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Sustainability science is an emerging field directed at advancing sustainable development. Informed by recent scholarship and institutional experiments, we identify key roles for economists and encourage their greater participation in this research. Our call to collaborative action comes from positive experiences with the Sustainability Solutions Initiative based at the University of Maine, where economists collaborate with other experts and diverse stakeholders on real-world problems involving interactions between natural and human systems. We articulate a mutually beneficial setting where economists’ methods, skills, and norms add value to the problem-focused, interdisciplinary research of sustainability science and where resources, opportunities, and challenges from science bolster economic research specifically and land/sea grant institutions broadly.

Rivers regulated by dams are typically characterized by altered biotic communities and habitat structure in downstream reaches. In the Jackson River (Alleghany Co., VA), a relatively constant flow regime below Gathright Dam and anthropogenic nutrient loading have apparently contributed to nuisance levels of periphyton (>300 mg chlorophyll a m−2). These nuisance growths cause low dissolved oxygen concentrations in the water column and altered benthic habitats in the Jackson River. The use of periodic pulsed flows has been suggested as a restoration practice that could potentially reduce periphyton biomass. We investigated the effects of increased flow on periphyton chlorophyll a (chl a), ash-free dry mass (AFDM), % organic matter (%OM) using streamside channels in which periphyton-colonized tiles were subjected to near-bed velocities ranging from 20 (control) to 240 cm s−1. Analysis of variance (ANOVA) and regression were used to examine periphyton responses to velocity treatments. There was a significant decrease in chl a and AFDM, and significant increase in %OM in velocity treatments of 150, 180 and 240 cm s−1 (p 100 cm s−1. Further study is needed to establish specific flow targets and evaluate the direct and indirect effects of pulsed flows on ecological conditions in the Jackson River. Copyright © 2009 John Wiley & Sons, Ltd.

Sustainable water resource management is constrained by three pervasive myths; that societal and environmental water demands always compete with one another; that technological solutions can solve all water resource management problems; and that environmental solutions to protect and maintain freshwater resources are more expensive and less dependable than technological solutions. We argue that conservation and good stewardship of water resources can go a long way toward meeting societal demands and values. Furthermore, water requirements to sustain ecosystem health and biodiversity in rivers and their associated coastal systems can be well aligned with options for human use and deliver a suite of ecosystem goods and services to society. However, to achieve ecologically sustainable water management, we propose several key issues that must be addressed. The objective of this opinion paper is to stimulate discussion across traditional discipline boundaries with the aim of forging new partnerships and collaborations to meet this pressing challenge of ecologically sustainable water management.

The Tennessee Valley Authority (TVA) initiated a Reservoir Releases Im- provement Program in 1991 to increase minimum flows and improve water quality by modifying its dam operations. We compiled a comprehensive data set from ecological monitoring below nine dams to evaluate the effects of these modifications on physico- chemical conditions and benthic macroinvertebrate assemblages. Abiotic and biotic data were collected in tailwaters by the TVA for three dam operation ''treatments'' (i.e., before any modifications, following flow modifications, and following both flow and dissolved oxygen (DO) modifications) at three different stations (Upper, Middle, and Lower) located at increasing longitudinal distances below each dam. Analysis of variance was used to test for differences in ecological conditions among treatments and stations. Dam modifications had significant effects on both abiotic and biotic variables, and macroinvertebrate assemblages exhibited significant longitudinal differences. Yearly mean DO and mean minimum velocity increased following dam modifications. Across all sam- pling stations, macroinvertebrate family richness increased and the percentage of pollution- tolerant macroinvertebrates (% Tolerant) decreased after dam modifications. Family richness also increased, and % Tolerant decreased, with increasing distance below the dams. Total abundance of macroinvertebrates increased after flow modifications and then decreased following changes in DO. The percentage of individuals belonging to the orders Ephem- eroptera, Plecoptera, and Trichoptera (% EPT) increased following flow and DO modifi- cations, but only at the Upper station. EPT family richness was unaffected by increased flow alone but increased following increases in both flow and DO. The design of the re- operation ''experiment'' made it difficult to ascertain the relative contributions of flow and DO changes to the observed biotic responses, but flow alone appeared to have a smaller beneficial effect than the combined effects of flow and DO.

Restoration of aquatic ecosystems is a high priority regionally and globally, yet only recently have such efforts adopted holistic approaches that include the restoration of streams and rivers flowing to coastal areas. As the largest estuary in the US, the Chesapeake Bay has been the focus of one of the most high-profile restoration programs ever undertaken in North America. While the primary emphasis has been on tidal waters, freshwater tributary clean-up strategies have recently been developed. We have compiled the first comprehensive database of over 4700 existing river and stream restoration projects in the Chesapeake Bay Watershed (CBW) to examine where dollars are being spent, what issues motivate restoration, and what approaches are used. By conservative estimates, in excess of $400 million has been invested in restoration projects since 1990. The majority of projects were implemented to restore forest vegetation in riparian areas and improve water quality. Although the CBW has an extremely high density of restoration activities relative to other regions of the US, only 5.4% of the project records indicated that related monitoring of project performance has occurred. To provide cost-effective management solutions, we recommend that a centralized tracking system be developed that includes restoration projects associated with both tidal and non-tidal waterways, along with a substantial increase in investment in the comprehensive monitoring of individual projects following implementation.

