COS 145-1 - CANCELLED - Revisiting Clements and Gleason: Insights from plant distributions on Pikes Peak, Clements’s life-long study site

Abstract: How do species’ distributions respond to their environments? This question was at the heart of the Clements-Gleason controversy, ecology’s most famous debate. Do species respond to environmental gradients in concerted ways leading to distinct assemblages, as Clements argued, or do species respond to gradients independently, as Gleason argued? Clements’s view was likely strongly influenced by his career-long study of plants along the elevation gradient of Pikes Peak (Colorado, USA). With the benefits of thousands of species occurrence records databased from the area and modern theoretical frameworks unavailable at the time of Clements and Gleason, we test for plant community patterns along the Pikes Peak gradient to gain insight into Clements’s perspective. We found mixed support for the paradigms. While distributions along the gradient showed evidence of clustering of species range edges, consistent with the Clementsian paradigm, the pattern was weak and neither range edges nor species turnover peaked at ecotone elevations, as expected under the Clementsian paradigm. Our results illuminate the Clements-Gleason debate by allowing us to identify outstanding issues, such as how we quantify environmental gradients, the potential mechanisms behind Clementsian and Gleasonian patterns, the scales at which they operate, and common misinterpretations of the polarized paradigms. The debate continues to have relevance to ecology today; its legacy has shaped our views of communities and the trajectory of our field.