Siers Shane R, Savidge Julie A, Reed Robert N
Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, Colorado, United States of America.
U.S. Geological Survey, Fort Collins Science Center, Fort Collins, Colorado, United States of America.
PLoS One. 2017 Jun 1;12(6):e0177671. doi: 10.1371/journal.pone.0177671. eCollection 2017.
Localized ecological conditions have the potential to induce variation in population characteristics such as size distributions and body conditions. The ability to generalize the influence of ecological characteristics on such population traits may be particularly meaningful when those traits influence prospects for successful management interventions. To characterize variability in invasive Brown Treesnake population attributes within and among habitat types, we conducted systematic and seasonally-balanced surveys, collecting 100 snakes from each of 18 sites: three replicates within each of six major habitat types comprising 95% of Guam's geographic expanse. Our study constitutes one of the most comprehensive and controlled samplings of any published snake study. Quantile regression on snake size and body condition indicated significant ecological heterogeneity, with a general trend of relative consistency of size classes and body conditions within and among scrub and Leucaena forest habitat types and more heterogeneity among ravine forest, savanna, and urban residential sites. Larger and more robust snakes were found within some savanna and urban habitat replicates, likely due to relative availability of larger prey. Compared to more homogeneous samples in the wet season, variability in size distributions and body conditions was greater during the dry season. Although there is evidence of habitat influencing Brown Treesnake populations at localized scales (e.g., the higher prevalence of larger snakes-particularly males-in savanna and urban sites), the level of variability among sites within habitat types indicates little ability to make meaningful predictions about these traits at unsampled locations. Seasonal variability within sites and habitats indicates that localized population characterization should include sampling in both wet and dry seasons. Extreme values at single replicates occasionally influenced overall habitat patterns, while pooling replicates masked variability among sites. A full understanding of population characteristics should include an assessment of variability both at the site and habitat level.
局部生态条件有可能导致种群特征的变化，如大小分布和身体状况。当这些特征影响成功管理干预的前景时，概括生态特征对这些种群特征的影响可能特别有意义。为了描述入侵的棕树蛇种群属性在栖息地类型内部和之间的变异性，我们进行了系统的、季节性平衡的调查，从18个地点中的每个地点收集了100条蛇：在占关岛地理面积95%的六种主要栖息地类型中的每种类型内进行了三次重复采样。我们的研究是已发表的任何蛇类研究中最全面、最可控的采样之一。对蛇的大小和身体状况进行分位数回归表明存在显著的生态异质性，灌丛和银合欢林栖息地类型内部和之间的大小等级和身体状况相对一致，而在峡谷森林、稀树草原和城市居民区之间则存在更多异质性。在一些稀树草原和城市栖息地重复采样中发现了更大、更强壮的蛇，这可能是由于较大猎物的相对可获得性。与湿季更均匀的样本相比，干季大小分布和身体状况的变异性更大。尽管有证据表明栖息地在局部尺度上影响棕树蛇种群（例如，在稀树草原和城市地点，较大的蛇——尤其是雄性蛇——的患病率更高），但栖息地类型内各地点之间的变异程度表明，在未采样地点对这些特征进行有意义预测的能力很小。各地点和栖息地内的季节性变异表明，局部种群特征描述应包括在湿季和干季进行采样。单个重复采样中的极值偶尔会影响总体栖息地模式，而合并重复采样则掩盖了各地点之间的变异性。对种群特征的全面理解应包括对地点和栖息地层面变异性的评估。