Summary 1. Increasingly, river managers are turning from hard engineering solutions to ecologically based restoration activities in order to improve degraded waterways. River restoration projects aim to maintain or increase ecosystem goods and services while protecting downstream and coastal ecosystems. There is growing interest in applying river restoration techniques to solve environmental problems, yet little agreement exists on what constitutes a successful river restoration effort. 2. We propose five criteria for measuring success, with emphasis on an ecological perspective. First, the design of an ecological river restoration project should be based on a specified guiding image of a more dynamic, healthy river that could exist at the site. Secondly, the river’s ecological condition must be measurably improved. Thirdly, the river system must be more self-sustaining and resilient to external perturbations so that only minimal follow-up maintenance is needed. Fourthly, during the construction phase, no lasting harm should be inflicted on the ecosystem. Fifthly, both pre- and postassessment must be completed and data made publicly available. 3. Determining if these five criteria have been met for a particular project requires development of an assessment protocol. We suggest standards of evaluation for each of the five criteria and provide examples of suitable indicators. 4. Synthesis and applications . Billions of dollars are currently spent restoring streams and rivers, yet to date there are no agreed upon standards for what constitutes ecologically beneficial stream and river restoration. We propose five criteria that must be met for a river restoration project to be considered ecologically successful. It is critical that the broad restoration community, including funding agencies, practitioners and citizen restoration groups, adopt criteria for defining and assessing ecological success in restoration. Standards are needed because progress in the science and practice of river restoration has been hampered by the lack of agreed upon criteria for judging ecological success. Without well-accepted criteria that are ultimately supported by funding and implementing agencies, there is little incentive for practitioners to assess and report restoration outcomes. Improving methods and weighing the ecological benefits of various restoration approaches require organized national-level reporting systems.

Real and apparent conflicts between ecosystem and human needs for fresh water are contributing to the emergence of an alternative model for conducting river science around the world. The core of this new paradigm emphasizes the need to forge new partnerships between scientists and other stakeholders where shared ecological goals and river visions are developed, and the need for new experimental approaches to advance scientific understanding at the scales relevant to whole-river management. We identify four key elements required to make this model succeed: existing and planned water projects represent opportunities to conduct ecosystem-scale experiments through controlled river flow manipulations; more cooperative interactions among scientists, managers, and other stakeholders are critical; experimental results must be synthesized across studies to allow broader generalization; and new, innovative funding partnerships are needed to engage scientists and to broadly involve the government, the private sector, and NGOs.

Habitat selection is often viewed as a major process determining the distribution and abundance of animals. If animals have limited control over their dispersal, however, they may sometimes be unable to colonize preferred habitats. In such cases, observed spatial variations in abundance may reflect the vagaries of colonization rather than true habitat preferences. Our study examined whether local variations in the density of stream insects are related to habitat quality or colonization history. We focused on larval black flies (Simulium vittatum), a representative group of suspension feeders that exhibit strong preferences for habitats characterized by high near-bed velocities. Despite these preferences, variations in the density of S. vittatum larvae across benthic substrates within the riffles of a Pennsylvania stream were often weakly related to velocity. Moreover, densities on substrates of similar velocity varied by more than six-fold. We conducted a field experiment to test whether these density differences reflect habitat preferences and employed a short-term behavioral assay based on larval emigration to quantify preference. We used a block design to compare emigration rates from paired substrates that had been colonized by markedly different larval densities despite their similar velocities. After removing these larvae, we added larvae to both substrate types in equal numbers, following which we measured larval emigration. There was no significant difference in emigration between these paired substrates even though statistical power was high, which indicates that the large density differences present at the end of the colonization period on substrates of similar velocity were unrelated to habitat preferences. There were, however, significantly more departures from blocks of substrates in lower velocities than from those in higher velocities, demonstrating that the duration of our experiment was sufficient for black fly larvae to express their habitat preferences. These results are consistent with the hypothesis that dispersal constraints associated with the settlement of drifting larvae limit their ability to reach preferred habitats. In fact, related studies predict that larval settlement rates are lowest in the high velocity habitats preferred by larvae. We conclude that such dispersal constraints may be important for a wide variety of freshwater, marine, and terrestrial organisms that are transported by moving fluids.

Riparian forest restoration has become a major focus of watershed initiatives to improve degraded stream ecosystems. In urban watersheds, however, the ability of riparian forests to improve stream ecosystems may be diminished due to widespread, upland disturbance. This paper presents the methodology and some preliminary results from the first year of fieldwork on a 3-year project designed to assess the ecological benefits of riparian reforestation in urban watersheds. The study is based on an integrated, multidisciplinary sampling of physical, chemical, and biological attributes at forested and non-forested sections of 12 streams with different amounts of urban developement within their watersheds. Restored sections of three streams are also being monitored over the 3-year duration of the project. Sampling and analysis will continue through December 2000.

