Keystone competitor creates spatial patterns of biodiversity

Abstract Conventional ecological theory on competition and competitive exclusion states that competition should limit diversity. However, diversity of all species is more common than competitive exclusion would suggest, especially in the tropics. Here, we use theoretical and field approaches to examine the relationship between a keystone ant competitor ( Azteca sericeasur ) and the richness of a ground-foraging ant community in a spatially explicit context. Theoretically, we demonstrate that a fixed keystone competitor can increase species diversity. In addition, we sampled the ground-foraging ant community in three differentially managed coffee habitats and found – with the exception of plots in the most intensified coffee habitat – a consistently higher species richness near to the keystone competitor and lower richness with increasing distance. These patterns show that keystone competitors may contribute to the maintenance of local species richness.