Does edge effect and patch size affect the interaction between ants and Croton lachnostachyus in fragmented landscapes of Chaco forest?

Abstract

Little is known about the role of ants visiting extrafloral nectaries (EFNs) of plants in fragmented forests of South America. The aim of this work was to determine whether patch size and edge effect affect the composition and frequency of ants that visit the EFNs of Croton lachnostachyus, and how these changes may alter the reproductive success of plants in a fragmented landscape of the Chaco forest, Argentina. Data were analyzed considering patch size and edge effects—as indicators of fragmentation—on ant assemblages visiting plants and on plant reproductive success through a field experiment. Ant species composition differed between the edge and interior of fragments, but not among fragments of different sizes. Dolichoderinae species and some bigger ants as Camponotus mus (Formicinae) were more abundant at the edges, whereas Myrmicinae ants dominated the interior of fragments. Foliar damage was higher in plants located at interior than at edges of fragments. The ant-exclusion experiment showed that seed mass, germinability, and foliar damage did not differ between control and ant-excluded plants. In contrast, fruit (year 2011) and seed production (years 2010 and 2011) was higher in control plants. We highlight the importance of studying ant–plant interactions combining different attributes of biodiversity (composition, structure, and function) to better understand ecological processes in fragmented landscapes.