Functional Equivalence in Seed Dispersal Effectiveness of Podocarpus parlatorei in Andean Fruit-Eating Bird Assemblages

BLENDINGER, PEDRO G.

Frontiers in Ecology and Evolution

Frontiers Media SA

Año: 2017 vol. 5

Most fleshy-fruited plants establish strong local interactions with a few fruit-eating speciesacross their distribution range, which can differ among sites and have a major impact forthe plant population dynamics. In turn, human disturbances alter both the original animalassemblage with which plants interact and the outcome of the mutualistic interaction.Negative consequences of human disturbances can be weakened when different seeddispersers exert similar effects on plant populations, being functionally equivalent. Tounderstand the consequences of variability in seed dispersers on the recruitment ofa long-lived tree species, I assessed changes in the assemblages of avian dispersersof Podocarpus parlatorei in subtropical Andean cloud-forests, and how these changesaffect the outcome of the interaction at different spatial scales. The seed dispersaleffectiveness (SDE) concept, defined as the likelihood of a seed removed by a fruit-eatingbird to be dispersed to a suitable site for seed survival and germination, provides theframework to compare the contributions of different birds to seed dispersal. I comparedthe SDE in two old-growth forests dominated by P. parlatorei and a human disturbedforest, and in the main habitat types of these sites. In all sites, highest SDE valueswere provided by ?gulpers? that swallow the whole fleshy cone (?fruit?), predominantlyElaenia and Turdus species. SDE was highest in forest edges and secondary forests,and negligible in other habitats. Equivalence in SDE was relatively low both within andbetween forest sites. Human forest disturbance modified the functional equivalence, thegeneralization in mutualistic interactions and the strength of SDE. Secondary forestsshowed the higher SDE and the greater richness of dispersers high in SDE; as aconsequence, the ecological equivalence increased in the most suitable habitat forrecruitment. This could lead to greater resilience of plant populations to local extinctionsof dispersers, and allows the recovery of human disturbed forests. This study shows thatin the replacement of functional equivalent species, the outcomes of the interactions arestrongly affected by disperser abundance and habitat use, at the expense of dispersers?trait redundancy on plant population dynamics and community structure.