Bock Carl E, Jones Zach F, Bock Jane H
Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309-0334, USA.
Ecol Appl. 2008 Jul;18(5):1093-106. doi: 10.1890/07-1689.1.
Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant but little-studied impacts on biological diversity. We counted birds in grasslands and savannas in southeastern Arizona that were grazed by livestock, embedded in low-density exurban housing developments, or both, or neither. Species richness and bird abundance were higher in exurban neighborhoods than in undeveloped landscapes, independent of livestock grazing. The positive response to development was particularly evident among doves, quail, hummingbirds, aerial insectivores, and some but not all ground-foraging sparrows. Effects of livestock grazing were comparatively minor and mostly involved birds with requirements for tall ground cover or the lack of it. The average rank correlation between counts of individual species and housing density was positive across all transects. However, this relationship disappeared among the exurban transects alone, and bird species richness on the exurban transects was negatively correlated with the number of homes nearby. These results suggest that the positive influence of exurban development on avian abundance and variety was greatest at the lowest housing densities. We attribute the attraction of many birds to exurban development to an oasis effect, in which resources otherwise scarce in arid southwestern environments (shade, nectar, nest sites, and especially water) are relatively abundant around exurban home sites. This finding is consistent with the hypothesis that exurban home sites represented resource supply points inside birds' home ranges otherwise consisting mostly of natural vegetation.
在美国西南部，牧场正被转变为远郊住宅区，这对生物多样性可能产生重大但研究较少的影响。我们对亚利桑那州东南部草原和稀树草原上的鸟类进行了统计，这些地方要么有牲畜放牧，要么位于低密度远郊住宅区，要么两者皆有，要么两者皆无。与未开发地区相比，远郊社区的物种丰富度和鸟类数量更多，且与牲畜放牧无关。这种对开发的积极反应在鸽子、鹌鹑、蜂鸟、食虫鸟类以及一些（而非全部）地面觅食的麻雀中尤为明显。牲畜放牧的影响相对较小，主要涉及那些对高地面覆盖物有需求或无此需求的鸟类。在所有样带中，单个物种数量与住房密度之间的平均等级相关性为正。然而，这种关系仅在远郊样带中消失，远郊样带上的鸟类物种丰富度与附近房屋数量呈负相关。这些结果表明，远郊开发对鸟类数量和种类的积极影响在住房密度最低时最为显著。我们将许多鸟类被远郊开发所吸引归因于绿洲效应，即在干旱的西南环境中原本稀缺的资源（树荫、花蜜、巢穴，尤其是水）在远郊住宅周围相对丰富。这一发现与以下假设一致：远郊住宅是鸟类活动范围内的资源供应点，而其活动范围原本大多由自然植被构成。
