Describes striking spatiotemporal variation in the antguard and pollinator mutualist assemblages of Calathea ovandensis (Marantaceae). Fifteen different ant taxa (in 5 subfamilies) and 5 pollinator taxa (4 euglossine bees and 1 anthophorid bee) were associated with the plants in Veracruz, Mexico. 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, particularly 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 most spatial and temporal comparisons. In each assemblage there was a single taxon that was the least variable, in both time and space, in its relative abundance. Results, coupled with 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 due to divergent patterns of constancy, rarity and quality. -from Authors
