Modeling the potential North American ranges of the invasive crayfishes Faxonius rusticus (rusty crayfish) and Procambarus clarkii (red swamp crayfish) under current and future climate projections

Carter Cranberg, School of Environmental Sustainability, Loyola University Chicago, Chicago, IL and Reuben P. Keller, Institute of Environmental Sustainability, Loyola University Chicago, Chicago, IL

Background/Question/Methods
Understanding the drivers of non-native species distributions is vital for management efforts and research on potential range expansion. In North America, the spread of the crayfish species Faxonius rusticus (rusty crayfish) and Procambarus clarkii (red swamp crayfish) from their native ranges has posed ecological problems for freshwater systems. Utilizing the software Maxent, high-resolution models of these species’ distributions can be built from available occurrence data. These models can then be combined with climate-change scenario models to generate projections of the invasive crayfishes’ distributions for future decades.
First, environmental variables for the initial distribution models were selected from relevant literature. These variables were assessed for over-correlation with a Pearson Correlation Matrix test, removing redundant variables. Occurrence data of the invasive crayfish was collected and sorted from the U.S. Geological Survey and the Global Biodiversity Information Facility. Variables and occurrence data were processed in Maxent, resulting in a “present-day” species-distribution probability map. This model was then re-processed in Maxent with the addition of “future” climatic variables (i.e., climate variables that have been calculated from climate-change models). Maxent was then used to produce species distribution projections for the years 2050 and 2070.

Results/Conclusions
Present-day models from Maxent display higher probability of distribution near the occurrence data for both species, but also forecast areas of high probability where occurrence data does not exist. The 2050 projections for both species display extensive northern range expansion across the entire North American continent – this trend continues in the 2070 projections. Individual pixels of the models represent 1 KM^2 and were used to calculate changes in the total area of suitable habitat predictions. Both species displayed range expansions from present day to 2070, with F. rusticus’s range expanding 190.16% and P. clarkii’s range expanding 12.5%.
The high-resolution of these models allows for the identification of waterbodies and waterways that are not currently suitable habitat for invaders but that may, in the future, become suitable. Notable freshwater bodies that appear to be at risk of invasion expansion in future projections are large areas of the Great Lakes, the Mississippi River, the Columbia River, and large coastal regions of Canada. These habitats represent some of the largest freshwater ecosystems in North America – understanding how and when invasive crayfish may be able to enter them is a key step in preventing the spread and damage caused by these non-native species.