience periodic large-scale disturbances (hurricanes).  In September 1989, Hurricane Hugo passed over the northeast corner of Puerto Rico causing major destruction in the Luquillo Experimental Forest.  Despite this destruction, plant and animal populations appeared to recover fairly quickly.  In September 1998, another hurricane (Hurricane Georges) passed through the interior portions of the island destroying much of what was in its path.  This caused major decreases in population sizes for a majority of the organisms living within the forest.  Once again, however, the plant and animal populations seemed to recover over time. Of all the organisms studied in the Luquillo Experimental Forest, the terrestrial gastropods best demonstrate the effects of large-scale disturbances.

Terrestrial gastropods are extremely sensitive to changes in moisture and temperature, both of which are altered following a disturbance.  Typically, the microclimate in which they live becomes hotter and drier, which causes the snails to dry out and die.  Consequently, the number of individuals within each species decreases rapidly.  As gaps in the canopy close and the forest begins to recover, population sizes increase.  The resulting pattern is cyclic in nature,as evidenced by two of the most numerically abundant species (Caracolus caracola and Nenia tridens).  The objective of this study is to use mathematical models to describe temporal changes in population sizes of these two gastropods to better understand how and why population sizes change with large-scale disturbance (hurricanes).