外来种(alien species)是指由于人类有意或无意的活动被带到其自然演化区域以外的物种(Richa- rdson et al., 2000)。外来种中只有少数会形成入侵和造成危害(Mack et al., 2000)。入侵植物(invasive alien plants)是指能在传入生境中自然生长繁殖并稳步扩展分布区的外来植物 (Richardson et al., 2000; Pyšek et al., 2004)。外来种入侵(生物入侵)不仅使生物多样性降低, 还威胁着全球的生态环境和经济发展(Pimentel et al., 2000, 2005; Rudgers & Orr, 2009)。外来种一旦入侵成功, 要彻底根除往往极为困难, 即使清除成功也往往已造成极大的损失(Zavaleta et al., 2001)。因此, 在引种前对外来植物的入侵性进行分析与判别, 对避免或减少入侵植物的危害是至关重要的(Goodwin et al., 1999)。
什么样的环境容易被入侵和什么样的物种容易形成入侵是生物入侵生态学的两个核心问题 (Alpert et al., 2000; Pyšek et al., 2009)。虽然人们对外来入侵植物的特性已进行了很多的研究, 并发现它们具有某些非入侵植物所不具有的功能性状(Pyšek & Richardson, 2007; Mason et al., 2008; Pyšek et al., 2009), 但目前仍无法对其入侵性进行有效预测(Alpert et al., 2000; Hawkes, 2007; van Kleunen et al., 2010)。
越来越多的研究案例表明, 植物入侵性往往是一系列功能性状和环境因子综合作用的结果(Pyšek & Richardson, 2007; Abhilasha & Joshi, 2009; Dawson et al., 2009), 而且在植物入侵的不同阶段可能对植物功能性状的需求不同(Dawson et al., 2009; Pyšek et al., 2009)。在外来植物引进的初期, 人类活动引起的繁殖体压力(propogule pressure)具有至关重要的作用; 而在植物入侵的中后期, 植物功能性状则发挥更加重要的作用(Dehnen-Schmutz et al., 2007; Flory & Clay, 2009; Pyšek et al., 2009)。因此, 系统地分析植物功能性状对外来植物不同入侵阶段的影响具有十分重要的意义。本文通过综合分析外来植物在入侵过程不同阶段对植物功能性状的需求, 探讨植物入侵性与其功能性状的关系和机理, 并对植物功能性状与入侵性关系的研究热点进行了展望。
1 植物入侵过程中不同阶段的划分
生物入侵的阶段划分一直存在争议, 根据不同的研究目的可以有不同的划分 (Williamson & Fitter, 1996; Liebhold & Bascompte, 2003; Williamson, 2006)。本文将植物入侵过程分为传播到达、定居建群和扩散入侵三个阶段, 分别定义如下:
(1)传播到达阶段: 外来植物在人类有意或无意活动的影响下到达其自然演化区域以外的地区并成活。
(2)定居建群阶段: 外来植物在新地区成活后, 在自然状态下通过与当地生态因子相互作用实现定居和建群。
(3)扩散入侵阶段: 外来植物在新地区定居建群后, 经过或不经过潜伏期, 通过自身繁殖和当地物种的竞争等, 不断扩大分布区造成生物入侵。
2 生长和形态性状
植物的生长和形态性状通过影响植物的传播、定居建群和竞争能力, 进而影响植物的入侵性。这些根、茎、叶等器官的形态性状都可通过影响植物的生理生态特性而影响其入侵性。有研究表明, 入侵植物的个体可能比较大, 但这个结论仅仅在无竞争的环境下成立(Blumenthal & Hufbauer, 2008), 因为有些入侵植物是由于善于传播和占据因干扰而产生的新生态位而实现入侵(Burns & Winn, 2006)。植物相对生长速度(relative growth rates, RGR)是区别入侵植物与非入侵植物的重要性状之一(Grotkopp et al., 2002), 但也不尽然(Bellingham et al., 2004 )。在高养分下具有较高相对生长速度的外来植物容易入侵, 而在低养分下没有这个规律。因此, 单纯的相对生长速度不能有效解释外来种为何能与本地植物有效竞争, 要解释植物入侵性需要考虑更多的植物功能性状(Smith & Knapp, 2001)。
在形态方面, 有的入侵植物的茎具有缠绕特性, 能绞杀本地物种, 例如恶性入侵植物薇甘菊(Mikania micrantha); 有的入侵植物在叶片特征方面能促进其竞争和入侵, 例如较大的比叶面积(specific leaf area, SLA)。虽然单纯的比叶面积不能有效解释外来种能与本地植物有效竞争的原因 (Smith & Knapp, 2001), 但已有研究显示比叶面积与植物入侵性的关系最大(Lake & Leishman, 2004), 整合分析(meta-analysis)也显示入侵植物的比叶面积显著大于非入侵植物(van Kleunen et al., 2009)。
在生物入侵的传播到达阶段, 外来植物主要借助人类活动实现传播。人类有意引进的物种主要受到物种应用价值的影响, 无意引进的物种则主要受到物种隐匿和传播能力的影响, 例如毒麦(Lolium temulentum)通过隐匿在小麦种子中实现传播(李振宇和解焱, 2002)。因此种子的形态性状对某些外来入侵植物的传播具有重要意义。
在定居建群阶段, 植物的生长和形态性状通过影响植物的生存和竞争能力而影响植物的入侵性, 作为植物资源有效利用的重要指标, 比叶面积和相对生长速度可能是外来入侵植物和非入侵植物的重要区别之一(Pyšek et al., 2009; van Kleunen et al., 2009)。在扩散入侵阶段, 植株高度、比叶面积等均具有重要作用, 这些性状都能通过提高植物的竞争能力而提高其入侵性。
3 生理性状
植物的生长、繁殖和竞争等均与其生理性状密切相关, 因此, 植物的生理性状对其适应能力和入侵性具有重要影响。例如, 入侵植物的光合速率高能促使其在竞争和入侵中获胜(郑丽和冯玉龙, 2005; Feng, 2008; Feng et al., 2009)。因为植物光合作用主要受水分和氮含量的限制, 入侵植物的光合系统往往具有较高的水分利用效率和氮利用效率, 使其在与本地种的竞争中处于优势地位(郑丽和冯玉龙, 2005; Feng et al., 2009)。
