Department of Biological Sciences, Chapman University, Orange, CA 92866, USA.
Oecologia. 2010 Apr;162(4):815-23. doi: 10.1007/s00442-009-1497-4. Epub 2009 Nov 16.
Invasive species may be released from consumption by their native herbivores in novel habitats and thereby experience higher fitness relative to native species. However, few studies have examined release from herbivory as a mechanism of invasion in oceanic island systems, which have experienced particularly high loss of native species due to the invasion of non-native animal and plant species. We surveyed putative defensive traits and leaf damage rates in 19 pairs of taxonomically related invasive and native species in Hawaii, representing a broad taxonomic diversity. Leaf damage by insects and pathogens was monitored in both wet and dry seasons. We found that native species had higher leaf damage rates than invasive species, but only during the dry season. However, damage rates across native and invasive species averaged only 2% of leaf area. Native species generally displayed high levels of structural defense (leaf toughness and leaf thickness, but not leaf trichome density) while native and invasive species displayed similar levels of chemical defenses (total phenolics). A defense index, which integrated all putative defense traits, was significantly higher for native species, suggesting that native species may allocate fewer resources to growth and reproduction than do invasive species. Thus, our data support the idea that invasive species allocate fewer resources to defense traits, allowing them to outperform native species through increased growth and reproduction. While strong impacts of herbivores on invasion are not supported by the low damage rates we observed on mature plants, population-level studies that monitor how herbivores influence recruitment, mortality, and competitive outcomes are needed to accurately address how herbivores influence invasion in Hawaii.
入侵物种可能会在新栖息地中摆脱其原生食草动物的消耗，从而相对于本地物种具有更高的适应性。然而，很少有研究检验过食草动物的释放作为海洋岛屿系统入侵的一种机制，这些系统由于非本地动植物物种的入侵而经历了特别高的本地物种丧失。我们调查了夏威夷的 19 对分类相关的入侵和本地物种的假定防御特征和叶片损伤率，代表了广泛的分类多样性。在雨季和旱季监测昆虫和病原体对叶片的损伤。我们发现，本地物种的叶片损伤率高于入侵物种，但仅在旱季。然而，本地和入侵物种的损伤率平均仅占叶片面积的 2%。本地物种通常表现出高水平的结构防御（叶片韧性和叶片厚度，但叶片毛状体密度较低），而本地和入侵物种表现出相似水平的化学防御（总酚）。防御指数，综合了所有假定的防御特征，本地物种显著较高，这表明本地物种可能比入侵物种分配更少的资源用于生长和繁殖。因此，我们的数据支持这样一种观点，即入侵物种分配较少的资源用于防御特征，从而通过增加生长和繁殖来胜过本地物种。虽然我们在成熟植物上观察到的低损伤率并不支持食草动物对入侵的强烈影响，但需要进行种群水平的研究，监测食草动物如何影响繁殖、死亡率和竞争结果，以准确解决食草动物如何影响夏威夷的入侵问题。
