黄土丘陵区不同立地条件下植物种群生态位研究

运用改进的Levins生态位宽度指数和Pianka生态位重叠指数,通过对不同立地条件下样带的比较,分析了主要植物种群在不同立地条件下的生态位变化以及种间关系、群落结构对立地条件的响应。结果表明,草地群落建群种本氏针茅的生态位宽度在4种立地条件下都表现为最大值,非建群种的生态位宽度随环境条件的改变呈较大的波动性。生态位重叠指数表明,生态位较宽的物种与其它物种间存在较大的生态位重叠,但在一定的立地条件下,生态位较窄的物种之间也存在着较大的生态位重叠,这种现象是种群对有限环境资源激烈竞争的体现;不同种间生态位重叠随立地条件的变化格局存在较大差异,这种差异是由植物种间生物生态学特性和需求差异造成的;但同一种对在不同立地条件下生态位重叠的变化是立地条件对种间关系影响的结果。总体来说,在黄土丘陵沟壑区,由于环境条件的影响,物种生态位重叠相对较低。

Studies on the niches of the main populations in different habitats of the Loess Hilly Region,China

The landscape of the Loess Hilly Region of China is very complex,with soil water conditions greatly varied.It is well known that the distribution of plant populations and the inter-specific relationships of grassland plants can be greatly affected by habitat conditions.As such,it is of great significance to both clarify the changing patterns of inter-specific relationships in different habitats in order to study the adaptabilities of plant populations to landforms and to forecast population dynamics and community succession trends.In this paper,both an improved Levins niche breadth index and a Pianka niche overlap index are used in order to compare and analyze transects from different habitats,varieties of niche breadth and responses of interspecific relationships and the community structures of various landforms.The results showed that the constructive species of the grassland community,Stipa bungeana,was hardly impacted on by their habitats.The values of niche breadth were highest in four habitats,which was due to the populations having a strong ability to utilize available resources and as they were well adapted to complicated environmental conditions.However,other plant populations were influenced greatly by habitats because these species had a stronger selectiveness to available resources and a relatively higher demand for certain environmental factors.Differences in changing patterns of niche breadth for different plant populations under various habitats were significant,which reflected their different responses to habitats.There were obvious variations in plant populations in different habitats,which was indicative that community structure of grasslands were strongly affected by their habitats.The niche overlap index indicated that there were large overlaps between species of broad niche breadth with others,the reason being that these species had a wide living space and had strong abilities to utilize resources.But there were also large overlaps between species of narrow niches in certain habitats due to a drastic competition for limited resources.With various habitats,there was shown to be changing patterns of niche overlapping with among different specie-pairs,which was mainly determined by biological characteristics and ecological demands of different species,whereas in contrast,the niche overlapping of the same pair-species in different habitats was the result of habitat infection.In conclusion,owing to influences of environmental stress,a higher differentiation in niches of plant populations and relatively lower niche overlaps between species were apparent in the Loess Hilly Region.