Top-down and bottom-up control of stream periphyton: Effects of nutrients and herbivores
- Vanderbilt Univ., Nashville, TN (United States)
- Oak Ridge National Lab., TN (United States)
Two experiments determineD the relative effects of herbivory and nutrients on an algal community in in a stream having effectively two trophic levels: primary producers and herbivorous snails. The first study (1989), in streamside channels, tested the effects of three factors: (1) stream water nitrogen (N), (2) phosphorus (P), and (3) snail grazing, on periphyton biomass, productivity, and community composition. The second study (1990), conducted in situ, tested the effects of snail grazing and nutrients (N + P). In the 1989 study, nutrients had positive effects, and herbivores had negative effects, on algal biomass and primary productivity. Likewise, both nutrients and snail grazing exerted effects (+ and [minus], respectively) on biomass measured in the 1990 study. Grazed communities, dominated by chlorophytes and cyanophytes, were overgrown by diatoms when herbivores were removed. Algal species , reduced the most by herbivores, were increased most by nutrient addition, and vice versa, suggesting a trade-off between resistance to herbivory and nutrient-saturated growth rates. The greatest changes in periphyton structure or function were observed when both N and P were added and simultaneously, grazers were removed, in contrast to lesser effects when nutrients were added under grazed conditions or grazers were removed at low nutrient levels, indicating dual control by both factors. Nutrient addition also positively affected snail growth in both experiments, indicating tight coupling between herbivore and algal growth (top-down effects) and that bottom-up factors that directly affected plant growth could also indirectly affect consumers belonging to higher trophic levels. Indices showed that the relative strength of top-down and bottom-up factors varied among biomass and productivity parameters and that top-down and bottom-up effects, alone, were less important than their combined effects. 67 refs., 8 figs., 7 tabs.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 6389501
- Journal Information:
- Ecology; (United States), Vol. 74:4; ISSN 0012-9658
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ALGAE
PLANT GROWTH
NUTRIENTS
BIOLOGICAL EFFECTS
SNAILS
STREAMS
DIATOMS
GRAZING
NITROGEN
PHOSPHORUS
PRODUCTIVITY
WATER
ANIMALS
AQUATIC ORGANISMS
CHROMOPHYCOTA
ELEMENTS
FEEDING
GROWTH
HYDROGEN COMPOUNDS
INVERTEBRATES
MOLLUSCS
NONMETALS
OXYGEN COMPOUNDS
PLANTS
SURFACE WATERS
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