The acoustic Doppler velocimeter (ADV) has recently been suggested as a promising instrument for characterizing near-bed flows, particularly in the first 10 mm above the bed where many benthic organisms live. Flow characteristics in such settings often exhibit steep vertical gradients, however, so the reliable use of the ADV requires knowledge of the size and location of the instrument's acoustic sampling volume. We describe simple procedures for quantifying the vertical size of the ADV's sampling volume and assessing its height above the bed. Our results indicate that the vertical size of the sample volume for the ADV we tested was much larger than expected based on the values predicted by software configuration. Moreover, this system incorrectly reported several distances needed to accurately position the sample volume near the bed (e.g., the transmitter-to-bed distance, the sample volume-to-bed distance, and the transmitter-to-sample volume distance). We also demonstrate that incorrect assumptions about the size and location of the sampling volume can lead to inaccurate near-bed flow measurements by comparing the time-averaged flow speed profiles generated by our ADV with those obtained using a hot-film velocimeter (HFV). At heights > 10 mm above the bed, both instruments yielded similar flow speed estimates. Closer to the bed, however, the flow speeds reported by ADV were as much as 60-80% less than those from HFV. These large errors in estimating near-bed flow speeds are a direct consequence of incorrect assumptions about the centerpoint and size of the ADV's sample volume. Specifically, when the vertical size of the sampling volume is larger than its nominal size, users may mistakenly position the ADV so that the bed is included within the sampling volume, which in turn results in the underestimation of flow speeds. By validating the size and location of the sampling volume, as well as carefully monitoring signal quality parameters, users can ensure proper placement of the ADV relative to the bed and avoid erroneous measurements.

Ecological theory suggests that the impact of predation can be strongly modified by the existence of regions of the environment in which prey are less accessible to predators, which underscores the need for empirical studies examining the factors influencing the availability and importance of such prey refuges. Our study tested whether benthic microhabitats with high flows provide suspension-feeding larval black flies (Simulium␣vittatum) with a spatial refuge in which the negative impact of predatory flatworms (Dugesia dorotocephala) is reduced. We conducted a short-term field experiment in Chester Creek (southeastern Pennsylvania, United States) to examine how the number of black fly larvae inhabiting tile substrates responded to manipulated variations in flatworm abundance and current speed. The abundance of flatworms declined with increasing current speed, thereby creating the potential for sites with high flows to provide larvae with a refuge from these predators. Multiple regression analysis revealed that the final abundance of larvae exhibited a significant negative relationship to flatworm abundance and a significant positive relationship to current speed. After adjusting for variations in elapsed time and initial larval abundance, flow and predators explained 38% of the variation in the rate of change in larval abundance. The positive correlation between larval abundance and flow had two components: a positive, direct effect of flow on larvae, which arises because these food-limited consumers prefer to reside within sites with faster flows where they can feed at higher rates; and a negative effect of flow on predators, and of predators on larvae, which combine to yield a positive indirect effect of flow on larvae. This indirect effect demonstrates the existence of flow-mediated refuges (i.e., microhabitats in which the impact of predation is reduced due to high flows), although the effect accounts for a small proportion of total variation in larval abundance. A consideration of biomechanical relationships suggests that microhabitats with high flows are likely to create prey refuges in a wide range of freshwater and marine benthic environments. In particular, predators will often experience greater dislodgement forces than prey because of their larger size and because they project farther above the bed where current speeds are faster. Moreover, the ability to resist a given dislodgement force may be greater for many prey, especially those that are sessile or semi- sessile.

Turbulence plays an important role in the transport of particles in many aquatic systems. In addition to various types of inorganic sediment (silt, sand, etc.), these particles typically include bacteria, algae, invertebrates, and fine organic debris. In this paper, we focus on one aspect of turbulent particle transport; namely, the average time required for a suspended particle to reach the bottom of a waterbody from a specified initial elevation. This is the mean hitting-time problem, and it is important in determining, for example, the effect of turbulence on downstream transport of organic particles, dispersal times and dispersal propagules. We approach this problem by developing a stochastic diffusion model of particle transport called the Local Exchange Model, which is an extension of a model posed by Denny & Shibata (1989) in an earlier study of the same problem. We show how the mean hitting-time of the Local Exchange Model varies with factors such as a particle's fall velocity an the shape of the vertical profile in turbulent mixing. We also show how the mean hitting-time is related to both the vertical profile in current velocity and the vertical profile in concentration of suspended particles, and how these relationships can be exploited in testing the model. Among other things, our results predict that, with the sole exception of neutrally buoyant particles that do not swim downward, there is always a region of the water-column in which turbulence increases rather than decreases the mean hitting-time. We discuss the significance of this and other results for dispersal by benthic organisms.

