Influence of temperature on exotic Daphnia lumholtzi and implications for invasion success

We investigated the effects of water temperature on the exotic cladoceran Daphnia lumholtzi in a eutrophic Kansas reservoir (USA) and under laboratory conditions. Daphnia lumholtzi demonstrated a distinct late summer appearance in the reservoir at temperatures between 26 and 31 degreesC, which corresponded with steep declines in the densities of native Daphnia spp. Laboratory life-table experiments confirmed that D. lumholtzi performs well at elevated water temperatures. The intrinsic rate of increase (r), net reproductive rate (R-4), age at first reproduction, survivorship (l(x)) and molting rated all demonstrate that D. lumholtzi has a high temperature optimum between 20 and 30 degreesC. A comparison of literature-reported r-values indicates that the reproductive rate of D. lumholtzi is comparable with other Daphnia spp. between 20 and 25 degreesC, but also implies that D. lumholtzi may out-perform some Daphnia spp. at temperatures > 25 degreesC. Collectively, these results suggest that D. lumholtzi may be taking advantage of a late summer thermal niche, and that this invader may continue to colonize lakes and reservoirs in the southern US. However, life table data also indicate that D. lumholtzi performs poorly at temperatures < 10<degrees>C, which may inhibit the range expansion of this invader into northern waters.