CHANGES IN SHALLOW MARINE FUNCTIONAL SPACE ACROSS THE RICHMONDIAN INVASION IN THE CINCINNATIAN ARCH (LATE ORDOVICIAN)

The use of the fossil record to understand the role of biotic invasion on ecosystem functioning is imperative; invasion is becoming more common as temperatures rise and biogeographical barriers break down. How species are distributed among functional groups in particular has important consequences for ecosystem functioning, as loss of species also does not always equate to loss of functions. Here we examine the effects of non-native species on functional ecospace using paleocommunities from six third order depositional sequences from the Late Ordovician in the Cincinnatian Arch (USA). We examined 813 species from museum collections and the Paleobiology Database, and grouped them using three common functional traits readily identifiable in fossil taxa: locomotion, tiering, and feeding mode. In the early phase of the invasion, two functional groups were lost and the number of species decreased, leading to reduced functional vulnerability, i.e. the percentage of functional groups with only one species (27.8 to 18.7). The invasion occurred in several pulses, during which vulnerability remained the same despite small fluctuations in the number of species and functional groups. After the invasion, vulnerability dropped significantly (6.6) coinciding with the loss of one functional group, while the number of species increased. Prior to invasion there were 157 species occupying 18 functional groups. By the end of the invasion, there were 224 species in 15 functional groups. This pattern suggests that invaders occupied existing functional groups, likely outcompeting incumbents. Overall, functional space was reduced by the invasion leading to an increase in the average number of species per functional group, as species were redistributed into fewer functional groups. An increase in the number of species did not result in an increase in the number of functional groups. While a decrease in functional vulnerability may have led to greater stability, the role of an ecological function is relative to the overall composition of the community (i.e., the food web), and the interactions among functions. Therefore, additional traits are currently being examined in conjunction with food web structure, such as trophic position, to assess whether functional changes corresponded to changes in stability.