Intervention Analysis of Hurricane Effects on Snail Abundance in a Tropical Forest Using Long-Term Spatiotemporal Data

Abstract

Large-scale natural disturbances, such as hurricanes, have profound effects on populations, either directly by causing mortality, or indirectly by altering ecological conditions or the quantity, quality, and spatial distribution of resources. In the last 20 years, two major disturbances, Hurricane Hugo in 1989 and Hurricane Georges in 1998, struck the Luquillo Mountains of Puerto Rico, providing an unique opportunity to understand the long-term effects of recurrent disturbances on the abundance of species. Nenia tridens is one of the most abundant and pervasive terrestrial gastropods in the Luquillo Mountains. Estimates of yearly abundance of N. tridens from 40 sites on the Luquillo Forest Dynamics Plot from 1991 to 2007 facilitate the development of a spatiotemporal model with intervention effects on the mean abundance over time in response to each hurricane. Intervention effects characteristically decay over time, similar to those in a time series analysis. Model parameters were estimated in a Bayesian framework. Model comparison and diagnostics suggest that our intervention model provides a plausible description of hurricanes effects on the abundances of N. tridens and may be useful for studying long-term spatiotemporal dynamics from the perspective of disturbance and succession.