Miriti Maria N
Department of Evolution, Ecology, and Organismal Biology, Room 300, Aronoff Laboratory, Ohio State University, 318 W. 12th Avenue, Columbus, Ohio 43210, USA.
Ecology. 2007 May;88(5):1177-90. doi: 10.1890/06-1006.
I present results from analyses of 20 years of spatiotemporal dynamics in a desert perennial community. Plants were identified and mapped in a 1-ha permanent plot in Joshua Tree National Park (California, USA) in 1984. Plant size, mortality, and new seedlings were censused every five years through 2004. Two species, Ambrosia dumosa and Tetracoccus hallii, were dominant based on their relative abundance and ubiquitous distributions. Spatial analysis for distance indices (SADIE) identified regions of significantly high (patches) or low (gaps) densities. I used SADIE to test for (1) transience in the distribution of patches and gaps within species over time and (2) changes in juvenile-adult associations with conspecific adults and adults of the two dominant species over time. Plant performance was quantified in patches and gaps to determine plant responsiveness to local spatial associations. Species identity was found to influence associations between juveniles and adults. Juveniles of all species showed significant positive spatial associations with the dominant A. dumosa but not with T. hallii. The broad distribution of A. dumosa may increase the spatial extent of non-dominant species that are facilitated by this dominant. The spatial location of patches and gaps was generally consistent over time for adults but not juveniles. Observed variability in the locations of juvenile patches and gaps suggested that suitable locations for establishment were broad relative to occupied regions of the habitat, and that conditions for seed germination were independent of conditions for seedling survival. A dramatic change in spatial distributions and associations within and between species occurred after a major drought that influenced data from the final census. Positive associations between juveniles and adults of all species were found independent of previous associations and most species distributions contracted to areas that were previously characterized by low density. By linking performance to spatial distribution, results from this study offer a spatial context for plant-plant interactions within and among species. Community composition could be influenced both by individual species tolerances of abiotic conditions and by the competitive or facilitative interactions individuals exert over neighbors.
我展示了对一个沙漠多年生植物群落20年时空动态分析的结果。1984年，在美国加利福尼亚州约书亚树国家公园的一个1公顷的永久样地中对植物进行了识别和绘图。直到2004年，每隔五年对植物大小、死亡率和新幼苗进行一次普查。根据其相对丰度和广泛分布，两种植物，即矮豚草（Ambrosia dumosa）和哈利四裂木（Tetracoccus hallii）占主导地位。距离指数的空间分析（SADIE）确定了高密度（斑块）或低密度（间隙）的显著区域。我使用SADIE来检验：（1）物种内斑块和间隙分布随时间的瞬变性；（2）随着时间的推移，幼体与同种成年个体以及两种优势物种成年个体之间的关联变化。在斑块和间隙中对植物表现进行了量化，以确定植物对局部空间关联的响应。发现物种身份会影响幼体与成年个体之间的关联。所有物种的幼体与优势种矮豚草都表现出显著的正空间关联，但与哈利四裂木没有。矮豚草的广泛分布可能会增加受该优势种促进的非优势物种的空间范围。对于成年个体，斑块和间隙的空间位置通常随时间保持一致，但幼体并非如此。观察到的幼体斑块和间隙位置的变异性表明，相对于栖息地的占据区域，适合定居的位置范围较广，并且种子萌发条件与幼苗存活条件无关。在一场影响了最后一次普查数据的重大干旱之后，物种内部和物种之间的空间分布及关联发生了巨大变化。发现所有物种的幼体与成年个体之间存在正关联，且与先前的关联无关，大多数物种分布收缩到了先前低密度特征的区域。通过将表现与空间分布联系起来，本研究结果为物种内部和物种之间的植物 - 植物相互作用提供了一个空间背景。群落组成可能既受个体物种对非生物条件的耐受性影响，也受个体对邻居施加的竞争或促进相互作用影响。
