Plant species' distribution patterns, functional traits, and range shifts along an elevation gradient

Knowledge about species' distributions is essential for understanding biodiversity patterns and predicting responses to climate change. The shapes of species' density distributions reflect how their performance varies across their range – shaped by environment, biotic interactions, and dispersal. Because these distributions reflect emergent properties of populations, they may reveal deterministic processes underlying species' past and future ranges and range shifts. Yet, distribution shape parameters (DSPs) are rarely considered in this context, leaving their potential largely unexplored. We addressed this gap by asking: 1) How do DSPs vary and covary among mountain plant species? 2) How are DSPs related to plant functional traits? 3) Can DSPs and functional traits explain recent range shifts? We quantified DSPs for 283 species across 626 plots spanning a 2000‐m elevation gradient on the Calanda massif, Graubünden, Switzerland, extracted functional traits from the TRY database, and compared DSPs and functional traits to range‐shift rates from two complementary data sources. We found that observed range shapes formed a subset of all possible shapes, suggesting trade‐offs in the drivers of distribution shapes. For example, we found that species abundant at higher elevations had shorter upslope and longer downslope distribution tails, consistent with abiotic stress limitation. Range limits and optima were also correlated with functional traits and distribution skew with species' dispersal distance. Finally, both distribution shapes and functional traits correlated with ongoing range shifts – DSPs outperformed functional traits, but considering both provided greater explanatory power. Overall, our results demonstrate that DSPs offer promising directions for future research into the factors influencing range shifts and our ability to predict them. Specifically, the drivers of DSPs and the relevant temporal scales over which they operate should be explored, potentially providing further insights into species' range shifts.