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Structural connectivity and dispersal ability are important constraints on functional connectivity among populations. For aquatic organisms that disperse among stream corridors, the regiona...

Studies of aquatic–terrestrial ecosystem linkages explore the mechanisms by which components of one ecosystem, such as the aquatic insect community in a stream, directly affect components o...

River biodiversity is threatened globally by hydropower dams, and there is a need to understand how dam management favors certain species while filtering out others. We examined aquatic invertebrate communities within the tailwaters 0–24 km downstream of seven large hydropower dams in the Colorado River Basin of the western United States. We quantified aquatic invertebrate dominance, richness, abundance, and biomass at multiple locations within individual tailwaters and across the basin and identified biological community responses associated with dam operations and distance from dam. We found that each tailwater was dominated by 3–7 invertebrate taxa, accounting for 95% of total abundance. Half of these dominant taxa were non‐insect, non‐flying species and thus were unavailable to terrestrial consumers. Consistent with previous studies, aquatic insects and sensitive taxa were negatively associated with hydropeaking intensity (magnitude of daily flow fluctuations associated with hydropower generation), which limits the composition and potentially the quality of the invertebrate food base. While total invertebrate abundance and biomass did not change with increasing distance downstream from dams, insect and sensitive taxa richness, abundance, and biomass all increased, suggesting that impacts of hydropeaking are most acute immediately downstream of dams. Our results demonstrate that tailwaters experiencing hydropeaking support high abundances of aquatic invertebrate, but the diversity of these communities is low.

Stream and river ecosystems provide subsidies of emergent adult aquatic insects and other resources to terrestrial food webs, and this lotic–land subsidy has garnered much attention in recent research. Here, we critically examine a list of biotic and abiotic variables—including productivity, dominant taxa, geomorphology, and weather—that should be important in affecting the nature of these subsidy dynamics between lotic and terrestrial ecosystems, especially the pathway from emergent aquatic insects to terrestrial predators. We also explore how interactions between these variables can lead to otherwise unexpected patterns in the importance of aquatic subsidies to terrestrial food webs. Utilizing a match-mismatch framework developed previously, we identify how these variables and interactions may be affected by a broad suite of stressors in addition to contaminants: climate change, land-use conversion, damming and water abstraction, and species invasions and extinctions. These stressors may all act to modify and potentially exacerbate the effects of contaminants on subsidies. The available literature on many variables is sparse, despite strong theoretical underpinnings supporting their importance for lotic–land subsidies. Notably, these understudied variables include those related to physical geomorphology and the structure of the stream/river and floodplain/riparian zone as well as species-specific interactions between aquatic and terrestrial organisms. We suggest that more explicit characterization of these variables and more research directly linking broad-scale stressors to subsidy resource–consumer interactions can help provide a more mechanistic understanding to lotic–land subsidy dynamics within a changing environment.

Evaluating environmental effects on fish growth can be challenging because environmental conditions may vary at relatively fine temporal scales compared with sampling occasions. Here we develop a Bayesian state-space growth model to evaluate effects of monthly environmental data on growth of fish that are observed less frequently (e.g., from mark–recapture data where time between captures can range from months to years). We assess effects of temperature, turbidity, food availability, flow variability, and trout abundance on subadult humpback chub (Gila cypha) growth in two rivers, the Colorado River (CR) and the Little Colorado River (LCR), and we use out-of-sample prediction to rank competing models. Environmental covariates explained a high proportion of the variation in growth in both rivers; however, the best growth models were river-specific and included either positive temperature and turbidity duration effects (CR) or positive temperature and food availability effects (LCR). Our approach to analyzing environmental controls on growth should be applicable in other systems where environmental data vary over relatively short time scales compared with animal observations.

We investigated the phenology of adult angel lichen moths (Cisthene angelus) along a 364-km long segment of the Colorado River in Grand Canyon, Arizona, USA, using a unique data set of 2,437 light-trap samples collected by citizen scientists. We found that adults of C. angelus were bivoltine from 2012 to 2014. We quantified plasticity in wing lengths and sex ratios among the two generations and across a 545-m elevation gradient. We found that abundance, but not wing length, increased at lower elevations and that the two generations differed in size and sex distributions. Our results shed light on the life history and morphology of a common, but poorly known, species of moth endemic to the southwestern United States and Mexico.