在植物入侵的不同阶段, 生理性状的影响显著不同。在传播到达阶段, 植物生理性状的影响较小; 在定居建群阶段, 外来植物的生理性状决定了它能否在新生境中生存和繁殖; 在扩散入侵阶段, 外来植物的生理性状决定了它的入侵能力。一般认为植物生理特性和生态抗逆性均对外来植物的入侵性具有重要影响(Ashton & Lerdau, 2008)。但少数研究发现入侵植物的抗逆性未必就强(Garcia-Serrano et al., 2009)。van Kleunen等(2009)通过大量研究案例的整合分析显示, 入侵植物的生理相关指标(如光合速率、呼吸速率、水分利用效率和氮素利用效率等)显著大于非入侵植物。
4繁殖性状
4.1 种子繁殖性状
植物的种子繁殖性状对它的传播、定居建群和竞争能力均具有重要影响, 例如花的形态、颜色与味道、花期、结实率等。自花受精和无融合生殖有利于入侵植物克服阿利效应(Allee effect)而实现入侵(Cheptou, 2007; van Kleunen & Johnson, 2007)。对甘松茅(Nardus stricta)和紫茎泽兰(Eupatorium adenophorum)等入侵植物的研究显示, 通过无融合生殖的方式能产生大量种子,确保入侵植物在缺乏传粉者的情况下实现入侵(鲁萍等, 2005; Kissling et al., 2006)。风媒植物更容易实现入侵, 虫媒植物在到达新分布区后往往由于缺乏合适的传播媒介而影响其入侵能力(Gassó et al., 2009)。因此植物繁殖性状对植物入侵性的影响, 尤其是植物克隆繁殖特性与植物入侵性的关系, 一直受到广泛的关注(Liu et al., 2006)。
花期长短对某些外来植物的入侵性也具有影响, 开花时间较长不但可以积累更多的光合产物以获得更大的定居潜力(colonization potential) (Baker, 1974), 还能与本地种竞争传粉昆虫(Moragues & Traveset, 2005)。但花期较长也会因为繁殖成本高而影响生长, 不利于入侵植物克服恶劣的环境。因此花期长是否有利于入侵会因生境特点和入侵阶段不同而异: 在入侵的初期可能是不利的, 而在入侵的扩散竞争阶段则可能有利于入侵。
种子性状是影响外来植物成功入侵的主要功能性状之一。外来入侵植物的远距离传播主要依靠种子完成(Tiebre et al., 2007)。种子的大小、形态、数量、寿命和传播方式对植物的传播扩散具有直接影响。在传播到达阶段, 种子大小、数量和萌发力对外来植物克服逆境, 适应新的生态环境并形成入侵具有重要作用。一般地, 入侵植物的种子比本地植物的种子更大更多, 这能增强其远距离传播和入侵的能力(Daws et al., 2007; Abhilasha & Joshi, 2009; Dawson et al., 2009)。在入侵的后期, 种子萌发能力与植物的入侵性正相关(Daws et al., 2007; Mason et al., 2008)。入侵植物种子的萌发效率高, 且萌发环境条件要求低, 这是入侵种能够实现入侵的一个重要因素(López-García & Maillet, 2005)。
此外, 种子性状对入侵性的影响还因为种子的传播方式而异, 风媒外来植物中种子小容易入侵, 而以动物为传播媒介的外来植物则是种子较大更容易形成入侵(Dawson et al., 2009)。
在传播到达和定居建群阶段, 种子繁殖性状对于其克服小种群的阿利效应具有重要影响; 而在扩散入侵阶段, 种子繁殖性状的影响因具体的环境而不同。
4.2 克隆繁殖性状
植物的克隆性对异质生境具有独特的适应能力, 主要由于其具有克隆整合、表型可塑、风险分摊、觅食行为和克隆分工等特性(Pyšek, 1997; Yu et al., 2004; 董鸣和于飞海, 2007)。植物入侵种中有相当一部分能够克隆繁殖, 其危害严重性与其克隆生长习性直接相关(Baker, 1974; Liu et al., 2006; Liu et al., 2008)。在入侵植物的建群初期, 种群较小的时候, 克隆繁殖方式可能对它的繁殖保障和克服阿利效应具有重要意义。
有性繁殖能产生新的基因型并通过种子长距离传播占据新生境, 而克隆繁殖则通过分株生长占据新的生境。部分入侵植物以克隆繁殖产生的克隆片段为主要传播方式(Wang et al., 2008), 尤其是湿地入侵植物主要通过克隆繁殖体实现传播(Wang et al., 2008; Okada et al., 2009)。另外, 克隆植物的克隆构型对其入侵性也具有重要的影响, 密集型克隆植物更容易形成入侵和造成危害(Cannas et al., 2003)。
在传播到达阶段, 由于克隆分株往往不能像种子一样远距离的传播 (Pyšek, 1997), 所以, 克隆植物在入侵的传播阶段可能处于劣势。Pyšek(1997)发现, 在欧洲中部的本地植物中, 克隆植物占69.4%, 非克隆植物只占30.6%; 而在外来植物中, 克隆植物只占36.2%, 非克隆植物的比例高达63.8%。外来植物中克隆植物的比例小于本地植物中克隆植物的比例。大尺度区域分布格局研究显示, 中国主要入侵植物中克隆植物和非克隆植物的分布格局没有显著差异(Liu et al., 2005), 这说明克隆繁殖方式对中国入侵植物的远距离传播没有显著影响。
在定居建群和扩散入侵阶段, 克隆性对植物入侵性具有重要贡献。如薇甘菊的茎萌生苗比其种子实生苗的成活率要高, 生长速度也快(胡玉佳和毕培曦, 1994)。克隆性对入侵性的贡献可能主要表现在外来植物到达新入侵地以后, 克隆性能增强外来植物的竞争和适应能力。在缺乏传粉媒介的情况下, 依然能确保其产生大量个体, 保障繁殖和克服阿利效应。
5 表型可塑性
表型可塑性是生物界中普遍存在的现象, 是生物在没有遗传变异的情况下适应环境的一种机制(Bradshaw, 1965; Sultan, 2004)。植物表型可塑性涉及植物的形态特性、生理特性和繁殖特性等。表型可塑性较强的物种具有更强的适应性, 能在更广泛的环境下生长和繁殖(Brock et al., 2005)。对于外来入侵植物而言, 表型可塑性可以通过改变植物的形态、生长、生物量分配和生理特性等来获取资源, 占据生境, 增强其入侵能力(Brock et al., 2005; Richards et al., 2006; Hulme, 2008)。例如, 表型可塑性较强促进了互花米草(Spartina alterniflora)成功入侵(Richards et al., 2005), 使得喜旱莲子草能够在陆地到水域等多种生境形成入侵(Geng et al., 2007)。
