Apparent competition occurs when species that otherwise may not directly interact still exhibit negative indirect effects on one another because they share a food-limited predator (enemy). Even though this type of indirect interaction has received significant theoretical and empirical attention, alternative mechanisms producing similar results have not been considered in the literature. In this paper we document the results of a series of microcosm experiments aimed to evaluate the importance of the generalist consumer Daphnia ambigua upon the relative abundance of the more specialized Moina micrura and Ceriodaphnia dubia (Cladocera). We compared the population parameters of M. micrura and C. dubia when alone, in coexistence, and in the presence and absence of D. ambigua. While M. micrura and C. dubia did not show evidence for interspecific competition, the addition of D. ambigua promoted a reduction in the maximal population density of M. micrura, causing a pattern of indirect competition with C. dubia that resembles predator-mediated apparent competition. This result suggests that non-predatory interactions need to be considered as a potential source of apparent interactions in natural communities.
Ginger Martinez, R. Medel