Abstract

Invasive plants are ubiquitous features of many wetland systems, resulting in impacts that are extremely costly in both economic and ecological terms. Approximately twenty years ago, these impacts and many of the mechanisms underlying invasion were crystallized in a pair of now-classic review papers on the topic. These two contributions have guided substantial research efforts over the past two decades. Here, using a state-of-the-art review, we present an overview of research progress from the past 20 years and identify research priorities for the next 20 years. We structure these insights around key themes that emerge from those earlier reviews and emphasize ways wetland invasions might be distinguished from plant invasions in uplands. We first highlight research progress and priorities around the impacts of wetland plant invasions. We then do the same for seven broad mechanisms that have been postulated to enhance invasion success in wetlands. Invasive plants clearly impact wetlands across all levels of ecological organization and up to landscape scales, but generalizable conclusions are still lacking concerning what drives variation in impact magnitudes. One of the key mechanisms underlying invasion success reflects site-level variation in resource availability and, although we know that increased resources often lead to more opportunities for invasion, the role of discrete resource pulses and the way resource availability may interact with propagule pressure variability are poorly understood. Second, although release from natural enemies is a long-held potential driver of invasion success, recent insights support speculation that these effects may be especially pronounced in wetlands. Third, although most invasive wetland plants are considered good competitors, their simultaneous role as stress tolerators raises questions about whether expectations regarding life history tradeoffs may be less applicable for wetland invaders than for the upland species around which these theories were designed. Fourth, despite a keen understanding that wetland plant invaders are opportunistic, establishing quickly in response to disturbance, the central importance of seed and seedling traits has not been adequately studied to integrate life history theory across ontogenetic stages. Fifth, although many invasive wetland plants reproduce both sexually and asexually, the extent to which this mixed strategy contributes to their success as invaders has not been rigorously assessed. Sixth, despite observations that wetland invaders often exhibit a high degree of phenotypic variability, causal connections between the success of wetland invaders and either high population genetic diversity or high phenotypic plasticity have not been clearly established. Lastly, despite long-standing interests in whether interspecific hybridization contributes to wetland invader success, recent studies have highlighted evolutionary processes leading to variation in polyploidy and genome size as alternatives requiring additional study. We conclude with a vision for prioritizing wetland plant invasions research, presenting insights from this review aimed at inspiring future studies on remaining key uncertainties regarding the relative impacts of wetland vs. upland invaders and the relative importance of phenotypic plasticity, population genetic diversity, enemy release, and anthropogenic disturbances for influencing the success of invasive plants in wetland vs. upland systems.

摘要

入侵植物是许多湿地系统普遍存在的特征，造成的影响在经济和生态方面都极其昂贵。大约二十年前，这些影响和许多入侵背后的机制在两篇关于该主题的现在经典的评论论文中得到了具体体现。这两项贡献指导了过去二十年的大量研究工作。在这里，我们利用最先进的综述，概述了过去 20 年的研究进展，并确定了未来 20 年的研究重点。我们围绕早期评论中出现的关键主题构建这些见解，并强调湿地入侵与高地植物入侵的区别方式。我们首先强调有关湿地植物入侵影响的研究进展和优先事项。然后，我们对被假设可以提高湿地入侵成功率的七种广泛机制进行同样的操作。入侵植物显然对湿地的生态组织各个层面和景观尺度都有影响，但关于影响程度变化的原因仍然缺乏普遍的结论。入侵成功的关键机制之一反映了资源可用性的站点水平变化，尽管我们知道增加的资源通常会导致更多的入侵机会，但离散资源脉冲的作用以及资源可用性与繁殖体压力变化相互作用的方式是不太了解。其次，尽管释放天敌是入侵成功的一个长期潜在驱动力，最近的研究结果支持这样的推测：这些影响在湿地中可能尤其明显。第三，尽管大多数入侵湿地植物被认为是良好的竞争者，但它们同时作为胁迫耐受者的角色引发了这样的问题：关于生活史权衡的期望是否可能不太适用于湿地入侵者，而不是这些理论所围绕的高地物种。第四，尽管人们深刻地认识到湿地植物入侵者是机会主义的，能够快速应对干扰，但种子和幼苗性状的核心重要性尚未得到充分研究，无法将生命史理论整合到个体发生阶段。第五，尽管许多入侵湿地植物都进行有性和无性繁殖，这种混合战略在多大程度上有助于他们作为入侵者的成功，这一点尚未得到严格评估。第六，尽管观察到湿地入侵者经常表现出高度的表型变异性，但湿地入侵者的成功与高种群遗传多样性或高表型可塑性之间的因果关系尚未明确建立。最后，尽管人们长期以来对种间杂交是否有助于湿地入侵者的成功感兴趣，但最近的研究强调了导致多倍体和基因组大小变化的进化过程，作为需要进一步研究的替代方案。最后，我们提出了优先考虑湿地植物入侵研究的愿景，