植物表型可塑性是预测入侵植物的重要指标, 大约50%的入侵植物的入侵性与其表型可塑性有关(Ren & Zhang, 2009), 因此基于物种的生物学特性建立模型能辅助预测外来种的入侵性(Rejmánek, 2000)。植物表型可塑性对入侵性的影响主要表现在定居建群和扩散入侵阶段, 因为表型可塑性能增强植物对多样环境的耐受性和适应性(Williams et al., 1995), 增强其资源捕获与利用能力, 使之表现出快速生长和繁殖的特性, 提高其竞争力(Prentis et al., 2008)。
6 遗传变异性
在物种入侵的初期, 奠基者效应(founder effect)导致植物遭受繁育及传粉限制, 基因流下降, 稀有等位基因丢失, 发生遗传漂变, 使种群内遗传变异下降, 种群间遗传分化增大(Husband & Barrett, 1991; Amsellem et al., 2000)。案例研究显示入侵物种在入侵过程中会经历严重的遗传多样性丢失(Tsutsui & Case, 2001), 尤其是对高度近交或自交的入侵物种来说(Novak & Mack, 2005)。Dlugosch和Parker(2007)分析了69个入侵物种, 发现等位基因丰富度(allelic richness)呈正态分布, 其中15.5%的物种发生了遗传变异的丢失。
但近来一些研究表明, 有些成功入侵的物种遗传多样性并未下降(Bossdorf et al., 2005; Jahodová et al., 2007; Roman & Darling, 2007)。导致这一现象的机制有多种, 例如有些入侵物种具有多个起源的重复引进(Walker et al., 2003; Koehler-Santos et al., 2006; Jahodová et al., 2007), 有些入侵物种未受到遗传瓶颈的影响(Jahodová et al., 2007), 另外快速进化、漂变与杂交也起了重要作用(Palumbi, 2001; Lavergne & Molofsky, 2007; Jahodová et al., 2007; Barrett et al., 2008)。入侵物种旱雀麦(Bromus tectorum) (Novak & Mack, 2005)、豚草(Ambrosia artemissifolia) (Genton et al., 2005)、薇甘菊(李钧敏等, 2007)、大花金鸡菊(Coreopsis grandiflora) (Liang et al., 2008)、独活(Heracleum mantegazzianum)、翅茎西番莲(Passiflora alata) (Koehler-Santos et al., 2006)等均由于在入侵地具有多个起源, 从而具有较高的遗传多样性(Jahodová et al., 2007)。
遗传多样性对入侵性的贡献主要体现在外来植物定居建群后能促进它对多样环境的适应。较高的遗传多样性有利于形成入侵能力较强的新基因型(Lavergne & Molofsky, 2007; Marrs et al., 2008)。但研究显示, 很多入侵植物, 尤其是具有克隆性的入侵植物的遗传多样性很低(Xu et al., 2003; Ye et al., 2003)。例如, RAPD技术揭示出凤眼莲(Eichhornia crassipes)具有很低的遗传变异, 整个中国的凤眼莲为单一的优势基因型组成的种群(Ren et al., 2005)。喜旱莲子草遗传多样性较低(Wang et al., 2005), 却对陆地到水域等多个生境具有较强的入侵能力。在入侵和扩散的过程中, 如果入侵种具有较强的表型可塑性, 则可能弥补遗传多样性低的不足, 减小对生态型分化的依赖, 从而适应多变的异质生境。另外, 外来植物入侵后的的适应性进化也能增强其入侵性, 导致原产地与入侵地之间的遗传分化(Marrs et al., 2008); 与基因型变异相关的表型可塑性则能消解不同生境带来的适合度的差异, 进一步促进入侵。因此, 无论入侵植物采取哪种策略加速入侵, 只要发生了适应性进化就可以获得各种资源, 占据多样的生境。
7 总结与展望
通过综合分析外来植物在不同入侵阶段对其功能性状的需求, 发现影响外来植物成功入侵的植物功能性状随不同入侵阶段而变化(表1)。在传播到达阶段, 影响外来植物成功入侵的功能性状主要是与种子或者繁殖体有关的性状; 而在定居建群阶段影响植物入侵性的因素是与植物抗逆性和适应性有关的生理性状和繁殖性状; 在扩散入侵阶段影响外来植物入侵性的包括克隆性状、生理性状和表型可塑性等方面, 因为这些性状都会影响植物对环境的适应能力以及与其他物种竞争的能力。
表1 植物功能性状在外来植物不同入侵阶段的贡献
Table 1
| 植物功能性状 Functional traits | 传播到达阶段 Introduction stage | 定居建群阶段 Establishment stage | 扩散入侵阶段 Explosion stage |
|---|---|---|---|
| 生长和形态性状 Traits of growth and morphology | √ | √ | √ |
| 生理性状 Physiological traits | ／ | √ | √ |
| 种子繁殖性状 Propagation traits | √ | √ | √ |
| 克隆繁殖性状 Clonal traits | ／ | √ | √ |
| 表型可塑性 Phenotypic plasticity | * | √ | √ |
| 遗传变异性 Genetic variation | * | ／ | * |
√: 主要作用; ／: 次要作用; *: 无作用或不确定
√ Dominant effect; ／ Subordinate effect; * Uncertain or no effect
