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

胡珀对社区集会模式的探索在过去的25年里一直在社区生态学中占据着地位，至今仍存在争议。一个普遍寻求的集合规则是，物种在群落中的共存将通过与竞争有限资源有关的特征的差异而增强(即生态位重叠被最小化)。换句话说，来自互补性行会或功能团体的剂量种比那些在资源使用特征上有强烈重叠的剂量种有更好的持续机会？关于植物群之间的互补性在构建群落中的作用的证据是零星的。外部随机过程(如干扰或定居的优先效应)与内部群落动态(如竞争或促进)之间的速率之间的平衡可能是决定内部群落动态被操纵的程度的关键。深入了解这个问题对于理解群落可能的结构以及这种结构对生态系统动力学的影响至关重要。我们提议进行一项为期五年的实验，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。Weseek检验了围绕以下问题的几个假说，这些假说通常分为两个主题：1)一个社区的初始组成是否塑造了它随后的发展？如果是，会持续多久？是否有不同的稳定终点？2)植物物种间的资源利用互补(即生态位分化)与优势地位在多大程度上支配着群落发展的格局？其他因素，如种子投入或气候条件，在决定群落组成时是否更重要？我们的目标不是证明或反驳集会规则的优势，而是更好地了解它们可能强烈影响群落组成而不是被其他因素淹没的条件。我们将使用一系列功能群组成和丰富度不同的加州蛇形草原群落作为我们的实验系统。自1992年地块建立以来，功能构成一直保持不变。在1999年和2000年秋季，添加了另外6个物种(两组各3个物种)的种子，以测试功能特性和多样性对生态系统入侵性的影响。因此，我们现在有了一个处理系统，其初始功能组成不同，具有许多额外物种的共同种子来源，并且将受到来自周围草原的持续种子降雨的影响。我们的计划是在未来五年跟踪社区组成的变化，因为社区从最初不同的起点发展起来。在未来几年对这些实验社区的植被变化进行监测提供了一个独特的机会，可以深入了解有助于塑造生态社区的各种过程之间的相互作用。

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.