Influence of secondary dispersal by ants on invasive processes of exotic species with fleshy fruits

Abstract

Invasive alien plant species (IAPS) are severely changing ecosystems on earth. Studying the interactions that allow IAPS to establish and spread in the new regions is crucial. Ants can disperse exotic fleshy fruits. We asked the following questions at three different sites of Chaco Mountain Forest (Córdoba, Argentina): (1) Do ants disperse diaspores of native, neonative and IAPS differentially? (2) Which is the ant species assemblage and their role in the secondary dispersal of each of the selected plant species? (3) Do ants interact in different ways with intact and manipulated fruits, and these interactions vary within plant species origin? and (4) Are diaspore traits different among the plant species considered? We selected four plant species: Celtis ehrenbergiana (native), Lantana camara (neonative), Pyracantha angustifolia and Ligustrum lucidum (IAPS). Two experiments were performed: (1) To disentangle the contribution of ants to the secondary dispersal process, and (2) To investigate the ant behavior of ground-foraging ant species when they encountered the fruits. Additionally, we measured fruit mass and the number of seeds per fruit. Ants were the main diaspore dispersers on the Chaco Mountain Forest ground. Twelve ant species interacted with the fruits; the native presented the higher number, followed by the neonative, and the two IAPS. Only Acromyrmex crassispinus and Pheidole cordyceps removed diaspores. Furthermore, the fruits differed in their mass and also in the number of seeds. Our results highlight the importance of ants and also diaspores traits in these diffuse mutualisms, and enhance their role in plant-invasive processes in subtropical ecosystems.