An important stabilizing mechanism in most diversity stability models is the insurance hypothesis, which involves correlation/covariance relationships among species. These models require that species do not fluctuate synchronously over time: that is, the correlation between pairs of species does not equal 1.0. However, the strength of this stabilizing mechanism increases as correlations decline away from 1.0, especially as they become more negative and also as the summed covariance across all species pairs becomes more negative. We evaluated the importance of the insurance hypothesis as a stabilizing mechanism by examining a variety of terrestrial assemblages using long-term data from the Global Population Dynamics Database, the Breeding Bird Survey, and a long-term site in southeastern Arizona, USA. We identified co-occurring assemblages of species and calculated the Spearman rank correlations of all pairs of species and the summed covariance of the entire assemblage. We found that, in most assemblages, positive correlations were two to three times more common than negative and that the magnitude of the positive correlations tended to be stronger than the negative correlations. For all but three assemblages, the summed covariance was positive. Data from larger spatial scales tended to exhibit more positive correlations, but even at the smallest spatial scales, positive correlations outnumbered negative. We suggest that species often covary positively because coexisting species respond similarly to fluctuations in their resource base driven by climatic fluctuations. As such, our review suggests that the insurance hypothesis may not be a strong mechanism stabilizing fluctuations in natural terrestrial communities.

译文

在大多数多样性稳定性模型中,一个重要的稳定机制是保险假说,它涉及物种之间的相关性/协方差关系。这些模型要求物种不会随时间同步波动: 也就是说,成对物种之间的相关性不等于1.0。然而,这种稳定机制的强度随着相关性远离1.0的下降而增加,尤其是当它们变得更负并且所有物种对的总协方差变得更负时。我们使用全球人口动态数据库,繁殖鸟类调查和美国亚利桑那州东南部的长期站点的长期数据,通过检查各种陆生组合,评估了保险假说作为稳定机制的重要性。我们确定了同时发生的物种组合,并计算了所有物种对的Spearman等级相关性以及整个组合的总协方差。我们发现,在大多数组合中,正相关是负相关的两到三倍,正相关的幅度往往强于负相关。对于除三个组合外的所有组合,总协方差均为正值。来自较大空间尺度的数据往往表现出更多的正相关性,但是即使在最小的空间尺度上,正相关性也超过了负相关性。我们建议物种通常呈正相关,因为共存物种对气候波动驱动的资源基础波动的反应相似。因此,我们的评论表明,保险假说可能不是稳定自然陆地社区波动的强大机制。

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