Data from: Metapopulation dynamics of species with cryptic life stages

Quantifying metapopulation dynamics is a challenging task. Difficulties particularly arise in species that possess unobservable resistance forms that bias the estimation of colonization and persistence rates. Here, we develop a general multistate occupancy model that allows estimation of species persistence for both normal and resistant forms, even when the latter are not detectable. We apply this model to an 11-year data set on the tropical freshwater snail Drepanotrema depressissimum in a network of 229 ponds. These ponds frequently dry out, and the snails can persist by aestivating in the ground, where they are not detected. Our model adequately captures this feature because it infers a high persistence rate for the resistant form, while models ignoring aestivation tend to overestimate extinction and colonization. In addition, we find that, surprisingly, colonization and persistence are even higher in sites prone to desiccation and during years with low rainfall than in more humid sites and years, suggesting that D. depressissimum favors unstable sites where competitors are rare and where it can rely on aestivation to persist. Our model has the potential to provide valuable insights into the metapopulation dynamics of many species that otherwise could hardly be studied because of the existence of undetectable life forms.量化集合种群动态是一项极具挑战性的研究课题。此类研究的难点尤其集中于存在不可观测抗性形态的物种——这类物种的定殖率与存续率估计往往会出现系统性偏差。为此，本文构建了一款通用多状态占有模型（multistate occupancy model），即便抗性形态无法被观测，该模型仍可实现物种正常形态与抗性形态的存续率估计。我们将此模型应用于一项为期11年的野外数据集，该数据集采集自229个池塘构成的网络中栖息的热带淡水螺Drepanotrema depressissimum。这些池塘常会周期性干涸，而该螺类可通过在土壤中夏蛰完成存续，此时其个体无法被观测到。本模型可充分契合这一特征：其推断得到的抗性形态存续率较高，而忽略夏蛰过程的传统模型往往会高估灭绝率与定殖率。此外，我们意外发现：相较于更为湿润的生境与年份，在易发生干涸的生境以及降雨偏少的年份中，定殖率与存续率反而更高。这表明Drepanotrema depressissimum更偏好竞争物种稀少、且可借助夏蛰实现存续的不稳定生境。本模型有望为诸多因存在不可观测生活史形态而难以开展研究的物种的集合种群动态研究提供极具价值的见解。