We used hot-film anemometry to quantify fine-scale spatial and temporal flow variations near the surfaces of stones inhabited by suspension-feeding larval blackflies (Simulium vittatum). We focused especially on within-stone patterns of covariation between patchy microdistributions of larvae and local spatial variations in current speed. Current speeds were sampled at 256 Hz for heights between 1 and 10 mm above the bed. Profiles of current speed exhibited complex shapes, and boundary-layer thicknesses ranged from 5 mm. Average current speeds measured 2 mm above the bed (the approximate height of larval feeding appendages) ranged between 7 and 59 cm s- ‘. Current speeds measured 10 mm above the bed were very poor predictors of speeds measured at the 2-mm height. Larval abundance exhibited a significant positive relationship to current speed at 2-mm height, and within-stone variations in speed explained -59% of the variation in abundance. Time series of current speed exhibited marked fine-scale temporal heterogeneity, fluctuating by as much as 80 cm s-l in ~0.1 s. Maximum accelerations sometimes exceeded 1 x lo4 cm s-*, which suggests that the forces tending to dislodge benthic organisms from the bed may be greater than previous estimates based on assumptions of steady flow. Observed levels of turbulence were greater than predicted from traditional boundary-layer theory. We suggest that much of the turbulence evident on individual stones is not produced by local shear but is inherited from upstream roughness elements that cause flow separation.

Experimental studies were used to examine the mechanisms governing the distribution and abundance of two major patch types in unshaded reaches of Augusta Creek, Michigan (USA). One patch type is dominated by Cladophora glomerata, a macroalga potentially able to monopolize space, whereas the other type is comprised of a low-growing, epilithic microalgal lawn inhabited by several species of sessile grazers (especially the caddisflies Leucotrichia pictipes and Psychomyia flavida). Cladophora patches are absent from mid-channel sites characterized by current velocities ≤ ca. 50 cm s−1; caging experiments indicate that their absence is due to grazing by crayfish (Orconectes propinquus). Cladophora's presence in sites with velocities >50 cm s−1 apparently results in part because crayfish foraging activity is impaired in high flow regimes. The presence of Cladophora strongly affects various other invertebrates due to its alteration of abiotic and biotic characteristics of the microhabitat. For example, the abundance of sessile grazers (e.g. Leucotrichia and Psychomyia) that inhabit microalgal patches is negatively correlated to the abundance of Cladophora, whereas the abundance of several other invertebrates (e.g. Stenonema mayflies and Taeniopteryx stoneflies) is positively correlated to Cladophora's abundance. Therefore, in some portions of this system, crayfish act as keystone predators because of their ability to regulate the abundance of Cladophora, which in turn has strong positive and negative effects on other components of the community. Cladophora does not always monopolize space at high velocities in the absence of crayfish, however. If sessile grazers arrive at such sites before Cladophora, they can prevent its establishment. Thus, where crayfish are absent, the likelihood that a site will be dominated by either Cladophora patches or sessile grazer — microalgal lawn patches depends on two sets of stochastic processes: (1) those that create bare space (e.g. disturbance and grazer emergence); and (2) those controlling the timing of recruitment by Cladophora or grazers at these bare sites. These priority effects (i.e. the ability of grazers and Cladophora to inhibit each other's establishment) contribute to the marked spatial heterogeneity of these two patch types. Collectively, these results demonstrate how interactions between competition, predation, and physical factors can generate a complex mixture of community patterns.

We analyzed diatom and water chemistry data collected by The Academy of Natural Sciences from 47 rivers throughout the eastern United States to address several ecological questions. How does the composition of diatom assemblages vary over large regional scales? What are the most important environmental factors affecting assemblage composition and how does their influence vary among regions and with spatial scale? How do distributions and autecological characteristics of individual taxa vary spatially? What are the implications of answers to these questions for use of diatoms as water quality indicators? Data for 186 samples at 116 sites were collected from 1951 to 1991 onmoderate- to large-sized rivers ranging fromMaine to Texas as part of Academy monitoring and survey programs, most initiated and implemented by Dr. Ruth Patrick. Several sites were highly impaired by point and non-point source pollution. Diatomassemblages grouped into four main categories, based on multivariate analyses. Group membership correlated equally well with intermediate-scale geographic regions and water chemistry: (1) Northeastern US rivers with lower alkalinity and hardness, and pH 6.5–7.8; (2) Primarily dilute coastal plain rivers in the southeastern United States with the lowest average pH (5.5–7.3) of all sites and some with high DOC; (3) Rivers within and west of the AppalachianMountains, generally having higherpH(>7.5) than those in other regions, but with relatively low chloride concentrations; and (4) Gulf Coast rivers with the highest chloride (>100 mg 1−1), hardness (>250 mg 1−1), and pH of rivers in all the groups. Hardness, pH, alkalinity, and Cl explained most of the variation among diatom assemblages, based on ordination analysis. Factors related to water quality problems, such as BOD, P, NH4, and turbidity explained much less variability at the eastern US scale, but were more important in the four intermediate-scale regions. Diatom taxa abundance-weighted mean values for water chemistry characteristics varied among the four intermediate-scale regions, often greatly, and in proportion to the average measured values for each region. Design of calibration data sets for development of water quality indicators should account for spatial scale in relation to species dispersal, regional geochemistry and habitat types, and human-influenced water chemistry characteristics.

