Hartmann Stefanie A, Oppel Steffen, Segelbacher Gernot, Juiña Mery E, Schaefer H Martin
Wildlife Ecology and Management, Albert-Ludwigs-University Freiburg, Tennenbacher Straße 4, 79106, Freiburg, Germany.
RSPB Centre for Conservation Science, Royal Society for the Protection of Birds, The David Attenborough Building, Pembroke Street, Cambridge, CB2 3QZ, UK.
Oecologia. 2017 Feb;183(2):597-606. doi: 10.1007/s00442-016-3763-6. Epub 2016 Nov 21.
Density-dependent processes are fundamental mechanisms for the regulation of populations. Ecological theories differ in their predictions on whether increasing population density leads to individual adjustments of survival and reproductive output or to dominance and monopolization of resources. Here, we use a natural experiment to examine which factors limit population growth in the only remaining population of the endangered pale-headed brush finch (Atlapetes pallidiceps). For three distinct phases (a phase of population suppression, 2001-2002; expansion due to conservation management, 2003-2008; and equilibrium phase, 2009-2014), we estimated demographic parameters with an integrated population model using population size, the proportion of successfully breeding pairs and their productivity, territory size, and mark-recapture data of adult birds. A low proportion of successful breeders due to brood parasitism (0.42, 95% credible interval 0.26-0.59) limited population growth before 2003; subsequent culling of the brood parasite resulted in a two-fold increase of the proportion of successful breeders during the 'expansion phase'. When the population approached the carrying capacity of its habitat, territory size declined by more than 50% and fecundity declined from 1.9 (1.54-2.27) to 1.3 (1.12-1.53) chicks per breeding pair, but the proportion of successful breeders remained constant (expansion phase: 0.85; 0.76-0.93; equilibrium phase: 0.86; 0.79-0.92). This study demonstrates that limiting resources can lead to individual adjustments instead of despotic behavior, and the individual reduction of reproductive output at high population densities is consistent with the slow life-history of many tropical species.
密度依赖过程是种群调节的基本机制。生态理论在预测增加种群密度是否会导致个体对生存和繁殖产出进行调整，还是导致对资源的支配和垄断方面存在差异。在这里，我们利用一项自然实验来研究哪些因素限制了濒危的淡头刷雀（Atlapetes pallidiceps）仅存种群的种群增长。对于三个不同阶段（种群抑制阶段，2001 - 2002年；因保护管理而扩张阶段，2003 - 2008年；以及平衡阶段，2009 - 2014年），我们使用综合种群模型，通过种群数量、成功繁殖对的比例及其生产力、领地大小以及成年鸟类的标记重捕数据来估计种群统计学参数。在2003年之前，由于巢寄生导致成功繁殖者的比例较低（0.42，95%可信区间为0.26 - 0.59），限制了种群增长；随后对巢寄生者的捕杀导致在“扩张阶段”成功繁殖者的比例增加了两倍。当种群接近其栖息地的承载能力时，领地大小下降了超过50%，繁殖力从每对繁殖对1.9（1.54 - 2.27）只雏鸟下降到1.3（1.12 - 1.53）只，但成功繁殖者的比例保持不变（扩张阶段：0.85；0.76 - 0.93；平衡阶段：0.86；0.79 - 0.92）。这项研究表明，有限的资源会导致个体调整而非专制行为，并且在高种群密度下个体繁殖产出的减少与许多热带物种的缓慢生活史相一致。
