Thomas Sean C, Weiner Jacob
Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
Department of Biology, Swarthmore College, 19081, Swarthmore, PA, USA.
Oecologia. 1989 Aug;80(3):349-355. doi: 10.1007/BF00379036.
Although considerable evidence exists that plant competition is generally asymmetric or "one-sided", with larger plants having a disproportionate competitive effect on smaller plants, currently employed measures of local interference generally assume that competition is "two-sided". We describe a simple measure of competitive asymmetry in which the effects of neighbors smaller than a focal individual are discounted by a constant factor, and include this variable in a composite measure of local interference. In this model competition varies between complete asymmetry (the effects of smaller plants are entirely discounted) and complete symmetry (the competitive effect of a neighbor is proportional to its size). The proposed method is applied to two natural populations and one experimental monoculture. In all cases an asymmetric model provides the best fit to the data. Completely two-sided models account for 26-39% of the variance in relative growth rate, while relatively one-sided models account for 44-57%. The increases in r values resulting from the inclusion of asymmetry are significant in the two cases in which the data permit randomization tests. Our results suggest that interference is completely asymmetric in a population of Impatiens pallida, a species with very low root allocation and a shallow crown, and somewhat less asymmetric in an experimental monoculture of Ambrosia artemisiifolia and a natural stand of Pinus rigida, cases in which competition for water and nutrient resources is likely to be of greater importance.
尽管有大量证据表明植物竞争通常是不对称的或“单边的”，即较大的植物对较小的植物具有不成比例的竞争效应，但目前所采用的局部干扰测量方法通常假定竞争是“双边的”。我们描述了一种简单的竞争不对称测量方法，其中比焦点个体小的邻居的影响会被一个恒定因子削弱，并将这个变量纳入局部干扰的综合测量中。在这个模型中，竞争在完全不对称（较小植物的影响被完全削弱）和完全对称（邻居的竞争效应与其大小成正比）之间变化。所提出的方法应用于两个自然种群和一个实验性单一栽培群体。在所有情况下，不对称模型对数据的拟合效果最佳。完全双边模型解释了相对生长率方差的26 - 39%，而相对单边模型解释了44 - 57%。在数据允许进行随机化检验的两个案例中，纳入不对称因素后r值的增加是显著的。我们的结果表明，在根部分配非常低且树冠较浅的淡色凤仙花种群中，干扰是完全不对称的；而在豚草的实验性单一栽培群体和硬叶松天然林中，干扰的不对称程度稍低，在这些案例中，对水分和养分资源的竞争可能更为重要。
