Patterns of Community Assembly in Serpentine Grasslands: The Roles of Initial Plant Composition and Functional Complementarity

[02131877]对群落聚集模式的研究在群落生态学中已经持续了25年，至今仍有争议。一个普遍寻求的组装规则是，物种在群落中的共存将通过与有限资源竞争相关的特征差异（即，生态位重叠最小化）而增强。换句话说，来自互补行会或功能群的物种是否比那些在资源利用特征上有强烈重叠的物种有更好的生存机会？植物类群在群落结构中的互补性作用的证据是零星的。外部随机过程（如干扰或殖民化的优先效应）与内部群落动态（如竞争或促进）的比率之间的平衡可能是决定内部组装动态表现程度的关键。深入了解这个问题对于理解群落的结构以及这种结构对生态系统动力学的影响至关重要。我们提出了一项为期5年的实验，以评估初始植物组成和功能互补性在蛇形一年生草地群落结构中的作用。每周测试几个假设，围绕以下问题，通常分为两个主题：1)社区的初始组成是否会影响其随后的发展？如果是，会持续多久？是否有不同的稳定端点？2)互补资源利用（即生态位分化）与植物物种间优势在多大程度上支配着群落发展模式？其他因素，如种子投入或气候条件在决定群落组成方面是否更重要？我们的目标不是证明或否定聚集规则的优势，而是更好地理解它们可能强烈影响社区组成的条件，而不是被其他因素所淹没。我们将使用一系列加利福尼亚蛇形草地群落作为我们的实验系统，这些群落在功能群组成和丰富度上有所不同。自1992年地块建立以来，功能组成一直保持不变。在1999年和2000年的秋天，为了测试功能特征和多样性对生态系统可入侵性的影响，又增加了6种种子（两组各3种）。因此，我们现在有了一个系统，其处理方法在初始功能组成上有所不同，对许多其他物种有共同的种子来源，并且将受到来自周围草原的持续种子雨的影响。我们的计划是跟踪未来五年社区组成的变化，因为社区从最初不同的起点发展起来。在接下来的几年里，对这些实验群落的植被变化进行监测，为深入了解有助于形成生态群落的各种过程之间的相互作用提供了一个独特的机会。

0213187HooperThe search for patterns of community assembly has occupied the last 25 years incommunity ecology and remains controversial today. A commonly sought assembly rule is thatspecies coexistence in communities will be enhanced by differences in traits related tocompetition for limiting resources (i.e., that niche overlap is minimized). Put another way, dospecies from complementary guilds or functional groups have a better chance of persisting thanthose with strong overlap in resource use characteristics? Evidence for the role ofcomplementarity among plant groups in structuring communities is sporadic. The balancebetween rates of external stochastic processes (such as disturbance or priority effects ofcolonization) compared to internal community dynamics (such as competition or facilitation)may be critical in determining the degree to which internal assembly dynamics are manifested.Gaining further insight into this question is critical for understanding how communities might bestructured, and for the implications of that structure for ecosystem dynamics.We propose a five-year experiment to assess the roles of initial plant composition andfunctional complementarity in structuring communities of serpentine annual grasslands. Weseek to test several hypotheses centered on the following questions, generally grouped into twothemes: 1) Does the initial composition of a community shape its subsequent development? If so,for how long? Are there different stable endpoints? 2) To what extent does complementaryresource use (i.e., niche differentiation) versus dominance among plant species govern patternsof community development? Are other factors, such as seed input or climatic conditions moreimportant in determining community composition? Our goal is not to prove or disprove thepredominance of assembly rules, but rather to better understand the conditions under which theymight strongly influence community composition versus be overwhelmed by other factors.We will use as our experimental system a series of California serpentine grasslandcommunities that vary in functional group composition and richness. Functional compositionhas been maintained since the plots were established in 1992. In fall 1999 and 2000, seeds of sixadditional species (3 species each from two groups) were added to test the effects of functionalcharacteristics and diversity on invasibility of ecosystems. Thus we now have a system withtreatments that differ in initial functional composition, that have had common seed sources for anumber of additional species, and that will be subject to continuing seed rain from surroundinggrasslands. Our plan is to track changes in community composition over the next five years asthe communities develop from their initially different starting points. Monitoring of vegetation changes in these experimental communities through the next several years provides a unique opportunity to gain insight into interactions among a variety of processes that help shape ecological communities.