Just the right size for the right seed: successful seed dispersal is associated with ant body size
Palesa Natasha Mothapo, Theresa Wossler , Palesa Natasha Mothapo
Stellenbosch University, South Africa; Stellenbosch University, South Africa ; Stellenbosch University, South Africa
The invasive Argentine ant disrupts an important see-dispersal mutualism in the Cape Floristic Region, a biodiversity hotspot, through the displacement of native ant species. The displacement of these keystone ant species can contribute you changes in plant diversity and ecosystem function as a direct impact of argentine ant invasion. Ants were collected in invaded and uninvaded sites within two protected areas using pitfall traps and baiting. Vegetation surveys were conducted and seeds from myrmecophore plants were collected during seed rain. Morphological measurements were conducted on ants that occurred in both invaded and uninvaded sites, along with seed size measurements from those plants that were most abundant in the respective sites. Cafeteria experiments were used to measure recruitment and removal of seeds by different species within each study area. The most important seed dispersers were eliminated from invaded sites, especially Anoplolepis custodiens. Using Structural Equation Modelling we found ant body size was strongly related to seed size. Invaded sites had up to 60% fewer ant species, and ants were more attracted to and removed smaller sized seeds. In contrast, a higher diversity of ants occurred in uninvaded sites and ants removed both large and small seeds of the test plants. Recruitment and removal rates differed significantly among ants in invaded and uninvaded sites; in invaded sites ants were slow to recruit and slow to remove seeds while the opposite was found in uninvaded sites. We show here that seed-dispersal mutualisms in the CFR are not exclusive, so that a plant is dispersed by a variety of ant species. Over time, there likely will be a shift in the vegetation structure and diversity of plants within the CFR due indirectly to Argentine ant invasion.