Collaborative Research: Using Demographic Techniques to Test for the Signatures of Environmental Change

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Morris/Doak 9806818 A major difficulty in assessing the real environmental importance of ongoing or future climate change is the lack of adequate monitoring data from the past. In particular, most methods used to infer the consequences of climate change rely upon past data to determine normal or baseline conditions. In the work proposed here, a technique is developed that circumvents this problem, relying instead on a comparison between current population size or age structures and those predicted by current demography to test for evidence of the ecological effects of local or global environmental change, in the absence of past data.. In the proposed work, the demography and population structure of Silene acaulis, a circumboreal alpine cushion plant, will be quantified. The work will be conducted in southcentral Alaska,. an area that has undergone rapid increases in temperature over the last three decades. At the field sites in Alaska's Wrangell Mountains, two types of data will be collected: 1) demographic measures of the growth, reproduction, and survival of individual plants; and 2) the size frequencies of plants in several distinct populations. By comparing the observed size frequencies to those predicted by stochastic computer models using the data on current demographic rates, specific hypotheses about how Silene demography may have changed due to environmental alteration will be tested (for examples, has earlier snowmelt and higher summer temperatures led to decreased seedling recruitment but an increase in the growth rates of adults?). In order to corroborate the most likely population responses to past climate changes identified by our models, additional experiments will be also be conducted to modify season length and temperature in order to directly assess the effects of climatic changes on demographic performance. These experiments will conform to the standard protocols of the International Tundra Experiment (ITEX, an international consortium of arctic and alpine global change researchers), thus allowing the results to be linked to a circumboreal assessment of climate change effects. By providing a method to look retrospectively at the population-level effects of environmental change, the work proposed will both expand the toolbox of methodologies available for detecting biotic effects of past changes and provide a baseline for determining whether effects of ongoing climate changes will accelerate in the future.