Data from: Roads increase population growth rates of a native leaf-cutter ant in Neotropical savannahs

A challenge in applied ecology is understanding the responses of native species to roads, which are ubiquitous drivers of environmental heterogeneity. While most studies highlight their negative effects, the potential for native species to increase in abundance near roads has been underappreciated, and the demographic mechanisms underlying abundance changes remain unclear. Elucidating these mechanisms requires first determining how demographic vital rates and life-history stages interact to influence population growth. One can then assess how roads alter the relative importance of the alternative demographic pathways – increased performance of early vs. late life stages – suggested as the principal drivers of increased population growth. We parameterized demographic models with 3 years of census data and conducted perturbation analyses to evaluate how proximity to roads altered abundance and demography. To do so, we used the leaf-cutter ant Atta laevigata as our model organism. Leaf-cutters are native ecosystem engineers and dominant herbivores in Neotropical ecosystems and also amongst the longest lived insects in nature. Our study was conducted in Cerrado savannahs, where road networks are rapidly expanding and Atta species are major agricultural pests. We found that 35–45% of adult colonies were located within 15 m of roads, which is significantly closer than expected at random. Population growth rates (λ) were >1 both near and far from roads, but λ near roads were significantly (41%) higher. Elasticities of λ to early survival and growth rates were proportionally much higher than those of adult stages, irrespective of habitat. Life-table response experiment results indicate that the higher λ near roads was due primarily to the much higher colonization and early-life performance there. Synthesis and applications. Road networks are proliferating throughout biodiversity-rich regions. Developing conservation and management guidelines for species whose abundance is altered by roads requires understanding the demographic mechanisms that underpin these changes. We demonstrate that the higher growth rate of roadside Atta laevigata populations is due to increased early-life performance. Thus, the expansion of road networks could have major ecological and economic consequences by facilitating the increased abundance of ecosystem engineers and agricultural pests. Accounting for A. laevigata early life stages and careful planning of road placement should improve management strategies of protected areas and agricultural systems in Neotropical savannahs.

应用生态学领域的核心挑战之一，是解析本土物种对道路的响应——道路是普遍存在的环境异质性驱动因子。尽管多数研究着重强调了道路的负面影响，但本土物种在道路周边种群丰度提升的潜力长期被低估，且丰度变化背后的种群统计机制仍未明晰。要阐明此类机制，需首先明确种群统计生命率与生活史阶段如何相互作用，进而影响种群增长；随后便可评估道路如何改变两类不同种群统计路径的相对重要性——即早期与晚期生活史阶段的性能提升，此前研究认为这两类路径是种群增长提升的主要驱动因素。本研究基于3年的野外普查数据对种群统计模型进行参数化，并开展扰动分析，以评估道路邻近性如何改变种群丰度与种群动态。为此，我们选取光滑切叶蚁（Atta laevigata）作为模式生物。切叶蚁是新热带区生态系统中的本土生态系统工程师（ecosystem engineers）与优势草食动物，同时也是自然界中寿命最长的昆虫类群之一。本研究在塞拉多稀树草原开展，该区域的道路网络正快速扩张，且切叶蚁属（Atta）物种是当地主要的农业害虫。研究发现，35%至45%的成熟蚁巢位于道路15米范围内，这一分布显著比随机分布更靠近道路。种群增长率（λ）在道路周边与远离道路的区域均大于1，但道路周边的λ值显著高出41%。无论生境类型如何，种群增长率λ对早期存活与生长速率的弹性值，在比例上均显著高于成熟蚁群阶段的弹性值。生命表响应实验（Life-table Response Experiment, LTRE）结果表明，道路周边更高的λ值，主要源于该区域更高的定殖率与早期生活史阶段性能。综合与应用：道路网络正于全球生物多样性丰富的区域快速扩张。对于丰度受道路影响的物种，制定保护与管理指南需先理解支撑其丰度变化的种群统计机制。本研究证实，道路周边光滑切叶蚁种群更高的增长率，源于其早期生活史阶段性能的提升。因此，道路网络的扩张可能通过促进生态系统工程师与农业害虫的丰度提升，引发重大的生态与经济后果。综合考虑光滑切叶蚁的早期生活史阶段，并对道路选址进行审慎规划，可有效改善新热带区稀树草原中保护区与农业系统的管理策略。