Spatial structure of ant-gardens: vertical distribution on host trees and succession/segregation of associated vascular epiphytes

Abstract

Questions Ant-gardens (AGs) involve a close association between epiphytes and ants with concurrent mutualistic interactions including protection, dispersal and nutrition; however, little is known about the spatial structure patterns that determine their establishment and formation. Our main questions were: 1) Do the AGs have a particular pattern of vertical distribution on their host trees? 2) Does a process of succession of epiphytes occur during the development of AGs? 3) Are epiphytes segregated in AGs? Location An anthropic landscape in southeastern Mexico. Methods We studied AGs built by Azteca gnava ants. We examined their vertical distribution on host trees as well as the diversity, composition and reproductive status of vascular epiphytes associated with the lower, medium and upper zones of small, medium and large AGs. Results A total of 859 AGs and 10,871 epiphytes, belonging to 26 different species, were recorded. We found that AGs are primarily (75%) located within tree crowns, and that the diversity and composition of epiphytes vary among AG sizes and among AG zones. We infer that the epiphytes that first become established in AGs are the bromeliad Aechmea tillandsioides and the gesneriad Codonanthe uleana, followed by the orchid Epidendrum flexuosum and the cactus Epiphyllum phyllanthus; these species were recorded, either individually or in co-occurrence, in 74% of the AGs examined. The species Ae. tillandsioides, Coryanthes picturata and Epid. flexuosum were most frequent in the upper AG zone, while Epidendrum pachyrachis was most frequent in the medium AG zone. Conclusions Our results show that AGs have distinct vertical distribution patterns on their tree hosts and that the establishment of epiphytes in AGs is successive and segregated, suggesting a spatial and temporal optimization in the establishment and development of these complex mutualistic systems. This article is protected by copyright. All rights reserved.