Functional response, seasonal decline and landscape differences in nest predation risk
Functional response, seasonal decline and landscape differences in nest predation risk
复制标题
巢穴捕食风险的功能反应、季节性下降和景观差异
作者：
Staffan Roos
抽象的。以前的研究密度依赖巢捕食风险遭受不自然的高巢密度（人工巢）或缺乏控制巢捕食者密度（观测数据真实的巢）。我设计了一个实验，在自然范围内的巢密度使用拉丁方设计（控制巢捕食者的密度在时间和空间上的差异），以避免以前的研究的缺点。我纳入混杂因素，如时间在繁殖季节和景观类型，以研究它们是否影响巢捕食风险。实验是在干燥的半天然灌木丰富的草地在瑞典，使用人工灌木巢含有两个鹌鹑（Coturnix coturnix）蛋和橡皮泥蛋。最后，我验证了我的结果从人工巢实验中得到的相对巢捕食风险的人工巢与巢捕食风险的真实的巢红背伯劳（Lanius collurio），灌木筑巢雀。鸦类是人工灌木巢上的主要巢捕食者，这一点从橡皮泥蛋上的痕迹可以看出。同时活跃的灌木巢的密度的自然变化内，乌鸦增加了它们的捕食率与人工巢的密度增加，表明功能性反应。巢捕食风险随时间的季节和不同的草地地块农田为主（高风险），农田-森林镶嵌（低风险），森林为主（低风险）的景观环境。此外，捕食风险的人工巢减少距离巢的至少一个corvid物种。繁殖红背伯劳选择人工巢捕食风险低的草地，伯劳繁殖成功率与人工巢成功率呈正相关。此外，成功的概率为人工和真实的红背伯劳巢增加距离最近的乌鸦巢。因此，人工巢实验的结果得到了红背伯劳种群研究结果的验证。因此，我的研究结果表明，捕食风险测量人工巢可以作为一个相对指标的空间和时间变化的巢捕食风险。我的研究结果还表明，在森林景观的草地应给予额外的关注保护方面，因为巢捕食风险较低，草原在更开放的栖息地。
Abstract. Previous studies investigating density-dependent nest predation risk have suffered from unnaturally high nest densities (artificial nests) or lack of controls for nest predator densities (observational data on real nests). I designed an experiment with artificial nests within the natural range of nest densities using a Latin square design (to control for differences in densities of nest predators in time and space) to avoid the shortcomings of previous studies. I incorporated confounding factors, such as time in the breeding season and landscape type, in order to study whether they affected nest predation risk. The experiment was performed in dry semi-natural shrub-rich grasslands in Sweden, using artificial shrub-nests containing two quail (Coturnix coturnix) eggs and a plasticine egg. Finally, I validated my results obtained from the artificial nest experiment by comparing relative nest predation risk on artificial nests with nest predation risk on real nests of red-backed shrikes (Lanius collurio), a shrub-nesting passerine. Corvids were the major nest predators on artificial shrub nests as revealed by marks in plasticine eggs. Within the natural variation in densities of simultaneously active shrub nests, corvids increased their rates of predation with increasing densities of artificial nests, indicating a functional response. Nest predation risk decreased with time in the season and differed between grassland plots in farmland-dominated (high risk), farmland-forest mosaic (low risk), and forest-dominated (low risk) landscape surroundings. Furthermore, predation risk on artificial nests increased with decreasing distance to nests of at least one corvid species. Breeding red-backed shrikes selected grasslands with a low nest predation risk on artificial nests and reproductive success of shrikes was positively related to success of artificial nests. Moreover, the probability of success for both artificial and real red-backed shrike nests increased with increasing distance from the nearest corvid nest. Thus, results from the artificial nest experiment were validated by the results from the red-backed shrike population study. My results therefore suggest that predation risk measured on artificial nests can be used as a relative index of spatial and temporal variation in nest predation risk. My results also indicate that grasslands in forested landscapes should be given extra attention for conservation aspects, since nest predation risk is lower there compared to grasslands in more open habitats.