Trophic interactions modify the temperature dependence of community biomass and ecosystem function

Jessica Garzke; Stephanie J Connor; Ulrich Sommer; Mary I O'Connor

doi:10.1371/journal.pbio.2006806

Trophic interactions modify the temperature dependence of community biomass and ecosystem function

PLoS Biol. 2019 Jun 10;17(6):e2006806. doi: 10.1371/journal.pbio.2006806. eCollection 2019 Jun.

Authors

Jessica Garzke^{1

2}, Stephanie J Connor³, Ulrich Sommer¹, Mary I O'Connor⁴

Affiliations

¹ Geomar Helmholtz Centre for Ocean Research Kiel, Department of Experimental Ecology - Food Webs, Germany.
² Institute of the Oceans and Fisheries, University of British Columbia, Vancouver, Canada.
³ Canadian Rivers Institute, Department of Biology, University of New Brunswick, Fredericton, Canada.
⁴ Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, Canada.

Abstract

Aquatic ecosystems worldwide continue to experience unprecedented warming and ecological change. Warming increases metabolic rates of animals, plants, and microbes, accelerating their use of energy and materials, their population growth, and interaction rates. At a much larger biological scale, warming accelerates ecosystem-level processes, elevating fluxes of carbon and oxygen between biota and the atmosphere. Although these general effects of temperature at finer and broader biological scales are widely observed, they can lead to contradictory predictions for how warming affects the structure and function of ecological communities at the intermediate scale of biological organization. We experimentally tested the hypothesis that the presence of predators and their associated species interactions modify the temperature dependence of net ecosystem oxygen production and respiration. We tracked a series of independent freshwater ecosystems (370 L) over 9 weeks, and we found that at higher temperatures, cascading effects of predators on zooplankton prey and algae were stronger than at lower temperatures. When grazing was weak or absent, standing phytoplankton biomass declined by 85%-95% (<1-fold) over the temperature gradient (19-30 °C), and by 3-fold when grazers were present and lacked predators. These temperature-dependent species interactions and consequent community biomass shifts occurred without signs of species loss or community collapse, and only modestly affected the temperature dependence of net ecosystem oxygen fluxes. The exponential increases in net ecosystem oxygen production and consumption were relatively insensitive to differences in trophic interactions among ecosystems. Furthermore, monotonic declines in phytoplankton standing stock suggested no threshold effects of warming across systems. We conclude that local changes in community structure, including temperature-dependent trophic cascades, may be compatible with prevailing and predictable effects of temperature on ecosystem functions related to fundamental effects of temperature on metabolism.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Aquatic Organisms / metabolism*
Biomass
Carbon / metabolism
Ecosystem*
Food Chain
Global Warming
Hydrobiology / methods
Phytoplankton / growth & development
Temperature*
Zooplankton / growth & development

Substances

Carbon

Grants and funding

University of British Columbia (grant number Mobility Funds). to JG. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. National Sciences and Engineering Research Council of Canada http://www.nserc-crsng.gc.ca/index_eng.asp (grant number Discovery Grant). to MIO. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.