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

由于各种干扰，水生生态系统正在经历前所未有的变化。最严重的后果之一是生物多样性的下降，这往往会导致物种相互作用、能量流动和生物质生产发生变化。虽然我们通常对环境应激源对个别物种的直接影响有很好的了解，但我们通常对社区一级的影响了解很少，因为间接影响发生在当地和区域范围内。如果在新的条件下生存和繁殖受到损害，敏感物种或基因类型可能会被根除。其他物种/基因类型可能能够适应变化的环境条件，如果有个人的特征使他们能够在新的环境中茁壮成长。这些人可能已经出现在当地环境中，或者他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，生物在生境之间的移动可以塑造当地的群落组成。然而，影响当地进程与扩散的相对重要性的因素并未得到很好的理解，尤其是对于面临环境变化的社区。例如，如果当地社区迅速适应新的条件并垄断资源，高度的当地多样性可能会减少来自区域物种池的分散者的影响，从而阻止到达物种的建立。或者，干扰可能会降低局部物种的丰度，降低物种相互作用的强度，并促进分散物种的建立。最后，到达物种的数量、频率和多样性可能会影响它们建立的能力。*了解群落反应的挑战与广泛的水生应激源有关，但区域钙含量下降可以说是加拿大盾上数千个湖泊面临的最紧迫但研究不足的威胁之一。与伐木相关的区域性酸化和生物量转移导致土壤和水体缺钙。湖泊中主要富含钙的食草动物的减少与水中钙浓度的降低有关。尽管如此，旨在了解低钙浓度对社区水平影响的研究很少。*我建议使用实验室和田间实验相结合的方法来解决以下问题：1)是否有证据表明局部适应对环境变化的反应？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)扩散特征如何可能影响来自区域种库的物种将在局部干扰环境中建立？对于提案的第四部分，我们将确定评估在我们的实验中揭示的机制使用景观规模的物种分布解释自然界模式的程度。*这项研究将使加拿大受益，因为它将增加我们对社区对环境变化的反应的了解，特别是钙浓度的广泛下降。这些信息将引导湖泊管理者和政策制定者将重点放在保护当地生物多样性的湖泊具体行动或维护区域多样性和湖泊连通性的区域规模的努力上。4名博士、1名硕士和至少13名理科学生将接受野外生物学、实验设计、统计分析和交流方面的培训。这些技能在环境领域备受追捧，但也会转移到其他需要批判性思维、量化技能、沟通和强大领导力的职业。

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.