Light, nutrients, and herbivore growth in oligotrophic streams

Journal Article · Mon Feb 01 00:00:00 EST 2010 · Ecology

DOI:https://doi.org/10.1890/09-0703.1· OSTI ID:1015729

Hill, Walter R ^[1]; Smith, John G ^[1]; Stewart, Arthur J ^[1]

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1. ORNL

The light : nutrient hypothesis posits that herbivore growth is increasingly constrained by low food quality as the ratio of light to nutrients increases in aquatic ecosystems. We tested predictions of this hypothesis by examining the effects of large seasonal cycles in light and nutrients on the mineral content of periphyton and the growth rate of a dominant herbivore (the snail Elimia clavaeformis) in two oligotrophic streams. Streambed irradiances in White Oak Creek and Walker Branch (eastern Tennessee, USA) varied dramatically on a seasonal basis due to leaf phenology in the surrounding deciduous forests and seasonal changes in sun angle. Concentrations of dissolved nutrients varied inversely with light, causing light : nitrate and light : phosphate to range almost 100-fold over the course of any individual year. Periphyton nitrogen and phosphorus concentrations were much lower than the concentrations of these elements in snails, and they bottomed out in early spring when streambed irradiances were highest. Snail growth, however, peaked in early spring when light:nutrient ratios were highest and periphyton nutrient concentrations were lowest, Growth was linearly related to primary production (accounting for up to 85% of growth variance in individual years), which in turn was driven by seasonal variation in light. Conceptual models of herbivore growth indicate that growth should initially increase as increasing light levels stimulate primary production, but then level off, and then decrease as the negative effects of decreasing algal nutrient content override the positive effects of increased food production. Our results showed no evidence of an inflection point where increasing ratios of light to nutrients negatively affected growth. Snail growth in these intensively grazed streams is probably unaffected by periphyton nutrient content because exploitative competition for food reduces growth rates to levels where the demand for nitrogen and phosphorus is small enough to be satisfied by even low levels of these nutrients in periphyton. Competition for limited food resources in habitats where herbivore densities are uncontrolled by predation or other mortality factors should strongly influence the potential for herbivores to be limited by mineral deficits in their food

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge National Environmental Research Park
• Sponsoring Organization: USDOE
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1015729
• Journal Information: Ecology, Vol. 91, Issue 2; ISSN 0012--9658
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
54 ENVIRONMENTAL SCIENCES
AQUATIC ECOSYSTEMS
AUFWUCHS
FOOD
FORESTS
HYPOTHESIS
MORTALITY
NITRATES
NITROGEN
NUTRIENTS
PHENOLOGY
PHOSPHATES
PHOSPHORUS
PRODUCTION
SEASONAL VARIATIONS
SNAILS
STREAMS
algae
competition
Elimia clavaeformis
herbivore
light : nutrient hypothesis
nitrogen
phosphorus
snails
streams