Asymmetric competitive effects during species range expansion: an experimental assessment of interaction strength between ‘equivalent’ grazer species at their range overlap

1. Biotic interactions are central to the development of theory and concepts in community ecology; experimental evidence has shown their strong effects on patterns of population and community organization and dynamics over local spatial scales. The role of competition in determining range limits and preventing invasions at biogeographic scales is more controversial, partly because of the complexity of processes involved in species colonization of novel habitats and the difficulties in performing appropriate manipulations and controls. 2. We examined experimentally whether competition is likely to affect poleward range expansion hindering or facilitating the establishment of the limpet Scurria viridula along the southeastern Pacific rocky shore (30°S, Chile) in the region occupied by the congeneric S. zebrina. We also assessed whether competition with the “invader” or range expanding species could reduce individual performance of the ‘native’ S. zebrina and depress local populations 3. G...