Data from: Inferring the effects of potential dispersal routes on the metacommunity structure of stream insects: as the crow flies, as the fish swims or as the fox runs?

1. Metacommunity research relies largely on proxies for inferring the effect of dispersal on local community structure. Overland and watercourse distances have been typically used as such proxies. A good proxy for dispersal should, however, take into account more complex landscape features that can affect an organism's movement and dispersal. The cost distance approach does just that, allowing determining the path of least resistance across a landscape. 2. Here, we examined the distance decay of assemblage similarity within a subarctic stream insect metacommunity. We tested whether overland, watercourse and cumulative cost distances performed differently as correlates of dissimilarity in assemblage composition between sites. We also investigated the effect of body size and dispersal mode on metacommunity organization. 3. We found that dissimilarities in assemblage composition correlated more strongly with environmental than physical distances between sites. Overland and watercourse distances showed similar correlations to assemblage dissimilarity between sites, being sometimes significantly correlated with biological variation of entire insect communities. In metacommunities deconstructed by body size or dispersal mode, contrary to our expectation, passive dispersers showed a slightly stronger correlation than active dispersers to environmental differences between sites, although passive dispersers also showed a stronger correlation than active dispersers to physical distances between sites. The strength of correlation between environmental distance and biological dissimilarity also varied slightly among the body size classes. 4. After controlling for environmental differences between sites, cumulative cost distances were slightly better correlates of biological dissimilarities than overland or watercourse distances between sites. However, quantitative differences in correlation coefficients were small between different physical distances. 5. Although environmental differences typically override physical distances as determinants of the composition of stream insect assemblages, correlations between environmental distances and biological dissimilarities are typically rather weak. This undetermined variation may be attributable to dispersal processes, which may be captured using better proxies for the process. We suggest that further modifying the measurement of cost distances may be a fruitful avenue, especially if complemented by more direct natural history information on insect dispersal behaviour and distances travelled by them.

1. 集合群落（Metacommunity）研究大多依赖替代指标来推断扩散对本地群落结构的影响。此前通常以陆地距离与河道距离作为此类替代指标。然而，优质的扩散替代指标需纳入能够影响生物体移动与扩散的复杂景观特征，而成本距离（cost distance）方法恰好可实现这一点，其能够测算出景观中最小阻力路径。
2. 本研究聚焦亚北极溪流昆虫集合群落，分析其群落相似性的距离衰减效应。我们对比了陆地距离、河道距离与累积成本距离作为样点间群落组成相异度相关指标的表现差异，并探究了体型大小与扩散模式对集合群落组织的影响。
3. 研究结果显示，样点间群落组成相异度与环境距离的相关性显著强于与物理空间距离的相关性。陆地距离与河道距离和群落相异度的关联模式相似，二者有时可显著反映整个昆虫群落的生物学变异。按体型大小或扩散模式拆解集合群落后，与预期相悖的是，被动扩散者与样点间环境差异的相关性略强于主动扩散者——尽管被动扩散者与样点间物理空间距离的相关性同样高于主动扩散者。此外，环境距离与生物学相异度之间的相关强度，在不同体型等级类群中也存在小幅差异。
4. 在控制样点间环境差异后，累积成本距离作为群落生物学相异度的相关指标，表现略优于陆地距离或河道距离。不过不同物理空间距离的相关系数数值差异极小。
5. 尽管环境差异作为溪流昆虫群落组成的决定因子，通常凌驾于物理空间距离之上，但环境距离与生物学相异度之间的相关性通常较弱。这种未解释的变异或许可归因于扩散过程，而采用更优质的扩散替代指标可捕捉该过程的影响。我们建议，进一步优化成本距离的测算方法或为可行的研究方向，尤其是结合关于昆虫扩散行为与实际扩散距离的更直接的物种自然史信息时，该方向更具价值。