Effects of Demography and Genetics on Extinction in Small Populations: Experiments with an Exploited Kelp

物种灭绝的过程是一个基本的生态和社会问题。 尽管人们对灭绝过程感兴趣，但关于导致灭绝的机制的经验信息很少，特别是在海洋系统中，因为灭绝事件涉及的种群规模很小，而且很少发生。小种群规模被认为通过几种不同的机制增加了灭绝的风险。生态机制包括由于偶然事件（人口统计随机性）和正密度依赖（即，在低密度下减少人口增长）。遗传机制包括由于偶然事件（遗传漂变）和近交衰退而导致的有利等位基因的丢失。该项目将通过实验解开与商业收获的海洋海带（海棕榈Postelsia palmaeformis）的小种群规模相关的不同机制的影响。 为了测试遗传变异的影响，实验群体将从单个建立者、来自同一群体的多个建立者或来自不同来源群体的多个建立者建立。遗传处理将与密度操作（大种群和小种群）相结合，以测试种群规模的生态效应。实验种群将被监测灭绝的时间，并通过标记个体植物和测量存活率，繁殖力和生长率来详细研究潜在的过程。这些数据将纳入人口模型，以确定人口增长对人口规模小的不同影响和不同生命阶段的相对敏感性。同时监测遗传结构的实验种群使用AFLP指纹技术将提供一个独立的测量遗传动态和影响人口的表现，并将验证研究的基本假设。该研究将增加我们对小种群规模对灭绝风险影响的理解，有助于描述海洋海带的生命周期，并为开发利用海洋物种的有效保护和补救策略提供重要信息。

The process of species extinction represents both a basic ecological and societal concern. Despite interest in extinction processes, there is little empirical information on mechanisms leading to extinction, particularly in marine systems, because extinction events involve small population sizes and are infrequent. Small population size is thought to increase the risk of extinction through several different mechanisms. Ecological mechanisms include increased variation in population growth rates due to chance events (demographic stochasticity), and positive density dependence (i.e., reduced population growth at low density). Genetic mechanisms include loss of favorable alleles due to chance events (genetic drift) and inbreeding depression. This project will experimentally disentangle the effects of different mechanisms associated with small population size in a commercially-harvested marine kelp, the sea palm Postelsia palmaeformis. To test effects of genetic variation, experimental populations will be established from either a single founder, multiple founders from the same population, or multiple founders from different source populations. The genetic treatment will be combined with a density manipulation (large and small populations) to test for ecological effects of population size. Experimental populations will be monitored for times to extinction, and the underlying processes will be studied in detail by marking individual plants and measuring survival, fecundity, and growth rates. These data will be incorporated into a population model to determine the relative sensitivity of population growth to different effects of small population size and to different life stages. Concurrent monitoring of genetic structure of the experimental populations using AFLP fingerprinting techniques will provide an independent measurement of genetic dynamics and effects on population performance, and will validate basic assumptions of the study. The study will increase our understanding of the effects of small population size on extinction risk, help to characterize the life cycle of marine kelps, and provide important information for developing effective conservation and remediation strategies for exploited marine species.