Seed dormancy increases population size via bet-hedging and by limiting negative interactions (e.g., competition) among individuals. On the other hand, individuals also interact positively (e.g., facilitation), and in some systems, facilitation among juveniles precedes competition among adults in the same generation. Nevertheless, studies of the benefits of seed dormancy typically ignore facilitation. Using a population growth model, we ask how the facilitation–competition balance interacts with seed dormancy rate to affect population dynamics in constant and variable environments. Facilitation increases the growth rate and equilibrium size (in both constant and variable environments) and reduces the extinction rate of populations (in a variable environment), and a higher rate of seed dormancy allows populations with facilitation to reach larger sizes. However, the combined benefits of facilitation and a high dormancy rate only occur in large populations. In small populations, weak facilitation does not affect the growth rate, but does induce a weak demographic Allee effect (where population growth decreases with decreasing population size). Our results suggest that facilitation within populations can interact with bet-hedging traits (such as dormancy) or other traits that mediate density to affect population dynamics. Further, by ensuring survival but limiting reproduction, ontogenetic switches from facilitation to competition may enable populations to persist but limit their maximum size in variable environments. Such intrinsic regulation of populations could then contribute to the maintenance of similar species within communities.
Bibliographical noteFunding Information:
information National Science Foundation, Grant/Award Number: DEB-1501710William F. Morris and Joseph S. Tumulty assisted in model development and analysis. We thank Kathleen Donohue and members of the Donohue lab (Duke University), members of the Shaw lab (University of Minnesota-Twin Cities), members of UMN's Theory Group, members of Duke's Pop Bio group, James Clark, Tom Mitchell-Olds, Justin Wright and anonymous reviewers for thoughtful feedback. L.D.L. was supported by a graduate fellowship provided by the Department of Biology at Duke, a summer fellowship provided by the Graduate School at Duke, and a Doctoral Dissertation Improvement Grant (#DEB-1501710) provided by the National Science Foundation.
© 2019 The Society of Population Ecology
- Allee effect
- annual plant