A large body of theory predicts that populations diffusing in heterogeneous environments reach higher total size than if non-diffusing, and, paradoxically, higher size than in a corresponding homogeneous environment. However, this theory and its assumptions have not been rigorously tested. Here, we extended previous theory to include exploitable resources, proving qualitatively novel results, which we tested experimentally using spatially diffusing laboratory populations of yeast. Consistent with previous theory, we predicted and experimentally observed that spatial diffusion increased total equilibrium population abundance in heterogeneous environments, with the effect size depending on the relationship between r and K. Refuting previous theory, however, we discovered that homogeneously distributed resources support higher total carrying capacity than heterogeneously distributed resources, even with species diffusion. Our results provide rigorous experimental tests of new and old theory, demonstrating how the traditional notion of carrying capacity is ambiguous for populations diffusing in spatially heterogeneous environments.
Bibliographical noteFunding Information:
The authors thank J. Kallman and C. Munro for helping with data collection, A. Murray and M. Mueller for providing strains, Chris Cosner, Carol Horvitz, Fangliang He and Michelle Afkhami for reviewing the manuscript, and the editor and Robert Holt and one anonymous reviewer provided insightful comments on the manuscript. This work was supported by The USGS's Greater Everglades Priority Ecosystem Science and Graduate Student Award to Promote Interdisciplinary Research in Biology from University of Miami to BZ, William H. Evoy Graduate Research and Savage Graduate Research Support Fund to AK, and NSF and NSFC to WN. DLD was supported by the Greater Everglades Priority Ecosystem Science program. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
- Carrying capacity
- consumer–resource model
- dispersal experiment
- environmental stressor
- heterogeneous resource distribution
- r-K relationship
- spatially distributed population