CRB: Plant Communities on Patchy Serpertine Outcrops: Spatial Structure and Ecological Interactions

9424137哈里森加利福尼亚北部的蛇形岩露头是生态岛屿，有丰富的本地植物群。本研究考察了蛇形土壤上植物群落结构的两个相关方面，与保护生物学的直接和一般相关。第一个问题是蛇形与非蛇形土壤上植物群落多样性的空间结构，以及这种空间结构如何受到蛇形斑块和其他属性的影响。在保持采样区大小和间隔不变的情况下，比较蛇形与非蛇形基质、斑块状与连续蛇形基质之间物种组成的空间更替。这将是对斑块与距离在产生群落多样性的空间成分方面的作用的第一次严格测试。为了评估特有和缺乏入侵的作用，将重复上述分析，分别排除特有和外来物种。对不同生境类型间的物种迁移进行距离和环境差异性回归，进一步量化空间迁移及其原因。第二个问题涉及多样性模式的生物原因。实验将检验关键生物相互作用的速率如何随蛇形斑块的大小和隔离程度而变化。在两个蛇形特有植物物种中，将沿着自然和实验斑块隔离梯度测量授粉和种子捕食。这项研究将阐明如何最好地保护加利福尼亚蛇形土壤上的植物群落，以及在几个空间尺度上斑块如何影响生态群落的结构和功能的更一般的问题。随着人类活动逐渐增加自然系统破碎化的速度和程度，这项研究变得更加重要。

9424137 Harrison Serpentine outcrops in Northern California are ecological islands with a rich native flora. This study examines two related aspects of plant community structure on serpentine soils, with both immediate and general relevance for conservation biology. The first question is how plant community diversity is spatially structured on serpentine versus non-serpentine soils, and how this spatial structure is affected by patchiness and other attributes of serpentine. Spatial turnover in species composition will be compared between serpentine and non-serpentine substrates, and between patchy and continuous serpentine, while holding the size and spacing of sampling areas constant. This well be the first rigorous test of the role of patchiness versus distance alone in producing the spatial component of community diversity. To assess the roles of endemism and lack of invasion, the above analyses will be repeated excluding endemics and alien species, respectively. Species turnover between pairs of sites will be regressed on distance and environmental dissimilarity within each habitat type to further quantify spatial turnover and its causes. The second question concerns biotic causes of patterns of diversity. Experiments will examine how the rates of key biotic interactions vary with the size and isolation of serpentine patches. Pollination and seed predation will be measured in two serpentine endemic plant species, along both natural and experimental gradients of patch isolation. This study will illuminate both how best to conserve plant communities on serpentine soils in California, and the more general issue of how patchiness at several spatial scales affects the structure and function of ecological communities. This research becomes even more important as human activities gradually increase the rate and degree of fragmentation of natural systems.