Indirect effects resulting from species sharing the same enemy can shape spatio-temporal variations in species occurrence. The strength of such effects remains poorly known in natural communities composed of species from different trophic levels interacting in heterogeneous landscapes. Benefiting from a well-known arctic vertebrate community and marked spatio-temporal variations in the density of key prey species, we examined the effects of direct predator-prey and indirect predator-mediated effects on species occurrence in the landscape. We found both positive effects of one prey (lemmings), as well as negative indirect effects of another prey (colonial nesting snow geese) on the occurrence of species (ground-nesting birds) belonging to different guilds and trophic levels but sharing a common predator (arctic fox). However, species using prey refuges available in the landscape were not or less affected by predator-mediated effects. Similarly, the smallest (a passerine) and the largest and most dangerous species (an owl) for the shared predator were not affected by these effects. Our study provides one of the rare empirical evidence of predator-mediated effects ascending the food web (i.e. negative indirect effect of an herbivore on avian predators) and underlines how habitat structure and species traits can modulate the strength of indirect effects in natural communities.

中文翻译：

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捕食者介导对北极陆生脊椎动物群落物种发生影响的可变强度

拥有相同敌人的物种产生的间接影响可以影响物种出现的时空变化。在由不同营养水平的物种在异质景观中相互作用组成的自然群落中，这种影响的强度仍然知之甚少。受益于众所周知的北极脊椎动物群落和关键猎物物种密度的显着时空变化，我们研究了直接捕食者-猎物和间接捕食者介导的影响对景观中物种发生的影响。我们发现了一种猎物（旅鼠）的积极影响，以及另一种猎物（殖民地筑巢雪雁）对属于不同行会和营养级别但共享共同捕食者的物种（地面筑巢鸟类）的发生的负面间接影响（白狐）。然而，使用景观中可用猎物避难所的物种没有或较少受到捕食者介导的影响。同样，对于共同捕食者来说，最小的（雀形目）和最大和最危险的物种（猫头鹰）不受这些影响。我们的研究提供了掠食者介导的影响上升食物网的罕见经验证据之一（即食草动物对鸟类捕食者的负面间接影响），并强调栖息地结构和物种特征如何调节自然群落中间接影响的强度。