Data from: Wolf in sheep's clothing: model misspecification undermines tests of the neutral theory for life histories

Understanding the processes behind change in reproductive state along life-history trajectories is a salient research program in evolutionary ecology. Two processes, state dependence and heterogeneity, can drive the dynamics of change among states. Both processes can operate simultaneously, begging the difficult question of how to tease them apart in practice. The Neutral Theory for Life Histories (NTLH) holds that the bulk of variations in life-history trajectories is due to state dependence and is hence neutral: Once previous (breeding) state is taken into account, variations are mostly random. Lifetime reproductive success (LRS), the number of descendants produced over an individual's reproductive life span, has been used to infer support for NTLH in natura. Support stemmed from accurate prediction of the population-level distribution of LRS with parameters estimated from a state dependence model. We show with Monte Carlo simulations that the current reliance of NTLH on LRS prediction in a null hypothesis framework easily leads to selecting a misspecified model, biased estimates and flawed inferences. Support for the NTLH can be spurious because of a systematic positive bias in estimated state dependence when heterogeneity is present in the data but ignored in the analysis. This bias can lead to spurious positive covariance between fitness components when there is in fact an underlying trade-off. Furthermore, neutrality implied by NTLH needs a clarification because of a probable disjunction between its common understanding by evolutionary ecologists and its translation into statistical models of life-history trajectories. Irrespective of what neutrality entails, testing hypotheses about the dynamics of change among states in life histories requires a multimodel framework because state dependence and heterogeneity can easily be mistaken for each other.解析生活史轨迹中繁殖状态变化背后的调控过程，是进化生态学领域的重要研究方向。状态依赖（state dependence）与异质性（heterogeneity）这两类过程，均可驱动状态间的变化动态，且二者可同时发挥作用，这引出了一个棘手的问题：实际研究中该如何将二者厘清区分？ 生活史中性理论（Neutral Theory for Life Histories, NTLH）认为，生活史轨迹中的绝大多数变异源于状态依赖，因此具备中性特征：只要纳入先前的（繁殖）状态作为控制变量，剩余变异大多呈随机分布。终生繁殖成功率（Lifetime reproductive success, LRS），即个体在整个繁殖生命周期内产生的后代总数，曾被用于推断自然种群中生活史中性理论的支持证据。此类支持证据的来源是：通过状态依赖模型估算的参数，能够精准预测种群水平的LRS分布。 我们通过蒙特卡洛模拟（Monte Carlo simulations）证明：当前生活史中性理论在零假设（null hypothesis）框架下依赖LRS预测的研究范式，极易导致模型误设、参数有偏估计以及推断结果存在缺陷。若数据中存在异质性却在分析中未予以纳入，状态依赖的估算会产生系统性正向偏差，进而使得生活史中性理论的支持证据实为伪证。当实际存在内在的生活史权衡（trade-off）时，这类偏差会导致适合度组分（fitness components）间出现虚假的正协方差。 此外，由于进化生态学家对生活史中性理论所蕴含的中性性的普遍认知，与其在生活史轨迹统计模型中的具体表征之间可能存在脱节，因此需要对该理论中的中性性概念加以澄清。无论中性性的具体内涵为何，检验生活史中状态变化动态的相关假说都需要采用多模型框架（multimodel framework），因为状态依赖与异质性二者极易被相互混淆。