AimQuantifying the relative contribution of environmental filtering versus limiting similarity in shaping communities is challenging because these processes often act simultaneously and their effect is scale‐dependent. Focusing on caves, island‐like natural laboratories with limited environmental variability and species diversity, we tested: (i) the relative contribution of environmental filtering and limiting similarity in determining community assembly in caves; (ii) how the relative contribution of these driving forces changes along environmental gradients.LocationEurope.Time periodPresent.Major taxa studiedSubterranean spiders.MethodsWe used data on distribution and traits for European cave spiders (n = 475 communities). We estimated the trait space of each community using probabilistic hypervolumes, and obtained estimations of functional richness independent of the species richness of each community via null modelling. We model functional diversity change along environmental gradients using generalized dissimilarity modelling.ResultsSixty‐three percent of subterranean spider communities exhibited a prevalence of trait underdispersion. However, most communities displayed trait dispersion that did not depart significantly from random, suggesting that environmental filtering and limiting similarity were both exerting equally weak or strong, yet opposing influences. Overdispersed communities were primarily concentrated in southern latitudes, particularly in the Dinaric karst, where there is greater subterranean habitat availability. Pairwise comparisons of functional richness across caves revealed these effects to be strongly scale‐dependent, largely varying across gradients of cave development, elevation, precipitation, entrance size and annual temperature range. Conversely, geographical distance weakly affected trait composition, suggesting convergence in traits among communities that are far apart.Main conclusionsEven systems with stringent environmental conditions maintain the potential for trait differentiation, especially in areas of greater habitat availability. Yet, the relative influence of environmental filtering and limiting similarity change with scale, along clear environmental gradients. The interplay of these processes may explain the assembly of species‐poor subterranean communities displaying high functional specialization.

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地下功能融合？欧洲洞穴蜘蛛群落组装过程的规模依赖性

量化环境过滤与限制相似性在塑造群落方面的相对贡献是具有挑战性的，因为这些过程通常同时起作用，而且它们的影响是与规模相关的。我们以洞穴、环境变异性和物种多样性有限的岛屿式自然实验室为重点，测试了：（i）环境过滤和限制相似性在确定洞穴中群落组装方面的相对贡献； （ii）这些驱动力的相对贡献如何沿着环境梯度变化。地点欧洲。时间段现在。研究地下蜘蛛的主要分类单元。方法我们使用了欧洲洞穴蜘蛛的分布和性状数据（n= 475 个社区）。我们使用概率超体积估计每个群落的性状空间，并通过零模型获得独立于每个群落物种丰富度的功能丰富度估计。我们使用广义相异性模型对沿环境梯度的功能多样性变化进行建模。结果 63% 的地下蜘蛛群落普遍存在性状分散不足的现象。然而，大多数群落表现出的特征分散并没有显着偏离随机，这表明环境过滤和限制相似性都发挥着同样弱或强但相反的影响。过度分散的群落主要集中在南部纬度地区，特别是在第纳喀斯特地区，那里有更多的地下栖息地。对各个洞穴功能丰富度的成对比较表明，这些影响强烈依赖于尺度，并且随着洞穴发育梯度、海拔、降水量、入口大小和年温度范围的变化而变化很大。相反，地理距离对性状组成的影响微弱，这表明相距较远的群落之间的性状趋同。主要结论即使环境条件严格的系统也保留了性状分化的潜力，特别是在栖息地可用性较大的地区。然而，环境过滤和限制相似性的相对影响随着规模的变化而变化，沿着明显的环境梯度。这些过程的相互作用可以解释物种贫乏的地下群落的组装，这些群落表现出高度的功能专业化。