Biodiversity and Conservation Biology, Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland.
Área de Investigación y Monitoreo de Avifauna, Aves y Conservación, BirdLife in Ecuador, Nuño de Valderrama OE7 y Av, Mariana de Jesús, Quito, Ecuador.
Oecologia. 2023 Mar;201(3):761-770. doi: 10.1007/s00442-023-05330-z. Epub 2023 Feb 9.
On-going land-use change has profound impacts on biodiversity by filtering species that cannot survive in disturbed landscapes and potentially altering biotic interactions. In particular, how land-use change reshapes biotic interactions remains an open question. Here, we used selectivity experiments with nectar feeders in natural and converted forests to test the direct and indirect effects of land-use change on resource competition in Andean hummingbirds along an elevational gradient. Selectivity was defined as the time hummingbirds spent at high resource feeders when feeders with both low and high resource values were offered in the presence of other hummingbird species. Selectivity approximates the outcome of interspecific competition (i.e., the resource intake across competing species); in the absence of competition, birds should exhibit higher selectivity. We evaluated the indirect effect of forest conversion on selectivity, as mediated by morphological dissimilarity and flower resource abundance, using structural equation models. We found that forest conversion influenced selectivity at low and mid-elevations, but the influence of morphological dissimilarity and resource availability on selectivity varied between these elevations. At mid-elevation, selectivity was more influenced by the presence of morphologically similar competitors than by resource abundance while at low-elevation resource abundance was a more important predictor of selectivity. Our results suggest that selectivity is influenced by forest conversion, but that the drivers of these changes vary across elevation, highlighting the importance of considering context-dependent variation in the composition of resources and competitors when studying competition.
正在进行的土地利用变化通过过滤无法在受干扰景观中生存的物种，以及潜在改变生物相互作用，对生物多样性产生深远影响。特别是，土地利用变化如何重塑生物相互作用仍然是一个悬而未决的问题。在这里，我们使用花蜜觅食者在自然和转化森林中的选择性实验，来检验资源竞争在安第斯蜂鸟沿海拔梯度上随土地利用变化的直接和间接影响。选择性被定义为在其他蜂鸟物种存在的情况下，当提供具有低和高资源值的喂料器时，蜂鸟在高资源喂料器上花费的时间。选择性近似于种间竞争的结果（即，竞争物种的资源摄入量）；在没有竞争的情况下，鸟类应该表现出更高的选择性。我们使用结构方程模型评估了森林转化通过形态差异和花资源丰度对选择性的间接影响。我们发现，森林转化对低海拔和中海拔的选择性有影响，但形态差异和资源可用性对选择性的影响在这些海拔之间有所不同。在中海拔，选择性受形态相似竞争者存在的影响大于资源丰富度的影响，而在低海拔，资源丰富度是选择性的更重要预测因子。我们的结果表明，选择性受到森林转化的影响，但这些变化的驱动因素在海拔上有所不同，这突出了在研究竞争时考虑资源和竞争者组成的上下文相关变化的重要性。
