Relations of Alpine Plant Communities across Environmental Gradients: Multilevel versus Multiscale Analyses

Abstract

Alpine plant communities vary, and their environmental covariates could influence their response to climate change. A single multilevel model of how alpine plant community composition is determined by hierarchical relations is compared to a separate examination of those relations at different scales. Nonmetric multidimensional scaling of species cover for plots in four regions across the Rocky Mountains created dependent variables. Climate variables are derived for the four regions from interpolated data. Plot environmental variables are measured directly and the presence of thirty-seven site characteristics is recorded and used to create additional independent variables. Multilevel and best subsets regressions are used to determine the strength of the hypothesized relations. The ordinations indicate structure in the assembly of plant communities. The multilevel analyses, although revealing significant relations, provide little explanation; of the site variables, those related to site microclimate are most important. In multiscale analyses (whole and separate regions), different variables are better explanations within the different regions. This result indicates weak environmental niche control of community composition. The weak relations of the structure in the patterns of species association to the environment indicates that either alpine vegetation represents a case of the neutral theory of biogeography being a valid explanation or that it represents disequilibrium conditions. The implications of neutral theory and disequilibrium explanations are similar: Response to climate change will be difficult to quantify above equilibrium background turnover.

高山植物社群相当多样, 而其环境共变量可能会影响它们对于气候变迁的回应。高山植物社群组成如何由阶层关係决定的单一多重层级模式, 将与在不同层级检视这些关係的个别研究进行比较。洛矶山四大区域地块之物种植被的非度量多重向度尺度化, 创造了依变项。从内插数据中取得了四大区域的气候变项。本文直接测量地块的环境变项, 记录三十七座场地特徵的存在, 并将之用来创造额外的自变项。多重层级和最佳子集迴归用来决定假设关係的力度。该标序显示出植物社群组合中的结构。进管多重层级分析揭露了显着的关係, 但却鲜少提出解释；对于场地变项而言, 与场地微气候相关者最为重要。在多重层级分析 (整体和各自区域中) 中, 不同的变项在不同的区域中是较佳的解释。该结果显示出社群组成的微弱环境利基控制。物种与环境关係的模式中的微弱结构关係, 意味着高山植被呈现出生物地理作为合理解释的中立理论案例, 抑或是其呈现出不均衡的情况。中立理论和不均衡解释的意涵是相似的：对于气候变迁的回应, 在均衡背景置换之上是难以量化的。

Las comunidades de plantas alpinas varían, y sus covariables ambientales podrían influennciar su respuesta al cambio climático. En el artículo se compara un modelo individual a nivel múltiple, referido a la manera como la composición de una comunidad de plantas alpinas se determina por relaciones jeraquizadas, con un examen separado de aquellas relaciones a diferentes escalas. Las variables dependientes se crearon al establecer la escala multidimensional no métrica de la cobertura de especies para parcelas, en cuatro regiones del área de las Montañas Rocosas. Para las cuatro regiones, las variables climáticas se derivan de datos interpolados. Las variables ambientales de las parcelas están medidas directamente, y la présencia de treinta y siete características del sitio se registró y se usó para crear variables independientes adicionales. Se usaron regresiones de nivel múltiple y de los mejores subconjuntos para determinar la fortaleza de las relaciones hipotetizadas. Las ordenaciones indican estructura en el ensamblaje de las comunidades de plantas. Los análisis de nivel múltiple, aunque revelan relaciones significativas, proveen poca explicación; de las variables del sitio, aquellas relacionadas con el microclima lugareño son las más importantes. En los análisis de multiescala (región completa y regiones separadas), las diferentes variables son mejores explicaciones dentro de las diferentes regiones. Este resultdo indica un control débil del nicho ambiental de la composición comunitaria. Las débiles relaciones de la estructura en los patrones de asociación de las especies con el medio indican que, o bien la representación alpina representa un caso de teoría neutral de la biogeografía como explicación válida o que condiciones de desequilibrio. Las implicaciones de la teoría neutral y las explicaciones de desequilibrio, son similares: La respuesta al cambio climático será difícil de cuantificar más allá de un equilibrio de antecedentes detectados.

Key Words:

• biogeography
• scale
• species diversity
• tundra
• vegetation

关键词：:

• 生物地理学
• 尺度
• 物种多样性
• 冻原
• 植被。

Palabras clave:

• biogeografía
• escala
• diversidad de especies
• tundra
• vegetación

Funding

This research was supported by National Science Foundation award 1121305. This material is based on work while George P. Malanson served at the National Science Foundation. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or the U.S. Geological Survey; any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Acknowledgments

Fieldwork and botany were provided by Jen Asebrook and Jen Hintz of Calypso Ecological, LLC; Peter Lesica; Steve Cooper; and Kevin Jacks. Logistical support was afforded by Bill Bowman.

Additional information

Notes on contributors

George P. Malanson

GEORGE P. MALANSON is the Coleman-Miller Professor in the Department of Geographical and Sustainability Sciences at the University of Iowa, Iowa City, IA 52242. E-mail: [email protected]. His research interests include ecological response to global change.

Dale L. Zimmerman

DALE L. ZIMMERMAN is the Robert V. Hogg Professor in the Department of Statistics and Actuarial Science at the University of Iowa, Iowa City, IA 52242. E-mail: [email protected]. His research interests include spatial statistics, linear models, longitudinal data analysis, and environmetrics.

Mitch Kinney

MITCH KINNEY is a PhD student in the School of Statistics at the University of Minnesota, Minneapolis, MN 55455. E-mail: [email protected]. His research is currently on image processing using neural networks. He was an undergraduate at the University of Iowa at the time this work was done.

Daniel B. Fagre

DANIEL B. FAGRE is Research Ecologist and Climate Change Research Coordinator for the Northern Rocky Mountain Science Center of the U.S. Geological Survey, c/o Glacier National Park, West Glacier, MT 59936. E-mail: [email protected]. His research interests include global-scale environmental changes affecting mountain ecosystems.