Guest Speaker- Margaret Evans
Affiliations- University of Arizona
Host: Amy Angert
Title: Space-for-time substitution: a widespread and dangerous practice in predictive ecology
Location: MSL Theatre
Abstract
The impacts of climate change on biodiversity and ecosystem functioning lead to a strong societal need to predict the dynamics and future state of ecological systems (ecosystems, communities, species, populations) and ecosystem services under future climates. Because long-term observations are typically lacking, ecologists often rely on patterns observed across spatial climatic gradients to make predictions of what will happen in response to climate change – a practice known as space for time substitution. For example, climate envelope or species distribution models are commonly used to predict how species will respond to climate change. In doing so, it is assumed that individual- and population-level responses to time-varying climate match species-level responses to spatial variation in climate. Using spatial networks of tree-ring time series data, we have tested the validity of this space-for-time substitution (SFTS). We fit regression models explaining variation in growth as a function of spatial and temporal variation in climate. In three important species – Douglas-fir, ponderosa pine, and common pinon – growth increases with temperature across space (warmer sites have higher average growth rates) but trees everywhere grow less in warmer-than-average years. Ubiquitous negative sensitivity of growth to time-varying temperature means that there is no “leading edge” of these species’ distributions where trees benefit from warming. Instead, demographic performance can be expected to decline with warming across their entire distributions. Further, we show that SFTS predicts increased growth with warming, whereas the observed impact of warming on tree growth is negative. Forecasting of ecological responses to climate change (e.g., forest carbon sequestration) based on SFTS should be viewed with caution and ideally should be validated. Thus, we caution against the direct translation of species-wide climatic tolerances into projections of productivity or range change. In the near term, organism-environment relationships estimated from time series data may be more predictive of outcomes than equilibrium responses estimated from spatial climate gradients.
Evans, M. E. K., S. M. N. Dey, K. A. Heilman, J. R. Tipton, R. J. DeRose, S. Klesse, E. L. Schultz, and J. D. Shaw. 2024. Tree rings reveal the transient risk of extinction hidden inside climate envelope forecasts. Proceedings of the National Academy of Sciences 121(24): e2315700121 https://doi.org/10.1073/pnas.2315700121
Perret, D., M. E. K. Evans, and D. Sax. 2024. A species’ response to spatial climatic variation does not predict its response to climate change. Proceedings of the National Academy of Sciences 121(1): e2304404120 https://doi.org/10.1073/pnas.2304404120
Klesse, S., R. J. DeRose, J. Shaw, F. Babst, L. Anderegg, J. Axelson, B. Black, A. Ettinger, H. Greisbauer, C. Guiterman, G. Harley, J. E. Harvey, Y. H. Lo, A. M. Lynch, C. O’Connor, C. M. Restaino, D. Sauchyn, D. Smith, L. Wood, J. Villanueva, and M. E. K. Evans. 2020. Continental-scale tree ring-based projection of Douglas-fir growth: testing the limits of space-for-time substitution. Global Change Biology 26: 5146-5163.