James R. Barnes

THE EFFECT OF INVERTEBRATE PREDATORS ON LEAF LITTER PROCESSING IN AN ALPINE STREAM

The effect of the predators Megarcys signata (Plecoptera: Perlodidae) and Rhyacophila sp. (Trichoptera: Rhyacophilidae) on the abundance of macroinvertebrates and on the rates of leaf processing in artificial leaf packs was studied by using manipulative field experiments. Predators were confined within artificially constructed leaf packs in an alpine stream in Utah. Both predators signif- icantly reduced the rate of breakdown of leaves in the fall, but had no effect in late winter, when the most important shredder, Zapada cinctipes, emerges. Predation on shredders caused a reduction in breakdown rates and an increase in the residence time of the leaf litter in the stream. In experimental treatments where predators significantly reduced the numbers of shredders and decreased the rate of leaf processing, leaf pack half-life increased an average of 10.3 d. These experiments demonstrate that invertebrate shredders can contribute substantially to the rate of leaf processing in streams and suggest that one of the factors limiting the abundance of natural shredder populations is predation.

Leaf litter processing in aquatic systems: A two variable model

A negative exponential model with one independent variable, days or accumulated time, was examined for adequacy as a descriptive equation for aquatic leaf litter processing. The effect of adding a second independent variable, degree days or accumulated temperature, to the model was also examined. The two variable negative exponential model was shown to have two advantages over the single variable model. The expanded model provided an adequate fit of litter processing data for more cases than the single variable model. Also, the two variable model allowed determination of rate coefficients corresponding to each temperature level of the experiment rather than assuming a single, constant rate coefficient as with the one variable model. The trends of the temperature dependent rate coefficients were useful for examining processing differences between experiments for different sites and seasons.

Seasonal Dynamics of Leaf Litter Breakdown in a Utah Alpine Stream

Seasonal breakdown patterns of leaf litter were studied in a Utah Rocky Mountain stream using box elder (Acer negundo) leaf packs between January 1976 and January 1977. Sets of 14, 5-g leaf packs were placed at two sites 400 m apart during the first week of each month. Two packs from each site were removed at 100-degree-day intervals. Leaf pack mass loss and community respiration rates were measured for each removal. Breakdown rates were fit to a negative exponential model using either days or degree days. For both days or degree days breakdown rate varied seasonally at each site and between sites. The fastest breakdown rates using days were in packs placed at the upper site in spring and summer and at the lower site in spring, summer and fall. Using degree days in the model, which factors out the temperature effect, the fastest breakdown rates at the upper site were in packs placed in July and in the following October-January period. At the lower site the fastest rates using degree days were in packs placed in July, late fall, and early winter. Highest respiration rates (mg O2/hr/g dry mass) were obtained for the June placement at the upper site and for the September placement at the lower site. These differences are probably due to differences in physical and biological conditions at the two sites.

Life history features of some macroinvertebrates in a French Polynesian stream

The invertebrate fauna of the Opunohu River catchment in Moorea, French Polynesia, studied 1988–1989, was numerically dominated by four species of neritid snails, one species of thiarid snail, two species of atyid shrimp, two species of palaemonid shrimp, and ten species of coenagrionid, chironomid, and simuliid insect larvae. Numbers of egg capsules of neritid snails were higher in riffles (maximum x density > 10,000/m2 surface area) than pools, were highest in riffles in September and pools in August, and were lowest in both habitats in March and December. The snail Neritina canalis Lamarck and the shrimp Atyoida pilipes Newport, Caridina weberi DeMan, Macrobrachium lar Fabricius, and Macrobrachium australe Guerin‐Meneville are diadromous: they enter freshwater as juveniles and migrate upstream; their larval offspring return to the ocean for growth and development. Ovigerous females of A. pilipes and M. lar were mainly found in austral fall; ovigerous females of C. weberi and M. australe were found in b...

Community Dynamics of Leaf Litter Breakdown in a Utah Alpine Stream

Leaf litter breakdown was examined in a Rocky Mountain stream in Utah during fall 1976 and winter 1977. Leaf mass loss, changes in macroinvertebrate community structure, and patterns in community respiration were measured on pairs of leaf packs removed from the stream every 2-3 d. Colonization of the leaf packs by macroinvertebrates was rapid. The dominant organisms during the initial colonization were shredders. Highest total oxygen consumption occurred during the initial colonization phase. Macroinvertebrate density, invertebrate biomass, and oxygen consumption adjusted for remaining leaf mass all showed a dramatic increase in variance associated with the final phase of decomposition (<20% leaf material remaining). The final phase of breakdown may have the most interesting biological interactions owing to the high variability in leaf biomass and long residence times that directly affect the utility of the leaf pack as habitat and food.

Stream Ecology: An Historical and Current Perspective

Stream ecology is coming of age. It has progressed from descriptive studies to the testing of general theoretical constructs in ecology and the formulation of new concepts in less than 25 years. Stream ecology can now make significant contributions to the development and testing of general ecological theory. As can be judged from the title of this book, our purpose is three fold: (1) to call attention to this new dimension in stream ecology, (2) to indicate the type of work that is currently being done by stream workers who are addressing basic ecological questions, and (3) to suggest new directions for future emphasis.