Rapid changes in seed dispersal traits may modify plant responses to global change
Abstract
When climatic or environmental conditions change, plant populations must either adapt to these new conditions, or track their niche via seed dispersal. Adaptation of plants to different abiotic environments has mostly been discussed with respect to physiological and demographic parameters that allow local persistence. However, rapid modifications in response to changing environmental conditions can also affect seed dispersal, both via plant traits and via their dispersal agents. Studying such changes empirically is challenging, due to the high variability in dispersal success, resulting from environmental heterogeneity, and substantial phenotypic variability of dispersal-related traits of seeds and their dispersers. The exact mechanisms that drive rapid changes are often not well understood, but the ecological implications of these processes are essential determinants of dispersal success, and deserve more attention from ecologists, especially in the context of adaptation to global change. We outline the evidence for rapid changes in seed dispersal traits by discussing variability due to plasticity or genetics broadly, and describe the specific traits and biological systems in which variability in dispersal is being studied, before discussing some of the potential underlying mechanisms. We then address future research needs and propose a simulation model that incorporates phenotypic plasticity in seed dispersal. We close with a call to action and encourage ecologists and biologist to embrace the challenge of better understanding rapid changes in seed dispersal and their consequences for the reaction of plant populations to global change.
What the paper shows and why it matters
(AI-generated)
When conditions change, plant populations can adapt where they stand or follow their suitable conditions by dispersing seeds. Rapid change in traits such as phenology (the timing of life-cycle events) has been studied much more often, but rapid change in the traits that determine where seeds go has received much less attention. One reading is that selection acts on local survival rather than on where seeds land. Given how much dispersal matters for fitness, the paper contends instead that adaptive change in dispersal does occur and that the lack of evidence mostly reflects how hard dispersal is to study. Predictive models, too, rarely include variation in dispersal traits. The paper addresses this gap: whether dispersal can change quickly with the environment, and so help plants cope.
The paper argues that seed dispersal, in plants and their dispersers, can change rapidly with the environment, through plasticity or genetic change, and that this deserves study and a place in models of plant responses to global change. Plasticity means one genotype producing different traits in different environments. Most dispersal studies the paper reviews show how traits vary with conditions without asking whether the variation is genetic or plastic; fewer address rapid change itself. In Crepis sancta, small fragmented urban habitat patches had a much higher proportion of non-dispersing seeds, a pattern that Cheptou et al. (2008) read as evolution within a few generations. The paper calls the smaller seeds of the palm Euterpe edulis in forests that have lost large fruit-eating birds, reported by Galetti et al. (2013), perhaps the most elegant demonstration of rapid change in dispersal. Its own simple model lets an annual plant make two seed types that disperse differently, in patchy habitat; in simulations a mix of the two types sometimes gave the fastest spread, depending on how well each type survived.
The paper concludes that there is evidence and potential for rapid regulation of dispersal, while the effects on plant fitness and plant communities are less clear. It asks for data on dispersal-trait variation within single plants that separates genetic from plastic sources; for theory of how dispersal traits change, linked to models of population spread and vegetation; and for predictions of which species cannot keep up with their niche that include such change.
References
- Cheptou et al. (2008). Rapid evolution of seed dispersal in an urban environment in the weed Crepis sancta. Proceedings of the National Academy of Sciences 105, 3796–3799. doi:10.1073/pnas.0708446105
- Galetti et al. (2013). Functional Extinction of Birds Drives Rapid Evolutionary Changes in Seed Size. Science 340, 1086–1090. doi:10.1126/science.1233774