Capers Robert S, Selsky Roslyn, Bugbee Gregory J, White Jason C
Connecticut Agricultural Experiment Station, P.O. Box 1106, 123 Huntington St., New Haven, Connecticut 06504, USA.
Ecology. 2007 Dec;88(12):3135-43. doi: 10.1890/06-1911.1.
Invasive species richness often is negatively correlated with native species richness at the small spatial scale of sampling plots, but positively correlated in larger areas. The pattern at small scales has been interpreted as evidence that native plants can competitively exclude invasive species. Large-scale patterns have been understood to result from environmental heterogeneity, among other causes. We investigated species richness patterns among submerged and floating-leaved aquatic plants (87 native species and eight invasives) in 103 temperate lakes in Connecticut (northeastern USA) and found neither a consistently negative relationship at small (3-m2) scales, nor a positive relationship at large scales. Native species richness at sampling locations was uncorrelated with invasive species richness in 37 of the 60 lakes where invasive plants occurred; richness was negatively correlated in 16 lakes and positively correlated in seven. No correlation between native and invasive species richness was found at larger spatial scales (whole lakes and counties). Increases in richness with area were uncorrelated with abiotic heterogeneity. Logistic regression showed that the probability of occurrence of five invasive species increased in sampling locations (3 m2, n = 2980 samples) where native plants occurred, indicating that native plant species richness provided no resistance against invasion. However, the probability of three invasive species' occurrence declined as native plant density increased, indicating that density, if not species richness, provided some resistance with these species. Density had no effect on occurrence of three other invasive species. Based on these results, native species may resist invasion at small spatial scales only in communities where density is high (i.e., in communities where competition among individuals contributes to community structure). Most hydrophyte communities, however, appear to be maintained in a nonequilibrial condition by stress and/or disturbance. Therefore, most aquatic plant communities in temperate lakes are likely to be vulnerable to invasion.
在小样方空间尺度上，入侵物种丰富度通常与本地物种丰富度呈负相关，但在较大区域则呈正相关。小尺度上的这种模式被解释为本地植物能够通过竞争排除入侵物种的证据。大尺度上的模式则被认为是由环境异质性等原因导致的。我们调查了美国东北部康涅狄格州103个温带湖泊中沉水和浮叶水生植物（87种本地物种和8种入侵物种）的物种丰富度模式，发现在小尺度（3平方米）上既没有始终如一的负相关关系，在大尺度上也没有正相关关系。在有入侵植物出现的60个湖泊中，有37个湖泊采样点的本地物种丰富度与入侵物种丰富度不相关；16个湖泊中呈负相关，7个湖泊中呈正相关。在更大的空间尺度（整个湖泊和县区）上，未发现本地和入侵物种丰富度之间存在相关性。丰富度随面积的增加与非生物异质性无关。逻辑回归表明，在有本地植物出现的采样点（3平方米，n = 2980个样本）中，5种入侵物种出现的概率增加，这表明本地植物物种丰富度并未对入侵产生抗性。然而，随着本地植物密度的增加，3种入侵物种出现的概率下降，这表明密度（而非物种丰富度）对这些物种提供了一定的抗性。密度对另外3种入侵物种的出现没有影响。基于这些结果，本地物种可能仅在密度较高的群落（即个体间竞争对群落结构有贡献的群落）的小空间尺度上抵抗入侵。然而，大多数水生植物群落似乎因压力和/或干扰而处于非平衡状态。因此，温带湖泊中的大多数水生植物群落可能容易受到入侵。