虽然植物功能性状对入侵性具有重要影响, 能解释很多外来植物的入侵性, 但对外来植物入侵性的预测还非常有限(Williamson, 2006), 很多性状只能增加实现入侵的可能性, 而难以准确预测其能否入侵(Herron et al., 2007; Pyšek & Richardson, 2007)。环境因素与植物功能性状的互作才能决定植物的入侵性, 因此未来的研究应该更加关注不同环境因素对入侵植物功能性状的影响, 尤其要关注繁殖体压力和引进时间两个因素(Lockwood et al., 2005; Thuiller et al., 2006; Pyšek et al., 2009)。在物种功能性状的比较研究中需要排除繁殖体压力和引进时间等因素的影响, 并结合植物的入侵阶段和具体环境因子, 才有可能找到决定外来植物入侵的关键性状。
虽然入侵植物功能性状的研究存在很多困难, 但其研究结果对外来入侵种的早期预测、及时防治与潜在危害的风险评估具有重要作用。以下四个方面的深入研究有望最终揭示影响植物入侵性的功能性状: (1)外来入侵种的生物地理学研究; (2)外来入侵种与本地近缘种的比较研究; (3)外来入侵种与外来非入侵种的比较研究; (4)案例研究的整合分析(meta-analysis)。
参考文献
Enhanced fitness due to higher fecundity, increased defence against a specialist and tolerance towards a generalist herbivore in an invasive annual plant
Invasiveness, invasibility, and the role of environmental stress in preventing the spread of non-native plants
Comparison of genetic diversity of the invasive weed Rubus alceifolius Poir. (Rosaceae) in its native range and in areas of introduction, using amplified fragment length polymorphism (AFLP) markers
DOI:10.1046/j.1365-294x.2000.00876.x
URL
PMID:10736047
[本文引用: 1]
Theory predicts that colonization of new areas will be associated with population bottlenecks that reduce within-population genetic diversity and increase genetic differentiation among populations. This should be especially true for weedy plant species, which are often characterized by self-compatible breeding systems and vegetative propagation. To test this prediction, and to evaluate alternative scenarios for the history of introduction, the genetic diversity of Rubus alceifolius was studied with amplified fragment length polymorphism (AFLP) markers in its native range in southeast Asia and in several areas where this plant has been introduced and is now a serious weed (Indian Ocean islands, Australia). In its native range, R. alceifolius showed great genetic variability within populations and among geographically close populations (populations sampled ranging from northern Vietnam to Java). In Madagascar, genetic variability was somewhat lower than in its native range, but still considerable. Each population sampled in the other Indian Ocean islands (Mayotte, La Reunion, Mauritius) was characterized by a single different genotype of R. alceifolius for the markers studied, and closely related to individuals from Madagascar. Queensland populations also included only a single genotype, identical to that found in Mauritius. These results suggest that R. alceifolius was first introduced into Madagascar, perhaps on multiple occasions, and that Madagascan individuals were the immediate source of plants that colonized other areas of introduction. Successive nested founder events appear to have resulted in cumulative reduction in genetic diversity. Possible explanations for the monoclonality of R. alceifolius in many areas of introduction are discussed.
