Invasive ants disperse seeds farther than native ants, affecting the spatial pattern of seedling recruitment and survival

Abstract

Mutualists can vary in the quantity and quality of service which they provide to their partners. Variation in seed disperser quality depends on seed-processing traits, dispersal distance, and deposition location, all of which ultimately affect plant fitness. Here, we compared these aspects of seed dispersal quality between a native and an invasive ant species, and examined how they affect competition and plant performance. Using experimental mesocosm communities, we examined how these two ant species affect the spatial pattern of recruitment and establishment for four myrmecochorous plant species, including one invasive species. We measured the locations of dispersed seedlings relative to ant nests, adult plants, and other dispersed seedlings, as well as measured the effects of location on plant performance. The invasive ant, Myrmica rubra, secondarily dispersed seeds farther from its nests, creating a less clumped pattern of seedling recruitment compared to the native ant, Aphaenogaster rudis. Plant species responded differently to dispersal. Invasive seedlings recruited farther from adult plants than native seedlings, and had higher survival the farther they were from conspecifics. In contrast, native plants had higher survival and grew taller when dispersed farther from invasive plants. We show that seed-dispersing ant partners differ in mutualist quality creating differences in dispersal distance and deposition location that affects a plant's competitive environment. Our results reveal the potential for long-term consequences on plant community structure with changing ant partner identity. We emphasize the need to examine dispersal quality in addition to quantity to uncover the importance of partner identity in structuring communities.

Keywords: Aphaenogaster rudis; Biological invasions; Myrmecochory; Myrmica rubra; Seed dispersal; Spatial patterns.