Department of Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, Oregon 97331, USA.
Ecol Appl. 2011 Oct;21(7):2459-68. doi: 10.1890/10-2142.1.
The recent range expansion of Barred Owls (Strix varia) into the Pacific Northwest, where the species now co-occurs with the endemic Northern Spotted Owl (Strix occidentalis caurina), resulted in a unique opportunity to investigate potential competition between two congeneric, previously allopatric species. The primary criticism of early competition research was the use of current species' distribution patterns to infer past processes; however, the recent expansion of the Barred Owl and the ability to model the processes that result in site occupancy (i.e., colonization and extinction) allowed us to address the competitive process directly rather than inferring past processes through current patterns. The purpose of our study was to determine whether Barred Owls had any negative effects on occupancy dynamics of nesting territories by Northern Spotted Owls and how these effects were influenced by habitat characteristics of Spotted Owl territories. We used single-species, multi-season occupancy models and covariates quantifying Barred Owl detections and habitat characteristics to model extinction and colonization rates of Spotted Owl pairs in southern Oregon, USA. We observed a strong, negative association between Barred Owl detections and colonization rates and a strong positive effect of Barred Owl detections on extinction rates of Spotted Owls. We observed increased extinction rates in response to decreased amounts of old forest at the territory core and higher colonization rates when old-forest habitat was less fragmented. Annual site occupancy for pairs reflected the strong effects of Barred Owls on occupancy dynamics with much lower occupancy rates predicted for territories where Barred Owls were detected. The strong Barred Owl and habitat effects on occupancy dynamics of Spotted Owls provided evidence of interference competition between the species. These effects increase the importance of conserving large amounts of contiguous, old-forest habitat to maintain Northern Spotted Owls in the landscape.
近年来，环斑林鸮（Strix varia）在太平洋西北地区的范围不断扩大，该地区现已与特有种北美斑点鸮（Strix occidentalis caurina）共存，这为研究两个同属近缘种之间的潜在竞争提供了独特的机会。早期竞争研究的主要批评是使用当前物种的分布模式来推断过去的过程；然而，环斑林鸮的最近扩张以及对导致地点占据（即殖民和灭绝）的过程进行建模的能力，使我们能够直接解决竞争过程，而不是通过当前模式推断过去的过程。我们的研究目的是确定环斑林鸮是否对北美斑点鸮筑巢领地的占据动态产生任何负面影响，以及这些影响如何受到斑点鸮领地栖息地特征的影响。我们使用单物种、多季节的占据模型和协变量来量化环斑林鸮的检测和栖息地特征，以模拟美国俄勒冈州南部斑点鸮对的灭绝和殖民率。我们观察到环斑林鸮的检测与殖民率之间存在强烈的负相关关系，以及环斑林鸮的检测对斑点鸮灭绝率的强烈正影响。我们观察到，随着领地核心内的老林面积减少以及老林栖息地破碎化程度降低，灭绝率增加，而殖民率增加。对成对的年度地点占据反映了环斑林鸮对占据动态的强烈影响，在检测到环斑林鸮的领地中，预测的占据率要低得多。环斑林鸮和栖息地对斑点鸮占据动态的强烈影响为这两个物种之间存在干扰竞争提供了证据。这些影响增加了保护大量连续的老林栖息地以维持景观中北方斑点鸮的重要性。
