捕食者种群在全球范围内受到威胁,部分原因是栖息地和营养相互作用的变化。理论和实验室研究表明,包含猎物避难所作为源栖息地的异质景观可以使捕食者和猎物种群受益,尽管异质性在自然系统中的重要性尚不确定。这里,我们检验了以下假设:景观异质性介导了加利福尼亚斑点猫头鹰(Strixoccidentalisoccidentalis)-一种成熟的森林物种-及其主要猎物之一之间的捕食者-猎物相互作用,昏暗的森林物种(Neotomafuscipes)-一种年轻的森林物种-对两者都有好处。我们这样做的方法是将实弹诱捕和VHF跟踪对木偶密度和存活率的估计与对异质和同质家庭范围内猫头鹰向依赖幼鸟的猎物交付的直接观察相结合。与成熟森林(727.3±51.9SE)相比,猫头鹰家庭范围(1412公顷)的Woodrat丰度约为2.5倍,具有更大的植被类型异质性(1805.0±50.2SE),在很大程度上是因为年轻森林中的高密度似乎是促进附近成熟森林中木材密度的来源。Woodrat死亡率在植被类型之间很低,并且在异质和同质家庭范围之间没有差异,然而所有观察到的猫头鹰捕食都发生在成熟的森林里,这表明年轻的森林可以充当森林避难所。猫头鹰表现出1型功能反应,在异质(31.1/月±5.2SE)与同质(12.7/月±3.7SE)家庭范围内消耗约2.5倍以上的林地。虽然在同质家庭范围内食用较小的替代猎物部分补偿了较低的木材消费量,尽管如此,猫头鹰在异质家庭中消耗了30%的生物量-大约相当于产生一个额外后代的能量需求。因此,包括年轻森林斑块在内的植被类型的马赛克增加了林地的丰度和可用性,反过来,为与森林相关的成熟斑点猫头鹰提供了活力和潜在的生殖益处。更广泛地说,我们的发现提供了强有力的经验证据,表明包含猎物避难所的异质景观可以使捕食者和猎物种群都受益。随着人为活动继续使全球景观同质化,促进具有猎物避难所的异构系统可能会使濒临灭绝的捕食者受益。本文受版权保护。保留所有权利。
Predator populations are imperiled globally, due in part to changing habitat and trophic interactions. Theoretical and laboratory studies suggest that heterogeneous landscapes containing prey refuges acting as source habitats can benefit both predator and prey populations, although the importance of heterogeneity in natural systems is uncertain. Here, we tested the hypothesis that landscape heterogeneity mediates predator-prey interactions between the California spotted owl (Strix occidentalis occidentalis)-a mature forest species-and one of its principal prey, the dusky-footed
woodrat (Neotoma fuscipes)-a younger forest species-to the benefit of both. We did so by combining estimates of
woodrat density and survival from live trapping and very high frequency tracking with direct observations of prey deliveries to dependent young by owls in both heterogeneous and homogeneous home ranges.
Woodrat abundance was ~2.5 times higher in owl home ranges (14.12 km2 ) featuring greater heterogeneity in vegetation types (1805.0 ± 50.2 SE) compared to those dominated by mature forest (727.3 ± 51.9 SE), in large part because of high densities in young forests appearing to act as sources promoting woodrat densities in nearby mature forests.
Woodrat mortality rates were low across vegetation types and did not differ between heterogeneous and homogeneous home ranges, yet all observed predation by owls occurred within mature forests, suggesting young forests may act as woodrat refuges. Owls exhibited a type 1 functional response, consuming ~2.5 times more woodrats in heterogeneous (31.1/month ± 5.2 SE) versus homogeneous (12.7/month ± 3.7 SE) home ranges. While consumption of smaller-bodied alternative prey partially compensated for lower
woodrat consumption in homogeneous home ranges, owls nevertheless consumed 30% more biomass in heterogeneous home ranges-approximately equivalent to the energetic needs of producing one additional offspring. Thus, a mosaic of vegetation types including young forest patches increased woodrat abundance and availability that, in turn, provided energetic and potentially reproductive benefits to mature forest-associated spotted owls. More broadly, our findings provide strong empirical evidence that heterogeneous landscapes containing prey refuges can benefit both predator and prey populations. As anthropogenic activities continue to homogenize landscapes globally, promoting heterogeneous systems with prey refuges may benefit imperiled predators.