POLLEN LIMITATION OF PLANT REPRODUCTION: ECOLOGICAL AND EVOLUTIONARY CAUSES AND CONSEQUENCES

TLDR

Seed production pollen limitation has been studied intensively, yet evidence is insufficient to assess its causes or consequences. The authors aim to critically evaluate theory and issues of pollen limitation, highlight the need for theoretical and empirical work on life‑history traits, Allee effects, and environmental perturbations in population declines, and call for research on its community and ecosystem effects. They formalize and extend Haig and Westoby’s conceptual model to guide research on the evolutionary consequences of pollen limitation. The synthesis concludes that a new approach is needed to discern whether pollen limitation reflects random fluctuations, adaptation to stochastic pollination, or chronic environmental perturbation, and that we are only beginning to understand its translation into plant population dynamics.

Abstract

Determining whether seed production is pollen limited has been an area of intensive empirical study over the last two decades. Yet current evidence does not allow satisfactory assessment of the causes or consequences of pollen limitation. Here, we critically evaluate existing theory and issues concerning pollen limitation. Our main conclusion is that a change in approach is needed to determine whether pollen limitation reflects random fluctuations around a pollen–resource equilibrium, an adaptation to stochastic pollination environments, or a chronic syndrome caused by an environmental perturbation. We formalize and extend D. Haig and M. Westoby's conceptual model, and illustrate its use in guiding research on the evolutionary consequences of pollen limitation, i.e., whether plants evolve or have evolved to ameliorate pollen limitation. This synthesis also reveals that we are only beginning to understand when and how pollen limitation at the plant level translates into effects on plant population dynamics. We highlight the need for both theoretical and empirical approaches to gain a deeper understanding of the importance of life-history characters, Allee effects, and environmental perturbations in population declines mediated by pollen limitation. Lastly, our synthesis identifies a critical need for research on potential effects of pollen limitation at the community and ecosystem levels.