Fish introductions and light modulate food web fluxes in tropical streams : a whole-ecosystem experimental approach
Collins, S. M., Thomas, S. A., Heatherly, T., MacNeill, K. L., Leduc, A. O. H. C., Lopez Sepulcre, A., Lamphere, B. A., El-Sabaawi, R. W., Reznick, D. N., Pringle, C. M., & Flecker, A. S. (2016). Fish introductions and light modulate food web fluxes in tropical streams : a whole-ecosystem experimental approach. Ecology, 97(11), 3154-3166. https://doi.org/10.1002/ecy.1530
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EcologyAuthors
Date
2016Copyright
© 2016 by the Ecological Society of America. Published in this repository with the kind permission of the publisher.
Decades of ecological study have demonstrated the importance of top-down and
bottom-up controls on food webs, yet few studies within this context have quantified the magnitude
of energy and material fluxes at the whole-ecosystem scale. We examined top-down and bottom-up
effects on food web fluxes using a field experiment that manipulated the presence of a consumer, the
Trinidadian guppy Poecilia reticulata, and the production of basal resources by thinning the riparian
forest canopy to increase incident light. To gauge the effects of these reach-scale manipulations
on food web fluxes, we used a nitrogen (15N) stable isotope tracer to compare basal resource treatments
(thinned canopy vs. control) and consumer treatments (guppy introduction vs. control). The
thinned canopy stream had higher primary production than the natural canopy control, leading to
increased N fluxes to invertebrates that feed on benthic biofilms (grazers), fine benthic organic matter
(collector-gatherers), and organic particles suspended in the water column (filter feeders). Stream
reaches with guppies also had higher primary productivity and higher N fluxes to grazers and filter
feeders. In contrast, N fluxes to collector-gatherers were reduced in guppy introduction reaches
relative to upstream controls. N fluxes to leaf-shredding invertebrates, predatory invertebrates, and
the other fish species present (Hart’s killifish, Anablepsoides hartii) did not differ across light or
guppy treatments, suggesting that effects on detritus-based linkages and upper trophic levels were
not as strong. Effect sizes of guppy and canopy treatments on N flux rates were similar for most
taxa, though guppy effects were the strongest for filter feeding invertebrates while canopy effects
were the strongest for collector-gatherer invertebrates. Combined, these results extend previous
knowledge about top-down and bottom-up controls on ecosystems by providing experimental,
reach-scale evidence that both pathways can act simultaneously and have equally strong influence
on nutrient fluxes from inorganic pools through primary consumers.
...


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