Trophic-level dependent effects on CO<inf>2</inf>emissions from experimental stream ecosystems
- Publication Type:
- Journal Article
- Global Change Biology, 2014, 20 (11), pp. 3386 - 3396
- Issue Date:
© 2014 John Wiley & Sons Ltd. Concern over accelerating rates of species invasions and losses have initiated investigations into how local and global changes to predator abundance mediate trophic cascades that influence CO2fluxes of aquatic ecosystems. However, to date, no studies have investigated how species additions or losses at other consumer trophic levels influence the CO2flux of aquatic ecosystems. In this study, we added a large predatory stonefly, detritivorous stonefly, or grazer tadpole to experimental stream food webs and over a 70-day period quantified their effects on community composition, leaf litter decomposition, chlorophyll-a concentrations, and stream CO2emissions. In general, streams where the large grazer or large detritivore were added showed no change in total invertebrate biomass, leaf litter loss, chlorophyll-a concentrations, or stream CO2emissions compared with controls; although we did observe a spike in CO2emissions in the large grazer treatment following a substantial reduction in chlorophyll-a concentrations on day 28. However, the large grazer and large detritivore altered the community composition of streams by reducing the densities of other grazer and detritivore taxa, respectively, compared with controls. Conversely, the addition of the large predator created trophic cascades that reduced total invertebrate biomass and increased primary producer biomass. The cascading effects of the predator additions on the food web ultimately led to decreased CO2emissions from stream channels by up to 95%. Our results suggest that stream ecosystem processes were more influenced by changes in large predator abundance than large grazer or detritivore abundance, because of a lack of functionally similar large predators. Our study demonstrates that the presence/absence of species with unique functional roles may have consequences for the exchange of CO2between the ecosystem and the atmosphere.
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