Data and code for: The role of indirect interspecific effects in the stochastic dynamics of a simple trophic system

Understanding indirect interspecific effects (IIEs) on population dynamics is key for predicting community dynamics. Yet, empirically teasing apart IIEs from other interactions and population drivers is data-demanding. We used stochastic population models parameterized with long-term vital rate time series to simulate population trajectories and examine IIEs in a high-arctic vertebrate trophic chain: Svalbard reindeer, its scavenger (Arctic fox), and a migratory fox prey (barnacle goose). Reindeer carcass supply shaped fox abundance fluctuations, subsequently affecting goose fluctuations. Yet reindeer and goose population growth rates were only weakly correlated, probably due to stochasticity, density dependence, and life history traits. However, by isolating the effects of individual processes within our simulation model, we demonstrate the presence of strong IIEs on goose population fluctuations and extinction probability. Thus, we highlight the long-term impact of species interactions, including IIEs, on species coexistence and communities, beyond immediate effects and short-term fluctuations.

解析种间间接效应（indirect interspecific effects，IIEs）对种群动态的影响，是预测群落动态的关键所在。然而，从其他种间相互作用与种群驱动因子中实证区分出IIEs，往往需要海量的数据支撑。我们采用以长期生命率时间序列进行参数化的随机种群模型，模拟种群动态轨迹，并在一条高北极脊椎动物食物链中探究IIEs：斯瓦尔巴驯鹿、其食腐捕食者北极狐（Arctic fox），以及作为狐类猎物的迁徙性鸟类——藤壶鹅（barnacle goose）。驯鹿尸体的供给量调控着狐类种群的数量波动，进而间接影响藤壶鹅的种群波动。然而驯鹿与藤壶鹅的种群增长率仅呈现弱相关关系，这大概率源于随机性、密度制约效应以及物种生活史特征的共同作用。不过，通过在模拟模型中拆分各独立过程的效应，我们证实了IIEs对藤壶鹅种群波动及灭绝概率存在显著影响。因此，我们着重强调了包括IIEs在内的物种相互作用，对物种共存与群落结构的长期影响——这类影响远超即时效应与短期波动的范畴。