While the effect of the global biodiversity crisis on local species loss is still debated, there is empirical evidence for major changes in local biodiversity attributed to increased species turnover. In communities exposed to a climate stressor, species turnover can lead to increased dominance of well-adapted species and consequently to an overall decline in species diversity. Despite the known importance of species turnover for community dynamics and functioning, experimental results on the connection between biodiversity loss and species turnover are scarce. We still do not fully understand which specific factors increase the rate of change in species composition, especially when considering natural compared to artificially lab assembled communities. In the present study, we experimentally tested whether a heatwave and dispersal increased species turnover and decreased species diversity in natural benthic diatom communities with different initial species compositions. We found that on the local scale, dispersal had overall positive effects on species richness while the relationship between exposure to the heatwave, species turnover, and diversity depended on initial community composition. However, on the regional (i.e. metacommunity) scale, exposure to the heatwave and dispersal both increased turnover and decreased Shannon diversity by almost 50%. Turnover in these metacommunities was not caused by a loss of species, but rather by a change in dominance patterns leading to homogenization, and consequently decreased diversity. Our study shows that climate change can destabilize community composition and degrade species diversity, but still after ca. 15 generations does not decrease the number of species in the community, demonstrating that the response of species diversity and richness to changing conditions can be fundamentally decoupled on ecological time scales.

中文翻译：

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热浪增加了微底栖动物群落的更新和区域优势

虽然全球生物多样性危机对当地物种丧失的影响仍有争议，但有经验证据表明，当地生物多样性的重大变化归因于物种周转率的增加。在暴露于气候压力源的社区中，物种更替会导致适应性强的物种的优势增加，从而导致物种多样性的整体下降。尽管已知物种周转对群落动态和功能的重要性，但关于生物多样性丧失与物种周转之间联系的实验结果很少。我们仍然不完全了解哪些特定因素会增加物种组成的变化率，尤其是在考虑与人工实验室组装的社区相比是自然的时。在目前的研究中，我们通过实验测试了热浪和扩散是否会增加具有不同初始物种组成的天然底栖硅藻群落中的物种周转率和物种多样性。我们发现，在局部范围内，散布对物种丰富度具有总体积极影响，而暴露于热浪、物种更新和多样性之间的关系取决于最初的群落组成。然而，在区域（即元社区）范围内，暴露于热浪和扩散都增加了营业额，并使香农多样性降低了近 50%。这些元群落的更替不是由物种的丧失引起的，而是由于优势模式的变化导致同质化，从而降低了多样性。我们的研究表明，气候变化会破坏群落组成并降低物种多样性，但在大约之后仍然存在。15 代不会减少群落中的物种数量，这表明物种多样性和丰富度对变化条件的响应可以在生态时间尺度上从根本上解耦。