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.应用生态学领域的一项核心挑战，是阐明本土物种对道路的响应规律——道路作为驱动环境异质性的普遍因子，广泛分布于各类生境中。尽管多数研究着重强调了道路的负面生态效应，但本土物种在道路附近种群丰度上升的潜力长期被低估，且丰度变化背后的种群动态机制仍不明晰。 阐明此类机制，首先需明确种群生命率（vital rates）与生活史阶段如何共同作用影响种群增长；随后便可评估道路如何改变两类替代种群动态路径的相对重要性，即早期生命阶段与晚期生命阶段的性能提升——这两类路径曾被认为是种群增长提升的主要驱动因子。 我们以3年的野外普查数据参数化种群动态模型，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特征。为此，我们选用切叶蚁（Atta laevigata）作为模式研究生物。切叶蚁是本土生态系统工程师（ecosystem engineers），为新热带区生态系统中的优势植食类群，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（Cerrado savannahs）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。我们的调查结果显示，35%~45%的成熟蚁群分布在距离道路15米以内的区域，其分布位置显著比随机分布更贴近道路。无论距离道路远近，种群增长速率（λ）均大于1，但道路附近的λ值显著高出41%。 无论生境类型如何，种群增长速率λ对早期存活与生长速率的弹性（elasticities）占比均远高于其对成熟阶段的弹性。生命表响应实验（life-table response experiment）结果表明，道路附近更高的λ值主要源于该区域更高的定殖成功率与早期生命阶段性能。 ### 综合与应用 道路网络正于全球生物多样性富集区域快速蔓延。针对种群丰度受道路影响发生改变的物种制定保护与管理指南，需要阐明支撑此类丰度变化的种群动态机制。本研究证实，道路附近的光滑切叶蚁（Atta laevigata）种群增长速率更高，其核心原因是该区域切叶蚁早期生命阶段的性能得到提升。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种群丰度上升，引发重大的生态与经济后果。在新热带区稀树草原的保护区与农业系统管理中，纳入光滑切叶蚁（Atta laevigata）的早期生命阶段因素，并对道路选址进行审慎规划，将有助于优化相关管理策略。