Limnetic zooplankton structure and the impact of invasion by an exotic cladoceran, Daphnia lumholtzi

A recent invader to Ohio is the cladoceran, Daphnia lumholtzi which was first reported in the state in 1993. A survey of 93 lakes and reservoirs was used to investigate the current distribution of D. lumholtzi in Ohio. Analysis of these samples revealed that D. lumholtzi has established in 19 of the waterbodies surveyed. Surface area was the only abiotic characteristic that exhibited a significant difference between invaded and non-invaded localities, thus it seems unlikely that local environmental conditions prohibit the invasion of D. lumholtzi. Additionally, it was found that D. lumholtzi is associated with smaller sized zooplankton communities. These results suggest that interactions with the native species, rather than abiotic characteristics, may be responsible for controlling the establishment of D. lumholtzi.;Sediment cores were processed for cladoceran remains and sedimentary pigments to determine community types that are vulnerable to invasion and the potential impact that D. lumholtzi may have on native communities. The paleolimnological study determined that lakes invaded by D. lumholtzi are characterized by lower species diversity and communities comprised of smaller sized zooplankton species. These results were supported in an experimental mesocosm study. A resource overlap study investigated the utilization of food resources by D. lumholtzi in comparison to native cladoceran species. This study concluded that there is minimum food resource overlap between D. lumholtzi and small bodied zooplankton species, while larger species consume larger particles and exhibit higher grazing rates than D. lumholtzi.;Each of the investigations suggests that communities with larger sized species may inhibit the establishment of D. lumholtzi as a result of high resource overlap. Communities dominated by smaller species may be more susceptible to invasion as D. lumholtzi does not appear to be in direct competition with these species. Further, the elongated spines of D. lumholtzi may allow it to persist in the high predation environments that characterize zooplankton communities dominated by small bodied species. This study concludes that the identities or traits of a particular species do shape the outcome of invasion; thus it is important to consider the structure of a community while investigating patterns of invasion.