Tolerance to herbivory, and not resistance, may explain differential success of invasive, naturalized, and native North American temperate vines
Plant reproductive systems and evolution during biological invasion
Seedling growth rate and survival do not predict invasiveness in naturalized woody plants in New Zealand
Increased plant size in exotic populations: a common-garden test with 14 invasive species
Phenotypic and genetic differentiation between native and introduced plant populations
DOI:10.1007/s00442-005-0070-z
URL
PMID:15891837
[本文引用: 1]
Plant invasions often involve rapid evolutionary change. Founder effects, hybridization, and adaptation to novel environments cause genetic differentiation between native and introduced populations and may contribute to the success of invaders. An influential idea in this context has been the Evolution of Increased Competitive Ability (EICA) hypothesis. It proposes that after enemy release plants rapidly evolve to be less defended but more competitive, thereby increasing plant vigour in introduced populations. To detect evolutionary change in invaders, comparative studies of native versus introduced populations are needed. Here, we review the current empirical evidence from: (1) comparisons of phenotypic variation in natural populations; (2) comparisons of molecular variation with neutral genetic markers; (3) comparisons of quantitative genetic variation in a common environment; and (4) comparisons of phenotypic plasticity across different environments. Field data suggest that increased vigour and reduced herbivory are common in introduced plant populations. In molecular studies, the genetic diversity of introduced populations was not consistently different from that of native populations. Multiple introductions of invasive plants appear to be the rule rather than the exception. In tests of the EICA hypothesis in a common environment, several found increased growth or decreased resistance in introduced populations. However, few provided a full test of the EICA hypothesis by addressing growth and defence in the same species. Overall, there is reasonable empirical evidence to suggest that genetic differentiation through rapid evolutionary change is important in plant invasions. We discuss conceptual and methodological issues associated with cross-continental comparisons and make recommendations for future research. When testing for EICA, greater emphasis should be put on competitive ability and plant tolerance. Moreover, it is important to address evolutionary change in characteristics other than defence and growth that could play a role in plant invasions.
Evolutionary significance of phenotypic plasticity in plants
A comparison of phenotypic plasticity in the native dandelion Taraxacum ceratophorum and its invasive congener T. officinale
A comparison of plastic responses to competition by invasive and non-invasive congeners in the Commelinaceae
Modelling biological invasions: species traits, species interactions, and habitat heterogeneity
DOI:10.1016/s0025-5564(02)00213-4
URL
PMID:12604137
[本文引用: 1]
In this paper we explore the integration of different factors to understand, predict and control ecological invasions, through a general cellular automaton model especially developed. The model includes life history traits of several species in a modular structure interacting multiple cellular automata. We performed simulations using field values corresponding to the exotic Gleditsia triacanthos and native co-dominant trees in a montane area. Presence of G. triacanthos juvenile bank was a determinant condition for invasion success. Main parameters influencing invasion velocity were mean seed dispersal distance and minimum reproductive age. Seed production had a small influence on the invasion velocity. Velocities predicted by the model agreed well with estimations from field data. Values of population density predicted matched field values closely. The modular structure of the model, the explicit interaction between the invader and the native species, and the simplicity of parameters and transition rules are novel features of the model.
Allee effect and self-fertilization in hermaphrodites: reproductive assurance in demographically stable populations
Do invasive species have bigger seeds? Evidence from intra- and inter-specific comparisons
Factors explaining alien plant invasion success in a tropical ecosystem differ at each stage of invasion
A century of the ornamental plant trade and its impact on invasion success
Founding events in species invasions: genetic variation, adaptive evolution, and the role of multiple introductions
DOI:10.1111/j.1365-294X.2007.03538.x
URL
PMID:17908213
[本文引用: 1]
Invasive species are predicted to suffer from reductions in genetic diversity during founding events, reducing adaptive potential. Integrating evidence from two literature reviews and two case studies, we address the following questions: How much genetic diversity is lost in invasions? Do multiple introductions ameliorate this loss? Is there evidence for loss of diversity in quantitative traits? Do invaders that have experienced strong bottlenecks show adaptive evolution? How do multiple introductions influence adaptation on a landscape scale? We reviewed studies of 80 species of animals, plants, and fungi that quantified nuclear molecular diversity within introduced and source populations. Overall, there were significant losses of both allelic richness and heterozygosity in introduced populations, and large gains in diversity were rare. Evidence for multiple introductions was associated with increased diversity, and allelic variation appeared to increase over long timescales (~100 years), suggesting a role for gene flow in augmenting diversity over the long-term. We then reviewed the literature on quantitative trait diversity and found that broad-sense variation rarely declines in introductions, but direct comparisons of additive variance were lacking. Our studies of Hypericum canariense invasions illustrate how populations with diminished diversity may still evolve rapidly. Given the prevalence of genetic bottlenecks in successful invading populations and the potential for adaptive evolution in quantitative traits, we suggest that the disadvantages associated with founding events may have been overstated. However, our work on the successful invader Verbascum thapsus illustrates how multiple introductions may take time to commingle, instead persisting as a 'mosaic of maladaptation' where traits are not distributed in a pattern consistent with adaptation. We conclude that management limiting gene flow among introduced populations may reduce adaptive potential but is unlikely to prevent expansion or the evolution of novel invasive behaviour.
