2017
Vadeboncoeur, Yvonne; Power, Mary
Attached Algae: The Cryptic Base of Inverted Trophic Pyramids in Freshwaters Journal Article
In: Annual Review of Ecology, Evolution, and Systematics, vol. 48, no. 1, pp. 255-279, 2017.
Abstract | Links | BibTeX | Tags: Cladophora, cyanobacteria, diatoms, ERCZO, grazers, lakes, microphytobenthos, periphyton, primary consumer, primary producer, rivers
@article{Vadeboncoeur2017,
title = {Attached Algae: The Cryptic Base of Inverted Trophic Pyramids in Freshwaters},
author = {Yvonne Vadeboncoeur and Mary Power},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Annu.-Rev.-Ecol.-Evol.-Syst.-2017-Vadeboncoeur.pdf},
doi = {https://doi.org/10.1146/annurev-ecolsys-121415-032340},
year = {2017},
date = {2017-08-11},
urldate = {2017-08-11},
journal = {Annual Review of Ecology, Evolution, and Systematics},
volume = {48},
number = {1},
pages = {255-279},
abstract = {It seems improbable that a thin veneer of attached algae coating submerged surfaces in lakes and rivers could be the foundation of many freshwater food webs, but increasing evidence from chemical tracers supports this view. Attached algae grow on any submerged surface that receives enough light for photosynthesis, but animals often graze attached algae down to thin, barely perceptible biofilms. Algae in general are more nutritious and digestible than terrestrial plants or detritus, and attached algae are particularly harvestable, being concentrated on surfaces. Diatoms, a major component of attached algal assemblages, are especially nutritious and tolerant of heavy grazing. Algivores can track attached algal productivity over a range of spatial scales and consume a high proportion of new attached algal growth in high-light, low-nutrient ecosystems. The subsequent efficient conversion of the algae into consumer production in freshwater food webs can lead to low-producer, high-consumer biomass, patterns that Elton (1927) described as inverted trophic pyramids. Human perturbations of nutrient, sediment, and carbon loading into freshwaters and of thermal and hydrologic regimes can weaken consumer control of algae and promote nuisance attached algal blooms.},
keywords = {Cladophora, cyanobacteria, diatoms, ERCZO, grazers, lakes, microphytobenthos, periphyton, primary consumer, primary producer, rivers},
pubstate = {published},
tppubtype = {article}
}
It seems improbable that a thin veneer of attached algae coating submerged surfaces in lakes and rivers could be the foundation of many freshwater food webs, but increasing evidence from chemical tracers supports this view. Attached algae grow on any submerged surface that receives enough light for photosynthesis, but animals often graze attached algae down to thin, barely perceptible biofilms. Algae in general are more nutritious and digestible than terrestrial plants or detritus, and attached algae are particularly harvestable, being concentrated on surfaces. Diatoms, a major component of attached algal assemblages, are especially nutritious and tolerant of heavy grazing. Algivores can track attached algal productivity over a range of spatial scales and consume a high proportion of new attached algal growth in high-light, low-nutrient ecosystems. The subsequent efficient conversion of the algae into consumer production in freshwater food webs can lead to low-producer, high-consumer biomass, patterns that Elton (1927) described as inverted trophic pyramids. Human perturbations of nutrient, sediment, and carbon loading into freshwaters and of thermal and hydrologic regimes can weaken consumer control of algae and promote nuisance attached algal blooms.
2006
Sklar, Leonard S.; Dietrich, William E.
The role of sediment in controlling bedrock channel slope: Implications of the saltation-abrasion incision model Journal Article
In: Geomorphology, vol. 82, no. 1-2, pp. 58-83, 2006.
