Assessing the Distribution of Iow a Darters (Etheostoma exile) in Streams of Northern Illinois

Species distribution models are good tools for predicting the possible range of species that are rare or difficult to effectively sample for. Populations of the state-listed Iowa Darter (Etheostoma exile) have been declining in Illinois for more than a century. However, recent observations in headwater streams of northern Illinois with no previous records of Iowa Darters revealed the need to update its known distribution. We used MaxEnt, generalized linear, and random forest models, along with targetted field surveys, to estimate the historical and current distribution of Iowa Darters in Illinois. Our model of the historical distribution in Illinois estimates Iowa Darters were sporadically distributed in northeastern Illinois, focused in the Chicago metro and suburban region. Using the current distribution model, we selected and sampled 30 potential sites divided evenly between having low, medium, and high probabilities of Iowa Darter occurrence. Wefound nine new Iowa Darter localities during the surveys. We revised the distribution model with the findings and found the range of Iowa Darters in Illinois has substantially decreased from its historical range. However, areas of suitable habitat still exist and remain unsampled. Sampling and monitoring of these areas could guide potential conservation efforts and lead to additional populations.