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

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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.