Differences in population dynamics and potential impacts of a freshwater invader driven by temporal habitat stability

Understanding population dynamics and population regulation of invasive species is critical for predicting their effects on native ecosystems as well as for control strategies. Many species of gastropod in the genus Pomacea are successful aquatic invaders that have caused economic and ecological impacts in Southeastern Asia where their large fecundity and broad reproductive window helps them to colonize and take advantages of ephemeral agricultural habitats. We followed the population dynamics of P. insularum in permanent, stable freshwater systems (ponds and streams), and in ephemeral agricultural habitats in the upper Texas Gulf Coast region, USA. We found that although P. insularum has a large reproductive potential, its density, biomass and size structure in stable permanent systems did not change significantly from March to November, and densities averaged <2 m^-2. This same species, however, displayed very different population dynamics in ephemeral agricultural environments. We found high densities (>130 m^-2), and no stable size structure through time. Differences in the stability and persistence of these two types of environments appear to drive these patterns. Stability and persistence of habitats can result in different predator communities and the risk of predation for snails. We suggest that such factors may cause the differences in population dynamics and structure observed. The ability of snails to escape population control and explode in ephemeral habitats could drive the types of impacts seen on agricultural crops.