Predation and nutrients drive population declines in breeding waders

Allee effects are defined as a decline in per capita fitness at low population density. We hypothesized that predation reduces population size of breeding waders and thereby the efficiency of predator deterrence, while total nitrogen through its effects on primary and secondary productivity increases population size. Therefore, nest predation could have negative consequences for population size because nest failure generally results in breeding dispersal and hence reduced local population density. To test these predictions we recorded nest predation in five species of waders for 4745 nests during 1987-2015 at the nature reserve Tipperne, Denmark. Predation rates were generally negatively related to conspecific and heterospecific population density, but positively related to overall population density of the entire wader community. Nest predation and population density were related to ground water level, management (grazing and mowing) and nutrients. High nest predation with a time lag o...阿利效应（Allee effects）被定义为低种群密度下个体适合度的下降。我们提出如下假说：捕食作用会降低繁殖型鸻鹬类的种群规模，进而削弱其反捕食效率；而总氮通过对初级、次级生产力的影响提升种群规模。因此，巢捕食可能对种群规模产生负面影响，因为巢失败通常会引发繁殖扩散，进而降低局域种群密度。为验证上述预测，我们于1987年至2015年间，在丹麦蒂珀讷自然保护区对5种鸻鹬类的4745个巢穴开展了巢捕食监测。总体而言，捕食率与同种、异种种群密度呈负相关，但与整个鸻鹬群落的总种群密度呈正相关。巢捕食与种群密度均与地下水位、生境管理（放牧与割草）以及营养物质相关。高巢捕食率存在时间滞后性……