Published by Oxford University Press on behalf of American Institute of Biological Sciences 2016. This work is written by (a) US Government employee(s) and is in the public domain in the US. The published article can be found at: http://bioscience.oxfordjournals.org/content/66/7/561

River-channel confluences create habitat heterogeneity by introducing multiple zones of hydraulic flow and increase macroinvertebrate densities and diversity via the input of coarse sediment, allochthonous detritus, and nutrients. Current understanding of confluence effects on stream community structure and function is based mostly on research conducted at medium-to-large tributary confluences where nutrient and detrital loads are typically high. Confluences of headwater streams and in streams without the input of these materials are understudied. In this study, we sampled macroinvertebrate communities and measured sediment and flow conditions upstream, within, and downstream of confluences. Our sampling included braided confluences, which lack allochthonous detritus and coarse sediment sources, and headwater-stream confluences. Braided confluences had lower macroinvertebrate densities and richness compared to up- and downstream reaches, whereas headwater-stream confluences had a negligible effect...

This chapter introduces key concepts and sampling methods concerning drift of benthic stream invertebrates, and the emergence and oviposition behavior of lotic insects, with a focus on the growing array of methods for their quantification being applied in food web and ecosystem studies. Methods are provided to measure the rate of net clogging (which informs the design of drift studies), compare drift among habitat types in wadeable streams and between day and night, and quantify the vertical distribution of drift in large rivers. Methods are also described for sampling emerging adults and estimating emergence flux, examining dispersal distances of adult insects laterally from a stream, and quantifying emergence or postemergent adults as prey available to terrestrial insectivores. Finally, methods are presented regarding a phenomenon closely linked to both emergence and drift, oviposition, including observing behavior and searching for insect eggs, quantifying egg densities and oviposition-site selection, rearing insect eggs, and measuring hatch success.

Insect emergence is a fundamental process in freshwaters. It is a critical life-history stage for aquatic insects and provides an important prey resource for terrestrial and aquatic consumers. Sticky traps are increasingly being used to sample these insects. The most common design consists of an acetate sheet coated with a nondrying adhesive that is attached to a wire frame or cylinder. These traps must be prepared at the deployment site, a process that can be time consuming and difficult given the vagaries of field conditions. Our goals were to develop a sturdy, low-cost sticky trap that could be prepared in advance, rapidly deployed and recovered in the field, and used to estimate the flight direction of insects. We used 150-mm Petri dishes with lids. The dishes can be coated cleanly and consistently with Tangle-Trap® adhesive. Deploying traps is simple and requires only a pole set near the body of water being sampled. Four dishes can be attached to the pole using Velcro and aligned in 4 differe...

Barcodes are used to label and track just about everything these days. Look around your office, in your medicine cabinet, at the package you just received in the mail, or on the shelves of any shop in town, and you will immediately grasp the ubiquity of their use. Interestingly, railroads and supermarkets were the early pioneers of barcode development: the former needing a way to track railway car location and ownership on a national scale, the latter needing a way to track a diverse array of products and to decrease checkout times (Nelson 1997). Barcodes first came to use in the sciences via the field of medicine, and the medical literature contains hundreds of publications describing how this technology has reduced errors in patient specimen identification and handling, where error mitigation is crucial. In short, barcodes have been adopted by many industries, and in many fields they are now synonymous with asset tracking.

Streams and adjacent terrestrial ecosystems are characterised by permeable boundaries that are crossed by resource subsidies. Although the importance of these subsidies for riverine ecosystems is increasingly recognised, little is known about how they may be influenced by global environmental change. Drawing from available evidence, in this review we propose a conceptual framework to evaluate the effects of global change on the quality and spatio-temporal dynamics of stream-terrestrial subsidies. We illustrate how changes to hydrologic and temperature regimes, atmospheric CO2 concentration, land-use, and the distribution of non-indigenous species can influence subsidy fluxes by affecting the biology and ecology of donor and recipient systems and the physical characteristics of stream-riparian boundaries. Climate-driven changes in the physiology and phenology of organisms with complex lifecycles will influence their development time, body size and emergence patterns, with consequences for adjacent terrestrial consumers. Also, novel species interactions can modify subsidy dynamics via complex bottom-up and top-down effects. Given the seasonality and pulsed nature of subsidies, alterations of the temporal and spatial synchrony of resource availability to consumers across ecosystems is likely to result in ecological mismatches that can scale up from individual responses, to communities, to ecosystems. Similarly, altered hydrology, temperature, CO2 concentration, and land-use will modify the recruitment and quality of riparian vegetation, the timing of leaf abscission, and the establishment of invasive riparian species. Along with morphological changes to streamterrestrial boundaries, these will alter the use and fluxes of allochthonous subsidies associated with stream ecosystems. Future research should aim to understand how subsidy dynamics will be affected by key drivers of global change, including agricultural intensification, increasing water use, and biotic homogenization. Our conceptual framework based on the match-mismatch between donor and recipient organisms may facilitate understanding of the multiple effects of global change and aid in the development of future research questions. This work was supported by the European Union under the Seventh framework Programme through the REFRESH and BioFresh projects. S. Larsen was also supported by a fellowship from the Synthesis Centre of the German Centre for Integrative Biodiversity research (iDiv).