Abstract | Links | BibTeX | Tags: erosion, Grain size, landscape evolution, Magnitude–frequency, rivers, sediment supply
@article{Sklar2006,
title = {The role of sediment in controlling bedrock channel slope: Implications of the saltation-abrasion incision model},
author = {Leonard S. Sklar and William E. Dietrich},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Sklar_2006_Geomorpho.pdf},
doi = {10.1016/j.geomorph.2005.08.019},
year = {2006},
date = {2006-12-06},
journal = {Geomorphology},
volume = {82},
number = {1-2},
pages = {58-83},
abstract = {The saltation–abrasion model is a mechanistic model for river incision into bedrock by saltating bedload, which we have previously derived and used experimental data to constrain all parameter values. Here we develop a method for applying the saltation–abrasion model at a landscape scale, and use the model as a reference for evaluating the behavior of a wide range of alternative incision models, in order to consider the implications of the saltation–abrasion model, as well as other models, for predicting topographic steady-state channel slope. To determine the single-valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock, we assume all runoff can be partitioned between a low-flow and a high-flow discharge, in which all bedload sediment transport occurs during high flow. We then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency, due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply. Incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for. Using the predictions of the saltation–abrasion model as a reference, we find that the threshold of motion is the most important effect that should be represented explicitly, followed in order of decreasing importance by the cover effect, the tools effect and the threshold of suspension effect. Models that lack the threshold of motion over-predict incision rate for low shear stresses and under-predict the steady-state channel slope for low to moderate rock uplift rates and rock strengths. Models that lack the cover effect over-predict incision rate for high sediment supply rates, and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage. Models that lack the tools effect over-predict incision rate for low sediment supply rates, and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value. Overall, the saltation–abrasion model predicts that steady-state channel slope is most sensitive to changes in grain size, such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible, but as yet poorly understood, influence on the size distribution of sediments delivered to channel networks by hillslopes.},
keywords = {erosion, Grain size, landscape evolution, Magnitude–frequency, rivers, sediment supply},
pubstate = {published},
tppubtype = {article}
}
The saltation–abrasion model is a mechanistic model for river incision into bedrock by saltating bedload, which we have previously derived and used experimental data to constrain all parameter values. Here we develop a method for applying the saltation–abrasion model at a landscape scale, and use the model as a reference for evaluating the behavior of a wide range of alternative incision models, in order to consider the implications of the saltation–abrasion model, as well as other models, for predicting topographic steady-state channel slope. To determine the single-valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock, we assume all runoff can be partitioned between a low-flow and a high-flow discharge, in which all bedload sediment transport occurs during high flow. We then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency, due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply. Incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for. Using the predictions of the saltation–abrasion model as a reference, we find that the threshold of motion is the most important effect that should be represented explicitly, followed in order of decreasing importance by the cover effect, the tools effect and the threshold of suspension effect. Models that lack the threshold of motion over-predict incision rate for low shear stresses and under-predict the steady-state channel slope for low to moderate rock uplift rates and rock strengths. Models that lack the cover effect over-predict incision rate for high sediment supply rates, and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage. Models that lack the tools effect over-predict incision rate for low sediment supply rates, and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value. Overall, the saltation–abrasion model predicts that steady-state channel slope is most sensitive to changes in grain size, such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible, but as yet poorly understood, influence on the size distribution of sediments delivered to channel networks by hillslopes.
Lowe, W. H.; Likens, Gene E.; Power, Mary E.
Linking Scales in Stream Ecology Journal Article
In: BioScience, vol. 56, no. 7, pp. 591-597, 2006.
Abstract | Links | BibTeX | Tags: 16S rRNA microarrays, networks, resiliency, rivers, streams
@article{111bf,
title = {Linking Scales in Stream Ecology},
author = {W. H. Lowe and Gene E. Likens and Mary E. Power},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Lowe_2006_BioScience.pdf},
doi = {10.1641/0006-3568(2006)56[591:LSISE]2.0.CO;2},
year = {2006},
date = {2006-07-01},
journal = {BioScience},
volume = {56},
number = {7},
pages = {591-597},
abstract = {The hierarchical structure of natural systems can be useful in designing ecological studies that are informative at multiple spatial scales. Although stream systems have long been recognized as having a hierarchical spatial structure, there is a need for more empirical research that exploits this structure to generate an understanding of population biology, community ecology, and species–ecosystem linkages across spatial scales. We review studies that link pattern and process across multiple scales of stream-habitat organization, highlighting the insight derived from this multiscale approach and the role that mechanistic hypotheses play in its successful application. We also describe a frontier in stream research that relies on this multiscale approach: assessing the consequences and mechanisms of ecological processes occurring at the network scale. Broader use of this approach will advance many goals in applied stream ecology, including the design of reserves to protect stream biodiversity and the conservation of freshwater resources and services.},
keywords = {16S rRNA microarrays, networks, resiliency, rivers, streams},
pubstate = {published},
tppubtype = {article}
}
The hierarchical structure of natural systems can be useful in designing ecological studies that are informative at multiple spatial scales. Although stream systems have long been recognized as having a hierarchical spatial structure, there is a need for more empirical research that exploits this structure to generate an understanding of population biology, community ecology, and species–ecosystem linkages across spatial scales. We review studies that link pattern and process across multiple scales of stream-habitat organization, highlighting the insight derived from this multiscale approach and the role that mechanistic hypotheses play in its successful application. We also describe a frontier in stream research that relies on this multiscale approach: assessing the consequences and mechanisms of ecological processes occurring at the network scale. Broader use of this approach will advance many goals in applied stream ecology, including the design of reserves to protect stream biodiversity and the conservation of freshwater resources and services.
