谁害怕把时间作为连续变量建模?

IF 6.3 2区 环境科学与生态学 Q1 ECOLOGY Methods in Ecology and Evolution Pub Date : 2024-09-02 DOI:10.1111/2041-210x.14394
Hanna Kokko
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引用次数: 0

摘要

生态和生态进化过程的大多数模型都涉及到创建某种事物随时间变化的轨迹,无论是种群密度、平均性状值还是环境状态。这就需要决定如何在模型中表示时间流。作为培训的一部分,大多数生态学家都接触过连续时间模型(通常是常微分方程形式),特别是著名的洛特卡-伏特拉捕食者-猎物动力学就是这样建立的。然而,很少有人接受过足够好的训练,能用连续时间模型完成自己的工作,而且可能缺乏对现有方法真正多功能性的了解。具体来说,离散个体可以使用吉莱斯皮算法(Gillespie algorithm)进行连续时间建模的知识并没有得到应有的普及。我将说明连续时间建模方法的灵活性,以便研究人员做出明智的选择,而不是在没有明确生物学动机的情况下将时间离散化作为 "默认"。我将提供三个基于实例的教程:(1) 洛特卡-伏特拉捕食者-猎物模型的确定性动态和随机动态比较;(2) 评估假定昆虫种群中的无配性(以及通过更有效地搜索或缩短每次交配后的 "退出时间 "来选择更频繁地交配);(3) 季节内密度依赖性,随后是出生脉冲,导致贝弗顿-霍尔特或里克动态,这取决于同种昆虫的死亡是否有助于降低其他昆虫的死亡率(补偿性死亡率)。我将重点介绍指数分布的特性,这些特性虽然与直觉相反,但在推导预期终生繁殖成功率或其他类似数量时却非常有用。如果所谓的无记忆性假设在特定情况下不成立,我还会指导如何继续研究,并说明如果生物情况决定将连续时间和离散时间自由混合,这将是首选方案。连续时间模型也可以根据经验拟合数据,我将简要回顾这对所谓 "野兔吃猞猁吗 "悖论的启示,该悖论一直困扰着哈德逊湾野兔和猞猁数据集的解释。
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Who is afraid of modelling time as a continuous variable?
Most models of ecological and eco‐evolutionary processes involve creating trajectories of something, be it population densities, average trait values, or environmental states, over time. This requires decision‐making regarding how to represent the flow of time in models. Most ecologists are exposed to continuous‐time models (typically in the form of ordinary differential equations) as part of their training, especially since the famous Lotka‐Volterra predator–prey dynamics are formulated this way. However, few appear sufficiently well trained to produce their own work with continuous‐time models and may lack exposure to the true versatility of available methods. Specifically, knowledge that discrete individuals can be modelled in continuous time using the Gillespie algorithm is not as widespread as it should be. I will illustrate the flexibility of continous‐time modelling methods such that researchers can make informed choices, and not resort to discretizing time as a ‘default’ without a clear biological motivation to do so. I provide three example‐based tutorials: (1) a comparison of deterministic and stochastic dynamics of the Lotka‐Volterra predator–prey model, (2) an evaluation of matelessness in a hypothetical insect population (and of selection to mate more often by either searching more efficiently or by shortening the ‘time out’ after each mating) and (3) within‐season density dependence followed by a birth pulse leading to Beverton‐Holt or Ricker dynamics depending on whether the deaths of conspecifics help reduce the mortality of others or not (compensatory mortality). I highlight properties of the exponential distribution that, while counter‐intuitive, are good to know when deriving expected lifetime reproductive success or other similar quantities. I also give guidance on how to proceed if the so‐called memorylessness assumption does not hold in a given situation, and show how continuous and discrete times can be freely mixed if the biological situation dictates this to be the preferred option. Continuous‐time models can also be empirically fitted to data, and I review briefly the insight this gives into the so‐called ‘do hares eat lynx?’ paradox that has been plaguing the interpretation of the Hudson Bay hare and lynx dataset.
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来源期刊
CiteScore
11.60
自引率
3.00%
发文量
236
审稿时长
4-8 weeks
期刊介绍: A British Ecological Society journal, Methods in Ecology and Evolution (MEE) promotes the development of new methods in ecology and evolution, and facilitates their dissemination and uptake by the research community. MEE brings together papers from previously disparate sub-disciplines to provide a single forum for tracking methodological developments in all areas. MEE publishes methodological papers in any area of ecology and evolution, including: -Phylogenetic analysis -Statistical methods -Conservation & management -Theoretical methods -Practical methods, including lab and field -This list is not exhaustive, and we welcome enquiries about possible submissions. Methods are defined in the widest terms and may be analytical, practical or conceptual. A primary aim of the journal is to maximise the uptake of techniques by the community. We recognise that a major stumbling block in the uptake and application of new methods is the accessibility of methods. For example, users may need computer code, example applications or demonstrations of methods.
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