Larval black flies often exhibit spatially aggregated distributions, and individuals within patches can potentially reduce the supply of suspended food particles to downstream neighbors by modifying local flow characteristics. We used hot-film anemometry to quantify the magnitude and spatial extent of flow modifications downstream from feeding Simulium vittatum larvae in a laboratory flume, and to determine whether temporal patterns of flow variation are related to movements of the larval feeding appendages. Mean velocity 1 mm downstream from feeding larvae was reduced by 75%, and the percent reduction in velocity diminished asymptotically with downstream distance. Reduced velocities were evident as much as 60 mm downstream from, and 3 mm to either side of, larvae. Turbulence intensity (i.e., the SD of the velocity time series) was generally higher in this region relative to control flow conditions. Three results demonstrate the major contribution of the larval feeding appendages (i.e., labral fans) to such flow modification. First, there was a minimal reduction in mean velocity 5 mm downstream from non-feeding larvae (i.e., with closed labral fans), whereas mean velocity at the same location was reduced markedly when larvae were feeding. Second, the power spectrum of the velocity time series exhibited greatest power at frequencies that corresponded to the frequency of labral fan motions. Third, fan flick times accounted for most of the variance in the velocity power spectrum. The large local flow modifications that we documented have potentially important consequences for the feeding performance and growth of individuals located within larval aggregations, and are likely to influence behavioral interactions and spacing patterns.

Benthic suspension feeders are important components of aquatic ecosystems, often dominating the use of space and influencing patterns of material cycling between the water column and benthos. Biomechanical theory predicts that feeding by these consumers is governed by the flux (i.e., product of food concentration and velocity) of particulate material to their feeding appendages. We performed a laboratory flume experiment to test how feeding by larval black flies (Simulium vittatum Zett.) responds to independent manipulations of flow and food concentration. We quantified larval body posture, flick rate of the labral fans, and ingestion rate as a function of two concentrations of a baker's yeast/chalk suspension (0.96 and 4.44 mg l-1) and five water velocities (20, 30, 45, 60, and 90 cm s-1). Using analysis of covariance, we found that both flick rate and ingestion rate increased in a decelerating manner with increasing velocity, while fan height decreased linearly with increasing velocity. In contrast, food concentration had no effect on any aspect of feeding behavior. Thus, although both velocity and food concentration contribute to particle flux, our results indicate that the two were not substitutable under the range of conditions tested here.

The authors of this Policy Forum developed a comprehensive database of >37,000 river restoration projects across the United States. Such projects have increased exponentially over the past decade with more than a billion dollars spent annually since 1990. Most are intended to enhance water quality, manage riparian zones, improve in-stream habitat, allow fish passage, and stabilize stream banks. Only 10% of project records document any form of project monitoring, and little if any of this information is either appropriate or available for assessing the ecological effectiveness of restoration activities.

We tested whether larval black flies actively control the positioning of their feeding appendages (labral fans), and if so, whether their posture represents a balance between the conflicting demands of drag and feeding. We compared the postures of live larvae with the postures of larvae killed by heat-shock in three different flow regimes in a laboratory experiment; we assumed that the postures of heat-killed larvae approximated a passive response to drag. The average height of the labral fans above the bed declined significantly in faster flows, and was significantly greater in live than dead larvae. There was also a significant interaction effect, since the difference between the fan heights of live and dead larvae was greater in slower flows. Two mechanisms may contribute to this result. Larvae in slower flows have to increase their fan heights more than larvae living in faster flows to achieve comparable increases in velocity and thus particle flux. In addition, muscular strength may limit the feeding postures larvae can assume. The fan heights of live larvae also varied depending on the concentration of food particles: larvae exposed to low food concentrations held their fans higher above the bed than did larvae exposed to high food concentrations in the same flow regime. This change in posture is due neither to an uneven particle concentration in the boundary layer nor to added drag from particles trapped in the labral fans. Collectively, our results indicate that these suspension feeders actively control their feeding posture, and suggest that these varying postures represent a dynamic balance between the conflicting needs of minimizing drag and maximizing feeding.

