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

0213187胡珀在过去的25年里，群落生态学一直在寻找群落聚集的模式，至今仍有争议。一个普遍寻求的集合规则是，群落中的物种共存将通过与有限资源竞争相关的性状差异而得到加强（即，该小生境重叠被最小化）。换句话说，来自互补性行业协会或功能团体的物种比那些在资源利用特征上有很强重叠的物种有更好的生存机会吗？植物类群之间的互补性在构建群落中的作用的证据是零星的。外部随机过程的速率平衡（如殖民化的干扰或优先效应）与内部群落动态相比（如竞争或促进）可能是决定内部组装动力学表现的程度的关键。进一步深入了解这个问题对于理解社区可能是如何构建的至关重要，我们提出了一个为期五年的实验，以评估初始植物组成和功能互补性在构建蛇形一年生草地群落中的作用。我们试图检验几个假设，这些假设集中在以下问题上，通常分为两个主题：1）一个社区的最初组成是否塑造了它随后的发展？如果是的话，会持续多久？是否存在不同的稳定终点？2)在何种程度上使用补充资源（即，生态位分化）与植物种间的优势支配群落发展模式？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反驳组装规则的优势，而是更好地理解它们可能强烈影响群落组成而不是被其他因素压倒的条件。我们将使用一系列加州蛇形草地群落作为实验系统，这些群落在功能组组成和丰富度方面各不相同。自1992年建立地块以来，功能组成一直保持不变。在1999年和2000年秋季，增加了6个物种的种子（两组各3个物种），以测试功能特征和多样性对生态系统入侵性的影响。因此，我们现在有了一个系统，其处理方法在初始功能组成上有所不同，对于许多其他物种来说有着共同的种子来源，并且将受到来自周围草原的持续种子雨的影响。我们的计划是在未来五年内跟踪社区组成的变化，因为社区从最初不同的起点发展。 在未来几年中，这些实验社区的植被变化监测提供了一个独特的机会，深入了解各种过程之间的相互作用，有助于塑造生态社区。

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.