Knickpoints are dynamic geomorphic formations in the longitudinal stream profile that have long been a subject of interest for geomorphologists, but have been largely unstudied in stream ecology. We measured discharge, bed sediment, and macroinvertebrate communities around knickpoints in forested and urban catchments. Knickpoints introduced microscale heterogeneity in discharge. This heterogeneity may be important in providing refugia for benthic biota during low-flow conditions, depending on the condition of the bed sediment below the knickpoint, which was highly variable. In addition, knickpoints supported a unique filterer-dominated community of macroinvertebrates not found elsewhere in the stream reach. The knickpoint itself also may maintain a higher overall density of macroinvertebrates in comparison to other habitats in the stream reach, but this prediction was only weakly supported. Instead, the largest differences in macroinvertebrate community metrics were consistently between urban a...

Dewatering disturbances are common in aquatic systems and represent a relatively untapped field of disturbance ecology, yet studying dewatering events along gradients in non-dichotomous (i.e. wet/dry) terms is often difficult. Because many stream restorations can essentially be perceived as planned hydrologic manipulations, such systems can make ideal test-cases for understanding processes of hydrological disturbance. In this study we used an experimental drawdown in a 440 ha stream/wetland restoration site to assess aquatic macroinvertebrate community responses to dewatering and subsequent rewetting. The geomorphic nature of the site and the design of the restoration allowed dewatering to occur predictably along a gradient and decoupled the hydrologic response from any geomorphic (i.e. habitat heterogeneity) effects. In the absence of such heterogeneous habitat refugia, reach-scale wetted perimeter and depth conditions exerted a strong control on community structure. The community exhibited an incremental response to dewatering severity over the course of this disturbance, which was made manifest not as a change in community means but as an increase in community variability, or dispersion, at each site. The dewatering also affected inter-species abundance and distributional patterns, as dewatering and rewetting promoted alternate species groups with divergent habitat tolerances. Finally, our results indicate that rapid rewetting – analogous to a hurricane breaking a summer drought – may represent a recovery process rather than an additional disturbance and that such processes, even in newly restored systems, may be rapid.

Soil biogeochemical processes and the ecological stability of wetland ecosystems under global warming scenarios have gained increasing attention worldwide. Changes in the capacity of microorganisms to maintain stoichiometric homeostasis, or relatively stable internal concentrations of elements, may serve as an indicator of alterations to soil biogeochemical processes and their associated ecological feedbacks. In this study, an outdoor computerized microcosm was set up to simulate a warmed (+5°C) climate scenario, using novel, minute-scale temperature manipulation technology. The principle of stoichiometric homeostasis was adopted to illustrate phosphorus (P) biogeochemical cycling coupled with carbon (C) dynamics within the soil-microorganism complex. We hypothesized that enhancing the flux of P from soil to water under warming scenarios is tightly coupled with a decrease in homeostatic regulation ability in wetland ecosystems. Results indicate that experimental warming impaired the ability of stoichiometric homeostasis (H) to regulate biogeochemical processes, enhancing the ecological role of wetland soil as an ecological source for both P and C. The potential P flux from soil to water ranged from 0.11 to 34.51 mg m(-2) d(-1) in the control and 0.07 to 61.26 mg m(-2) d(-1) in the warmed treatment. The synergistic function of C-P acquisition is an important mechanism underlying C∶P stoichiometric balance for soil microorganisms under warming. For both treatment groups, strongly significant (p

Recently, an interest has emerged in the role of aquatic biota as geomorphic agents. Although it is difficult to untangle the interconnectedness of the biotic and abiotic constituents within channel networks, a few theoretical efforts and several recent empirical studies have capitalized on this interconnectivity, providing research that narrows the gap between the once widely separated fields of stream ecology and fluvial geomorphology. This chapter provides a review of the existing literature by focusing on specific process- and form-based research involving biological organisms as geomorphic agents. Wherever possible, comparisons are drawn from the more well-understood and documented hydraulic-based research. We conclude that with the exception of beaver and large grazing animals, the reviewed literature suggests that aquatic and semi-aquatic species act as limited geomorphic agents. That is, their scope of influence on channel forms and processes is typically direct, seasonally variable, and usually only meaningful at reach-scales during base-flow conditions.

