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）研究在很大程度上依赖替代指标来推断扩散对本地群落结构的影响。过往研究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更多可影响生物体移动与扩散的复杂景观特征。成本距离（cost distance）方法恰好满足这一需求，可用于确定景观中阻力最小的移动路径。 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性的关联因子时表现是否存在差异；同时探究了体型与扩散模式对集合群落组织的影响。 3. 研究结果显示，样点间群落组成的相异性与环境距离的相关性强于物理距离。陆地距离与河道距离对样点间群落相异性的关联模式相似，二者有时可显著关联于整个昆虫群落的生物学变异。与我们的预期相反，在按体型或扩散模式拆分的集合群落中，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距离的相关性同样强于主动扩散者。不同体型类群间，环境距离与生物学相异性的关联强度也存在小幅差异。 4. 在控制样点间环境差异后，累积成本距离作为样点间生物学相异性的关联因子，表现略优于陆地距离或河道距离。不过，不同物理距离指标间的相关系数仅存在微小的量化差异。 5. 尽管环境差异通常作为溪流昆虫群落组成的主导因子，其权重高于物理距离，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可能源于扩散过程，而该过程可通过更优质的过程替代指标加以捕捉。我们建议，进一步优化成本距离的测量方法或为富有成效的研究方向，尤其是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。