Predator-mediated coexistence of exotic and native crustaceans in a freshwater lake?

Abstract

The predatory effects of a Dipteran insect, Chaoborus, on the competition between exotic cladoceran Daphnia lumholtzi and two natives, D. catawba and D. pulex, were studied for a period of three years in a freshwater reservoir, Lake James, North Carolina (USA). D. lumholtzi was first encountered in September 1997 and it was present only between August and October when population densities of native species were low and that of Chaoborus sp. was high. The patterns observed in the population dynamics of the exotic D. lumholtzi and two natives, Chaoborus suggest that a 'predator mediated coexistence' phenomenon might be taking place in Lake James. The strong positive correlation between Chaoborus and D. lumholtzi and the negative correlation between Chaoborus, D. catawba and D. pulex is supportive of this hypothesis.