Programa de Pós-Graduação em Biologia Vegetal, Universidade Federal de Pernambuco, Recife, Brazil.
Departamento de Botânica, Universidade Federal de Pernambuco, Recife, Brazil.
J Anim Ecol. 2018 Jul;87(4):1022-1033. doi: 10.1111/1365-2656.12820. Epub 2018 Apr 6.
Anthropogenic disturbance and climate change might negatively affect the ecosystem services provided by mutualistic networks. However, the effects of such forces remain poorly characterized. They may be especially important in dry forests, which (1) experience chronic anthropogenic disturbances (CADs) as human populations exploit forest resources, and (2) are predicted to face a 22% decline in rainfall under climate change. In this study, we investigated the separate and combined effects of CADs and rainfall levels on the specialization of mutualistic networks in the Caatinga, a seasonally dry tropical forest typical of north-eastern Brazil. More specifically, we examined interactions between plants bearing extrafloral nectaries (EFNs) and ants. We analysed whether differences in network specialization could arise from environmentally mediated variation in the species composition, namely via the replacement of specialist by generalist species. We characterized these ant-plant networks in 15 plots (20 × 20 m) that varied in CAD intensity and mean annual rainfall. We quantified CAD intensity by calculating three indices related to the main sources of disturbance in the Caatinga: livestock grazing (LG), wood extraction (WE) and miscellaneous resource use (MU). We determined the degree of ant-plant network specialization using four metrics: generality, vulnerability, interaction evenness and H '. Our results indicate that CADs differentially influenced network specialization: we observed positive, negative, and neutral responses along LG, MU and WE gradients, respectively. The pattern was most pronounced with LG. Rainfall also shaped network specialization, markedly increasing it. While LG and rainfall were associated with changes in network species composition, this trend was not related to the degree of species specialization. This result suggests that shifts in network specialization might be related to changes in species behaviour, not species composition. Our study highlights the vulnerability of such dry forest ant-plant networks to climate change. Moreover, dry forests experience highly heterogeneous anthropogenic disturbances, creating a geographic mosaic of selective forces that may shape the co-evolution of interactions between ants and EFN-bearing plants.
人为干扰和气候变化可能会对共生网络提供的生态系统服务产生负面影响。然而，这些力量的影响仍未得到充分描述。它们在干旱森林中可能尤为重要，干旱森林（1）由于人口对森林资源的开发而长期受到人为干扰（CAD），（2）预计在气候变化下降雨量将下降 22%。在这项研究中，我们调查了 CAD 和降雨量水平对巴西东北部典型季节性干旱热带森林——卡廷加共生网络专业化的单独和综合影响。更具体地说，我们研究了具有额外花蜜腺（EFN）的植物与蚂蚁之间的相互作用。我们分析了网络专业化的差异是否可以归因于环境介导的物种组成变化，即通过将专食物种替换为广食物种。我们在 15 个（20×20 m）不同 CAD 强度和年平均降雨量的样地中对这些蚂蚁-植物网络进行了特征描述。我们通过计算与卡廷加地区三种主要干扰源相关的三个指数来量化 CAD 强度：牲畜放牧（LG）、木材采伐（WE）和各种资源利用（MU）。我们使用四个指标来确定蚂蚁-植物网络的专业化程度：一般性、脆弱性、相互作用均匀度和 H'。我们的结果表明，CAD 以不同的方式影响网络专业化：我们在 LG、MU 和 WE 梯度上分别观察到正、负和中性响应。LG 的模式最为明显。降雨量也塑造了网络专业化，显著增加了网络专业化。虽然 LG 和降雨量与网络物种组成的变化有关，但这种趋势与物种专业化程度无关。这一结果表明，网络专业化的变化可能与物种行为的变化有关，而不是与物种组成有关。我们的研究强调了这种干旱森林蚂蚁-植物网络对气候变化的脆弱性。此外，干旱森林经历着高度异质的人为干扰，形成了一个选择压力的地理镶嵌体，这可能会塑造蚂蚁和具有 EFN 的植物之间相互作用的共同进化。
