Regional equivalence in seed dispersal of core bird species: the key to explain seed-dispersal syndromes emergence?

Most mutualistic networks have a great number of species interacting in a given moment and space, and a core of few species disproportionally affecting the remaining species. Geographical variation in core disperser diversity would intuitively avoid the emergence of seed-dispersal syndromes. However, if different core species from different sites were equivalent in the seed dispersal provided, they could act as a unique selective force for fruit traits in a regional scale. We monitored bird-fruit interactions in 10 sites of Yungas forest, in three latitudes and three altitudes. We recorded 3579 interactions between 54 bird and 69 fleshy-fruited plant species. Previous analyses have determined eight core bird species, and six functional groups of fleshy-fruited plants in the study area. For each plant group, we calculated the quantitative component (QC) of seed-dispersal effectiveness provided by each core bird species at each site. We built bi-plots with mean QC at x-axis and ΔQC at y-axis, comparing QC’s of all core bird species pairs from different altitudes in a given latitude, and vice-versa. We found (1) pools of 1-3 core birds per site with high and equivalent QC’s provided to all plant groups, recognized as point groups close to the right lower corner of bi-plots; and (2) core species with even higher QC’s in 1-2 sites, without equivalencies, provided to singular plant groups. We discuss how the combined action of these two core bird groups could be implied in the emergence of seed-dispersal syndromes at a regional scale.