Individual-based networks reveal the highly skewed interactions of a frugivore mutualist with individual plants in a diverse community

While plant-animal interactions occur fundamentally at the individual
level, the bulk of research examining the mechanisms that drive
interaction patterns has focused on the species or population level. In
seed-dispersal mutualisms between frugivores and plants, little is known
about the role of space and individual-level variation among plants in
structuring patterns of frugivore foraging and, thus, seed dispersal in a
plant community. Here we use an animal perspective to examine how space
and variation between individual plants affect movement and visitation by
frugivores foraging on individual fruiting plants. To do this, we used a
spatially explicit network approach informed by observations of the
movement and foraging of a frugivorous lemur species (Eulemur rubriventer)
amongst individual plants in a diverse plant community in Madagascar. The
resulting hierarchical networks, in which a few individual plants received
the bulk of the interactions, demonstrated how a generalist frugivore
species could act as an individual-plant specialist within a plant
community. The few individual plants that dominated interactions with the
lemurs shaped the modular spatial structure of frugivory interactions in
the community and facilitated visitation to near neighbors. This
interaction structure was primarily driven by extrinsic factors, as lemur
movements among plants were significantly influenced by the individual
plant’s spatial position and the species richness of fruiting plants in
its immediate neighborhood. Individual plants in central spatial
locations, with a rich fruiting neighborhood and large fruit crops,
received the most visits. The observed drastic inequality in the
interactions of a generalist frugivore within a highly diverse plant
community highlights the importance of considering individual-level
variation for essential ecosystem processes, such as seed dispersal.