Bartra-Cabré Laura, Hansen Brage B, Lee Aline M, Layton-Matthews Kate, Loonen Maarten J J E, Fuglei Eva, Loe Leif E, Grøtan Vidar
Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, Trondheim, Norway.
Department of Terrestrial Ecology, Norwegian Institute for Nature Research, Trondheim, Norway.
J Anim Ecol. 2024 Dec;93(12):1896-1909. doi: 10.1111/1365-2656.14198. Epub 2024 Oct 24.
Indirect interspecific effects (IIEs) occur when one species affects another through a third intermediary species. Understanding the role of IIEs in population dynamics is key for predicting community-level impacts of environmental change. Yet, empirically teasing apart IIEs from other interactions and population drivers has proven challenging and data-demanding, particularly in species-rich communities. We used stochastic population models parameterized with long-term time series of individual data to simulate population trajectories and examine IIEs in a simple high-arctic vertebrate food chain consisting of the wild Svalbard reindeer, its scavenger (the Arctic fox) and the barnacle goose, a migratory prey of the fox. We used the simulated population trajectories to explore co-fluctuations between the species within the food chain. Additionally, we adjusted the model in two ways: first, to isolate the impact of fluctuations in the abundance of a species by keeping its abundance constant; and second, to isolate the impact of a trophic interaction on the dynamics of other species by setting the abundance of the influencing species to zero. We found that fluctuations in reindeer carcasses shaped fox abundance fluctuations, which subsequently affected goose population dynamics. Reindeer and goose population growth rates were nevertheless only weakly correlated, probably in part due to demographic and environmental stochasticity, density dependence and lagged dynamics in the geese. However, removing the fluctuations in reindeer abundance or setting reindeer abundance to zero indeed demonstrated strong underlying IIEs on goose population dynamics and extinction probability. This study thus highlights the importance of species interactions, including IIEs, on species coexistence and communities in the long-term, that is beyond immediate effects and covariation in short-term fluctuations.
当一个物种通过第三个中间物种影响另一个物种时，间接种间效应（IIEs）就会发生。了解间接种间效应在种群动态中的作用是预测环境变化对群落水平影响的关键。然而，从经验上区分间接种间效应与其他相互作用和种群驱动因素已被证明具有挑战性且需要大量数据，尤其是在物种丰富的群落中。我们使用由个体数据的长期时间序列参数化的随机种群模型来模拟种群轨迹，并在一个简单的高北极脊椎动物食物链中研究间接种间效应，该食物链由野生斯瓦尔巴德驯鹿、其食腐动物（北极狐）和北极鹅组成，北极鹅是狐狸的迁徙猎物。我们使用模拟的种群轨迹来探索食物链中物种之间的共同波动。此外，我们以两种方式调整模型：第一，通过保持一个物种的丰度不变来分离该物种丰度波动的影响；第二，通过将影响物种的丰度设置为零来分离营养相互作用对其他物种动态的影响。我们发现驯鹿尸体的波动塑造了狐狸丰度的波动，进而影响了鹅的种群动态。然而，驯鹿和鹅的种群增长率之间的相关性很弱，这可能部分是由于人口统计学和环境随机性、密度依赖性以及鹅的滞后动态。但是，消除驯鹿丰度的波动或将驯鹿丰度设置为零确实证明了对鹅的种群动态和灭绝概率存在强烈的潜在间接种间效应。因此，这项研究强调了物种相互作用，包括间接种间效应，对长期物种共存和群落的重要性，这超出了短期波动中的直接影响和协变。
