Molting is a stressful event in insect development. When an insect molts, the individual discards its exoskeleton and sheds and renews the interior lining of substantial portions of the respiratory (tracheal) system. We profiled for the first time the disruptive pattern of respiration during the molting process in larvae of the mayfly Cloeon dipterum (Ephemeroptera:Baetidae). Molting induces a precipitous drop in O₂ consumption immediately followed by a surge in O₂ consumption that appears to be compensatory in nature. Postmolt metabolic suppression is consistently observed during which O₂ consumption rates lag relative to those of nonmolting larvae. Furthermore, the magnitude of respiratory disturbance during the molt increases as a function of temperature. Increasing temperatures increase molting frequency and the apparently stressful nature of the molt itself. Thus, the insect molt appears to be a previously unappreciated route by which warming conditions may affect aquatic insects.

Collaboration is an essential skill for modern ecologists because it brings together diverse expertise, viewpoints, and study systems. The Lotic Intersite Nitrogen eXperiments (LINX I and II), a 17-y research endeavor involving scores of early- to late-career stream ecologists, is an example of the benefits, challenges, and approaches of successful collaborative research in ecology. The scientific success of LINX reflected tangible attributes including clear scientific goals (hypothesis-driven research), coordinated research methods, a team of cooperative scientists, excellent leadership, extensive communication, and a philosophy of respect for input from all collaborators. Intangible aspects of the collaboration included camaraderie and strong team chemistry. LINX further benefited from being part of a discipline in which collaboration is a tradition, clear data-sharing and authorship guidelines, an approach that melded field experiments and modeling, and a shared collaborative goal in the form of a universal commitment to see the project and resulting data products through to completion.

Among terrestrial insects, there is a rich guild of specialized necrophagous taxa, i.e., that feed directly on carrion. These organisms constitute a significant functional component of terrestrial ecosystems, and have recently been extensively studied because of their importance in forensic entomology. Nothing similar exists in lotic environments, although paradoxically, insects are the most important group of invertebrates in streams and rivers, where they constitute up to 70 to 90% of benthic communities. We present some hypotheses as to why specialized necrophagous taxa have evolved among terrestrial, but not among aquatic insects. We suppose that the lack of specialized necrophagous aquatic insects was the result of many synergic evolutionary pressures, partly related to the distinctive physical features of lotic environments and partly to processes of competitive exclusion with other closely related arthropods.

Characterizing biologically relevant stream disturbance regimes is challenging, but necessary to answer questions about disturbance effects on ecological processes. No universally accepted approach exists for characterizing stream regimes. Our goal was to evaluate approaches that can be applied to test effects of disturbance on benthic organisms. We defined disturbance as events or environmental conditions caused by changes in stream discharge that affect the stability or habitability of the stream bed. We used several metrics to describe disturbance regimes of mountain streams that were not permanently gauged in 1 catchment, and considered the trade-off between effort required to obtain the data and the quality of information gained. We used an innovative photographic method to assess substrate particle movement empirically as a benchmark for comparison to other indicators of channel stability and to metrics describing hydrologic variability relevant to streambed stability. We used a model selection procedure to choose the best combination of individual variables to explain variation in substrate particle movement and included those variables in a multivariate axis of disturbance that can be applied to evaluate effects of disturbance on benthic organisms. Individual variables with the highest explanatory power were maximum daily increase in discharge and the Pfankuch index of channel stability. Substrate particle size and stream size (drainage basin area) were related to the multivariate index of disturbance, but channel gradient was not. Protocols used to measure substrate stability and to obtain the multivariate index of disturbance were labor intensive, but our analyses indicate it may be reasonable to use more easily measured variables (e.g., Pfankuch index) to estimate disturbance to benthic organisms at local scales, although explanatory power may be reduced. Our analyses provide a menu of options to estimate variation in local disturbance regimes of ungauged mountain streams that may not be adequately explained by extrapolation from hydrographs of gauged streams.

Riverine ecosystems are linked to their watersheds, and both land use and physiographic environmental conditions influence nutrient dynamics and water quality. We assessed aquatic nutrients and their relationship with land use and physiographic conditions at multiple spatial scales in the Brazos River watershed (Texas, USA) to examine the interactions between land use and physiography and their combined influences on riverine nutrient dynamics. Patterns in physiography and land use were highly correlated, but physiographic gradients explained ∼2× more of the variability in riverine nutrient concentrations than land use (25 and 12%, respectively). The response of nutrient concentrations to spatial patterns of land use and physiography depended on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients, whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients when studying the interactions between a river and its watershed, especially in large, complex watersheds or those that cross steep environmental gradients.