Power, M. E.
Environmental controls on food web regimes: a fluvial perspective Journal Article
In: Progress in Oceanography, vol. 68, pp. 125-133, 2006.
Links | BibTeX | Tags: Fluxes, Food web controls, Landscapes, Longitudinal gradients, Mapping, rivers, Seascapes, Sensing, Tracing technology, Watersheds
@article{111bg,
title = {Environmental controls on food web regimes: a fluvial perspective},
author = {M. E. Power},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Power_2006_ProgInOcean.pdf},
doi = {10.1016/j.pocean/2006.02.001},
year = {2006},
date = {2006-03-22},
journal = {Progress in Oceanography},
volume = {68},
pages = {125-133},
keywords = {Fluxes, Food web controls, Landscapes, Longitudinal gradients, Mapping, rivers, Seascapes, Sensing, Tracing technology, Watersheds},
pubstate = {published},
tppubtype = {article}
}
2005
Stock, J. D.; Montgomery, D. R.; Collins, B. D.; Dietrich, W. E.
In: GSA Bulletin, vol. 117, no. 1-2, pp. 174-194, 2005.
Abstract | Links | BibTeX | Tags: erosion, geomorphology, neotectonics, rivers, Weathering
@article{Stock2005,
title = {Field measurements of incision rates following bedrock exposure: Implications for process controls on the long profiles of valleys cut by rivers and debris flows},
author = {J. D. Stock and D. R. Montgomery and B. D. Collins and W. E. Dietrich},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Stock_2005_GSABulletin.pdf},
doi = {10.1130/B25560.1},
year = {2005},
date = {2005-01-01},
journal = {GSA Bulletin},
volume = {117},
number = {1-2},
pages = {174-194},
abstract = {Until recently, published rates of incision of bedrock valleys came from indirect dating of incised surfaces. A small but growing literature based on direct measurement reports short-term bedrock lowering at geologically unsustainable rates. We report observations of bedrock lowering from erosion pins monitored over 1–7 yr in 10 valleys that cut indurated volcanic and sedimentary rocks in Washington, Oregon, California, and Taiwan. Most of these channels have historically been stripped of sediment. Their bedrock is exposed to bed-load abrasion, plucking, and seasonal wetting and drying that comminutes hard, intact rock into plates or equant fragments that are removed by higher flows. Consequent incision rates are proportional to the square of rock tensile strength, in agreement with experimental results of others. Measured rates up to centimeters per year far exceed regional long-term erosion-rate estimates, even for apparently minor sediment-transport rates. Cultural artifacts on adjoining strath terraces in Washington and Taiwan indicate at least several decades of lowering at these extreme rates. Lacking sediment cover, lithologies at these sites lower at rates that far exceed long-term rock-uplift rates. This rate disparity makes it unlikely that the long profiles of these rivers are directly adjusted to either bedrock hardness or rock-uplift rate in the manner predicted by the stream power law, despite the observation that their profiles are well fit by power-law plots of drainage area vs. slope. We hypothesize that the threshold of motion of a thin sediment mantle, rather than bedrock hardness or rock-uplift rate, controls channel slope in weak bedrock lithologies with tensile strengths below ∼3–5 MPa. To illustrate this hypothesis and to provide an alternative interpretation for power-law plots of area vs. slope, we combine Shields' threshold transport concept with measured hydraulic relationships and downstream fining rates. In contrast to fluvial reaches, none of the hundreds of erosion pins we installed in steep valleys recently scoured to bedrock by debris flows indicate any postevent fluvial lowering. These results are consistent with episodic debris flows as the primary agent of bedrock lowering in the steepest parts of the channel network above ∼0.03–0.10 slope.},
keywords = {erosion, geomorphology, neotectonics, rivers, Weathering},
pubstate = {published},
tppubtype = {article}
}
