Zvereva Elena L, Zverev Vitali, Kozlov Mikhail V
Department of Biology, University of Turku, Turku, Finland.
J Anim Ecol. 2020 Dec;89(12):2946-2957. doi: 10.1111/1365-2656.13350. Epub 2020 Oct 9.
The latitudinal biotic interaction hypothesis (LBIH) predicts that the strength of various biotic interactions decreases from low to high latitudes. Inconsistency between studies testing this hypothesis may result from variations among different types of interactions and among study systems. Therefore, exploration of multiple interactions within one system would help to disentangle latitudinal patterns across individual interactions and to evaluate latitudinal changes in the overall impact of enemies on prey. We tested the prediction based on the LBIH that the pressure of natural enemies on herbivorous insects decreases with increase in latitude across the boreal forest zone. We also asked whether the impacts of major groups of these enemies exhibit similar latitudinal patterns and whether these patterns are consistent across study years. In 10 forest sites located from 60°N to 69°N in Northern Europe, each summer, from 2016 to 2019, we measured (a) mortality of three groups of leafmining insects caused by birds, ants, parasitoids and unknown factors, (b) bird attacks on caterpillar-shaped plasticine models and (c) birch foliar damage caused by defoliators and leafminers. Latitudinal patterns in both insect herbivory on birch and top-down pressure on herbivorous insects varied considerably and inconsistently among the four study years, so that only some of the year-specific correlations with latitude were statistically significant. Nevertheless, meta-analysis combining correlations across years, preys and enemies revealed general decreases in predation by birds (on both natural and model prey) and ants, but an increase in parasitism rates, from low to high latitudes. We found that the direction of latitudinal changes in the strength of biotic interactions was interaction-specific: predation and herbivory supported LBIH, whereas parasitism exhibited an opposite trend. Consequently, the overall impact of natural enemies on herbivorous insects did not change with latitude and was therefore an unlikely reason for the poleward decrease in herbivory observed in our gradient. Considerable among-year variation in the strength of the latitudinal patterns in all the studied interactions suggests that this variation is a widespread phenomenon.
纬度生物相互作用假说（LBIH）预测，各种生物相互作用的强度会从低纬度向高纬度递减。检验该假说的研究之间存在不一致，可能是由于不同类型的相互作用以及研究系统之间存在差异。因此，在一个系统内探索多种相互作用，将有助于理清个体相互作用的纬度模式，并评估天敌对猎物总体影响的纬度变化。我们基于LBIH检验了这样一个预测：在北方森林带，随着纬度升高，天敌对植食性昆虫的压力会降低。我们还研究了这些主要天敌类群的影响是否呈现相似的纬度模式，以及这些模式在不同研究年份是否一致。在北欧北纬60°至69°的10个森林地点，从2016年到2019年的每个夏天，我们测量了：（a）鸟类、蚂蚁、寄生蜂和未知因素导致的三类潜叶昆虫的死亡率；（b）鸟类对毛虫形状橡皮泥模型的攻击；（c）食叶者和潜叶者对桦树叶造成的损害。在四个研究年份中，桦树上昆虫食草作用的纬度模式以及对食草昆虫的自上而下压力差异很大且不一致，因此只有一些特定年份与纬度的相关性具有统计学意义。然而，结合多年、猎物和天敌之间相关性的荟萃分析显示，从低纬度到高纬度，鸟类（对天然猎物和模型猎物）和蚂蚁的捕食作用总体上减少，但寄生率增加。我们发现，生物相互作用强度的纬度变化方向因相互作用类型而异：捕食和食草作用支持LBIH，而寄生作用则呈现相反趋势。因此，天敌对食草昆虫的总体影响不会随纬度变化，因此不太可能是我们在该梯度中观察到的食草作用向极地减少的原因。所有研究相互作用中纬度模式强度的显著年际变化表明，这种变化是一种普遍现象。
