Context-dependency and anthropogenic effects on individual plant-frugivore networks

MIGUEL, M. F.; JORDANO, P.; TABENI S.; CAMPOS, C. M.

OIKOS

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2018 vol. 127 p. 1045 - 1059

0030-1299

Anthropogenic activities, such as grazing by domestic animals, areconsidered drivers of context variation that may influence the structure ofindividual interaction networks. One aspect of growing interest in ecology isto explain how the topology of complex ecological networks emerges fromthe interactions that actually occur among individuals. The study ofindividual-based interaction networks allows exogenous explanatoryvariables for testing specific hypotheses on how species-level interactionpatterns emerge from the pooled interaction modes of individuals withinpopulations. Exponential random graph models (ERGMs) examine theglobal structure of networks by allowing the inclusion of specific nodeproperties as explanatory covariates. Here we assessed the structure ofindividual plant-frugivore interaction networks at different land usemanagements (grazed vs ungrazed, protected areas) and whether differentmanagement practices affect how ecological variables influence the modeof interaction between individual plants and their frugivore species. Wequantified the number of visits, the number of fruits removed per visit andthe interaction strength of mammal frugivore species at each individualtree. Additionally we measured a set of ecological variables at theindividual, microhabitat and landscape scales that might have produced theinteraction networks at both land uses. Individual plant-frugivore networkswere significantly modular in both land uses but the number of moduleswas higher in the grazed areas. By applying ERGMs we found interactionnetworks for grazed and ungrazed lands were structured by individualecological traits, by the microhabitat beneath the tree canopy and wereaffected by habitat modifications of anthropogenic origin. Theneighborhood surrounding each individual plant influenced plant-frugivoreinteractions only at the grazed-land trees. We conclude that anthropogenicland uses influence the topological patterns of plant-frugivore networks andthe frugivore visitation to trees through modification of both habitatcomplexity and the ecological traits underlying interactions betweenindividual plants and frugivore species.