Positive interactions (mutualisms and commensalisms) are becoming more widely known as important processes in natural and agricultural communities. They can have strong and direct effects on associated species by creating hospitable environments for organisms lacking the morphological and/or physiological ability to cope without neighbors. Despite the recent recognition of the importance of positive interactions, we know little about how they influence the population dynamics of higher trophic levels. In this study, we have coupled our previous research on positive plant interactions among salt marsh plants with experiments on higher trophic levels to investigate the relative contribution of positive interactions to herbivore and predator population dynamics in a southern New England salt marsh. We experimentally manipulate salt marsh host plants with and without the physical buffering effects of plant neighbors to investigate the colonization dynamics and population growth rates of aphid herbivores. We s...