Strength of the modular pattern in Amazonian symbiotic ant–plant networks

Abstract

In natural environments, distinct species interact with differing level of specialization, and thereby generate complex interaction networks. Recent studies have shown that certain antagonistic and mutualistic networks have a highly modular structure. This indicates that within an ecological network, densely connected semi-independent compartments occur and reflect different levels of the structural and functional system. Despite strong evidence for the existence of a modular structure in obligate and symbiotic networks involving ants and myrmecophytes, it is still uncertain whether these networks are modular. Here, we used the modularity index (M) to evaluate whether symbiotic ant–myrmecophyte networks exhibit a modular pattern of interactions. The analyses were based on a large data set of ant–myrmecophyte networks collected in mature and secondary forests of the Brazilian Central Amazon. Our results indicate that symbiotic ant–myrmecophyte networks are highly modular (M = 0.53 ± 0.13) regardless of forest type. Using other network descriptors, we found no difference in links per species (Links = 0.68 ± 0.15) and network connectance (C = 0.31 ± 0.17) among the different types of forest. Furthermore, the composition of ants and myrmecophytes did not differ among forest types (ANOSIM; P > 0.05), reinforcing the idea that this symbiotic interaction can be resistant to different local and landscape environmental factors. In summary, this study contributes to a better understanding of the way biodiversity is organized in obligate and symbiotic ant–plant mutualisms.