Ant mounds extend the duration of plant phenology events and enhance flowering success

Abstract

Mound-forming ants are important ecosystem engineers as they increase habitat heterogeneity, thus supporting multiple biotic interactions. How these ant-mediated changes in abiotic factors translate into temporal biotic heterogeneity, is a less studied subject. In a case study localized on a Danish heath, we investigated how ant mounds (mineral and organic mounds) affected the phenology and flowering success of five plant species growing on or between ant mounds (Lasius flavus and Formica exsecta). Specifically, we focused on the phenophases’ stem elongation, flowering and seed set. All plant species showed significantly earlier phenophases on the mounds compared to control patches between mounds. These advances resulted in two distinct flowering seasons for one plant species and prolonged continuous flowering seasons for the four other species, when mound and non-mound plant seasons were combined. Likewise, stem elongation and seed set seasons were prolonged, with either two distinct seasons or one continuous season, depending on plant species. Two plant species exhibited increased survival up to the flowering stage when growing on ant mounds, since they flowered before a drought killed a large part of the population. Probable drivers behind these effects, as revealed by a structural equation model, were elevated surface temperature and other soil edaphic factors responsible for plant growth. Furthermore, the direct effects of the ant mounds were nearly twice as high for the organic mounds of F. exsecta compared with the mineral mounds of L. flavus. Possible implications are more resilient ecosystems, as prolonged seasons can mitigate phenological mismatches between interacting species.