Until recently, published rates of incision of bedrock valleys came from indirect dating of incised surfaces. A small but growing literature based on direct measurement reports short-term bedrock lowering at geologically unsustainable rates. We report observations of bedrock lowering from erosion pins monitored over 1–7 yr in 10 valleys that cut indurated volcanic and sedimentary rocks in Washington, Oregon, California, and Taiwan. Most of these channels have historically been stripped of sediment. Their bedrock is exposed to bed-load abrasion, plucking, and seasonal wetting and drying that comminutes hard, intact rock into plates or equant fragments that are removed by higher flows. Consequent incision rates are proportional to the square of rock tensile strength, in agreement with experimental results of others. Measured rates up to centimeters per year far exceed regional long-term erosion-rate estimates, even for apparently minor sediment-transport rates. Cultural artifacts on adjoining strath terraces in Washington and Taiwan indicate at least several decades of lowering at these extreme rates. Lacking sediment cover, lithologies at these sites lower at rates that far exceed long-term rock-uplift rates. This rate disparity makes it unlikely that the long profiles of these rivers are directly adjusted to either bedrock hardness or rock-uplift rate in the manner predicted by the stream power law, despite the observation that their profiles are well fit by power-law plots of drainage area vs. slope. We hypothesize that the threshold of motion of a thin sediment mantle, rather than bedrock hardness or rock-uplift rate, controls channel slope in weak bedrock lithologies with tensile strengths below ∼3–5 MPa. To illustrate this hypothesis and to provide an alternative interpretation for power-law plots of area vs. slope, we combine Shields’ threshold transport concept with measured hydraulic relationships and downstream fining rates. In contrast to fluvial reaches, none of the hundreds of erosion pins we installed in steep valleys recently scoured to bedrock by debris flows indicate any postevent fluvial lowering. These results are consistent with episodic debris flows as the primary agent of bedrock lowering in the steepest parts of the channel network above ∼0.03–0.10 slope.
1997
Kupferberg, Sarah J.
Bullfrog (Rana catesbeiana) invasion of a California river: the role of larval competition Journal Article
In: Ecology, vol. 78, no. 6, pp. 1736-1751, 1997, ISSN: 0012-9658.
Abstract | Links | BibTeX | Tags: algae, biological invasions, California, grazing, Hyla regilla, Rana boylii, Rana catesbeiana, rivers, size-structured competition
@article{Kupferberg1997,
title = {Bullfrog (Rana catesbeiana) invasion of a California river: the role of larval competition},
author = {Sarah J. Kupferberg},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Kupferberg_Ecology1997.pdf},
issn = {0012-9658},
year = {1997},
date = {1997-09-00},
journal = {Ecology},
volume = {78},
number = {6},
pages = {1736-1751},
abstract = {I studied the invasion of Rana catesbeiana (the bullfrog) into a northern California river system where bullfrogs are not native. Native yellow-legged frogs, Rana boylii, a species of special concern, were almost an order of magnitude less abundant in reaches where bullfrogs were well established. I assessed the potential role of larval competition in contributing to this displacement in a series of field manipulations of tadpole density and species composition. The impact of R. catesbeiana on native tadpoles in the natural community agreed with the outcome of more artificial experiments testing pairwise and three-way interactions. In 2-m(2) enclosures with ambient densities of tadpoles and natural river biota, bullfrog tadpoles caused a 48% reduction in survivorship of R. boylii, and a 24% decline in mass at metamorphosis. Bullfrog larvae had smaller impacts on Pacific treefrogs, Hyla regilla, causing 16% reduction in metamorph size, and no significant effect on survivorship. Bullfrog tadpoles significantly affected benthic algae, although effects varied across sites. Responses to bullfrogs in field settings were similar qualitatively