Mutualisms can play important roles in influencing species coexistence and determining community composition. However, few studies have tested whether mutualisms may affect species distributions by altering the niches of partner species. In a new study published in AoB PLANTS, Kazenel et al. show that a fungal endophyte is associated with a shift in the soil moisture niche of its host plant relative to a co-occurring, endophyte-free congener. The endophyte appeared to initially restrict its host’s distribution to wetter microsites before positively affecting its growth, suggesting the value of considering symbiont effects at different partner life stages. Their study identifies a symbiotic relationship as a potential mechanism facilitating the coexistence of two species, suggesting that symbiont effects on host niche may have community-level consequences.