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，以推断扩散对本地群落结构的影响。过往研究通常将陆上距离（overland distance）与河道距离（watercourse distance）作为此类替代指标。然而，优质的扩散替代指标需纳入更多能影响生物体移动与扩散的复杂景观特征。成本距离（cost distance）方法恰好可实现这一目标，能够确定穿越景观的最小阻力路径。 2. 本研究针对亚北极溪流昆虫集合群落，分析了群落相似性的距离衰减效应。我们检验了陆上距离、河道距离与累积成本距离（cumulative cost distance）作为样点间群落组成相异性的关联因子时，是否表现存在差异。同时还探究了体型（body size）与扩散模式（dispersal mode）对集合群落组织的影响。 3. 研究发现，相较于样点间的物理距离（physical distance），群落组成相异性与环境距离（environmental distance）的相关性更强。陆上距离与河道距离与群落相异性的相关性水平相近，且有时会与整个昆虫群落的生物学变异呈显著相关。按体型或扩散模式拆解集合群落后，与我们的预期相反，被动扩散者（passive disperser）相较于主动扩散者（active disperser），与样点间环境差异的相关性略强——尽管被动扩散者与样点间物理距离的相关性也强于主动扩散者。不同体型类群间，环境距离与生物学相异性的相关强度也存在小幅差异。 4. 在控制样点间环境差异的条件下，累积成本距离作为样点间生物学相异性的关联因子，表现略优于陆上距离或河道距离。不过，不同物理距离间的相关系数（correlation coefficient）定量差异较小。 5. 尽管环境差异作为溪流昆虫群落组成的决定因素，通常会凌驾于物理距离之上，但环境距离与生物学相异性之间的相关性通常较弱。这种未被解释的变异或许可归因于扩散过程，而借助更贴合该过程的替代指标可捕捉此类变异。我们建议，进一步优化成本距离的测量方法或是一条富有成效的研究路径，尤其是若能辅以关于昆虫扩散行为与扩散距离的更直接的自然历史信息时。