Global change factors interact and modify competitive interactions among alpine tundra species: A population dynamic modeling approach

Background/Question/Methods

Global change is multifaceted, comprising simultaneous changes in many environmental factors, and these factors may have non-additive effects on plant communities.  Moreover, these global change factors can influence species both by directly affecting performance and by modifying the competitive environment.  In this study, we incorporate components of global change into population dynamic models and fit them to experimental data to determine how global change factors affect population dynamics and how species interactions are altered by global change.  We use the alpine tundra as a model system since alpine ecosystems are particularly sensitive to global change.  Data are derived from species composition censuses from a 5-year experiment manipulating nitrogen, summer temperature, and winter precipitation (snowpack) in factorial combinations.  We hypothesize that global change factors will have non-additive effects on population growth rates and that species interactions may become more competitive under global change treatments.

Results/Conclusions

We found that for one of the co-dominant species, the forb Geum rossii, N has an overall negative effect on population growth but warming influences it in a non-additive way such that warming may act to moderate the negative effects of N.  Intraspecific interactions for Geum become more negative with warming and become facilitative under elevated N.  For the other co-dominant species, the grass Deschampsia cespitosa, N increased growth rate considerably, and intra- and inter-specific interactions became more negative under elevated N.  For a third species, a forb, Artemisia scopulorum, N has a very negative effect on growth rate and warming exacerbates this effect in a non-additive way; also interspecific interactions become more facilitative with increased nitrogen and snowpack.  These results suggest that global change factors can affect population dynamics directly and by modifying competitive interactions among species.  Moreover, effects of global change factors can be non-additive, suggesting that experiments manipulating multiple global change factors are necessary to predict community dynamics under future climate scenarios.