Community response to environmental change: the role of dispersal, local adaptation, and species interactions

由于各种各样的干扰，水生生态系统正在经历前所未有的变化。最严重的影响之一是生物多样性的下降，这往往导致物种相互作用、能量流动和生物量生产的改变。虽然我们通常对环境压力源对单个物种的直接影响有很好的了解，但由于在局部和区域尺度上都有间接影响，我们对社区水平的影响的了解通常很差。如果在新的条件下生存和繁殖受到损害，敏感的物种或基因型可能会被消灭。其他物种/基因型可能能够适应改变的环境条件，如果有个体的特征使他们能够在新环境中蓬勃发展。这些个体可能已经存在于当地环境中，或者它们可能来自该地区的其他栖息地。*在过去的几十年里，生态学家已经认识到生物在栖息地之间的移动可以塑造当地群落的组成。然而，影响本地过程相对于扩散的相对重要性的因素尚未得到很好的理解，特别是对于面临环境变化的社区。例如，如果当地群落迅速适应新的条件并垄断资源，那么高的本地多样性可能会减少来自区域物种库的分散者的影响，从而阻止到达物种的建立。或者，干扰可能降低局部丰度，降低物种相互作用的强度，促进分散物种的建立。最后，到达的物种的数量、频率和多样性可能会影响它们的建立能力。*了解社区反应的挑战与广泛的水生压力源有关，但区域钙含量下降可以说是加拿大地盾上数千个湖泊面临的最紧迫但尚未得到充分研究的威胁之一。与伐木有关的区域酸化和生物质的去除导致了土壤和水体的缺钙。湖泊中主要富钙食草动物数量的减少与水中钙浓度的降低有关。尽管如此，仍缺乏旨在了解低钙浓度对社区水平影响的研究。*我建议使用实验室和实地实验相结合的方法来解决以下问题：1)是否有证据表明地方适应环境变化？2)环境变化如何影响物种相互作用（竞争和捕食）的强度以及随后区域分散者的建立？3)区域物种库中的物种在局部扰动环境中可能建立的扩散特征如何影响？对于提案的第四个组成部分，我们将确定评估在我们的实验中揭示的机制在多大程度上利用景观尺度的物种分布来解释自然界的模式。*这项研究将增加我们对社区对环境变化的反应的理解，特别是对钙浓度广泛下降的理解，从而使加拿大受益。这些信息将引导湖泊管理者和决策者将重点放在保护当地生物多样性的具体湖泊行动或维持区域多样性和湖泊连通性的区域尺度努力上。四名博士、一名硕士和至少13名理学士将接受野外生物学、实验设计、统计分析和通信方面的培训。这些都是环境领域急需的技能，但也可以转移到其他需要批判性思维、定量分析能力、沟通能力和强大领导能力的职业中。

Aquatic ecosystems are experiencing unprecedented change owing to a wide range of disturbances. One of the most serious repercussions is a decline in biodiversity, which often results in altered species interactions, energy flow, and biomass production. While we often have a good understanding of direct effects of environmental stressors on individual species, we have a generally poor understanding of the community-level effects because of indirect effects occurring at both a local and regional scale. Sensitive species or genotypes may be extirpated if survival and reproduction is impaired under the new conditions. Other species/genotypes may be able to adapt to altered environmental conditions if there are individuals with traits enabling them to flourish in the new environment. These individuals may already be present in the local environment or they may arrive from other habitats in the region. *Over the past several decades, ecologists have recognized that the movement of organisms between habitats can shape local community composition. However, factors that influence the relative importance of local processes versus dispersal are not well understood, particularly for communities facing environmental change. For example, high local diversity may reduce the influence of dispersers from the regional species pool if local communities quickly adapt to the new conditions and monopolize resources, thereby preventing the establishment of arriving species. Alternatively, the disturbance may reduce local abundances, lessening the intensity of species interactions and facilitating establishment of dispersing species. Finally, the number, frequency, and diversity of arriving species may influence their ability to establish.*The challenge of understanding community response is relevant to a wide range of aquatic stressors, but regional calcium-decline is arguably one of the most pressing but understudied threats facing thousands of lakes on the Canadian Shield. Regional acidification and biomass removal associated with logging have resulted in calcium-depleted soils and water bodies. Declines in key calcium-rich herbivores in lakes have been linked with reduced aqueous calcium concentrations. Despite this, there is a paucity of studies aimed at understanding community-level effects of low calcium concentrations.*I propose to use a combination of laboratory and field experiments to address the following questions: 1) Is there evidence of local adaptation in response to environmental change? 2) How does environmental change influence the strength of species interactions (competition & predation) and subsequent establishment of regional dispersers? and 3) How do characteristics of dispersal influence probably that species from the regional species pool will establish in local disturbed environments? For the fourth component of the proposal, we will determine evaluate the extent to which mechanisms revealed in our experiments explain patterns in nature using landscape-scale species distributions. *This research will benefit Canada by increasing our understanding of community response to environmental change, in particular, wide spread decline of calcium concentration. This information will direct the focus of lake managers and policy-makers to lake-specific actions for preserving local biodiversity or regional-scale efforts for maintaining regional diversity and lake-connectivity. Four PhD, 1 MSc, and at least 13 BSc students will be trained in field biology, experimental design, statistical analyses, and communication. These are highly sought skills in environmental fields, but also transfer to other careers that require critical thinking, quantitative skills, communication, and strong leadership.