Stressor response and spatial dynamics of mountain lake communities

• Author / Creator

  Loewen, Charlie J

• Multiple novel and rapidly changing environmental factors (i.e. anthropogenic stressors) are increasingly affecting ecological communities, and their functional roles in ecosystems. Consequently, freshwater biodiversity has declined worldwide; however, the functional impacts of this loss should be contingent upon local species’ traits and the potential for tolerant species to compensate for sensitive taxa. In a metacommunity (i.e. a set of local communities connected regionally by species dispersal) context, stressor resistance may further depend on the arrival of stress-tolerant colonists from the regional species pool. My research, in collaboration with international colleagues, combines quantitative literature review, a manipulative field experiment, and innovative multivariate analyses of continental-scale observational data to address scientific knowledge gaps concerning the impacts of multiple stressors on freshwater communities. First, a meta-analytic approach was used to assess the tendency for freshwater stressors to interact by comparing the independent and combined effects of paired stressors across 286 experimental responses from 88 published articles. The nature of multiple stressor interactions is a key source of uncertainty for conservation practitioners, as co-occurring stressors may generate unanticipated non-additive interactions (i.e. ecological surprises) that either dampen or amplify their individual direct effects. Net impacts of stressors varied, but were less than expected (i.e. antagonistic) overall, indicating a potentially high degree of co-adaptation to stressors within freshwater ecosystems. Further, aggregate functional properties of communities were less sensitive than biodiversity, suggesting that compensation by stress-tolerant species may frequently lessen the functional consequences of co-occurring environmental changes. Among the greatest threats to freshwater ecosystems are climate change and biological invasions. There is also growing evidence to suggest that cold-adapted mountain lake communities are uniquely sensitive to warming and impacts from exotic sportfish, which have been introduced to create angling opportunities around the world. To explore potential interactions among invasive fish, higher temperatures, and importation of a regional species pool, I conducted a large outdoor mesocosm experiment introducing rainbow trout to planktonic communities collected from fishless alpine lakes. Fish introduction exerted strong negative impacts on prey species richness and biomass production, which were relatively unaffected by warming. However, importation of fish-tolerant species from neighbouring lakes rescued local alpine zooplankton communities from the adverse predatory effects of exotic salmonids. These findings indicated that native species’ traits mediate the impacts of invasive species and highlighted the importance of maintaining habitat connectivity to buffer against future stressors. Finally, I compiled and analyzed historical zooplankton records for 1,234 waterbodies across the North American Cordillera, from Yukon Territory, Canada, to California, USA, to evaluate the hierarchical importance of fish introduction and climatic factors among the multiple covarying local and regional drivers of continental-scale biodiversity patterns. Spatially structured local environmental factors (climate, catchment features, and fish stocking history) explained more variance in species composition than the degree of connectivity among sampled sites or their geographic variables. Further, the inferred effects of species sorting and dispersal processes varied based on species’ traits. These findings highlighted the greater sensitivity of mountain lake communities to local catchment and climate conditions than dispersal limitation, and the importance of terrestrial–aquatic linkages and fisheries management under a changing climate. My doctoral research provides several novel insights into the impacts of multiple stressors on ecological communities, with clear implications for the conservation of freshwater resources. I discovered that stressor interactions are frequently antagonistic, and using mountain lakes as a model ecosystem, I found that species’ traits play an important role in mediating metacommunity assembly and stressor response along geographic gradients. By integrating experimental and observational evidence, my thesis demonstrates a rigorous scientific approach to identifying the functional consequences of global change.

• Subjects / Keywords

  • Metacommunity
  • Functional traits
  • Climate change
  • Ecological surprises
  • Functional structure
  • Antagonism
  • Functional resistance
  • Community assembly
  • Sportfish
  • Multiple stressors
  • Connectivity
  • Reversals
  • Beta diversity
  • Spatial insurance effects
  • Terrestrial–aquatic linkages
  • Biodiversity–ecosystem functioning
  • Mountain lakes
  • Zooplankton
  • Biotic resistance
  • Species sorting
  • Predator–prey interactions
  • Trait analysis
  • Dispersal limitation
  • Cumulative impacts
  • Biodiversity
  • Synergy
  • Invasive species

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3H12VN4D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.