To understand and predict the dynamics of a population it is necessary to determine whether processes such as dispersal, growth and mortality are density-dependent and how these processes may influence patterns of abundance and distribution. Newly hatched individuals (neonates) are a common dispersal stage in many terrestrial and marine invertebrates, and may affect where, and in what abundance, older stages are subsequently found, hence underscoring the potential importance of supply-side processes in governing the ecology of those systems. In streams, benthic invertebrates might be expected to experience strong density-dependent competition near oviposition sites due to the often clumped distribution of eggs, yet the ecology of the early life-history stages has been poorly studied. In laboratory experiments, we examined whether newly hatched black fly larvae (Simulium vittatum) disperse from egg masses, via water currents, in a density-dependent fashion, and the likelihood that the strength of density-dependence is modulated by current speed. To understand better the mechanisms controlling neonatal dispersal, we also determined the amount of time an average larva spent fighting, and the relationship between fights and dispersal events. The experimental results demonstrate that the dispersal rate of neonates from egg masses was strongly density-dependent. A second-order polynomial regression model reflecting this density effect explained 91% and 75% of the variation in dispersal rates for the fast and slow current speed treatment, respectively. Dispersal was lower at fast than at slow current speeds, indicating that these patterns of drift are not the result of passive dislodgment by water currents. Current speed also modified the effect of density on dispersal rate. The increase in dispersal with a unit change in density was lower at fast than at slow current speeds. Increasing larval density and low current speed increased the proportion of time a larva spent fighting, but most larvae did not disperse immediately after being attacked. The density effect suggests that dispersal by black fly neonates can be a voluntary response to reduced feeding rates stemming from competition with neighboring larvae. In general, it appears that the tendency of neonates to remain at the oviposition site depends on the suitability of the microhabitat for feeding. The high dispersal rates we documented (up to 4.5% of individuals min -1 ) occurred in response to levels of larval density, current speed, and food concentration that are probably typical of many field settings. This implies that many neonates may also disperse in a density-dependent manner via water currents in the field. The distances traveled by large numbers of dispersing neonates may decouple the number of larvae in an area from the number of adults that oviposited there, which suggests that supply-side phenomena may be important in streams. The development of a clearer understanding of the role of density-dependent dispersal as a potential regulatory factor in black fly populations depends upon the assessment of the fate of drifting individuals, coupled with measurement of other sources of mortality in these populations.

manipulate and quantify the relationship between chlorophyll a biomass and `4C productivity for various algal assemblages. We observed an asymptotic relationship between algal productivity and biomass over a sixteen-fold range of algal standing crops, which differs from the hump-shaped relationship expected for populations following logistic growth. Our results demonstrate that primary productivity would increase significantly if Leucotrichia maintained a higher algal biomass within its territory (e.g. by reducing its short-term harvesting rate), which implies that it is not a prudent predator. Because some of this production is consumed by territorial intruders, however, the yield to Leucotrichia may be maximized at a lower algal biomass than that which maximizes total productivity.

Two points are evident from a review of the literature describing feeding territoriality in aquatic insects. First, feeding territoriality is much more common in this group than was previously recognized. Second, most of the examples involve species that have small foraging areas and harvest rapidly renewing resources, such as filterable particles and attached microalgae. To interpret these patterns, I discuss how the net benefits of territorial defense vary as a function of several components of food availability. I present the results of recent laboratory and field experiments testing cost-benefit models that predict patterns of territory size and defense frequency. Feeding-territory size in grazing caddisfly larvae increases with the resident's body size and is inversely related to food abundance, which agrees with the predictions of several models of optimal territory size. Two kinds of stream insects that rely on food items delivered by water currents ( i.e. , surface-feeding water striders and filter-feeding larval black flies) respond to increases in food abundance by reducing their allocation of time to territorial defense.In black flies, complex interactions between competitor density and food abundance also influence the amount of time spent defending a territory. I consider several connections between territorial behavior and interspecific competition. The distribution and abundance of both territorial species and their competitors may depend in part upon how the costs and benefits of feeding territoriality vary along resource abundance gradients. The tendency of some territorial grazers to settle preferentially near conspecifics may occur because animals living in groups exclude interspecific competitors more efficiently than isolated individuals, which suggests some simple tests of optimal group size models. I conclude by summarizing the strengths and weaknesses of these study systems, both as a source of new and broader theories of feeding territoriality, and as a testing ground for those theories. An important strength of these consumer-resource systems is the ability to conduct realistic experimental studies examining the causes and consequences of territoriality. One important weakness is the lack of information on the time-energy budgets of these insects. The acquisition of such information deserves a high priority, since it will permit more rigorous tests of cost-benefit models that evaluate the adaptive significance of territorial behavior.

