When things don't add up: quantifying impacts of multiple stressors from individual metabolism to ecosystem processing

Nika Galic, Lauren L Sullivan, Volker Grimm, Valery E Forbes

Research output: Contribution to journalLetterpeer-review

97 Scopus citations


Ecosystems are exposed to multiple stressors which can compromise functioning and service delivery. These stressors often co-occur and interact in different ways which are not yet fully understood. Here, we applied a population model representing a freshwater amphipod feeding on leaf litter in forested streams. We simulated impacts of hypothetical stressors, individually and in pairwise combinations that target the individuals' feeding, maintenance, growth and reproduction. Impacts were quantified by examining responses at three levels of biological organisation: individual-level body sizes and cumulative reproduction, population-level abundance and biomass and ecosystem-level leaf litter decomposition. Interactive effects of multiple stressors at the individual level were mostly antagonistic, that is, less negative than expected. Most population- and ecosystem-level responses to multiple stressors were stronger than expected from an additive model, that is, synergistic. Our results suggest that across levels of biological organisation responses to multiple stressors are rarely only additive. We suggest methods for efficiently quantifying impacts of multiple stressors at different levels of biological organisation.

Original languageEnglish (US)
Pages (from-to)568-577
Number of pages10
JournalEcology letters
Issue number4
StatePublished - Apr 2018

Bibliographical note

Publisher Copyright:
© 2018 John Wiley & Sons Ltd/CNRS


  • Antagonism
  • detritivores
  • ecosystem services
  • energy budgets
  • individual-based model
  • population dynamics
  • stressor interactions
  • synergism


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