Abstract
Competition for limiting resources is among the most fundamental ecological interactions and has long been considered a key driver of species coexistence and biodiversity. Species’ minimum resource requirements, their R*, are key traits that link individual physiological demands to the outcome of competition. However, a major question remains unanswered -- to what extent are species’ competitive traits able to evolve in response to resource limitation? To address this knowledge gap, we performed an evolution experiment in which we exposed Chlamydomonas reinhardtii for approximately 285 generations to seven environments in chemostats which differed in resource supply ratios (including nitrogen, phosphorus and light limitation) and salt stress. We then grew the ancestors and descendants in common garden experiments and quantified their competitive abilities for essential resources. We investigated constraints on trait evolution by testing whether changes in resource requirements for different resources were correlated. Competitive abilities for phosphorus improved in all populations, while competitive abilities for nitrogen and light increased in some populations and decreased in others. In contrast to the common assumption that there are trade-offs between competitive abilities for different resources, we found that improvements in competitive ability for a resource came at no detectable cost. Instead, improvements in competitive ability for multiple resources were either positively correlated or not significantly correlated. Using resource competition theory, we then demonstrated that rapid adaptation in competitive traits altered the predicted outcomes of competition. These results highlight the need to incorporate contemporary evolutionary change into predictions of competitive community dynamics over environmental gradients.
Footnotes
Data and code accessibility: Data and code are available at https://github.com/JoeyBernhardt/chlamee-r-star and will be deposited in the Dryad digital data repository should the manuscript be accepted. DNA sequences have been deposited in the Sequence Read Archive (SRA) under the BioProject ID PRJNA558172.
Conflicts of interest: The authors have no competing interests.
Funding: Funding was provided by a postdoctoral fellowship from the Nippon Foundation Nereus Program to JRB, European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement TROPHY No. 794264 to MKT, an Eawag postdoctoral fellowship, an Eawag Seed Grant and a Swiss National Science Foundation Project Grant (31003A_176069) to AN.