Data from: Estimating effects of species interactions on populations of endangered species

Global change causes community composition to change considerably through time, with ever-new combinations of interacting species. To study the consequences of newly established species interactions, one available source of data could be observational surveys from biodiversity monitoring. However, approaches using observational data would need to account for niche differences between species and for imperfect detection of individuals. To estimate population sizes of interacting species, we extended N-mixture models that were developed to estimate true population sizes in single species. Simulations revealed that our model is able to disentangle direct effects of dominant on subordinate species from indirect effects of dominant species on detection probability of subordinate species. For illustration, we applied our model to data from a Swiss amphibian monitoring program and showed that sizes of expanding water frog populations were negatively related to population sizes of endangered yellow-bellied toads and common midwife toads and partly of natterjack toads. Unlike other studies that analyzed presence and absence of species, our model suggests that the spread of water frogs in Central Europe is one of the reasons for the decline of endangered toad species. Thus, studying population impacts of dominant species on population sizes of endangered species using data from biodiversity monitoring programs should help to inform conservation policy and to decide whether competing species should be subject to population management.

全球变化会导致生物群落组成随时间发生显著改变，不断形成全新的物种互作组合。为探究新形成的物种互作所带来的后果，现有可获取的数据来源之一为生物多样性监测的观测调查数据。然而，基于观测数据的研究方法需要考虑物种间的生态位差异，以及个体检测不完全的问题。为估算互作物种的种群数量，我们对仅针对单物种真实种群数量估算的N-mixture模型（N-mixture model）进行了拓展。模拟实验表明，本模型能够区分优势物种对从属物种的直接影响，以及优势物种对从属物种检测概率的间接影响。为进行示例演示，我们将本模型应用于瑞士两栖动物监测项目的数据，结果显示：扩张中的水蛙种群规模与濒危的黄腹铃蟾（yellow-bellied toad）、普通助产蟾（common midwife toad）以及部分欧洲锄足蟾（natterjack toad）的种群规模呈负相关关系。与其他仅分析物种存在与否的研究不同，本模型表明，中欧地区水蛙的扩散是濒危蟾蜍类群种群衰退的原因之一。因此，借助生物多样性监测数据开展优势物种对濒危物种种群数量影响的研究，将有助于为保护政策制定提供科学依据，并辅助决策是否需要对竞争物种实施种群管理。