Sticky traps are a convenient tool for assessing adult aquatic insect population dynamics, but there are many practical questions about how trap sampling artefacts may affect observed results. Utilising study sites on the Colorado River and two smaller streams in northern Arizona, USA, we evaluated whether catch rates and sex ratios of Chironomidae, a ubiquitous aquatic insect, were affected by spraying traps with insecticide, placing traps at different heights above ground, and placing traps at different locations within a terrestrial habitat patch. We also evaluated temporal variation in Chironomidae counts monthly over a 9-month growing season. We found no significant variation in catch rates or sex ratios between traps treated versus untreated with insecticide, nor between traps placed at the upstream or downstream end of a terrestrial habitat patch. Traps placed near ground level did have significantly higher catch rates than traps placed at 1.5m, although sex ratios were similar across heights. Chironomidae abundance and sex ratios also varied from month-to-month and seemed to be related to climatic conditions. Our results inform future sticky trap studies by demonstrating that trap height, but not insecticide treatment or precise trap placement within a habitat patch, is an important source of variation influencing catch rates.

It has been proposed that de novo synthesis of long-chain acyl-CoA (LC-CoA) is a signal for glucose-stimulated insulin secretion (GSIS). Key enzymes involved in synthesis of fatty acids from glucose include ATP-citrate lyase (CL) and fatty acid synthase (FAS). An inhibitor of CL, hydroxycitrate (HC), has been reported to inhibit insulin secretion in some laboratories but not in others. Here we show that high concentrations of NaCl created during preparation of HC by standard methods explain the inhibition of GSIS, and that removal of the excess NaCl prevents the effect. To further investigate the role of CL, two small interfering RNA adenoviruses (Ad-siCL2 and Ad-siCL3) were generated. Ad-siCL3 reduced CL mRNA levels by 92 +/- 6% and CL protein levels by 75 +/- 4% but did not affect GSIS in 832/13 cells compared with cells treated with a control adenovirus (Ad-siControl). Similar results were obtained with Ad-siCL2. Ad-siCL3-treated cells also exhibited a 52 +/- 7% reduction in cytosolic oxaloacetate, an 83 +/- 4% reduction in malonyl-CoA levels, and inhibition of [U-(14)C]glucose incorporation into lipid by 43 +/- 4%, all expected metabolic out-comes of CL suppression. Similarly, treatment of 832/13 cells with a recombinant adenovirus specific to FAS (Ad-siFAS) reduced FAS mRNA levels by 81 +/- 2% in 832/13 cells, resulting in a 59 +/- 4% decrease in [U-(14)C]glucose incorporation into lipid, without affecting GSIS. Finally, treatment of primary rat islets with Ad-siCL3 or Ad-siFAS reduced CL and FAS mRNA levels by 65 +/- 4% and 52 +/- 3%, respectively, but had no effect on GSIS relative to Ad-siControl-treated islets. These findings demonstrate that a normal rate of flux of glucose carbons through CL and FAS is not required for GSIS in insulinoma cell lines or rat islets.

Dam decommissioning projects, although numerous, rarely include complete sets of data before and after restoration for evaluating the ecological consequences of such projects. In this study, we used a before-after control-impact (BACI) design to assess changes in leaf litter decomposition and associated macroinvertebrate and fungal decomposers following dam decommissioning in Fossil Creek, Arizona, USA. Leaf litterbags were deployed in a relatively pristine site above the dam and a highly disturbed site below the dam where over 95% of the flow was previously diverted for hydropower generation. Leaf litter decomposition was significantly slower below the dam both measurement years (pre- and post- restoration) with no site-year interaction, indicating that decomposition in this stream section was not affected by increased flow. In contrast, both macro- invertebrates and fungi differed significantly above and below the dam prior to restoration but were similar post-restoration, supporting the concept that decomposer communities can quickly rebound fol- lowing reintroduction of full flow. Our results indicate that some aquatic ecosystem variables can return to a more natural state following ecological restoration activities such as water flow restoration.