Species’ geographic range limits often result from maladaptation to the novel environments beyond the range margin. However, we rarely know which aspects of the n-dimensional environment are driving this maladaptation. Especially of interest is the influence of abiotic versus biotic factors in delimiting species’ distributions. We conducted a 2-year reciprocal transplant experiment involving manipulations of the biotic environment to explore how spatiotemporal gradients in precipitation, fatal mammalian herbivory, and pollination affected lifetime fitness within and beyond the range of the California annual plant, Clarkia xantiana ssp. xantiana. In the first, drier year of the experiment, fitness outside the range edge was limited mainly by low precipitation, and there was some evidence for local adaptation within the range. In the second, wetter year, we did not observe abiotic limitations to plant fitness outside the range; instead biotic interactions, especially herbivory, limited fitness outside the range. Together, protection from herbivory and supplementation of pollen resulted in three- to sevenfold increases in lifetime fitness outside the range margin in the abiotically benign year. Overall, our work demonstrates the importance of biotic interactions, particularly as they interact with the abiotic environment, in determining fitness beyond geographic range boundaries.
Bibliographical noteFunding Information:
JWB and DAM designed and conducted the experiments. JWB performed all analyses with substantial input from DAM. JWB wrote the manuscript with DAM contributing substantially to revisions. The authors thank Lana Bolin, Haley Branch, Alexai Faulkner, Adam Kostanecki, Sarah Tran, and Anna Peschel for assistance with field and lab work. The authors appreciate insightful comments from Peter Kennedy, Ruth Shaw, and Peter Tiffin on experimental design, analyses, and interpretation of results. Our work was generously supported by grants from the National Science Foundation (DEB-1701072 to JWB and DAM and DEB-1255141 to DAM), the Society for the Study of Evolution (JWB), and the Bell Museum at the University of Minnesota (JWB). Any opinions, findings, and conclusions expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Pending acceptance, all data and code will be archived in the Dryad Digital Repository. The doi for data is https://doi.org/10.5061/dryad.8mb0c27.
© 2019 The Author(s). Evolution © 2019 The Society for the Study of Evolution.
- Biotic interactions
- Clarkia xantiana ssp. xantiana
- geographic range limit
- reciprocal transplant
- species distributions