Abstract
Interactions mediated by extrafloral nectary (EFN)-bearing plants that reward ants with a sweet liquid secretion are well documented in temperate and tropical habitats. However, their distribution and abundance in deserts are poorly known. In this study, we test the predictions that biotic interactions between EFN plants and ants are abundant and common also in arid communities and that EFNs are only functional when new vegetative and reproductive structures are developing. In a seasonal desert of northwestern Argentina, we surveyed the richness and phenology of EFN plants and their associated ants and examined the patterns in ant-plant interaction networks. We found that 25 ant species and 11 EFN-bearing plant species were linked together through 96 pairs of associations. Plants bearing EFNs were abundant, representing ca. 19 % of the species encountered in transects and 24 % of the plant cover. Most ant species sampled (ca. 77 %) fed on EF nectar. Interactions showed a marked seasonal pattern: EFN secretion was directly related to plant phenology and correlated with the time of highest ant ground activity. Our results reveal that EFN-mediated interactions are ecologically relevant components of deserts, and that EFN-bearing plants are crucial for the survival of desert ant communities.
Highlights
For many ant species, carbohydrates represent a critical energy resource for colony growth, worker activity and worker survival (Davidson et al 2003; Grover et al 2007; Lach et al 2009; Byk and Del-Claro 2011; Wilder et al 2013; Kay et al 2014)
Of the 63 species of plants encountered in transects in the Jarillal and Piedmont sites, we found 11 extrafloral nectary (EFN)-bearing plant species (17.46 % of total species sampled)
Extrafloral nectaries are reported for the first time in four of these species, Opuntia sulphurea, Tephrocactus alexenderi, T. articulatus and S. rigida
Summary
Carbohydrates represent a critical energy resource for colony growth, worker activity and worker survival (Davidson et al 2003; Grover et al 2007; Lach et al 2009; Byk and Del-Claro 2011; Wilder et al 2013; Kay et al 2014). Some of the forms in which carbohydrate-rich liquid food is available for ants are extrafloral (EF) nectar, honeydew from sap-feeding hemipterans and secretions from lepidopteran larvae. These sweet secretions constitute the basis for protective mutualisms: plants provide ants with food, and ants protect plants from herbivores and animals from predators (Heil and McKey 2003). The importance of carbohydrates as an energy resource for ants and the abundance of ants in most terrestrial ecosystems might explain why mutualistic associations between ants and plants or animals that provide such sugar-rich liquids have evolved many times and are widespread in nature (Rico-Gray and Oliveira 2007). Extrafloral nectar is an aqueous solution, especially rich in mono- and disaccharides (fructose, glucose and sucrose), and includes free amino acids (Koptur 2005)
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