Data from: Coexistence through mutualist-dependent reversal of competitive hierarchies

Mechanisms that allow for the coexistence of two competing species that share a trophic level can be broadly divided into those that prevent competitive exclusion of one species within a local area, and those that allow for coexistence only at a regional level. While, the presence of aphid-tending ants can change the distribution of aphids among host-plants, the role of mutualistic ants has not been fully explored to understand coexistence of multiple aphid species in a community.The tansy plant (Tanacetum vulgare) hosts three common and specialised aphid species, with only one being tended by ants. Often, these aphids species will not coexist on the same plant, but will coexist across multiple plant hosts in a field. In this study, we aim to understand how interactions with mutualistic ants and predators affect the coexistence of multiple species of aphid herbivores on tansy. We show that the presence of ants drives community assembly at the level of individual plant, i.e. the local community, by favouring one ant-tended species, Metopeurum fuscoviride, while preying on the non-tended Macrosiphoniella tanacetaria and, to a lesser extent, Uroleucon tanaceti. Competitive hierarchies without ants were very different from those with ants. At the regional level, multiple tansy plants provide a habitat across which all aphid species can coexist at the larger spatial scale, while being competitively excluded at the local scale. In this case, ant mutualist-dependent reversal of the competitive hierarchy can drive community dynamics in a plant-aphid system.