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Most plants that inhabit ant-gardens (AGs) are cultivated by the ants. Some orchids occur in AGs; however, it is not known whether their seeds are dispersed by AG ants because most orchid seeds are tiny and dispersed by wind. We performed in situ seed removal experiments, in which we simultaneously provided Azteca gnava ants with seeds of three AG orchid species and three other AG epiphyte species (Bromeliaceae, Cactaceae and Gesneriaceae), as well as the non-AG orchid Catasetum integerrimum. The seeds most removed were those of the bromeliad Aechmea tillandsioides and the gesneriad Codonanthe uleana, while seeds of AG orchids Coryanthes picturata, Epidendrum flexuosum and Epidendrum pachyrachis were less removed. The non-AG orchid was not removed. Removal values were positively correlated with the frequency of the AG epiphytes in the AGs, and seeds of AG orchids were larger than those of non-AG orchids, which should favour myrmecochory. Our data show that Azt. gnava ants discriminate and preferentially remove seeds of the AG epiphytes. We report for the first time the removal of AG orchid seeds by AG ants in Neotropical AGs.

Ant-gardens (AGs) are considered one of the most complex mutualist systems between ants and plants, since interactions involving dispersal, protection, and nutrition occur simultaneously in them; however, little is known about the effects of the transformation of ecosystems on their diversity and interactions. In five environments with different land use within an anthropic landscape in southeastern Mexico, we investigated the diversity and composition of epiphytes and host trees of AGs built by Azteca gnava. A total of 10,871 individuals of 26 epiphytic species, associating with 859 AGs located in 161 host trees, were recorded. The diversity and composition of epiphytes tended to be different between environments; however, Aechmea tillandsioides and Codonanthe uleana were the most important species and considered true AG epiphytes, because they were the most frequent, abundant, and occurred exclusively in AGs. Other important species were the orchids Epidendrum flexuosum, Coryanthes picturata, and Epidendrum pachyrachis, and should also be considered true AG epiphytes, because they occurred almost exclusively in the AGs. The AG abundance in agroforestry plantations was similar or even greater than in riparian vegetation (natural habitat). The AGs were registered in 37 host species but were more frequent in Mangifera indica and Citrus sinensis. We conclude that true epiphytes of A. gnava AGs persist in different environments and host trees, and even these AGs could proliferate in agroforestry plantations of anthropic landscapes.

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 AGs have a particular pattern of vertical distribution on their host trees; (2) does a process of succession of epiphytes occur during development of AGs; and (3) are epiphytes segregated in AGs?Location: Anthropic landscape in southeast 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, middle 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 cooccurrence, in 74% of the AGs examined. The species Ae. tillandsioides, Coryanthes picturata and Epid. flexuosum were most frequent in the upper AG zone, while Epid. pachyrachis was most frequent in the middle 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 spatial and temporal optimization in the establishment and development of these complex mutualistic systems.

Question:The distribution and interactions of terrestrial biodiversity are influenced by environmental gradients. In general, tropical species present a hump-shaped altitudinal species richness pattern related to gradients of temperature and precipitation. However, the effects of the elevational and environmental gradients on the co-occurrence of species that form specialized mutualisms in the lowland tropical forest canopy and the relative importance of these species in interaction networks are unknown. We studied ant-gardens, which are constituted by vascular epiphytes that inhabit ant nests exclusively. Our main question was: do the vegetation type, elevation, temperature, and precipitation alter the diversity and interactions of the associated species in ant-gardens?Location: Southeastern Mexico. Methods:We recorded epiphytes and ants associated with ant-gardens in 21 sites in southeastern Mexico (elevational range of 23-643 m a.s.l.), which is located on the northern limit of the distribution of Neotropical ant-gardens. We tested whether the vegetation type and gradients of elevation, temperature and precipitation influence the diversity (richness and composition) and interactions (centrality, i.e., relative importance of each species in epiphyte-epiphyte interaction networks) of the ant-gardens. Results:We found a total of 126 ant-gardens formed by 15 epiphyte species and two ant species. Seven epiphytes and only one ant (Azteca gnava) are specialists of antgardens (true ant-garden epiphyte and ant species respectively). Neither vegetation type nor elevational and environmental gradients influenced the richness, composition and centrality of the epiphytes, although some species only occurred in sites with greater precipitation. The true ant-garden epiphytes were more central than the non-true ant-garden epiphytes, with the orchid Epidendrum flexuosum being the most frequent and central epiphytic species in Mexican ant-gardens.Conclusions: Unlike guilds of epiphytes and ants considered individually, the antgardens represent a mutualism that maintains their patterns of diversity and interspecific interactions along gradients of elevation, temperature and precipitation.