Indicators of the Statuses of Amphibian Populations and Their Potential for Exposure to Atrazine in Four Midwestern U.S. Conservation Areas

Extensive corn production in the midwestern United States has physically eliminated or fragmented vast areas of historical amphibian habitat. Midwestern corn farmers also apply large quantities of fertilizers and herbicides, which can cause direct and indirect effects on amphibians. Limited field research regarding the statuses of midwestern amphibian populations near areas of corn production has left resource managers, conservation planners, and other stakeholders needing more information to improve conservation strategies and management plans. We repeatedly sampled amphibians in wetlands in four conservation areas along a gradient of proximity to corn production in Illinois, Iowa, Minnesota, and Wisconsin from 2002 to 2005 and estimated site occupancy. We measured frequencies of gross physical deformities in recent metamorphs and triazine concentrations in the water at breeding sites. We also measured trematode infection rates in kidneys of recently metamorphosed Lithobates pipiens collected from nine wetlands in 2003 and 2004. We detected all possible amphibian species in each study area. The amount of nearby row crops was limited in importance as a covariate for estimating site occupancy. We observed deformities in美国中西部大规模玉米种植已物理性清除并碎片化了大片历史两栖动物栖息地。中西部玉米种植户还会施用大量化肥与除草剂，此类药剂可对两栖动物造成直接与间接影响。目前针对玉米种植区周边中西部两栖动物种群现状的实地研究较为匮乏，致使资源管理者、保护规划者及其他利益相关方亟需更多信息，以优化保护策略与管理方案。2002年至2005年间，我们在伊利诺伊州、艾奥瓦州、明尼苏达州与威斯康星州的4处保护地内，沿着与玉米种植区的临近梯度对湿地中的两栖动物进行了多次采样，并估算了位点占用率。我们统计了刚完成变态的个体的严重体表畸形发生率，并测定了繁殖位点水体中的三嗪类（triazine）化合物浓度。2003年与2004年，我们还对从9处湿地采集的刚变态的美洲豹蛙（Lithobates pipiens）的肾脏吸虫感染率进行了测定。我们在每个研究区域均检出了所有可能存在的两栖动物物种。在估算位点占用率时，周边大田作物占比作为协变量的重要性有限。我们观察到了畸形个体