Effects of Competition and Forest Type on Size and Abundance of an Arboreal Snail Along an Elevational Gradient
MetadataShow full metadata
Intra- and interspecific competition has been shown through numerous studies to negatively affect individual size and population densities of organisms. Along an elevational gradient, these competitive effects may intensify due to differences in environmental conditions. Elevational clines are known to give rise to changes in soils, vegetation, insolation and temperature, which can directly affect availability of resources, or even the organisms themselves. For terrestrial gastropods, which are at high risk of desiccation, increases in altitude pose a greater threat to survival in temperate systems, but this relationship has not been studied in tropical mountains. I analyzed maximum size and mean densities of the Puerto Rican land snail, Pleurodonte caracolla, among two different groups of forest types along an elevational gradient to evaluate possible effects of intra- or interspecific competition. Maximum shell size was weakly correlated with total snail density and elevation in both forest types, and P. caracolla density was negatively correlated with elevation in both forest types. The high productivity of the study site likely reduces competition by providing an abundance of resources for all snails present. Low population densities are hypothesized to be due to temperature fluctuations, lower egg hatching success, and higher predation rates on juveniles. More studies are needed on gastropod populations in other tropical montane systems.