The terminology and conception of clonal plant ecology
Photosynthesis, nitrogen allocation and specific leaf area in invasive Eupatorium adenophorum and native Eupatorium japonicum grown at different irradiances
DOI:10.1111/j.1399-3054.2008.01072.x
URL
PMID:18312498
[本文引用: 1]
The mechanisms underlying biological invasions are still not well elucidated. In this study, ecophysiological traits of invasive Eupatorium adenophorum and native E. japonicum were compared at 10 irradiances in field. I hypothesized that the invader may allocate a higher fraction of leaf nitrogen (N) to photosynthesis and have higher light-saturated photosynthetic rate (P(max)) and specific leaf area (SLA) than E. japonicum. The invader had a significantly higher ability to acclimate to high irradiance than E. japonicum, while it showed a similar shade-tolerant ability. The invader indeed allocated a higher fraction of leaf N to photosynthesis than E. japonicum, which, with its high leaf N content (N(A)), resulted in a higher N content in photosynthesis (N(P)), contributing to its higher biochemical capacity for photosynthesis and P(max). However, the invader had a significantly lower SLA than E. japonicum, contributing to its higher P(max) but increasing its area-based leaf construction cost. The abilities to acclimate to a wider range of irradiance and to allocate a higher fraction of leaf N to photosynthesis, and the higher P(max), N(A), N(P) and leaf area ratio may contribute to the invasion of the invader. High SLA is not always necessary for invasive species.
Evolutionary tradeoffs for nitrogen allocation to photosynthesis versus cell walls in an invasive plant
Effects of roads and forest successional age on experimental plant invasions
Physiological comparison of alien Senecio inaequidens and S. pterophorus and native S. malacitanus: implications for invasion
Exploring species attributes and site characteristics to assess plant invasions in Spain
DOI:10.1111/ddi.2009.15.issue-1 URL [本文引用: 1]
Phenotypic plasticity rather than locally adapted ecotypes allows the invasive alligator weed to colonize a wide range of habitats
DOI:10.1007/s10530-006-9029-1
URL
[本文引用: 1]
Both phenotypic plasticity and locally adapted ecotypes may contribute to the success of invasive species in a wide range of habitats. Here, we conducted common garden experiments and molecular marker analysis to test the two alternative hypotheses in invasive alligator weed (Alternanthera philoxeroides), which colonizes both aquatic and terrestrial habitats. Ninety individuals from three pairs of aquatic versus terrestrial populations across southern China were analyzed, using inter simple sequence repeat (ISSR) marker, to examine population differentiation in neutral loci. Two common gardens simulating aquatic and terrestrial habitats were set up to examine population differentiation in quantitative traits. We found no evidence of population differentiation in both neutral loci and quantitative traits. Most individuals shared the same ISSR genotype. Meanwhile, plants from different habitats showed similar reaction norms across the two common gardens. In particular, plants allocated much more biomass to the belowground roots in the terrestrial environment, where alligator weed may lose part or all of the aboveground shoots because of periodical or accidental disturbances, than those in the aquatic environment. The combined evidence from molecular marker analysis and common garden experiments support the plasticity hypothesis rather than the ecotype hypothesis in explaining the adaptation of alligator weed in a wide range of habitats.]]>
High genetic diversity in French invasive populations of common ragweed, Ambrosia artemisiifolia, as a result of multiple sources of introduction
DOI:10.1111/j.1365-294X.2005.02750.x
URL
PMID:16313592
[本文引用: 1]
Ambrosia artemisiifolia is an aggressive North American annual weed, found particularly in sunflower and corn fields. Besides its economic impact on crop yield, it represents a major health problem because of its strongly allergenic pollen. Ragweed was imported inadvertently to Europe in the 18th century and has become invasive in several countries, notably in the Rhone Valley of France. It has recently expanded in both the Provence-Alpes-Cote-d'Azur and Bourgogne regions. As first steps towards understanding the causes and mechanisms of ragweed invasion, genetic variability of French and North American populations was analysed using microsatellites. Overall genetic variability was similar in North America and in the Rhone-Alpes region, but within-population levels of genetic variability were surprisingly lower in native than in invasive French populations. French populations also exhibited lower among-population differentiation. A significant pattern of isolation by distance was detected among North American populations but not among French populations. Assignment tests and distribution of rare alleles did not point to a single origin for all French populations, nor for all individuals within populations and private alleles from different North American populations were found in the same French populations. Indeed, within all French populations, individual plants were roughly equally assigned to the different North American populations. Altogether, these results suggest that the French invasive populations include plants from a mixture of sources. Reduced diversity in populations distant from the original area of introduction indicated that ragweed range expansion probably occurred through sequential bottlenecks from the original populations, and not from subsequent new introductions.
