Background

Gradients in local environmental characteristics may favour the abundance of species with particular traits, while other species decline, or favour species with different traits at the same time, without an increase in average species abundances. Therefore, we asked: do variations in species and traits differ along gradients of deadwood variables? Do species abundance and trait occurrence change with species richness within or between functional groups? Thus, we analysed the beetle assemblages of five forest sites located in Italy, along the Apennines mountains.

Methods

From 2012 to 2018 we sampled beetles and five deadwood types in 193 plots to characterise the deadwood gradient: standing dead trees, snags, dead downed trees, coarse woody debris, and stumps. We modelled beetle species relative abundances and trophic traits occurrences against the deadwood variables using joint species distribution models.

Results

Out of 462 species, only 77 showed significant responses to at least one deadwood type, with a weak mean response across species. Trophic groups showed mostly negative responses to deadwood variables. Species abundance increased with species richness among sites only for phytophagous and saproxylophagous. Trait occurrence did not increase with species richness among sites, except for phytophagous and saproxylophagous. However, trait occurrence changed significantly with species richness of several trophic groups within some sites. We found that increases in species richness do not result in decreases in species abundance of a given trophic group, but rather null or positive relationships were found suggesting low interspecific competition.

Conclusions

Our findings suggest that in Mediterranean mountain forests there is still room for increasing the level of naturalness, at least for what concerns deadwood management. On one side, our findings suggest that competition for deadwood substrates is still low, on the other side they indicate that increasing deadwood volume and types to improve overall beetle richness may increase also beetle abundances.

中文翻译：

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沿枯木梯度的甲虫物种和功能特征的多样性表明环境过滤较弱

背景

局部环境特征的梯度可能有利于具有特定特征的物种的丰度，而其他物种减少，或同时有利于具有不同特征的物种，而平均物种丰度没有增加。因此，我们问：物种和性状的变化是否随着枯木变量的梯度而不同？物种丰度和性状发生是否随着功能组内或功能组之间的物种丰富度而变化？因此，我们分析了位于意大利亚平宁山脉沿线的五个森林遗址的甲虫组合。

方法

从 2012 年到 2018 年，我们在 193 个地块中对甲虫和五种枯木类型进行了采样，以表征枯木梯度：直立枯树、障碍物、倒下的枯树、粗糙的木质碎片和树桩。我们使用联合物种分布模型针对枯木变量对甲虫物种相对丰度和营养性状发生进行了建模。

结果

在 462 个物种中，只有 77 个物种对至少一种枯木类型表现出显着反应，物种之间的平均反应较弱。营养组对枯木变量大多表现出负面反应。物种丰度随着物种丰富度的增加而增加，只有植食性和腐木食性的地点。除植食性和腐木性外，性状的发生并没有随着地点间物种丰富度的增加而增加。然而，性状发生随着一些地点内几个营养群的物种丰富度而发生显着变化。我们发现物种丰富度的增加不会导致给定营养群的物种丰度减少，而是发现无效或正相关关系表明种间竞争较低。

结论

我们的研究结果表明，在地中海山区森林中，仍有提高自然水平的空间，至少在枯木管理方面如此。一方面，我们的研究结果表明，对枯木基质的竞争仍然很低，另一方面，它们表明增加枯木的数量和类型以提高整体甲虫丰富度可能也会增加甲虫的丰度。