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Context dependency of top-down and bottom-up effects in a Northern Australian tropical river

Garcia, Erica A., Townsend, Simon A. and Douglas, Michael M. (2015). Context dependency of top-down and bottom-up effects in a Northern Australian tropical river. Freshwater Science,34(2):679-690.

Document type: Journal Article
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IRMA ID 84376995xPUB220
Title Context dependency of top-down and bottom-up effects in a Northern Australian tropical river
Author Garcia, Erica A.
Townsend, Simon A.
Douglas, Michael M.
Journal Name Freshwater Science
Publication Date 2015
Volume Number 34
Issue Number 2
ISSN 2161-9565   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-84953747486
Start Page 679
End Page 690
Total Pages 12
Place of Publication United States of America
Publisher University of Chicago Press
HERDC Category C1 - Journal Article (DIISR)
Abstract Top-down and bottom-up forces (consumer and resource limitation, respectively) influence biomass of primary producers and primary consumers in natural food webs. Few investigators experimentally examine both in concert, especially in the tropics. Tropical systems probably are more sensitive than temperate systems to eutrophication and other disturbances, such as destruction of riparian canopy cover, because of wide windows of ecological opportunity. We experimentally examined the relative importance of top-down and bottom-up effects at 2 sites in the Edith River in the Australian wet–dry tropics during baseflow conditions. We used large fish-exclusion cages to examine top-down effects of fish, and we used nutrient-diffusing substrates to manipulate bottom-up effects of nutrients. Macroinvertebrates were significantly more abundant in fish-exclusion cages than in open control areas at both sites. At 1 site, chlorophyll a on rock substrate was 1.5× greater and ash-free dry mass was 1.4× greater in fish-exclusion than in open cages. Chlorophyll a was >3× greater in the high-N and -P nutrient treatment than in the unamended control at both sites. Top-down effects on the algae on nutrient-diffusing substrates were detected at only 1 site. Bottom-up factors seem to be relatively more important in controlling primary producer biomass compared to top-down factors, with no evidence of a trophic cascade. Bottom-up and top-down effects on macroinvertebrates were strong and consistent, whereas top-down effects on algae were context dependent and varied depending on benthic habitat, current speeds, and community structure. These results indicated spatial variation at the scale of tens of meters.
Keywords Top-down
Benthic algae
Primary production
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Created: Tue, 26 Jul 2016, 12:59:04 CST