Does pollen limitation limit plant ranges? Evidence and implications

Background/Question/Methods

Sexual reproduction often declines toward species’ range edges, reducing fitness, dispersal, and adaptive potential. For plants, sexual reproduction is frequently limited by inadequate pollination. Case studies show that pollen limitation can limit plant distributions, while theory and data syntheses suggest that biotic interactions are more likely to limit species low-latitude ranges. However, the extent to which pollination commonly declines towards plant range edges, and whether this varies between high- and low-latitude range edges, is unknown. We ask, does pollination increasingly limit seed production toward plant range edges? We combine global databases of pollen-supplementation experiments (GLoPL; to derive the strength of pollen limitation) and plant occurrence data (GBIF; to determine how close each pollen-limitation measurements was to the species’ range edge). Using a phylogenetically controlled meta-analysis, we test whether pollen limitation increases towards plant range edges, and whether this varies with absolute latitude and how equatorward the range edge was. We also summarize targeted experiments measuring pollen limitation toward a known range limit.

Results/Conclusions

While there was significant pollen limitation across studies, we found little evidence that pollen limitation increases towards plant range edges, nor towards the tropics. Meta-analysis results are consistent with results from targeted experiments, in which pollen limitation increased significantly towards only 14% of 14 plant range edges, suggesting that pollination contributes to range limits less often than do other interactions. Together, these results suggest that pollination is one of the rich variety of potential ecological factors that can contribute to range limits, rather than a generally important constraint on plant distributions.