Microclimate drives demographic compensation in a narrow endemic tropical species

Demographic compensation occurs when reductions in some vital rates are offset by increases in others, allowing populations to maintain similar performance across varying environments. This mechanism may help explain species’ ecological distributions and range limits. We investigated demographic compensation in Ipomoea cavalcantei, a narrow-range but locally abundant species endemic to Amazonian ironstone outcrops (cangas), by comparing populations in two contrasting habitats: open- and shrubby-canga. We also assessed how microclimatic factors influence regeneration processes, including seed production, seedling emergence, germination, and establishment.Using three years of demographic data, we built matrix population models and conducted a life table response experiment. We also carried out germination and seedling establishment experiments under different temperature and light conditions simulating the two habitats to identify the potential environmental drivers and their effects on key life-cycle events.Despite contrasting environmental conditions, both populations exhibited similar population growth rates (λ), with opposing contributions of growth and fecundity—evidence of demographic compensation. The open-canga population had lower growth but higher recruitment, driven by favorable temperature regimes for seed dormancy release and germination. In contrast, reduced growth was associated with physiological stress under high irradiance and shallow soils.Our results show that demographic compensation allows I. cavalcantei to persist across microhabitats, highlighting the importance of fine-scale environmental heterogeneity in shaping species distributions—even within narrow endemic ranges.种群人口统计补偿（demographic compensation）指的是某些生命率的下降被其他生命率的上升所抵消，使得种群在不同环境下仍能维持相近的种群表现。这一机制或可解释物种的生态分布与分布边界。 我们以狭域分布但局部种群繁盛的亚马逊铁质岩露头（cangas）特有种Ipomoea cavalcantei为研究对象，通过对比其在两种截然不同的生境——开阔型canga与灌丛型canga——中的种群，探究了该物种的种群人口统计补偿现象。此外，我们还评估了微气候因子对种群更新过程的影响，包括种子生产、幼苗出土、萌发与定植。 基于三年的种群人口统计数据，我们构建了矩阵种群模型（matrix population models）并开展了生命表响应实验（life table response experiment）。同时，我们在模拟两种生境的不同温度与光照条件下开展了萌发与幼苗定植实验，以明确潜在的环境驱动因子及其对关键生活史事件的作用效果。 尽管生境环境条件差异显著，两种种群的种群增长率（λ）却较为相近，且种群增长与繁殖力的贡献呈相反态势——这正是种群人口统计补偿的有力证据。开阔型canga种群的增长水平较低但更新率更高，这得益于其更适宜的温度条件，能够促进种子休眠破除与萌发。与之相反，灌丛型canga种群的增长受限则与高辐照度与浅层土壤下产生的生理胁迫密切相关。 我们的研究结果表明，种群人口统计补偿使得Ipomoea cavalcantei能够在不同微生境中存续，这凸显了精细尺度环境异质性在塑造物种分布中的重要意义——即便在狭域特有种的分布范围内亦是如此。