Department of Biological Sciences, Division of Systematics, Ecology, and Evolution, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Ecology. 2011 Mar;92(3):676-86. doi: 10.1890/10-1001.1.
Two prominent mechanisms proposed to structure biodiversity are niche-based ecological filtering and chance arrival of propagules from the species pool. Seed arrival is hypothesized to play a particularly strong role in high-diversity plant communities with large potential species pools and many rare species, but few studies have explored how seed arrival and local ecological filters interactively assemble species-rich communities in space and time. We experimentally manipulated seed arrival and multiple ecological filters in high-diversity, herbaceous-dominated groundcover communities in longleaf pine savannas, which contain the highest small-scale species richness in North America (up to > 40 species/m2). We tested three hypotheses: (1) local communities constitute relatively open-membership assemblages, in which increased seed arrival from the species pool strongly increases species richness; (2) ecological filters imposed by local fire intensity and soil moisture influence recruitment and richness of immigrating species; and (3) ecological filters increase similarity in the composition of immigrating species. In a two-year factorial field experiment, we manipulated local fire intensity by increasing pre-fire fuel loads, soil moisture using rain shelters and irrigation, and seed arrival by adding seeds from the local species pool. Seed arrival increased species richness regardless of fire intensity and soil moisture but interacted with both ecological filters to influence community assembly. High-intensity fire decreased richness of resident species, suggesting an important abiotic filter. In contrast, high-intensity fire increased recruitment and richness of immigrating species, presumably by decreasing effects of other ecological filters (competition and resource limitation) in postfire environments. Drought decreased recruitment and richness of immigrating species, whereas wet soil conditions increased recruitment but decreased or had little effect on richness. Moreover, some ecological filters (wet soil conditions and, to a lesser extent, high-intensity fire) increased similarity in the composition of immigrating species, illustrating conditions that influence deterministic community assembly in species-rich communities. Our experiment provides insights into how dispersal-assembly mechanisms may interact with niche-assembly mechanisms in space (spatial variation in disturbance) and time (temporal variation in resource availability) to structure high-diversity communities and can help guide conservation of threatened longleaf pine ecosystems in the face of habitat fragmentation and environmental change.
两种突出的机制被提出用于构建生物多样性，分别是基于生态位的生态过滤和来自物种库的繁殖体偶然到达。种子到达被假设在具有大的潜在物种库和许多稀有物种的高多样性植物群落中发挥特别重要的作用，但很少有研究探索种子到达和当地生态过滤器如何在空间和时间上互动组装物种丰富的群落。我们在长叶松草原的高多样性草本为主的地被群落中，实验性地操纵了种子到达和多种生态过滤器，该地区拥有北美的最高小尺度物种丰富度（高达 > 40 种/平方米）。我们测试了三个假设：（1）本地群落构成相对开放的成员集合，来自物种库的增加种子到达强烈增加物种丰富度；（2）当地火强度和土壤湿度施加的生态过滤器影响移民物种的繁殖和丰富度；（3）生态过滤器增加移民物种组成的相似性。在为期两年的因子现场实验中，我们通过增加预火燃料负荷来操纵当地火强度，使用雨棚和灌溉来操纵土壤湿度，通过添加来自本地物种库的种子来操纵种子到达。无论火强度和土壤湿度如何，种子到达都会增加物种丰富度，但与两种生态过滤器相互作用，影响群落组装。高强度火灾降低了本地物种的丰富度，表明存在重要的非生物过滤器。相比之下，高强度火灾增加了移民物种的繁殖和丰富度，这可能是通过减少火灾后环境中其他生态过滤器（竞争和资源限制）的影响。干旱降低了移民物种的繁殖和丰富度，而湿润的土壤条件增加了繁殖，但减少或对丰富度没有影响。此外，一些生态过滤器（湿润的土壤条件，在较小程度上还有高强度火灾）增加了移民物种组成的相似性，说明了影响物种丰富群落中确定性群落组装的条件。我们的实验提供了关于扩散-组装机制如何与空间（干扰的空间变化）和时间（资源可利用性的时间变化）中的生态位-组装机制相互作用来构建高多样性群落的见解，并有助于指导面对栖息地破碎化和环境变化时保护受到威胁的长叶松生态系统。
