In ecological networks, neutral predictions suggest that species' interaction frequencies are proportional to their relative abundances. Deviations from neutral predictions thus correspond to interaction preferences (when positive) or avoidances (when negative), driven by non-neutral (e.g. niche-based) processes. Exotic species interact with many partners with which they have not coevolved, and it remains unclear whether this systematically influences the strength of neutral processes on interactions, and how these interaction-level differences scale up to entire networks. To fill this gap, we compared interactions between plants and frugivorous birds at nine forest sites in New Zealand varying in the relative abundance and composition of native and exotic species, with independently sampled data on bird and plant abundances from the same sites. We tested if the strength and direction of interaction preferences differed between native and exotic species. We further evaluated whether the performance of neutral predictions at the site level was predicted by the proportion of exotic interactions in each network from both bird and plant perspectives, and the species composition in each site. We found that interactions involving native plants deviated more strongly from neutral predictions than did interactions involving exotics. This "pickiness" of native plants could be detrimental in a context of global biotic homogenization where they could be increasingly exposed to novel interactions with neutrally-interacting mutualists. However, the realization of only a subset of interactions in different sites compensated for the neutrality of interactions involving exotics, so that neutral predictions for whole networks did not change systematically with the proportion of exotic species nor species composition. Therefore, the neutral and niche processes that underpin individual interactions may not scale up to entire networks. This shows that seemingly simplistic neutral assumptions entail complex processes and can provide valuable understanding of community assembly or invasion dynamics.

中文翻译：

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棘手的合作伙伴：本土植物比外来植物表现出更强的互动偏好

在生态网络中，中性预测表明物种的相互作用频率与其相对丰度成正比。因此，与中性预测的偏差对应于由非中性（例如基于生态位）过程驱动的交互偏好（当积极时）或回避（当消极时）。外来物种与许多未与之共同进化的伙伴相互作用，目前尚不清楚这是否会系统地影响相互作用的中性过程的强度，以及这些相互作用水平的差异如何扩大到整个网络。为了填补这一空白，我们比较了新西兰九个森林地点的植物和食果鸟类之间的相互作用，这些地点的本地和外来物种的相对丰度和组成各不相同，来自同一地点的鸟类和植物丰度的独立采样数据。我们测试了本地和外来物种之间交互偏好的强度和方向是否不同。我们进一步评估了站点级别中性预测的性能是否由每个网络中从鸟类和植物角度的外来相互作用的比例以及每个站点的物种组成来预测。我们发现涉及本地植物的相互作用比涉及外来植物的相互作用更偏离中性预测。在全球生物同质化的背景下，本地植物的这种“挑剔”可能是有害的，在这种情况下，它们可能越来越多地暴露于与中性相互作用的互惠者的新相互作用中。然而，在不同地点仅实现相互作用的一个子集补偿了涉及外来物种的相互作用的中立性，因此对整个网络的中性预测不会随着外来物种的比例或物种组成而系统地改变。因此，支撑个体交互的中立和利基过程可能无法扩展到整个网络。这表明看似简单的中性假设需要复杂的过程，并且可以提供对社区组装或入侵动态的有价值的理解。支持个人互动的中立和利基过程可能无法扩展到整个网络。这表明看似简单的中性假设需要复杂的过程，并且可以提供对社区组装或入侵动态的有价值的理解。支持个人互动的中立和利基过程可能无法扩展到整个网络。这表明看似简单的中性假设需要复杂的过程，并且可以提供对社区组装或入侵动态的有价值的理解。