A case for the “Competitive exclusion – tolerance rule” as a general cause of species turnover along environmental gradients

Closely-related, ecologically-similar species often segregate their distributions along environmental gradients of time, space, and resources, but previous research suggests diverse underlying causes. Here, we review reciprocal removal studies in nature that experimentally test the role of interactions among species in determining their turnover along environmental gradients. We find consistent evidence for asymmetric exclusion coupled with differences in environmental tolerance causing the segregation of species pairs, where a dominant species excludes a subordinate from benign regions of the gradient, but is unable to tolerate challenging regions to which the subordinate species is adapted. Subordinate species were consistently smaller and performed better in regions of the gradient typically occupied by the dominant species compared to their native distribution. These results extend previous ideas contrasting competitive ability with adaptation to abiotic stress to include a broader ..., Literature review and meta-analysis. Please see Methods of paper., Includes R script.