Abstract
We observed striking spatiotemporal variation in the antguard and pollinator mutualist assemblages of a neotropical herb. Fifteen different ant taxa (in five subfamalies) and five pollinator taxa (four euglossine bees and one anthrophorid bee) were associated with the plants during censuses at four sites. Ants and pollinators were censused for 4 and 3 yr, respectively. The mean number of taxa per site per year was 6.8 for ants and 3.6 for pollinators. The ant assemblage varied more than the pollinator assemblage, paticularly spatially. The ant assemblage varied more through space than through time (means of the proportional similarities for pairwise comparisons of assemblages were 0.37 and 0.51, respectively), while the pollinator assemblage varied equally through space and time (means of the proportional similarities were 0.53 and 0.50, respectively). For individual taxa of both assemblages, the coefficient of variation in relative abundance was large (>75%) for the majority of spatial and temporal comparisons. In each assemblage there was a single taxon (in the antguard, a rare taxon, but in the pollinators, an abundant taxon) that was the least variable, surprisingly in both time and space, in its relative abundance. These results, coupled with our previous findings of significant variation among mutualist taxa in the magnitude of their beneficial effects, indicate that plants may be subject to highly variable selection by their mutualist assemblages. The most beneficial antguard was consistently rare; the most beneficial pollinator was abundant in one site—year but rare or absent in most site—years. The taxon that was consistently abundant was not an efficient pollinator. Evolutionary specialization of plants on particular animals may be constrained by lack of constancy in the relative abundance of animals and the opportunity for specialization may differ greatly between interactions (e.g., antguards and pollinators) due to divergent patterns of constancy, rarity, and quality.
