Inequalities in intraspecific plant-lemur interactions drive seed dispersal patterns

Biotic interactions occur between individuals and accumulate to shape
species-level interaction structure across a community. Skewed interaction
structures, where a few individuals are highly connected and most have few
interactions, are increasingly identified at the individual-level.
However, how individual-level interactions accumulate to shape
species-level interaction outcomes remains unclear. We studied the
interactions of three frugivorous lemur species (Varecia variegata
editorum, Eulemur rufifrons, and Eulemur rubriventer) with individual
plants within a defined area of 4km2. We examined the consistency of
skewed patterns across time, lemur species, and plant species; compared
individual- and species-level network structure; investigated the
intrinsic (DBH and fruit crop size) and extrinsic (fruit availability and
richness) factors affecting interaction structure; and tested interaction
structure impact on seed dispersal. We found a substantial and consistent
skew in the interactions of individual plants with the lemurs, such that
we observed a single visit for 70% of all plant individuals. This skewed
pattern was consistent across time, lemur species, and plant species.
Highly visited plant individuals (with > 20 visits per lemur
species) occurred infrequently and only for visitation by V. variegata
editorum and E. rubriventer. These differences in lemur visitation were
significant at the individual level, and non-significant at the species
scale. Individual interaction networks were smaller, more specialized, and
had lower connectivity than their species counterparts. These differences
demonstrate the importance of individual-level interactions, which contain
substantial interaction variation not present at the species scale.
Individual-level interactions were positively influenced only by DBH, and
fruit crop size across the study area. This skewed interaction structure
impacted seed dispersal patterns, such that seeds were most likely to be
deposited within 15 m of highly visited plants. Our results highlight the
importance of individual-level interaction variation for seed dispersal
mutualisms and call for further study on the consistency of such patterns
across ecosystems.