García-Navas Vicente, Tarifa Rubén, Salido Teresa, González-Robles Ana, López-Orta Antonio, Valera Francisco, Rey Pedro J
Department of Ecology and Evolution, Estación Biológica de Doñana EBD, CSIC, Seville, Spain.
Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
Ecol Appl. 2025 Jul;35(5):e70057. doi: 10.1002/eap.70057.
Olive groves are the most representative crop of the Mediterranean basin. This agroforestry system is undergoing a strong transformation in recent decades as a result of the agricultural intensification process prevailing in the Northern Hemisphere. Although some authors have suggested that farmland biodiversity responds non-linearly to the complexity of agricultural landscapes, few studies have used community thresholds to identify potential tipping points. Here, we examined the existence of synchronous responses in bird abundance across a gradient of decreasing agricultural intensification in Spanish olive groves. Our study system comprised 25 sites, each consisting of a pair of farms: one with intensive management and the other one with extensive management of the herbaceous cover. We explored whether bird abundances exhibit non-linear threshold responses to ant abundance and tree density at a local (field) scale, plant diversity (both herbaceous and woody plants) at a local (farm) scale, and to proportion of natural habitat at a landscape scale using Threshold Indicator Taxa ANalysis (TITAN). We found a higher incidence of positive responses with decreasing levels of intensification, and these were not restricted to certain guilds or avian families. Few indicator species showed a significant negative response. Thresholds detected were not sharp but rather gradual changes along the environmental gradients. Although they do not necessarily support evidence of ecological thresholds characterized by rapid changes in species abundance or distribution, these patterns can help identify optimal change points for management decisions. Specifically, our results indicate that reaching a minimum threshold of ~85 and 15 species of herbaceous and woody plants, respectively, per unit of surface can entail a gain in terms of bird diversity for olive farms with virtually no detrimental effects. Overall, this study shows that the adoption of agri-environmental measures like the maintenance of ground cover and patches of natural habitat has a positive impact on different species inhabiting this woody crop, and this effect occurs at different spatial scales.
橄榄林是地中海盆地最具代表性的作物。近几十年来，由于北半球盛行的农业集约化进程，这种农林业系统正在经历剧烈变革。尽管一些作者认为农田生物多样性对农业景观复杂性的反应是非线性的，但很少有研究使用群落阈值来确定潜在的临界点。在这里，我们研究了西班牙橄榄林中鸟类数量在农业集约化程度降低梯度上的同步反应情况。我们的研究系统包括25个地点，每个地点由一对农场组成：一个采用集约化管理，另一个对草本植被采用粗放式管理。我们使用阈值指示分类分析（TITAN）方法，探究鸟类数量在局部（田地）尺度上对蚂蚁数量和树木密度、在局部（农场）尺度上对植物多样性（草本和木本植物）以及在景观尺度上对自然栖息地比例是否表现出非线性阈值反应。我们发现，随着集约化程度降低，积极反应的发生率更高，而且这些反应并不局限于某些鸟类群落或科。很少有指示物种表现出显著的负面反应。检测到的阈值并非急剧变化，而是沿环境梯度逐渐变化。尽管它们不一定支持以物种数量或分布快速变化为特征的生态阈值的证据，但这些模式有助于确定管理决策的最佳变化点。具体而言，我们的结果表明，对于橄榄农场来说，每单位面积分别达到约85种草本植物和15种木本植物的最低阈值，可能会在鸟类多样性方面有所收获，而且几乎没有不利影响。总体而言，这项研究表明，采取诸如维持地被植物和自然栖息地斑块等农业环境措施，对栖息在这种木本作物中的不同物种有积极影响，而且这种影响发生在不同的空间尺度上。
