Data from: A demographic ménage à trois: interactions between disturbances both amplify and dampen population dynamics of an endemic plant

Natural and anthropogenic disturbances co-occur in most systems, but how
they interact to shape demographic outcomes remains poorly understood.
Such interactions may alter dynamics of populations in non-additive ways,
making demographic predictions challenging when focusing on only one
disturbance. Thus, understanding the interactive effects of such
disturbances is critically important to determine the population viability
of most species under a diversity of stressors. We used a hierarchical
integral projection model (IPM), parameterized with 13 years of field data
across 20 populations, encompassing 2435 individuals of an endangered
herb, Liatris ohlingerae. We examined interactive effects of vertebrate
herbivory, fire and anthropogenic activities (sand roads) on vital rates
(e.g. survival, growth, reproduction, recruitment) and ultimately on
population growth rates (λ), to test the hypothesis that interactions
amplify or dampen differences in λ depending on environmental contexts. We
constructed megamatrices to determine coupled dynamics in individuals
damaged vs. not damaged by herbivores in roadsides and in Florida scrub
with different times since fire. We identified strong interactive effects
of fire with herbivory and habitat with herbivory on vital rates and on
population growth rates in the IPM model. We also found different patterns
of variation in λ between habitat and time-since-fire scenarios;
population growth rates were higher in roadside populations compared to
scrub populations and declined with increasing time since fire. Herbivory
had interactive effects with both fire and human disturbances on λ.
Herbivory resulted in decreased differences in λ due to anthropogenic
disturbance and slightly increased differences in λ due to time since
fire. Synthesis. The co-occurrence of various disturbances may both
amplify and dampen the effects of other disturbances on population growth
rate, thus shaping complex population dynamics that are neither linear nor
additive. These realistic nonlinearities represent challenges in
understanding and projecting of population dynamics. Here, we examined the
effects of various sources of disturbance on the population dynamics of an
endangered plant species, finding complex interactions affecting
population growth rates. We argue that integration of multiple,
interacting stressors in IPMs will allow more accurate estimation of the
overall effects of ecological processes on species viability.

多数生态系统中自然干扰与人为干扰往往相伴发生，但二者如何交互作用以塑造种群动态结果，目前仍缺乏深入认知。这类交互作用可能以非加和模式改变种群动态，使得仅聚焦单一干扰时的种群预测工作极具难度。因此，明确此类干扰的交互效应，对于评估多数物种在多重胁迫下的种群生存力至关重要。

本研究采用分层积分投影模型（hierarchical integral projection model, IPM），基于覆盖20个种群、总计2435株濒危草本Liatris ohlingerae的13年野外监测数据完成模型参数化。我们针对脊椎动物植食、火烧以及人为活动（砂石路）对生命率（如存活、生长、繁殖、种群补充）的交互效应展开分析，并进一步探究其对种群增长率（λ）的影响，以验证“交互作用会依据环境背景放大或削弱种群增长率λ的差异”这一假说。

我们构建了巨型矩阵（megamatrices），用以分析不同火烧后时长的佛罗里达灌丛与路边生境中，受植食损害与未受植食损害个体的耦合动态。基于IPM模型，我们发现火烧与植食、生境与植食对生命率及种群增长率均存在显著交互效应。此外，我们还发现生境与火烧后时长两类情境下的种群增长率变异模式存在差异：路边种群的种群增长率高于灌丛种群，且随火烧后时长增加而下降。

植食作用与火烧、人为干扰均对种群增长率λ存在交互效应：植食会缩小人为干扰带来的种群增长率差异，却小幅扩大了由火烧后时长差异导致的种群增长率差异。

综合分析表明，多种干扰的共存既可能放大也可能削弱其他干扰对种群增长率的影响，进而塑造出既非线性亦非加和的复杂种群动态。这类现实存在的非线性特征，为种群动态的理解与预测带来了挑战。

本研究针对一种濒危植物的种群动态，探究了多种干扰源的效应，发现复杂交互作用会对种群增长率产生影响。我们认为，在IPM模型中整合多种交互作用的胁迫因子，将能够更精准地评估生态过程对物种生存力的整体影响。