Do ecological interactions promote the coevolution of ecological niches in the acacias (Fabaceae: <i>Vachellia</i> spp.) and their mutualistic ants (Formicidae: <i>Pseudomyrmex ferrugineus</i> group)?

Abstract Ecological interactions are a fundamental aspect of species niches and could play a crucial role in their evolution. The defensive mutualism between swollen-thorn acacias (Vachellia spp.) and ants of the Pseudomyrmex ferrugineus group exemplifies a well-documented coevolutionary relationship. In this mutualism, acacias provide food and nesting space for ants; in return, ants offer aggressive defence against intruders. Our research aims to understand the impact of this mutualism on the evolution of species’ ecological niches. We assessed phylogenetic niche conservatism within each lineage by fitting macroevolutionary models to the distribution of traits of species’ ecological niches, specifically niche breadth and niche position. Additionally, we compared ecological niche similarities among sister species pairs against a null model. The niche similarity between interacting and noninteracting species was assessed, alongside the potential of ecological niche similarity to reflect interaction time between species. The results showed no evidence of phylogenetic niche conservatism within each lineage. However, interacting species pairs exhibited significantly greater ecological niche similarity than noninteracting species pairs. Despite this, no relationship was found between the duration of interaction and ecological niche similarity. Our findings suggest that mutualistic coevolutionary dynamics in the swollen-thorn acacias and their mutualistic ants may influence their niche evolution, highlighting the significance of ecological interactions.