Data from: Within-species trait variation can lead to size limitations in seed dispersal of small-fruited plants

The inability of small-gaped animals to consume very large fruits may
limit seed dispersal of the respective plants. This has often been shown
for large-fruited plant species that remain poorly dispersed when
large-gaped animal species are lost due to anthropogenic pressure. Little
is known about whether gape-size limitations similarly influence seed
dispersal of small-fruited plant species that can show a large variation
in fruit size within species. In this study, fruit sizes of 15 plant
species were compared with the gape sizes of their 41 animal dispersers in
the temperate, old-growth Białowieża Forest, Poland. The effect of
gape-size limitations on fruit consumption was assessed at the plant
species level, and for a subset of nine plant species, also at the
individual level, and subindividual level (i.e., fruits of the same plant
individual). In addition, for the species subset, fruit-seed trait
relationships were investigated to determine whether a restricted access
of small-gaped animals to large fruits results in the dispersal of fewer
or smaller seeds per fruit. Fruit sizes widely varied among plant species
(74.2%), considerably at the subindividual level (17.1%), and to the
smallest extent among plant individuals (8.7%). Key disperser species
should be able to consume fruits of all plant species and all individuals
(except those of the largest-fruited plant species), even if they are able
to consume only 28-55% of available fruits. Fruit and seed traits were
positively correlated in eight out of nine plant species, indicating that
gape size limitations will result in 49% fewer (in one plant species) or
16-21% smaller seeds (in three plant species) dispersed per fruit by
small-gaped than by large-gaped main dispersers, respectively. Our results
show that a large subindividual variation in fruit size is characteristic
for small-fruited plant species, and increases their connectedness with
frugivores at the level of plants species and individuals. Simultaneously,
however, the large variation in fruit size leads to gape-size limitations
that may induce selective pressures on fruit size if large-gaped
dispersers become extinct. This study emphasizes the mechanisms by which
gape-size limitation at the species, individual and subindividual level
shape plant-frugivore interactions and the co-evolution of small-fruited
plants.