to results seen in smaller-scale experiments designed to study size-structured competition among disparate age/size classes of species pairs and trios. Competition from large overwintering bullfrog larvae significantly decreased survivorship and growth of native tadpoles. Competition from recently hatched bullfrog larvae also decreased survivorship of R. boylii and H. regilla. Native species competed weakly, both interspecifically and intraspecifically. The only suggestion of a negative impact of a native species on bullfrogs was a weak effect of H. regilla on recent hatchlings. Competition appeared to be mediated by algal resources, and there was no evidence for behavioral or chemical interference. These results indicate that, through larval interactions, bullfrogs can exert differential effects on native frogs and perturb aquatic community structure.},
keywords = {algae, biological invasions, California, grazing, Hyla regilla, Rana boylii, Rana catesbeiana, rivers, size-structured competition},
pubstate = {published},
tppubtype = {article}
}
I studied the invasion of Rana catesbeiana (the bullfrog) into a northern California river system where bullfrogs are not native. Native yellow-legged frogs, Rana boylii, a species of special concern, were almost an order of magnitude less abundant in reaches where bullfrogs were well established. I assessed the potential role of larval competition in contributing to this displacement in a series of field manipulations of tadpole density and species composition. The impact of R. catesbeiana on native tadpoles in the natural community agreed with the outcome of more artificial experiments testing pairwise and three-way interactions. In 2-m(2) enclosures with ambient densities of tadpoles and natural river biota, bullfrog tadpoles caused a 48% reduction in survivorship of R. boylii, and a 24% decline in mass at metamorphosis. Bullfrog larvae had smaller impacts on Pacific treefrogs, Hyla regilla, causing 16% reduction in metamorph size, and no significant effect on survivorship. Bullfrog tadpoles significantly affected benthic algae, although effects varied across sites. Responses to bullfrogs in field settings were similar qualitatively to results seen in smaller-scale experiments designed to study size-structured competition among disparate age/size classes of species pairs and trios. Competition from large overwintering bullfrog larvae significantly decreased survivorship and growth of native tadpoles. Competition from recently hatched bullfrog larvae also decreased survivorship of R. boylii and H. regilla. Native species competed weakly, both interspecifically and intraspecifically. The only suggestion of a negative impact of a native species on bullfrogs was a weak effect of H. regilla on recent hatchlings. Competition appeared to be mediated by algal resources, and there was no evidence for behavioral or chemical interference. These results indicate that, through larval interactions, bullfrogs can exert differential effects on native frogs and perturb aquatic community structure.
1995
Power, M. E.
Floods, food chains and ecosystem processes in rivers Journal Article
In: Linking Species and Ecosystems, pp. 52-60, 1995.
Abstract | Links | BibTeX | Tags: Floods, food chains, rivers
@article{Power1995d,
title = {Floods, food chains and ecosystem processes in rivers},
author = {M. E. Power},
editor = {C. L. Jones and J. H. Lawton},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Power_1995_Floods.pdf},
year = {1995},
date = {1995-00-00},
journal = {Linking Species and Ecosystems},
pages = {52-60},
abstract = {Chapman and Hall, N.Y.},
keywords = {Floods, food chains, rivers},
pubstate = {published},
tppubtype = {article}
}
Chapman and Hall, N.Y.
1988
Power, Mary E.; Stout, R. Jean; Cushing, Colbert E.; Harper, Peter P.; Hauer, F. Richard; Matthews, William J.; Moyle, Peter B.; Statzner, Bernhard; Badgen, Irene R. Wais De
Biotic and abiotic controls in river and stream communities Journal Article
In: Journal of the North American Benthological Society, vol. 7, no. 4, pp. 456-479, 1988.
