Gradients in elevation impose changes in environmental conditions, which in turn modulate species distribution and abundance as well as the interactions they maintain. Along the gradient, interacting species (e.g., predators, parasitoids) can respond to changes in different ways. This study aims to investigate how egg parasitism of a forest pest, the pine processionary moth (PPM), Thaumetopoea pityocampa, vary along an elevational gradient (190–2000 m.a.s.l.) in a mountain range of SE Spain, including areas of recent elevational expansion, for a seven years period (2008–2014). We used generalized linear mixed models to ascertain the effect of both elevation and the winter North Atlantic Oscillation (NAO) index (a proxy of interannual climatic conditions) on the rate of parasitism, and the occurrence probabilities of two parasitoid species: a PPM specialist and a generalist species. Since four pine species are stratified along the elevational gradient, we repeated all the analyses separately for lowlands (190–1300 m. a.s.l.) and uplands (1350–2000 m. a.s.l.). Results showed a decrease in both parasitism rate and probability of occurrence of the two main parasitoid species with elevation, although decline was more severe for the specialist species. The effect of elevation was more conspicuous and intense in uplands than in lowlands. Positive NAO winter values, associated with cold and dry winters, reduced the rate of parasitism and the probability of occurrence of the two main parasitoid species—but particularly for the generalist species—as elevation increases. In a context of climate warming, it is crucial to mitigate PPM elevational and latitudinal expansion. Increasing tree diversity at the PPM expansion areas may favor the establishment of parasitoids, which could contribute to synchronizing host– parasitoid interactions and minimize the risk of PPM outbreaks.

中文翻译：

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森林有害生物海拔范围的扩大：寄生虫能追踪其寄主吗？

海拔梯度会导致环境条件发生变化，进而改变物种的分布和丰度以及它们保持的相互作用。沿着梯度，相互作用的物种（例如捕食者，寄生动物）可以以不同的方式对变化做出响应。这项研究的目的是调查森林害虫，松树前进蛾（PPM），丘脑披皮虫的卵寄生性，在西班牙东南山区（包括最近的海拔扩展区域），沿着海拔梯度（190-2000 masl）变化了七年（2008-2014）。我们使用广义线性混合模型来确定海拔和冬季北大西洋涛动指数（NAO）（年际气候状况的代名词）对寄生率的影响以及两种寄生虫种类的发生概率：PPM专家和多才多艺的物种。由于四种松树物种沿海拔梯度分层，因此我们分别对低地（190-1300 masl）和高地（1350-2000 masl）重复了所有分析。结果表明，两种寄生虫的寄生率和发生率均随海拔升高而降低，尽管特殊种的下降更为严重。与低地相比，高地在高地上的影响更为明显和强烈。随着海拔的升高，与寒冷和干燥的冬季相关的NAO冬季正值降低了寄生率和两种主要的寄生性寄生虫（特别是通才种）的发生率。在气候变暖的情况下，减轻PPM的海拔和纬度膨胀至关重要。PPM扩展区树木多样性的增加可能有利于建立寄生虫，这可能有助于同步宿主－寄生虫的相互作用，并使PPM爆发的风险降到最低。降低了寄生虫的发病率，并降低了两种主要寄生虫的发生率（特别是对通才种），因为海拔升高了。在气候变暖的情况下，减轻PPM的海拔和纬度膨胀至关重要。PPM扩展区树木多样性的增加可能有利于建立寄生虫，这可能有助于同步宿主－寄生虫的相互作用，并使PPM爆发的风险降到最低。降低了寄生虫的发病率，并降低了两种主要寄生虫的发生率（特别是对通才种），因为海拔升高了。在气候变暖的情况下，减轻PPM的海拔和纬度膨胀至关重要。PPM扩展区树木多样性的增加可能有利于建立寄生虫，这可能有助于同步宿主－寄生虫的相互作用，并使PPM爆发的风险降到最低。