Topological change of Andean plant–pollinator networks along an altitudinal gradient

Abstract

Pollination interaction networks exhibit structural regularities across a wide range of natural environments. Long-tailed degree distribution, nestedness, and modularity are the most prevalent topological patterns found in most bipartite networks analyzed up to day. In this work we evaluate the variation of these topological properties along an altitudinal gradient. To this end,we examined four plant– pollinator networks from the Chilean Andes at 338S, in range from 1800 to 3600 m elevation. Our results indicate that network topology is strongly and systematically affected by elevation. At increasing altitude, thenumber of potential visitors per plant decreased, and species’ degree distributions are closer to random expectations. On the other hand, the nested structure of mutualistic interactions systematically decreased with elevation, and networkmodularity was significantly higher than randomexpectations over the entire altitudinal range. Inaddition, at increasing elevations thepollinationnetworks were organized infewer and more strongly connectedmodules.Our results suggest that the severe abiotic conditions found at increased elevations translate into less organized pollination networks.