Data from: Competitors and predators alter settlement patterns and reproductive success of an intraguild prey

The spatial distribution of predators is affected by intra- and interspecific interactions within the predator guild. Studying these interactions under fluctuating food availability, while taking habitat characteristics into account, offers a quasi-experimental set up to determine the relative impact of con- and heterospecifics on reproductive success of predators. We analyzed the settlement decisions and reproductive success of Eurasian pygmy owls (Glaucidium passerinum) in the presence of both breeding conspecifics and their competitor and intraguild predator, Tengmalm's owls (Aegolius funereus), under fluctuating abundance of their primary prey (voles). We used detailed data, collected across 11 years in a large study area (1300 km²), on the spatial and temporal variation of habitat characteristics in all available nesting sites, local densities of both species, and vole abundance. We found that pygmy owls strongly avoided breeding close to conspecifics but did not avoid Tengmalm's owl nests. Nest box occupation of pygmy owls was positively correlated to the proportion of old spruce, mature and old pine forests and farmlands, and occupation probability was higher at high vole abundance and in areas occupied in previous years. Pygmy owl avoidance of conspecifics decreased when voles were abundant. At high conspecific density, pygmy owls showed lower hatching success and delayed hatching date, in agreement with the observed spatial avoidance. Finally, even though breeding pygmy owls did not spatially avoid Tengmalm's owls, the density of heterospecifics correlated with low hatching and fledging success in pygmy owls. This suggests short term fitness costs when living close to competitors, even when lethal effects of intraguild interactions are subtle. Our results suggest that joint costs of exploitative and interference competition by Tengmalm's owls, as well as intraguild predation, were lower than those induced by intraspecific competition only. This result might be due to the similar body size between the species considered, Tengmalm's owls being only twice as large as pygmy owls. Interactions among con- and heterospecifics can therefore modify the spatial settlement and reproductive success of individuals on a landscape scale, also within the predator guild.

捕食者的空间分布受到捕食者类群（predator guild）内部种内相互作用（intraspecific interactions）与种间相互作用（interspecific interactions）的影响。在食物可获得性波动的背景下，结合生境特征研究此类相互作用，可为探明同种个体（conspecifics）与异种个体（heterospecifics）对捕食者繁殖成功率（reproductive success）的相对影响提供一套准实验设计（quasi-experimental setup）。本研究针对其主要猎物田鼠（voles）的种群丰度波动情境，分析了同时存在繁殖同种个体、竞争者兼类群内捕食者鬼鸮（Aegolius funereus）时，花头鸺鹠（Glaucidium passerinum）的巢址选择决策与繁殖成功率。我们使用了在1300平方千米的大型研究区域内耗时11年收集的精细化数据，涵盖所有可利用巢址的生境特征时空变化、两种鸟类的本地种群密度以及田鼠丰度等信息。研究结果显示，花头鸺鹠会强烈规避与同种个体邻近繁殖，但不会避开鬼鸮的巢址。花头鸺鹠的巢箱占用率（nest box occupation）与老龄云杉林、成熟及老龄松林和农田的占比呈正相关；在田鼠丰度较高的区域，以及过往年份已被占用的生境中，其巢箱占用概率更高。当田鼠种群丰度较高时，花头鸺鹠对同种个体的规避行为会有所减弱。在同种种群密度较高的区域，花头鸺鹠的孵化成功率（hatching success）更低且孵化日期更晚，这与观测到的空间规避行为相一致。最后，尽管繁殖中的花头鸺鹠并未在空间上避开鬼鸮，但异种个体密度与花头鸺鹠较低的孵化成功率和出飞成功率（fledging success）存在相关性。这表明即便类群内相互作用的致死效应并不显著，与竞争者邻近栖息仍会带来短期的适合度代价（fitness costs）。我们的研究结果表明，鬼鸮所引发的利用性竞争（exploitative competition）与干扰性竞争（interference competition），以及类群内捕食（intraguild predation）所带来的联合代价，均低于仅由种内竞争（intraspecific competition）所引发的代价。该结果可能与两种鸟类体型相近有关——鬼鸮的体型仅为花头鸺鹠的两倍。因此，同种与异种个体间的相互作用能够在景观尺度上改变捕食者类群内个体的空间巢址选择与繁殖成功率。