The use and defense of food and space in the territorial larval caddisfly Leucotrichia pictipes (Trichoptera: Hydroptilidae) were evaluated through field observations and experiments in southwestern Michigan. These grazing stream insects live in silk cases attached to hard substrates and aggressively expel intruders (both conspecifics and other species) that enter their algal-covered foraging areas. Defended areas contained significantly greater algal standing crops, which were a benefit resulting from resource defense. This territorial behavior often led to patterns of uniform spacing between larvae in high-density patches. Exceptions to these patterns tended to "prove the rule"; when Leucotrichia cases were much closer than normal, at least one of the individuals had entered a nonterritorial life history stage. Larval territory size was determined by food requirements and food availability. For example, territory size is related to the resident's body mass according to the equation: Area = 2.39 Mass084. The exponent for this power function is similar to the exponent relating metabolic rate to mass in many insects, further supporting the view that territoriality in Leucotrichia is related to the defense of a limiting food resource. Testing the effect of food availability on territory size provided support for several optimal feeding-territory-size models; when availability was experimentally reduced, res- idents expanded the size of their territories relative to control larvae. Ordinarily, other competing grazer species (e.g., the mayfly nymph Baetis flavistriga) spent less time per unit area foraging within Leucotrichia's territory than they spent foraging elsewhere. However, when resident caddisflies were experimentally removed from their territories, these mayfly nymphs spent more time inside than outside the territory. The territory of Leucotrichia often provided a resource "oasis" containing sig? nificantly higher algal standing crops than unprotected areas, which were heavily utilized by a diverse guild of grazers. The mayfly nymphs seem to have adopted a territory-parasite strategy similar to that of some nectar-feeding birds, in that they regularly robbed resources from Leucotrichia territories by a combination of stealth and speed. Other members of the grazer guild were less able to gain access to these limited resources, so that Leucotrichia acted as a dominant competitor in this community.

SUMMARY 1. The functional response of the filter-feeding blackfly larva Frosimulium mixtum/fuscum was examined in laboratory experiments. We focused on the relationship between a component of the particle handling process (the cephalic fan flick rate) and ingestion rate, to determine whether ingestion rate is limited by handling-time. The influence of food deprivation on ingestion rate and feeding efficiency also was assessed. 2. Ingestion rate rose asymptotically with increasing food availability, leveling off at a concentration of about 100 mg1−1. Satiation did not account for this plateau. Flick rate (the frequency with which larvae open and close their cephalic fans) increased in a similar fashion, though flick rate only accounted for about two-thirds of the variation in ingestion rate. 3. A simple equation describing the components of the feeding process in blackfly larvae was developed to investigate alternate flick rate ‘decision rules’ capable of predicting relationships between food concentration, flick rate and ingestion rate. The flick rate did not follow a fixed time rule, in which larvae allow particles to accumulate in the fan for a fixed amount of time prior to retraction. For most food densities, flick rate patterns more closely approximated a fixed number rule, in which fans are retracted after a fixed number of particles accumulate. 4. Flick rate rose with increasing food concentration even after the ingestion rate had levelled off, whereas several optimal filter-feeding models predict that filtering rate should decline as food concentration increases above this level. This predicted behavior was not observed because the number of particles ingested per flick failed to increase with increasing food concentration. 5. The efficiency of particle ingestion (number ingested × number available−1× 100) was very low (

The objectives of this paper are to characterize an "ideal" environmental impact assessment (e.i.a.); to review the contemporary status of e.i.a. for several major activities and areas of development; and to identify successes, failures, and future needs in e.i.a.The institutional procedures to be followed for e.i.a. have been formalized in a number of countries, but the scientific basis and methods are still developing. We propose that the following elements comprise an ideal e.i.a.: (1) definition of scientific objectives, (2) background preparation, (3) identification of main impacts, (4) prediction of effects, (5) formulation of usable recommendations, (6) monitoring and assessment, (7) sufficient lead time, (8) public participation, (9) adequate funding, and (10) evidence that recommendations were used.The "best available" predictive, preoperational e.i.a.'s involving aquatic resources (power plants, fossil fuels, recreation, reservoirs, wastewater treatment, forestry, and dredging and water diversion in estuaries) were reviewed and scored on a 0–5 scale for each of the elements identified above. Mean scores for the criteria which could be assessed (nos. 1–8) indicated that the quality of the best available e.i.a.'s does not exceed our defined average but improves when legally required documents are excluded from the calculations. The lowest means, for criteria within the scientist's control (nos. 1–5), were obtained for "Prediction of effects" and ' "Formulation of usable recommendations." Overall mean scores for each development area (criteria 1–5) indicated three broad groups which included studies of above average quality (wastewater treatment, recreation); studies of approximately average quality (estuarine impacts, power plants, reservoirs, and fossil fuels); and studies of below average quality (forestry practices).Environmental impact assessment has had the following successes: increased environmental awareness due to public involvement in e.i.a., some environmental protection, and elucidation of intriguing research problems. The list of failures of e.i.a. is, however, longer: "tokenism," unrealistic time constraints, uncertainty of program or development schedules, difficult access to e.i.a. literature, questionable ethics, lack of coordination among studies, and poor research design.Future organizational/administrative needs of e.i.a. include improved access to e.i.a. literature, increased accountability for e.i.a.'s and their authors, improved public input into project decisions and designs, and improved organization and presentation of e.i.a. reports. Future scientific/research needs include development of methods to define and quantify relationships between biological, esthetic, and economic impacts; support for independent biological inventory programs; adequate time frames; improved design of research; inclusion of monitoring and assessment in every e.i.a.; study of cumulative impacts on a regional or national scale; and improved communication between scientists and planners.Key words: environmental impact assessment, aquatic ecology, power plants, fossil fuels, recreation, reservoirs, wastewater treatment, forestry, dredging and water diversion (estuaries)

