解析人类活动压力梯度上的“环境异质性-生物多样性”关系暨检验“生境面积-环境异质性权衡”假说

环境异质性和生境面积是生态系统维持物种多样性的两个最基本因素。环境异质性的提升，会促进生态位分化，从而增加物种多样性；但是环境异质性的持续增加，必然会导致生境破碎和面积萎缩，限制物种的适应和扩散，增大局域灭绝风险，导致生物多样性下降。因此，学界提出“生境面积-环境异质性权衡”假说，认为环境异质性和物种多样性应呈单峰曲线关系。然而，大量的实证研究支持了“环境异质性和物种多样性”之间的正关系、负关系和中性关系，却很少支持二者间的单峰关系。学界排除诸多因素后，认为人类活动是未被充分考虑的，但对“环境异质性和物种多样性”关系产生重大影响的唯一要素。我们拟在中国东部草原，量化人类活动压力，在人类活动压力梯度上调查植被异质性和物种多样性；将人类活动压力作为随机变量加以控制，拟合并判断二者间的最优关系；最后，结合物种的适应和扩散等生态学基本过程，从表观和机理上检验“生境面积-环境异质性权衡”假说。

Environmental heterogeneity and habitat area are two fundamental factors for maintaining species diversity in an ecosystem or a landscape. In theory, the increasing of environmental heterogeneity could promote the niche partitioning, thus provide more habitat for more species, and increase species diversity. On the other hand, the increasing of environmental heterogeneity will inevitably isolate these habitats in an ecosystem or a landscape, and reduce the size of their area. Small and fragmented habitats limit the adaption and spreading of species, increase the risk of local extinct, and therefore reduce the species diversity. Based on the above theoretical analysis, ecologists have developed the “area-heterogeneity tradeoff” hypothesis, which described the “environmental heterogeneity and species diversity relationship” as a unimodal relationship. However, most of the empirical studies supported the positive, negative, or neutral relationship between environmental heterogeneity and species diversity, but only very few empirical evidences confirmed their unimodal relationship and the “area-heterogeneity tradeoff” hypothesis. Therefore, there is a gap between theoretical derivation and empirical studies. Ecologists found human pressures were one of the key factors which can impact the relationship between the environmental heterogeneity and habitat area, but its influence had not been fully studied for the limitation in the estimation of human pressures. We will estimate the human pressures in the eastern part of China grasslands, survey the vegetation heterogeneity and species diversity along the human pressures gradient. We will use the mixed models to fit the relationship between vegetation heterogeneity and species diversity, and assign human pressures index as the random factor to control the human influence. We use the model selection method to determine the optimal relationship between vegetation heterogeneity and species diversity. At last, we will integrate the optimal relationship with evidences from niche partitioning, species adaption and spreading, to test the “area-heterogeneity tradeoff” hypothesis.