FRESHWATER COMMUNITIES AND BIOLOGICAL INVASIONS: ODONATA, AMPHIBIA AND PROCAMBARUS CLARKII
Creators: name: SIESA, MATTEO ELIO
Publisher: name: Universit� degli Studi di Milano
Year: 2011

description: This research work analyses processes and dynamics occurring during the early stages of a biological invasion in freshwater habitats. I analysed processes determining the Procambarus clarkii invasion and the impact on native amphibians and odonates that have complex life cycles, I surveyed 148 among temporary and permanent wetlands of running and standing waters in a region that is at the edge of the invasion range of P. clarkii, I performed repeated sampling sessions in each wetland obtaining both qualitative and quantitative data on freshwater communities, I characterized each wetland using standard parameters, and I used GIS software for the description of the surrounding landscape. I analysed all data using spatial models and considering the spatial autocorrelation.
Data analysis showed that the environmental features are important in determining the early phases of the crayfish invasion; in the study area, P. clarkii spreads more frequently in association with large and permanent wetlands in human-altered landscapes, and the autocorrelation of its populations is stronger at distances up to 2500 m suggesting that dispersion affect invasion processes up to this distance. Further analysis showed that environment shapes both alien invasive species (AIS) and freshwater communities, but considering the optimal environmental features for P. clarkii and for amphibians and odonates, I observed important differences related to wetland size, depth, hydroperiod, exposition, presence of aquatic macrophytes, and surrounding landscape features. The observed relationships among distribution and composition of native communities and distribution of P. clarkii suggests that the invasive crayfish has only a limited direct impact on adult amphibians and odonates, but the analysis of juvenile stages of native communities (larvae of amphibians, larvae and exuviae of odonates) showed the dramatic loss of their abundance and richness in wetlands invaded by the crayfish, indicating that, despite adults attempt reproduction in invaded sites, P. clarkii causes, with its activities, the fall down of their reproductive success. This research confirms the strong negative impact of AIS on native communities. My data indicate that P. clarkii determines the loss of reproductive sites, and the decrement of the reproductive success when native populations use the invaded sites for breeding. This research highlights the importance of studying the early stages of an invasion, confirming that in this phase AIS populations have larger environmental needs that might make them more vulnerable at management actions. Through the analysis and description of the mechanisms determining the AIS impact on native communities, this research helps to identify the ongoing processes at early stages of the AIS invasion, and the consequences that the invasive crayfish will have in the near future, allowing managers to start conservation actions before that the invasion consequences become irreversible.