Testing a Metapopulation Model of Coexistence in the Insect Community on Ragwort (Senecio jacobaea)

We tested a metapopulation model of coexistence for the insect herbivores of ragwort. Previous research suggested that some of them survive the intense but patchy defoliation of ragwort by the cinnabar moth (Tyria jacobaeae) by continually colonizing new patches of ragwort. We confirmed prior findings of strong asymmetric competition among these insects. However, we found that all insects, including the cinnabar moth, readily colonized experimental patches up to 380 m from a source. In our study system (60 ragwort patches in a 1.3-km2 area), median and maximum distances between natural patches were 20 m and 85 m, respectively. Because of the high level of dispersal relative to interpatch distances, a metapopulation model is unlikely to apply in this system. We propose other means of coexistence and suggest that metapopulation hypotheses require more critical examination than they have been given.