很多研究表明，在入侵地外来种缺少原产地的专性天敌（Specialists），入侵地的广普天敌（Generalists）又因各种原因很少危害外来种，致使天敌逃逸，这可能是外来种成功入侵的重要原因。天敌逃逸不仅可以直接提高外来入侵种对本地种（有天敌）的竞争能力，而且还可以通过影响外来入侵种的进化提高其入侵能力。增强竞争能力的进化（EICA）假说认为，入侵地的天敌缺乏将使外来种通过进化降低天敌防御能力，而把原来用于天敌防御的资源用于生长和繁殖等过程，从而提高竞争力，促进入侵。该假说的前提是植物的防御是有成本的，生长和防御有权衡关系，而这种权衡关系也已被很多研究所证实。
然而，最近美国蒙大拿大学、科罗拉多州立大学和中科院西双版纳热带植物园生物入侵生态学研究组的合作研究表明，外来入侵植物斑点矢车菊（Centaurea maculosa）入侵种群的生长速度和竞争能力高于原产地种群，但是入侵种群高的竞争能力并不是以天敌防御能力降低为代价的。相反，入侵种群对广普天敌和专性天敌的防御能力要高于原产地种群，它们不仅能更好地抑制天敌取食（抗性），也能更好地忍耐天敌的攻击（耐性）。入侵种群高的天敌防御能力与其高的化防物质前体含量、坚韧的叶片和多的叶毛有关。入侵种群的这些特性是由遗传因素决定的。该研究表明，增强竞争能力的进化并不总是由能量或资源向生长和防御分配的生理权衡造成的，这与传统的生态学理论不同，与Blossey等提出的EICA假说也不同，与中国科学院西双版纳热带植物园冯玉龙等提出的氮分配进化假说也不一致，必将促进今后相关领域的研究。
该研究成果发表在世界著名生态学期刊《生态学专论》（Ecological Monographs）上。（生物谷Bioon.com）
生物谷推荐原始出处：
Ecological Monographs，Volume 78, Issue 3，pp. 369–386，Wendy M. Ridenour，Ragan M. Callaway
NO EVIDENCE FOR TRADE-OFFS: CENTAUREA PLANTS FROM AMERICA ARE BETTER COMPETITORS AND DEFENDERS
Wendy M. Ridenour1,4, Jorge M. Vivanco2, Yulong Feng3, Jun-ichiro Horiuchi2, and Ragan M. Callaway1
1 Division of Biological Sciences, The University of Montana, Missoula, Montana 59812 USA
2 Department of Horticulture, Colorado State University, Fort Collins, Colorado 80523 USA
3 Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming 650223 Yunnan Province, China
The natural enemies hypothesis has led to a number of ideas by which invaders might evolve superior competitive ability. In this context, we compared growth, reproduction, competitive effect, competitive response, and defense capabilities between invasive North American populations of Centaurea maculosa and populations in Europe, where the species is native. We found that Centaurea from North America were larger than plants from European populations. North American Centaurea also demonstrated stronger competitive effects and responses than European Centaurea. However, competitive superiority did not come at a cost to herbivore defense. North American plants were much better defended against generalist insect herbivores and slightly better defended against specialists. North Americans showed a stronger inhibitory effect on the consumers (resistance) and a better ability to regrow after attack by herbivores (tolerance). Better defense by North Americans corresponded with higher constitutive levels of a biochemical defense compound precursor, tougher leaves, and more leaf trichomes than Europeans. North American F1 progeny of field collected lines retained the traits of larger size and greater leaf toughness suggesting that genetic differences, rather than maternal effects, may be the cause of intercontinental differences, but these sample sizes were small. Our results suggest that the evolution of increased competitive ability may not always be driven by physiological trade-offs between the allocation of energy or resources to growth or to defense. Instead, we hypothesize that Centaurea maculosa experiences strong directional selection on novel competitive and defense traits in its new range.