Predicting invasiveness of plant species based on biological information
Toward a causal explanation of plant invasiveness: seedling growth and life-history strategies of 29 pine ( Pinus) species
DOI:10.1086/338995
URL
PMID:18707424
[本文引用: 1]
We studied 29 pine (Pinus) species to test the hypothesis that invasive species in disturbed habitats have distinct attributes. Seedling relative growth rate (RGR) and measures of invasiveness were positively associated across species as well as within phylogenetically independent contrasts. High RGR, small seed masses, and short generation times characterize pine species that are successful invaders in disturbed habitats. Discriminant analysis and logistic regression revealed that RGR was the most significant factor among these life-history traits separating invasive and noninvasive species. We also explored the causes of differences in RGR among invasive and noninvasive species. While net assimilation rate, leaf mass ratio, and specific leaf area (SLA) were all found to be contributing positively to RGR, SLA was found to be the main component responsible for differences in RGR between invasive and noninvasive pines. We investigated differences in SLA further by studying leaf anatomy, leaf density, and leaf thickness. We also evaluated relative leaf production rate as an important aspect of SLA. We proposed a hypothetical causal network of all relevant variables.
Are invaders moving targets? The generality and persistence of advantages in size, reproduction, and enemy release in invasive plant species with time since introduction
Invasive plants and their ecological strategies: prediction and explanation of woody plant invasion in New England
A study on life cycle and response to herbicides of Mikania micrantha
Phenotypic plasticity and plant invasions: is it all jack?
DOI:10.1111/j.1365-2435.2007.01369.x URL [本文引用: 1]
Colonisation history and population genetic structure of Eichornia paniculata in Jamaica
Invasive species of Heracleum in Europe: an insight into genetic relationships and invasion history
Agamospermous seed production of the invasive tussock grass Nardus stricta L. (Poaceae) in New Zealand: evidence from pollination experiments
Molecular genetic variation in Passiflora alata (Passifloraceae), an invasive species in southern Brazil
Invasion success of exotic plants in natural ecosystems: the role of disturbance, plant attributes and freedom from herbivores
Increased genetic variation and evolutionary potential drive the success of an invasive grass
Population genetic differentiations in the invasive plant Mikania micrantha in China
Genetic diversity of the invasive plant Coreopsis grandiflora at different altitudes in Laoshan Mountain, China
The Allee effect, stochastic dynamics and the eradication of alien species
Invasive alien plants in China: role of clonality and geographical origin
Effects of clonal integration on photosynthesis of the invasive clonal plant Alternanthera philoxeroides
Invasive alien plant species in China: regional distribution patterns
The role of propagule pressure in explaining species invasions
DOI:10.1016/j.tree.2005.02.004
URL
PMID:16701373
[本文引用: 1]
Human-mediated species invasions are a significant component of current global environmental change. There is every indication that the rate at which locations are accumulating non-native species is accelerating as free trade and globalization advance. Thus, the need to incorporate predictive models in the assessment of invasion risk has become acute. However, finding elements of the invasion process that provide consistent explanatory power has proved elusive. Here, we propose propagule pressure as a key element to understanding why some introduced populations fail to establish whereas others succeed. In the process, we illustrate how the study of propagule pressure can provide an opportunity to tie together disparate research agendas within invasion ecology.
Biological characteristics of an invasive South African species
Progress and prospects in research of exotic invasive species, Eupatorium adenophorum
Biotic invasions: causes, epidemiology, global consequences, and control
When invasion increases population genetic structure: a study with Centaurea diffusa
Reproductive output of invasive versus native plants
Effect of Carpobrotus spp. on the pollination success of native plant species of the Balearic Islands
Predicting the distribution of the invasive alien Heracleum mantegazzianum at two different spatial scales
Clonal spread of invasive Ludwigia hexapetala and L. grandiflora in freshwater wetlands of California
Humans as the world’s greatest evolutionary force
Environmental and economic costs of non-indigenous species in the United States
Update on the environmental and economic costs associated with alien-invasive species in the United States
Adaptive evolution in invasive species
DOI:10.1016/j.tplants.2008.03.004
URL
PMID:18467157
[本文引用: 1]
Many emerging invasive species display evidence of rapid adaptation. Contemporary genetic studies demonstrate that adaptation to novel environments can occur within 20 generations or less, indicating that evolutionary processes can influence invasiveness. However, the source of genetic or epigenetic variation underlying these changes remains uncharacterised. Here, we review the potential for rapid adaptation from standing genetic variation and from new mutations, and examine four types of evolutionary change that might promote or constrain rapid adaptation during the invasion process. Understanding the source of variation that contributes to adaptive evolution in invasive plants is important for predicting future invasion scenarios, identifying candidate genes involved in invasiveness, and, more generally, for understanding how populations can evolve rapidly in response to novel and changing environments.
Planting intensity, residence time, and species traits determine invasion success of alien woody species
DOI:10.1890/08-0857.1
URL
PMID:19886483
[本文引用: 6]
We studied the relative importance of residence time, propagule pressure, and species traits in three stages of invasion of alien woody plants cultivated for about 150 years in the Czech Republic, Central Europe. The probability of escape from cultivation, naturalization, and invasion was assessed using classification trees. We compared 109 escaped-not-escaped congeneric pairs, 44 naturalized-not-naturalized, and 17 invasive-not-invasive congeneric pairs. We used the following predictors of the above probabilities: date of introduction to the target region as a measure of residence time; intensity of planting in the target area as a proxy for propagule pressure; the area of origin; and 21 species-specific biological and ecological traits. The misclassification rates of the naturalization and invasion model were low, at 19.3% and 11.8%, respectively, indicating that the variables used included the major determinants of these processes. The probability of escape increased with residence time in the Czech Republic, whereas the probability of naturalization increased with the residence time in Europe. This indicates that some species were already adapted to local conditions when introduced to the Czech Republic. Apart from residence time, the probability of escape depends on planting intensity (propagule pressure), and that of naturalization on the area of origin and fruit size; it is lower for species from Asia and those with small fruits. The probability of invasion is determined by a long residence time and the ability to tolerate low temperatures. These results indicate that a simple suite of factors determines, with a high probability, the invasion success of alien woody plants, and that the relative role of biological traits and other factors is stage dependent. High levels of propagule pressure as a result of planting lead to woody species eventually escaping from cultivation, regardless of biological traits. However, the biological traits play a role in later stages of invasion.
