Landcare Research, Lincoln, New Zealand.
PLoS One. 2013 Sep 9;8(9):e73544. doi: 10.1371/journal.pone.0073544. eCollection 2013.
Predator-prey systems can extend over large geographical areas but empirical modelling of predator-prey dynamics has been largely limited to localised scales. This is due partly to difficulties in estimating predator and prey abundances over large areas. Collection of data at suitably large scales has been a major problem in previous studies of European rabbits (Oryctolagus cuniculus) and their predators. This applies in Western Europe, where conserving rabbits and predators such as Iberian lynx (Lynx pardinus) is important, and in other parts of the world where rabbits are an invasive species supporting populations of introduced, and sometimes native, predators. In pastoral regions of New Zealand, rabbits are the primary prey of feral cats (Felis catus) that threaten native fauna. We estimate the seasonal numerical response of cats to fluctuations in rabbit numbers in grassland-shrubland habitat across the Otago and Mackenzie regions of the South Island of New Zealand. We use spotlight counts over 1645 km of transects to estimate rabbit and cat abundances with a novel modelling approach that accounts simultaneously for environmental stochasticity, density dependence and varying detection probability. Our model suggests that cat abundance is related consistently to rabbit abundance in spring and summer, possibly through increased rabbit numbers improving the fecundity and juvenile survival of cats. Maintaining rabbits at low abundance should therefore suppress cat numbers, relieving predation pressure on native prey. Our approach provided estimates of the abundance of cats and rabbits over a large geographical area. This was made possible by repeated sampling within each season, which allows estimation of detection probabilities. A similar approach could be applied to predator-prey systems elsewhere, and could be adapted to any method of direct observation in which there is no double-counting of individuals. Reliable estimates of numerical responses are essential for managing both invasive and threatened predators and prey.
捕食者-猎物系统可以延伸到很大的地理区域，但对捕食者-猎物动态的经验模型研究在很大程度上仅限于局部尺度。这部分是由于在大面积上估计捕食者和猎物丰度存在困难。在以前对欧洲兔（Oryctolagus cuniculus）及其捕食者的研究中，收集适当大尺度的数据一直是一个主要问题。在西欧，保护兔子和像伊比利亚猞猁（Lynx pardinus）这样的捕食者很重要，而在世界其他地区，兔子是一种入侵物种，支持着引入的、有时是本地的捕食者的种群。在新西兰的牧区，兔子是威胁到当地动物群的野化猫（Felis catus）的主要猎物。我们估计了猫在新西兰南岛奥塔哥和麦肯齐地区的草原-灌木栖息地中对兔子数量波动的季节性数量反应。我们使用聚光灯计数，在 1645 公里的样带上估计兔子和猫的数量，采用一种新的模型方法，同时考虑环境随机性、密度依赖性和变化的检测概率。我们的模型表明，猫的数量与春季和夏季的兔子数量密切相关，这可能是因为兔子数量的增加提高了猫的繁殖力和幼崽的存活率。因此，保持兔子数量低应该会抑制猫的数量，减轻对本地猎物的捕食压力。我们的方法提供了在很大地理区域内猫和兔子数量的估计。这是通过在每个季节内重复采样实现的，这允许估计检测概率。这种类似的方法可以应用于其他地方的捕食者-猎物系统，并可以适应任何没有个体重复计数的直接观察方法。可靠的数量反应估计对于管理入侵和受威胁的捕食者和猎物都是必不可少的。
