Daphnia species invasion, competitive exclusion, and chaotic coexistence

The cladoceran Daphnia lumholtzi has invaded many US rivers and lakes. To better understand the ecological factors and consequences associated with D. lumholtzi invasion, we carried out a microcosm experiment evaluating competition of D. lumholtzi with a widespread native daphnid, D. pulex. We applied two light treatments to these two different microcosms and found strong context-dependent competitive exclusion in both treatments. We observed that D. lumholtzi out-competed D. pulex in the high light treatment, while D. pulex out-competed D. lumholtzi in the low light treatment. To better understand these results we developed and tested a mechanistically formulated stoichiometric population interaction model. This model exhibits chaotic coexistence of the competing species of Daphnia. The rich dynamics of this model allow us to suggest some plausible strategies to control the invasive species D. lumholtzi.