The movement patterns and time–activity budgets of Dicosmoecus gilvipes were quantified from underwater observations of marked individuals in a northern California stream, during two studies in early and late June, 1977. Individuals traveled several metres per day. The only striking differences between the observed patterns of movement and those predicted from a random walk model are the following: (a) in both studies, large larvae moved significantly farther than small larvae; (b) in both studies, there is a pronounced diel rhythm to movement, with animals traveling faster during the day; (c) rates of travel in late June are ~3 times faster than those in early June. Since more than two-thirds of the total time–activity budget of these larval insects is dedicated to feeding, we suggest that the patterns of movement reported here largely reflect activities related to food acquisition. Several observations indicate that food is locally limiting and heterogeneously distributed across the stream bottom, thus requiring animals to move from patch to patch in order to meet their food requirements. Seasonal differences in rates of movement appear to result from phenological changes in the quantitative and qualitative food requirements of these stream insect grazers.

Field and laboratory experiments were conducted to determine whether intraspecific competition for food occurs during the larval stage of the periphyton-grazing caddisfly Glossosoma nigrior (Trichoptera: Glossosomatidae). Larvae were placed in field enclosures at densities less than, equal to, or greater than their natural densities. Most of these individuals began to pupate after ∼3 weeks, whereupon the mass of each individual was determined. Final mass declined significantly as larval densities increased, whereas neither developmental rate nor mortality/emigration rate was significantly affected by density manipulations. a supplemental experiment comparing the final mass of individuals grown at reduced densities in a laboratory stream with individuals from a natural stream bottom confirmed the results of the more extensive field experiment: reductions in density resulted in significant increases in final mass. Periphyton availability in field enclosures declined according to a negative exponential function as larval densities increased. Over the ∼25-fold range of larval densities used in these experiments, the final mass of individuals increased linearly with periphyton standing crops. This result suggests that Glossosoma larvae may compete for food even at densities below those employed in this study. Path analysis was used to explore the importance of indirect (i.e., exploitative) and direct (i.e, interference) mechanisms for the observed competitive effects. The analysis indicates that a model based solely on exploitation explains nearly as much of the variance in mass as a model incorporating both interference and exploitation.

Of the ecological factors that shape populations and communities, competition holds a prominent position. As ecology seeks to gain predictive power as a growing science, it will become increasingly important to know what role competitive interactions play in producing patterns within natural populations and communities. In this review, I consider some of the evidence suggesting the relative importance of such competitive interactions within stream ecosystems, emphasizing studies of stream Invertebrates. Though rigorous studies of such processes are few, I will conclude that the role of competition in these ecosystems has been underestimated. I suggest some of the fruitful paths towards a better understanding of this process, and consider the broader role of competition relative to other processes which organize stream benthic communities.

I report the results of descriptive and experimental studies of territorial behavior in filter-feeding stream insects. Blackfly larvae are sometimes evenly spaced on a substrate, suggesting that individuals may react negatively to the presence of other larvae. Direct observations indicate that larvae often behave aggressively towards neighbors. Three kinds of evidence support the hypothesis that this aggressive behavior is associated with the defense of filterable food resources. First, aggressive behavior is initiated almost exclusively towards upstream neighbors, which are the only larvae capable of altering the availability of filterable particles being delivered to an individual by the current. If an individual succeeds in aggressively displacing its upstream neighbor(s), it ceases to behave aggressively, and returns to its normal filter-feeding behavior. Second, following the successful displacement of such neighbors, the individual's short-term ingestion rate (measured indirectly) increases significantly. Third, the frequency of territorial behavior declines when the availability of filterable particles is experimentally increased. Taken together, these results indicate that larvae defend a local feeding site in order to maintain higher ingestion rates than would otherwise be possible, and that the net benefits of such aggressive behavior decline when food availability is high.

Larvae of the stream caddisfly Dicosmoecus gilvipes Hagen (Trichoptera: Limnephilidae) graze a periphyton resource that is heterogeneously distributed in space and time. Aspects of this resource patchiness were experimentally manipulated in the field, in order to assess their effect on larval foraging behavior. Individuals respond to spatial patchiness by concentrating their activity within patches containing high food levels. Larvae spend significantly less time in patches that have been recently grazed. There is a strong correlation between the amount of time spent in a food patch, and the amount of time elapsed since that patch was last grazed (oc the level of resource accumulation). Larvae tend to minimize the turn angle they make in moving from one patch to the next, which reduces the probability that they will return to a recently grazed patch. An assessment of the rate of periphyton removal effected by grazers in this habitat, relative to resource renewal rates, suggests that periphyton is a limiting resource for which D. gilvipes larvae compete exploitatively.

Etude descriptive et experimentale sur le terrain (Augusta Creek, Michigan) de l'aptitude des larves de Leucotrichia pictipes (Trichoptera) a mediatiser les interactions entre les populations algales d'une biocenose benthique en modifiant l'abondance locale et la composition specifique de ces populations

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