Edge effects on the pollination of tropical cloud forest plants

Exposure to edge is one consequence of habitat fragmentation that can result in detrimental effects on the fauna and flora of fragmented habitats. In this study, edge is defined as a sharp transition between natural and anthropogenic habitats, such as between forest and pastures. I assessed the effect of proximity to the edge on the pollination levels of 13 cloud forest plant species in Colombia. I collected the styles of plants located in three zones of each of three forest fragments: edge (0-10 m), transition zone (10-50 m), and interior (50-200 m).; Pollination levels, measured as the median number of pollen tubes that reached the base of the styles, were not consistently affected in their pollination by the proximity to the edge. Intra-individual coefficient of variation, i.e., variation in pollination levels among flowers in individuals was also not affected by the proximity to the edge. Few plant species were significantly affected by the edge, and those that were affected differed in the direction of the edge effects. To measure the edge effect on the potential for limitation of seed set and its penetration on successive levels of the plant- pollinator interaction, I measured the proportion of flowers in each individual with a number of pollen tubes equal to or larger than half the number of ovules. In one of two cases where there was an edge effect on pollination levels, the potential for seed set was also affected. Edge effects, when present, were inconsistent between flowering seasons.; Field experiments with two introduced plant species showed no differences in pollination levels between the plants placed at the edge and in the forest interior. There are several possible explanations for these results. First, above-ground environmental conditions do not differ between the edge and the interior, thus making it unlikely that the pollinators are affected by the edge. Second, below-ground conditions are affected only for the first 10 m into the forest, and this affects the densities of the focal plants in only one of the fragments. Finally, plant-pollinator interactions can be robust to some perturbations because generally, these interactions have little species-specificity.