As climate change accelerates, species are shifting poleward and subtropical and tropical species are colonizing temperate environments.1, 2, 3 A popular approach for characterizing such responses is the community temperature index (CTI), which tracks the mean thermal affinity of a community. Studies in marine,⁴ freshwater,⁵ and terrestrial⁶ ecosystems have documented increasing CTI under global warming. However, most studies have only linked increasing CTI to increases in warm-affinity species. Here, using long-term monitoring of marine fishes across the Northern Hemisphere, we decomposed CTI changes into four underlying processes—tropicalization (increasing warm-affinity), deborealization (decreasing cold-affinity), borealization (increasing cold-affinity), and detropicalization (decreasing warm-affinity)—for which we examined spatial variability and drivers. CTI closely tracked changes in sea surface temperature, increasing in 72% of locations. However, 31% of these increases were primarily due to decreases in cold-affinity species, i.e., deborealization. Thus, increases in warm-affinity species were prevalent, but not ubiquitous. Tropicalization was stronger in areas that were initially warmer, experienced greater warming, or were deeper, while deborealization was stronger in areas that were closer to human population centers or that had higher community thermal diversity. When CTI (and temperature) increased, species that decreased were more likely to be living closer to their upper thermal limits or to be commercially fished. Additionally, warm-affinity species that increased had smaller body sizes than those that decreased. Our results show that CTI changes arise from a variety of underlying community responses that are linked to environmental conditions, human impacts, community structure, and species characteristics.

随着气候变化的加速，物种正在向极地转移，亚热带和热带物种正在温带环境中定居。1,2,3 表征这种反应的一种流行方法是群落温度指数 (CTI)，它跟踪群落的平均热亲和力。研究海洋，⁴淡水，⁵和陆地⁶生态系统已经记录了在全球变暖下 CTI 的增加。然而，大多数研究仅将 CTI 的增加与暖亲和物种的增加联系起来。在这里，通过对北半球海洋鱼类的长期监测，我们将 CTI 的变化分解为四个基本过程——热带化（增加暖亲和性）、去北极化（降低冷亲和性）、北极化（增加冷亲和性）和去热带化（降低暖亲和性）——我们为此检查了空间变异性和驱动因素。CTI 密切跟踪海面温度的变化，在 72% 的地点增加。然而，这些增加中的 31% 主要是由于冷亲和物种的减少，即解冻。因此，暖亲和物种的增加很普遍，但并不普遍。在最初温暖、经历更大变暖或更深的地区，热带化程度更强，而在靠近人口中心或社区热多样性较高的地区，热带化程度更高。当 CTI（和温度）升高时，降低的物种更有可能生活在接近其温度上限或进行商业捕捞的情况下。此外，增加的暖亲和物种的体型比减少的要小。我们的研究结果表明，CTI 变化源于与环境条件、人类影响、群落结构和物种特征相关的各种潜在群落反应。而在靠近人口中心或具有较高社区热多样性的地区，去北极化程度更高。当 CTI（和温度）升高时，降低的物种更有可能生活在接近其温度上限或进行商业捕捞的情况下。此外，增加的暖亲和物种的体型比减少的要小。我们的研究结果表明，CTI 变化源于与环境条件、人类影响、群落结构和物种特征相关的各种潜在群落反应。而在靠近人口中心或具有较高社区热多样性的地区，去北极化程度更高。当 CTI（和温度）升高时，降低的物种更有可能生活在接近其温度上限或进行商业捕捞的情况下。此外，增加的暖亲和物种的体型比减少的要小。我们的研究结果表明，CTI 变化源于与环境条件、人类影响、群落结构和物种特征相关的各种潜在群落反应。增加的温暖亲和物种的体型比减少的要小。我们的研究结果表明，CTI 变化源于与环境条件、人类影响、群落结构和物种特征相关的各种潜在群落反应。增加的温暖亲和物种的体型比减少的要小。我们的研究结果表明，CTI 变化源于与环境条件、人类影响、群落结构和物种特征相关的各种潜在群落反应。