Abstract | Links | BibTeX | Tags: algae, COMMUNITIES, discharge, disturbance., fish, life histories, rivers, streams, zoobenthos
@article{Power1988,
title = {Biotic and abiotic controls in river and stream communities},
author = {Mary E. Power and R. Jean Stout and Colbert E. Cushing and Peter P. Harper and F. Richard Hauer and William J. Matthews and Peter B. Moyle and Bernhard Statzner and Irene R. Wais De Badgen},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Power_1988_BenthoSoc.pdf},
doi = {10.2307/1467301},
year = {1988},
date = {1988-12-00},
journal = {Journal of the North American Benthological Society},
volume = {7},
number = {4},
pages = {456-479},
abstract = {Lotic ecologists share a major goal of explaining the distribution and abundance of biota in the world's rivers and streams, and of predicting how this biota will respond to change in fluvial ecosystems. We discuss five areas of research that would contribute to our pursuit of this goal. For mechanistic understanding of lotic community dynamics, we need more information on:
1. Physical conditions impinging on lotic biota, measured on temporal and spatial scales relevant to the organisms.
2. Responses of lotic biota to discharge fluctuations, including the processes that mediate community recovery following resets caused by spates or droughts.
3. Movements of lotic organisms that mediate gene flow, resource tracking, and multilevel species interactions.
4. Life history patterns, with special emphasis on ontogenetic bottlenecks that determine the vulnerability of populations confronting environmental perturbation.
5. Consequences of species interactions for community- and ecosystem-level processes in rivers and streams.
Without attempting to be comprehensive in our review, we discuss limits and limitations of our knowledge in these areas. We also suggest types of data and technological development that would advance our understanding. While we appreciate the value and need for empirical and comparative information, we advocate search for key mechanisms underlying community interactions as the crucial step toward developing general predictions of responses to environmental change. These mechanisms are likely to be complex, and elucidation of interacting bilateral, or multilateral, biotic and abiotic controls will progress only with the continuing synthesis of community- and ecosystem-level approaches in lotic ecology.},
keywords = {algae, COMMUNITIES, discharge, disturbance., fish, life histories, rivers, streams, zoobenthos},
pubstate = {published},
tppubtype = {article}
}
Lotic ecologists share a major goal of explaining the distribution and abundance of biota in the world’s rivers and streams, and of predicting how this biota will respond to change in fluvial ecosystems. We discuss five areas of research that would contribute to our pursuit of this goal. For mechanistic understanding of lotic community dynamics, we need more information on:
1. Physical conditions impinging on lotic biota, measured on temporal and spatial scales relevant to the organisms.
2. Responses of lotic biota to discharge fluctuations, including the processes that mediate community recovery following resets caused by spates or droughts.
3. Movements of lotic organisms that mediate gene flow, resource tracking, and multilevel species interactions.
4. Life history patterns, with special emphasis on ontogenetic bottlenecks that determine the vulnerability of populations confronting environmental perturbation.
5. Consequences of species interactions for community- and ecosystem-level processes in rivers and streams.
Without attempting to be comprehensive in our review, we discuss limits and limitations of our knowledge in these areas. We also suggest types of data and technological development that would advance our understanding. While we appreciate the value and need for empirical and comparative information, we advocate search for key mechanisms underlying community interactions as the crucial step toward developing general predictions of responses to environmental change. These mechanisms are likely to be complex, and elucidation of interacting bilateral, or multilateral, biotic and abiotic controls will progress only with the continuing synthesis of community- and ecosystem-level approaches in lotic ecology.
1. Physical conditions impinging on lotic biota, measured on temporal and spatial scales relevant to the organisms.
2. Responses of lotic biota to discharge fluctuations, including the processes that mediate community recovery following resets caused by spates or droughts.
3. Movements of lotic organisms that mediate gene flow, resource tracking, and multilevel species interactions.
4. Life history patterns, with special emphasis on ontogenetic bottlenecks that determine the vulnerability of populations confronting environmental perturbation.
5. Consequences of species interactions for community- and ecosystem-level processes in rivers and streams.
Without attempting to be comprehensive in our review, we discuss limits and limitations of our knowledge in these areas. We also suggest types of data and technological development that would advance our understanding. While we appreciate the value and need for empirical and comparative information, we advocate search for key mechanisms underlying community interactions as the crucial step toward developing general predictions of responses to environmental change. These mechanisms are likely to be complex, and elucidation of interacting bilateral, or multilateral, biotic and abiotic controls will progress only with the continuing synthesis of community- and ecosystem-level approaches in lotic ecology.