黑河上游天然草地蝗虫密度与地形关系的GAM分析

Grasshopper (Orthoptera: Acrididae) density on natural grasslands in upper reaches of Heihe River, Northwest China in relation with topography: An analysis with generalized additive models (GAM)

地形差异性导致的环境异质性是小尺度范围内生物空间格局形成与维持的重要机制之一,也是导致物种密度分布差异的前提条件。借助GIS和S-Plus软件,利用广义可加模型(GAM)于2009年7—8月对影响蝗虫分布的地形因子进行了研究,在定量分析黑河上游祁连山区北坡地形特征的基础上,研究了该区域蝗虫密度与地形之间的关系。结果表明:蝗虫密度受地形因子影响的顺序为坡向>海拔>坡度>坡位>平面曲率>剖面曲率;蝗虫密度在坡位、平面曲率以及剖面曲率各个梯度上的分布比较均衡,在坡向和坡度梯度上呈二次抛物线分布,在海拔梯度上呈"S"曲线分布;从分布区域上来看,蝗虫主要分布在海拔2550～2650m区域,坡向上则主要集中在西北坡和西坡,与实际观测情况一致。蝗虫密度与地形因子之间的相互关系及其分布状态反映了地形特征对水热等条件的影响,使蝗虫分布格局呈现多元化和以及破碎化状态。

The environmental heterogeneity caused by topographical diversity is an important mechanism of the formation and maintenance of bio-geographic spatial distribution pattern at mi- cro-scale, and also, the prerequisite for the difference in the distribution of species richness. With the help of GIS and S-Plus, the GAM model was used to study the topographic indices af- fecting the distribution of grasshopper on the natural grasslands in the upper reaches of Heihe River on the northern slope of Qilian Mountains from July to August 2009, and the relationship between the regional grasshopper number and terrain complexity was also studied, based on the quantitative analysis of the topographic variation characteristics. The topographical factors affect- ing the grasshopper density were in the order of aspect 〉 elevation 〉 slope 〉 position 〉 plane cur vature 〉 profile curvature. The distribution of grasshopper was almost balanced at different gradi- ents of position, plane curvature, and profile curvature, and presented a quadratic parabola dis- tribution at different gradients of aspect and slope and an ＂S＂ distribution at different gradients of evaluation. There was a higher grasshopper density in the whole region, but the grasshopper was mainly distributed in the region with an altitude of 2550-2650 m, and concentrated in the north- west and west aspect, which was consistent with the actual observation. The relationships be- tween the grasshopper density and terrain factors and the distribution of the grasshopper indicated that the redistribution of water and heat conditions due to topographic factors caused the diversifi-cation and fragmentation of the distribution pattern of the grasshopper.