Traits associated with invasiveness in alien plants: where do we stand?
Alien plants in checklists and floras: towards better communication between taxonomists and ecologists
Invasive plants: approaches and predictions
The relative generality of plant invasion mechanisms and predicting future invasive plants
Random amplified polymorphic DNA markers reveal low genetic variation and a single dominant genotype in Eichhornia crassipes populations throughout China
Jack of all trades, master of some? On the role of phenotypic plasticity in plant invasions
DOI:10.1111/j.1461-0248.2006.00950.x
URL
PMID:16913942
[本文引用: 1]
Invasion biologists often suggest that phenotypic plasticity plays an important role in successful plant invasions. Assuming that plasticity enhances ecological niche breadth and therefore confers a fitness advantage, recent studies have posed two main hypotheses: (1) invasive species are more plastic than non-invasive or native ones; (2) populations in the introduced range of an invasive species have evolved greater plasticity than populations in the native range. These two hypotheses largely reflect the disparate interests of ecologists and evolutionary biologists. Because these sciences are typically interested in different temporal and spatial scales, we describe what is required to assess phenotypic plasticity at different levels. We explore the inevitable tradeoffs of experiments conducted at the genotype vs. species level, outline components of experimental design required to identify plasticity at different levels, and review some examples from the recent literature. Moreover, we suggest that a successful invader may benefit from plasticity as either (1) a Jack-of-all-trades, better able to maintain fitness in unfavourable environments; (2) a Master-of-some, better able to increase fitness in favourable environments; or (3) a Jack-and-master that combines some level of both abilities. This new framework can be applied when testing both ecological or evolutionary oriented hypotheses, and therefore promises to bridge the gap between the two perspectives.
Habitat range and phenotypic variation in salt marsh plants
Naturalization and invasion of alien plants: concepts and definitions
Paradox lost: genetic diversity and the success of aquatic invasions
Non-native grass alters growth of native tree species via leaf and soil microbes
Physiological and morphological traits of exotic, invasive exotic, and native plant species in tallgrass prairie
Promising directions in plant phenotypic plasticity
Interactions between environment, species traits and human uses describe patterns of plant invasions
Hybridization and sexual reproduction in the invasive alien Fallopia (Polygonaceae) complex in Belgium
Population genetics and colony structure of the argentine ant (Linepithema humile) in its native and introduced ranges
Are invaders different? A conceptual framework of comparative approaches for assessing determinants of invasiveness
South African Iridaceae with rapid and profuse seedling emergence are more likely to become naturalized in other regions
A meta-analysis of trait differences between invasive and non-invasive plant species
DOI:10.1111/j.1461-0248.2009.01418.x
URL
PMID:20002494
[本文引用: 3]
A major aim in ecology is identifying determinants of invasiveness. We performed a meta-analysis of 117 field or experimental-garden studies that measured pair-wise trait differences of a total of 125 invasive and 196 non-invasive plant species in the invasive range of the invasive species. We tested whether invasiveness is associated with performance-related traits (physiology, leaf-area allocation, shoot allocation, growth rate, size and fitness), and whether such associations depend on type of study and on biogeographical or biological factors. Overall, invasive species had significantly higher values than non-invasive species for all six trait categories. More trait differences were significant for invasive vs. native comparisons than for invasive vs. non-invasive alien comparisons. Moreover, for comparisons between invasive species and native species that themselves are invasive elsewhere, no trait differences were significant. Differences in physiology and growth rate were larger in tropical regions than in temperate regions. Trait differences did not depend on whether the invasive alien species originates from Europe, nor did they depend on the test environment. We conclude that invasive alien species had higher values for those traits related to performance than non-invasive species. This suggests that it might become possible to predict future plant invasions from species traits.
Population genetics of an invasive species, Heracleum mantegazzianum: implications for the role of life history, demographics and independent introductions
Genetic diversity of Alternanthera philoxeroides in China
Clonal integration supports the expansion from terrestrial to aquatic environments of the amphibious stoloniferous herb Alternanthera philoxeroides
Ecophysiology of introduced Pennisetum setaceum on Hawaii: the role of phenotypic plasticity
Explaining and predicting the success of invading species at different stages of invasion
The characters of successful invaders
Genetic diversity of alligator weed in China by RAPD analysis
Genetic uniformity of Alternanthera philoxeroides in south China
Clonal integration helps Psammochloa villosa survive sand burial in an inland dune
Viewing invasive species removal in a whole-ecosystem context
The effects of ecophysiological traits on carbon gain in invasive plants
