A Biogeographic Comparison of Spiders within Illinois and Indiana

Abstract

In March 2017, the Indiana Academy of Science held a biodiversity symposium prior to their annual meeting. Spiders were among the taxa discussed. Although published data on spider distribution records in both states (Indiana and Illinois) are sparse – especially in Indiana – an online collection network (SCAN) exists that supplements these data. I examined each recorded species from the online collection network that contained the most spider records and attempted to determine each record’s validity by comparing the distance from its previously known range to either Indiana or Illinois. In addition, I calculated the numbers of species present in each state and within both states using published records. I also determined the general geographic range of each species based on known distribution data (northern, eastern, mid/eastern, southern, western, and widespread) and used a chi-square analysis with an adjusted residual post-hoc analysis to reveal significant differences from expected values. There were a significantly higher than expected number of spiders found in Indiana only that had eastern distributions and there were a significantly higher than expected number of spiders found in Illinois only that had western and northern distributions. Finally, there were a higher than expected number of spiders found in both states that possessed mid/eastern and widespread distributions. Records from the online database were not used because it became apparent that 10%–21% of the records may be misidentifications. These results emphasize that although the two states are adjacent to each other, the spider composition between the states have significant differences.