Competition in Cladocera: implications of the trophic resources use overlap

Although numerous evidence reveals the use of different feeding strategies among cladocerans, the impact of trophic niche overlap on their patterns of coexistence has been underestimated due to the classical description of pa ssive feeding behavior. Under microcosm conditions, paired experiments of p opulation dynamics were conducted for the cladocerans Moina micrura (Moinid ae) and Ceriodaphnia dubia (Daphnidae), specialists on the resources Chlore lla sp. and Oocystis sp. (Chlorococcales) respectively, and for the general ist species Daphnia ambigua (Daphnidae), during 35 - 45 days. While, the sp ecialists M. micrura and C. dubia did not show evidences of competition, th eir presence lead to a significant decrease in the density of the generalis t D. ambigua and in some cases even led to extinction. Although the general ist qualitatively affected the dynamics of each specialist, it did not affe ct their density, thus resulting in an asymmetrical interaction among each specialist with the generalist species. These results demonstrate that the feeding behavior and resource use overlap should be determinant conditions in the composition of cladoceran assemblages.