Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Representing calcification in distribution models for aquatic invasive species: surrogates perform as well as CaCO3 saturation state.

Abstract

Modeling of invasive species' potential distributions is critical for preventing new invasions. Distribution models use environmental characteristics of observed distributions to determine the suite of conditions that allows invasion. Some variables are directly related to species' biological needs, while others are surrogates that do not directly influence distributions. For aquatic invasive species (AIS) with calcified shells and exoskeletons, one common limiting factor is the chemical restriction on forming calcium carbonate (CaCO3), which is usually represented by conductivity or dissolved calcium. We predicted that conductivity and calcium would not serve as accurate surrogates for CaCO3 saturation state, which is more directly linked to calcification potential. To test this prediction, we fit classification trees to field surveys of northern Wisconsin lakes for three calcifying AIS - rusty crayfish (Orconectes rusticus), banded mystery snail (Viviparus georgianus), and Chinese mystery snail (Cipanguladina chinensis). Along with lake area, variables associated with calcification were the best predictors of species distributions. Even though saturation state is the most biologically mechanistic variable, it did not improve model predictions or explain more variability in species presence than its surrogates. Overall, surrogates are sufficient for species distribution modeling in these lakes that exhibit a wide range of chemical states.