基于零模型的腾格里沙漠东南缘固定沙地种群点格局分析

Point pattern analysis based on null models of populations in fixed sand at the southeastern edge of the Tengger Desert

植物种群空间分布格局是种群生物学特性、种内或种间关系以及与环境因子综合作用的结果。明确植物空间分布格局对认识植物生态适应性与多样性维持机制具有重要意义。本研究选择腾格里沙漠东南缘30~40年固定沙地,基于点格局的完全空间随机模型、泊松聚块模型和嵌套双聚块模型分析并检验了小画眉草、狗尾草、虎尾草、猪毛菜、雾冰藜5种常见植物种群空间分布格局。结果表明:种群密度大小排序为:小画眉草>狗尾草>虎尾草>雾冰藜>猪毛菜。完全空间随机模型下,小画眉草种群在0~1000 cm尺度呈现出从聚集分布过渡到均匀分布,再转换为聚集分布的变化规律;其余4个物种在0~295 cm尺度表现为聚集分布,且聚集分布尺度随种群密度降低而降低。泊松聚块模型下,小画眉草、雾冰藜和猪毛菜物种在0~35 cm尺度内表现为聚集分布,其他尺度为随机分布;而狗尾草和虎尾草种群分别在0~55 cm、405~835 cm和0~75 cm、465~945 cm尺度表现为聚集分布,其他尺度均随机分布。嵌套双聚块模型下,5个物种在0~1000 cm尺度基本呈现随机分布,即在大聚块中都分布着小聚块。综合3种模型的检验结果,种子扩散限制、灌木的“沃岛”效应和藻结皮特性引起的微生境异质性共同决定了腾格里沙漠东南缘30~40年固沙区植被空间多聚块分布特征。

The spatial distribution patterns of vegetation populations result from the combined effects of populations’biological characteristics,intraspecific relationships,and interspecific relationships.Understanding the spatial distribution patterns of plants is of great significance for elucidating how plants adapt to their ecological environment,and how populations maintain diversity.In this study,we analyzed vegetation populations in fixed sandy lands on the southeast edge of the Tengger Desert.Areas where the sandy lands have been fixed for 30 to 40 years were selected for analysis.The formation of spatial patterns of five common plant species,namely Eragrostis minor,Setaria viridis,Chloris virgata,Salsola collina,and Grubovia dasyphylla,was analyzed and tested using point pattern analyses.The null models used in the tests of spatial randomness were the complete spatial randomness model,the Poisson cluster model,and the nested double-cluster model.According to the results,the populations were ranked from highest to lowest density,as follows:E.minor,S.viridis,C.virgata,G.dasyphylla,and S.collina.When using the complete spatial randomness null model,the population of E.minor showed a trend towards changing from an aggregated distribution to a uniform distribution and then to an aggregated distribution at the scale of 0-1000 cm.The other four species appeared to have aggregated distributions,and the scale of aggregated distribution reduced as population density decreased.Using the Poisson cluster null model,E.minor,G.dasyphylla,and S.collina showed an aggregated distribution at 0-35 cm scales,but a random distribution at other scales.S.viridis,showed an aggregated distribution at scales of 0-55 cm and 405-835 cm,and C.virgata at scales of 0-75 cm and 465-945 cm,but a random distribution at other scales.Using the double-cluster null model,the five species showed random distributions at 0-1000 cm scales,that is,small clusters were spread across large clusters.In conclusion,the restriction of seed dispersal,the“fertile island”effect of shrubs,and the characteristics of the algal crust may determine the patchiness of populations of common plants in areas with 30-40 years of sand fixation on the southeast edge of the Tengger Desert.