PREMISE Abiotic factors and plant species traits have been shown to drive latitudinal gradients in herbivory, and yet, population-level factors have been largely overlooked within this context. One such factor is plant density, which may influence the strength of herbivory and may vary with latitude. METHODS We measured insect herbivory and conspecific plant density (CPD) of oak (Quercus robur) seedlings and saplings along a 17° latitudinal gradient (2700 km) to test whether herbivory exhibited a latitudinal gradient, whether herbivory was associated with CPD, and whether such an association changed with latitude. RESULTS We found a positive but saturating association between latitude and leaf herbivory. Furthermore, we found no significant relationship between CPD and herbivory, and such lack of density effects remained consistent throughout the sampled latitudinal gradient. CONCLUSIONS Despite the apparently negligible influence of plant density on herbivory for Q. robur, further research with other plant taxa and in different types of plant communities are needed to investigate density-dependent processes shaping geographical variation in plant-herbivore interactions.

中文翻译：

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纬度和同种植物密度对橡树苗和幼苗昆虫叶食性的影响

前提 非生物因素和植物物种特性已被证明会驱动食草动物的纬度梯度，然而，在这种情况下，种群水平的因素在很大程度上被忽视了。其中一个因素是植物密度，这可能会影响食草动物的强度并可能随纬度而变化。方法我们沿 17° 纬度梯度（2700 公里）测量了橡树 (Quercus robur) 幼苗和树苗的昆虫食草和同种植物密度 (CPD)，以测试食草动物是否表现出纬度梯度，食草动物是否与 CPD 相关，以及一种关联随纬度而变化。结果我们发现纬度和叶草食性之间存在积极但饱和的关联。此外，我们发现 CPD 和食草动物之间没有显着关系，并且这种密度效应的缺乏在整个采样的纬度梯度中保持一致。结论 尽管植物密度对 Q. robur 的食草动物的影响显然可以忽略不计，但仍需要对其他植物分类群和不同类型的植物群落进行进一步研究，以研究影响植物-食草动物相互作用地理变异的密度依赖性过程。