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——道路作为无处不在的环境异质性驱动因子，深刻塑造着生态系统格局。尽管多数研究着重强调了道路的负面影响，但本土物种在道路附近丰度提升的潜力长期被低估，且驱动丰度变化的种群动态机制仍不明晰。
阐明此类机制的首要步骤，是明确种群生命率（demographic vital rates）与生活史阶段如何相互作用，进而影响种群增长。后续便可进一步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素。
我们基于3年的野外普查数据为种群动态模型设定参数，并开展扰动分析，以量化道路邻近性对物种丰度与种群动态的影响。为此，本研究选用光滑切叶蚁（Atta laevigata）作为模式生物。切叶蚁属于本土生态系统工程师（ecosystem engineers），是新热带区（Neotropical）生态系统中的优势草食动物，同时也是自然界中寿命最长的昆虫类群之一。
本研究的开展区域为塞拉多稀树草原（Cerrado savannahs），该区域的道路网络正快速扩张，而切叶蚁属（Atta）物种是当地主要的农业害虫。研究结果显示，35%至45%的成熟蚁群位于距离道路15米的范围内，这一分布距离显著低于随机分布的预期水平。道路附近与远离道路的区域内，种群增长率（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，种群增长率λ对早期存活与生长速率的弹性（elasticities）在比例上均显著高于成熟阶段的弹性。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率与早期生命阶段的性能表现。
综合与应用：道路网络正在全球生物多样性丰富的区域快速蔓延。对于丰度受道路调控的物种，制定科学的保护与管理指南，需要先理解支撑其丰度变化的种群动态机制。本研究证实，道路附近光滑切叶蚁种群更高的增长率，源于早期生命阶段性能的显著提升。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，带来重大的生态与经济后果。在新热带稀树草原的保护区与农业系统管理中，充分考虑光滑切叶蚁的早期生命阶段，并对道路选址进行审慎规划，将有助于优化相关管理策略。