Data from: Temperature effects on long-term population dynamics in a parasitoid-host system

Long-term environmental changes will likely alter the strengths of interactions between species and consequently their population dynamics, leading to changes in the stability of ecological systems. While an increasing number of empirical studies have shown that environmental changes can alter the strengths of species interactions, these studies are typically short (<1–2 generations) and therefore give only partial information about longer term population dynamics. To focus on longer term dynamics, we investigated population cycles of pea aphids and their most common parasitoid, Aphidius ervi, in Wisconsin, USA. Data collected over three years in alfalfa fields showed an apparent host–parasitoid population cycle. Furthermore, higher pea aphid population growth rates and increased parasitism were correlated with higher naturally occurring temperatures. While these effects were observed with seasonal fluctuations in temperature, they beg the question of how long-term changes in mean annual temperature might change aphid–parasitoid population cycles, a question which we further pursued with laboratory experiments. To quantify temperature-dependent demographic parameters, we used short-term (<1 generation) experiments conducted at 20°C and 27°C. The higher temperature increased aphid and parasitoid development rates, adult aphid life span and fecundity, and parasitoid attack rates. We then conducted multi-generation population-level laboratory experiments to reveal the effects of temperature (20°C vs. 27°C) on population dynamics. We fit the resulting time series data using a nonlinear age-structured state-space model to estimate population-level processes that could not be estimated in short-term laboratory experiments. Using the model, we parsed out the demographic rates that had the largest impacts on aphid–parasitoid population cycles. This analysis showed that there were frequent contrasts in the effects of temperature operating through different demographic rates. For example, the temperature-dependent increase in aphid development rate decreased cycle amplitude, while the increase in parasitoid attack rate increased cycle amplitude. There were also striking interactions among demographic rates. For example, the temperature-dependent increase in aphid development rate could either increase or decrease the cycle period depending on the values of other demographic rates. Although these complexities make predictions difficult, overall they suggest that increasing long-term mean temperature will decrease the period, increase the amplitude, and tend to destabilize pea aphid–A. ervi dynamics.

长期环境变化或会改变物种间相互作用的强度，进而影响种群动态，最终改变生态系统的稳定性。尽管越来越多的实证研究表明环境变化能够改变物种相互作用的强度，但这类研究的周期通常较短（不足1~2个世代），因此仅能提供关于长期种群动态的部分信息。为聚焦长期种群动态，我们在美国威斯康星州开展了豌豆蚜（pea aphid）及其最常见寄生蜂埃氏蚜茧蜂（Aphidius ervi）的种群周期研究。我们在苜蓿田中历时三年收集的数据显示，存在清晰的寄主-寄生蜂种群周期现象。此外，豌豆蚜种群增长率的提升与寄生率的升高，均与自然环境温度的升高呈显著相关。尽管这些效应是在温度的季节性波动中被观测到的，但它们也引发了一个亟待解答的问题：年平均温度的长期变化会如何改变蚜茧蜂-豌豆蚜的种群周期？为此我们进一步开展了室内实验来解答该问题。为量化温度依赖的种群统计参数，我们在20℃与27℃条件下开展了短期实验（不足1个世代）。相较于20℃，更高的27℃温度提升了蚜虫与寄生蜂的发育速率、成虫寿命与繁殖力，以及寄生蜂的攻击率。随后我们开展了多世代种群水平的室内实验，以探明温度（20℃与27℃对比）对种群动态的影响。我们采用非线性年龄结构状态空间模型（nonlinear age-structured state-space model）对所得的时间序列数据进行拟合，以此估算无法通过短期室内实验测得的种群水平过程。借助该模型，我们拆解出了对蚜茧蜂-豌豆蚜种群周期影响最大的种群统计速率。该分析显示，温度通过不同种群统计速率产生的影响往往存在显著差异。例如，温度依赖的蚜虫发育速率提升会降低种群周期的振幅，而寄生蜂攻击率的提升则会增大周期振幅。种群统计速率之间还存在显著的交互效应。例如，温度依赖的蚜虫发育速率提升对种群周期时长的影响方向，取决于其他种群统计速率的取值。尽管这些复杂性为预测带来了挑战，但整体而言，研究结果表明长期平均温度的升高会缩短种群周期时长、增大周期振幅，并倾向于破坏豌豆蚜-埃氏蚜茧蜂种群系统的稳定性。