Questions: Functional redundancy in assemblages may insure ecosystem processes after perturbation, potentially causing temporary or permanent local species extinctions. Yet, functional redundancy has only been inferred by indirect evidence or measuredby methods that may not be the most appropriate. Here, we apply an existing method to measure functional redundancy, which is the fraction of species diversity not expressed by functional diversity, to assess whether functional redundancy affects community resilience after disturbance. Location: Subtropical grassland, southBrazil (30°05'46"S, 51°40'37"W). Method: Species traits and community composition were assessed in quadrats before grazing and after community recovery. Grazing intensity (G) was measured in each quadrat. We used traits linked to grazing intensity to define functional redundancy (FR) as the difference of Gini-Simpson index of species diversity (D) and Rao's quadratic entropy (Q). Also, with the same traits, we defined community functional stability (S) as the similarity between trait-based community composition before grazing and 47 and 180 d after grazing ending. Using path analysis we assessed different postulated causal models linking functional diversity (Q), functional redundancy (FR), grazing intensity (G) and community-weighted mean traits to community stability (S) under grazing. Results: Path analysis revealed the most valid causal model FR -> S <— G, with a significant positive path coefficient for FR -> S and a marginally significant negative one for S <— G. Since FR and G were independent in their covariation and in their effects on S, the model discriminated community resistance to grazing (the effect of G on S) from community resilience after grazing caused by functional redundancy (indicated by the effect of FR on S). Conclusion: We show that expressing functional redundancy mathematically is a useful tool for testing causal models linking diversity to community stability. The results support the conclusion that functional redundancy enhanced community resilience, therefore corroborating the insurance hypothesis.
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机译：问题：组合中的功能冗余可能会确保扰动后的生态系统过程，从而可能导致本地物种暂时或永久灭绝。但是，功能冗余仅是通过间接证据推断出来的，或者是通过可能不是最合适的方法来衡量的。在这里，我们应用现有的方法来测量功能冗余（即功能多样性未表达的物种多样性的一部分），以评估功能冗余是否在干扰后影响社区的复原力。位置：巴西南部亚热带草原（南纬30°05'46“，西纬51°40'37”）。方法：在放牧前和恢复后的四方动物中评估物种特征和群落组成。在每个方格中测量放牧强度（G）。我们使用与放牧强度相关的性状将功能冗余（FR）定义为物种多样性（D）的基尼-辛普森指数和Rao二次熵（Q）的差。同样，在具有相同性状的情况下，我们将社区功能稳定性（S）定义为放牧前基于特征的社区组成与放牧结束后47和180 d之间的相似性。使用路径分析，我们评估了不同的假定因果模型，这些模型将功能多样性（Q），功能冗余（FR），放牧强度（G）和社区加权平均性状与放牧下的社区稳定性（S）联系起来。结果：路径分析显示了最有效的因果模型FR-> S <-G，对于FR-> S具有显着的正路径系数，而对S <-G具有显着的负系数。由于FR和G在协变中是独立的在对S的影响方面，该模型将社区对放牧的抵抗力（G对S的影响）与功能冗余导致的放牧后的社区弹性（由FR对S的影响所表明）区分开来。结论：我们表明，数学表达功能冗余是测试将多样性与社区稳定性联系起来的因果模型的有用工具。结果支持功能冗余增强了社区弹性的结论，从而证实了保险假说。
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