The use of gradient analysis studies in advancing our understanding of the ecology of urbanizing landscapes: current status and future directions

Over the past decade, the urban–rural gradient approach has been effectively used to study the ecology of cities and towns around the world. These studies have focused on understanding the distribution of plants and animals as well as ecosystem processes along gradients of urbanization that run from densely urbanized inner city to more rural exurban environments. We reviewed 300 papers investigating urbanization gradients that were published in peer-reviewed journals between 1990 and May 2007. Sixty-three percent of the papers investigated the distribution of organisms along urbanization gradients. Only five papers addressed the measures used to quantify the urbanization gradient itself. Within the papers addressing the distribution of organisms, 49% investigated the responses of birds to urbanization gradients, and <10% of the papers investigated more cryptic organisms. Most of these studies utilized a variety of broad measures of urbanization, but future advances in the field will require the development of some standardized broad measures to facilitate comparisons between cities. More specific measures of urbanization can be used to gain a mechanistic understanding of species and ecosystem responses to urbanization gradients. While the gradient approach has made a significant contribution to our understanding of the ecology of cities and towns, there is now a need to address our current knowledge gaps so that the field can reach its full potential. We present two examples of research questions that demonstrate how we can enhance our understanding of urbanization gradients, and the ecological knowledge that we can obtain from them.     

鸡传染性支气管炎病毒中国地方流行株的分离与鉴定

对海南省和广西省的几个发生呼吸罗音、鸡群全群发病、死亡率不高的疑是鸡传染性支气管炎病（IB）的鸡群，进行了病毒分离和鉴定。结果分离到了4株IBV分离株（HaN-1/95、HaN-2/95、GX－1／98、GX-2/98），并对分离病毒进行了病毒的致病性、病理组织切片、鸡胚矮小化、对NDV的干扰、电镜特征等生物特性鉴定及IBV基因组特异性3′末端非编码区的一段保守序列的RT－PCR和巢氏PCR鉴定。结果表明4株IBV分离株，均能产生呼吸困难、罗音等临床症状；病理组织切片，气管、肾脏等组织表现为上皮细胞受损、固有层充血、出血和淋巴细胞的浸润及组织坏死；对NDV－B1株有明显的干扰作用；其各自的传代物都有明显的致鸡胚矮小化作用；在透射电镜下观察到典型的冠状病毒粒子，多数近似为圆形，直径75-200nm，有囊膜，表面有一圈杆状纤突排列成花冠状，符合IBV的典型特征；基因组3′末端UTR的RT－PCR和巢氏PCR鉴定，4个分离株分别都扩增到293bp和172bp的特异目的片段，通过测序比较毒株间的核苷酸序列同源性在99％以上，与GeneBank中IBV H52等标准株的3′末端UTR的核苷酸序列高度同源。以上结果表明4株分离病毒都是IBV，为下一步的IBV分子流行病学的研究打下了基础。