Along the most critical issues in anticipating, and thus preparing for, the effects of global climate change is predicting how the abundances and geographic distributions of plants and animals will be impacted by altered weather patterns. Alpine and arctic plants are among the species believed to be most susceptible to such changes. This project will continue a long-term study of two arctic/alpine plants across their range from arctic tundra in Alaska to high alpine areas of Colorado. Data collected to date show that as their southern limits are approached, both species show declining average success in survival and reproduction and higher variability in these performance measures. The planned project will tie these ecological responses to local and regional climate patterns and then using predicted climate changes and population ecology models to predict the future range limits of these species.
The proposed work would foster involvement of graduate and undergraduate students in both lab and field aspects of ecological research. Both PIs are also involved in public education programs in the states where this work will be conducted. Most importantly, this research will build capacity to anticipate climate change impacts, including the development of methodologies that can be extended to other species and ecosystems.
Anticipating how the geographical ranges of species will shift is a major challenge in projecting the biotic consequences of global climate change. In turn, predicting range shifts will require an understanding of the population- and community-level mechanisms setting range limits. With initial (this award) and renewed LTREB support, this project comprises a long-term study (currently 17 years) aimed at understanding the demographic factors limiting the latitudinal and climatic ranges of two tundra plant species in western North America. Twenty-nine populations of marked individuals of the two species from near the southern range limits in New Mexico to northern Alaska (Figure1) have been censused every year for at least 4 and up to 17 years, yielding multi-year, quantitative estimates of all vital rates (survival, growth, reproductive output, and recruitment): since 2001, we have collected over 65,000 and 45,000 plant-years of demographic data across our study populations for moss campion and alpine bistort, respectively. In addition, we have collected micro-climate data and performed an experiment in which we manipulate neighboring plants to understand how competition and facilitation may interact with climate in their effects on plant populations. The main finding of this study is that compensatory changes in demographic rates are buffering southern populations of our two focal species against the negative effects of a warming climate, slowing their northward range shifts, but that this buffering is unlikely to continue indefinitely. Southern populations of both species showed lower survival and recruitment but higher growth of individual plants, possibly owing to longer, warmer growing seasons. Because of these and other compensatory changes, the population growth rates of southern populations are not at present lower than those of northern ones. However, continued warming may yet prove detrimental, as most demographic rates that improved in moderately warmer years declined in the warmest years, with the potential to drive future population declines (Figure 2). Our results emphasize the need for long-term, range-wide measurement of all population processes to detect contrasting effects of warming on different demographic rates and to identify nonlinear responses that may lead to sudden range shifts as climatic tipping points are exceeded. In addition to this result, our research has also lead to the development of demographic approaches that have been applied to multiple other species and study systems. In addition, we have contributed our data to synthetic studies comparing ecological patterns across different taxonomic groups. Finally, we have made all our data available on the web for other scientists to use. Broader Impacts: Over the course of this award, 15 undergraduate and 6 graduate students have been supported and trained in both modeling and field methods of population ecology. These students have come from Duke, University of Wyoming, and other institutions. In addition, four REUs have been supported in this project. Beyond this training component, this research has important impacts in building capacity to anticipate climate change impacts (both direct and indirect, i.e., mediated by interactions with other species) on some of the ecosystems thought to be most susceptible to warming effects, alpine and arctic tundra. Our work received considerable media attention in fall 2010, with publication of a Nature paper on our findings. Over 17 news outlets covered this paper, and it was also featured on the NSF website.
