Impaired ecosystem process despite little effects on populations: modeling combined effects of warming and toxicants

Nika Galic, Volker Grimm, Valery E. Forbes

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

Freshwater ecosystems are exposed to many stressors, including toxic chemicals and global warming, which can impair, separately or in combination, important processes in organisms and hence higher levels of organization. Investigating combined effects of warming and toxicants has been a topic of little research, but neglecting their combined effects may seriously misguide management efforts. To explore how toxic chemicals and warming, alone and in combination, propagate across levels of biological organization, including a key ecosystem process, we developed an individual-based model (IBM) of a freshwater amphipod detritivore, Gammarus pseudolimnaeus, feeding on leaf litter. In this IBM, life history emerges from the individuals’ energy budgets. We quantified, in different warming scenarios (+1–+4 °C), the effects of hypothetical toxicants on suborganismal processes, including feeding, somatic and maturity maintenance, growth, and reproduction. Warming reduced mean adult body sizes and population abundance and biomass, but only in the warmest scenarios. Leaf litter processing, a key contributor to ecosystem functioning and service delivery in streams, was consistently enhanced by warming, through strengthened interaction between the detritivorous consumer and its resource. Toxicant effects on feeding and maintenance resulted in initially small adverse effects on consumers, but ultimately led to population extinction and loss of ecosystem process. Warming in combination with toxicants had little effect at the individual and population levels, but ecosystem process was impaired in the warmer scenarios. Our results suggest that exposure to the same amount of toxicants can disproportionately compromise ecosystem processing depending on global warming scenarios; for example, reducing organismal feeding rates by 50% will reduce resource processing by 50% in current temperature conditions, but by up to 200% with warming of 4 °C. Our study has implications for assessing and monitoring impacts of chemicals on ecosystems facing global warming. We advise complementing existing monitoring approaches with directly quantifying ecosystem processes and services.

Original languageEnglish (US)
Pages (from-to)2973-2989
Number of pages17
JournalGlobal change biology
Volume23
Issue number8
DOIs
StatePublished - Aug 2017

Bibliographical note

Funding Information:
Nika Galic was partly supported by the Program of Excellence in Population Biology of the School of Biological Sciences, University of Nebraska-Lincoln. We thank Amelie Schmolke for verifying the model code. Authors acknowledge two anonymous reviewers who provided helpful comments on an earlier version of the manuscript.

Publisher Copyright:
© 2017 John Wiley & Sons Ltd

Keywords

  • dynamic energy budgets
  • ecosystem services
  • freshwater ecosystems
  • individual-based model
  • leaf litter processing
  • multiple stressors
  • population dynamics

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