The rapid range expansion of the toxigenic marine haptophytic alga Prymnesium parvum in inland aquatic systems across the southern USA and beyond has prompted great interest in the ecology and evolutionary biology of this invasive bloom-forming species. Researchers have speculated that increased toxicity and heterotrophy in suboptimal environments allow blooms to develop in these new inland habitats that seem to represent extremes relative to P. parvum's perceived optimal niche. We used a laboratory-based study to elucidate the roles of salinity and nutrient availabilities in P. parvum growth and toxicity under environmental conditions representative of hypereutrophic reservoirs of the southwestern USA in which P. parvum blooms are now common. We found evidence that nutrient conditions favoring toxigenesis in P. parvum are suboptimal for growth and bloom formation, whereas conditions conducive to high growth rates are less favorable for toxigenesis. In contrast, both growth and toxicity scaled positively with salinity. Taken in the context of the documented biogeography of P. parvum and that toxigenesis in P. parvum probably evolved in support of heterotrophic nutrient acquisition, our results suggest that P. parvum's apparent range expansion into and across the USA is driven by increasing availabilities of salty and nutrient-rich systems, rather than by its toxigenic abilities.

Changing rainfall patterns resulting from climate change are predicted to influence cyanobacterial blooms and associated production of toxins and other metabolites, but few studies have demonstrated this link. We explored seasonal and interannual trends in 2-methylisoborneol (MIB) concentrations and the correlation of these data with rainfall and hydrologic data from 2000 to 2013. We also conducted a detailed study of cyanobacterial abundances and MIB during 2 hydrologically extreme years, a prolonged drought in 2007 followed by an extremely wet year in 2008. The goal was to assess whether cyanobacterial abundances and explanatory variables that are often correlated with cyanobacterial abundances were useful predictors of MIB concentration. From 2000 to 2013, mean annual rainfall was negatively related to mean annual MIB (r = -0.50, p = 0.08) and explained 25% of the variation in MIB. In 2007, MIB and cyanobacterial abundance were high, whereas in 2008, MIB and cyanobacterial abundance were low. The total N:total P (TN:TP) mass ratio was strongly related to MIB concentration during the drought and explained 44% of the variation in MIB concentration (r = -0.66, p = 0.003). Our results suggest that rainfall and the TN:TP mass ratio may be useful predictors for MIB in drinking-water reservoirs.

The boreal landscape is a mosaic of wetlands with distinct ecosystem properties. Algae are important for wetland functioning, but relatively little is known about the structure of algal communities among boreal wetlands. We documented spatial and temporal variability of algal community dynamics and productivity during a growing season in 6 wetlands (1 rich and 1 poor fen, 1 tussock, and 3 riverine marshes) in interior Alaska. Algal biomass and productivity were greater in the poor fen and a riverine marsh than in all other wetlands. Water depth and nutrients were significant predictors of benthic algal biomass and productivity among wetlands and were greatest immediately after the spring thaw and decreased during the growing season. Water depth and nutrients (N and P) explained the most variability in algal community structure. Algal community structure differed among wetlands, and temporal variation in environmental conditions was a significant predictor of the relative abundance of algal genera in individual wetlands. N₂-fixing cyanobacteria increased in abundance with a seasonal decline in water depth and nutrient concentrations. Our characterization of algal community dynamics and productivity in relation to environmental characteristics will help to forecast future wetland function in a changing boreal landscape.

Bryophytes can strongly influence biodiversity and ecosystem function in low-order streams. Mosses and liverworts have substantial biodiversity and biomass in streams, yet few investigators have examined which factors influence bryophyte species distributions, and fewer have examined assemblages across a wide pH gradient. We examined bryophyte assemblages across a pH gradient in 26 southeastern New York (USA) streams. We recorded bryophyte species richness, diversity, and abundance, in conjunction with pH, width, depth, canopy cover, substratum size, temperature, dissolved O₂, turbidity, conductivity, current velocity, dissolved organic C, dissolved Ca, Mg, Fe, NH₄ , NO₃^-, soluble reactive P (SRP), and abundance of other autotrophs. pH ranged from ∼4 to 7 and corresponded to the type of underlying bedrock. Nearly all streams had low or undetectable concentrations of SRP. Several species, e.g., Hygrohypnum eugyrium and Codriophorus aduncoides, were apparent pH generalists, whereas others were pH specialists. For example, Hygrohypnum ochraceum occurred only in neutral pH, whereas Andreaea rothii was restricted to low-pH sites. Vector fitting on a nonmetric multidimensional scaling ordination identified stream pH and amount of bedrock as key factors affecting species distributions. Latitude, longitude, altitude, canopy cover, and aqueous Ca, Mg, SRP, and turbidity also were correlated with species distributions, but many factors were colinear. Nearly all sites had low SRP, and species distributions were strongly related to pH, so we assayed several species and populations for Phosphomonoesterase (PMEase) activity under different pH conditions. Species and populations from low-pH streams tended to have stronger PMEase activity at lower pH than those from higher pH streams, suggesting that species and populations may be adapted to specific pH conditions. Differential PMEase activity may be one mechanism by which aquatic bryophytes persist in low-pH environments.

In situ seed banks are a promising avenue for restoration of plant communities damaged by anthropogenic changes. The invasive rusty crayfish (Orconectes rusticus) has had well documented effects on macrophytes in north temperate lakes. To understand mechanisms of macrophyte recovery from the seed bank, we examined seed banks from lakes with different durations of exposure to O. rusticus and compared these findings to longterm macrophyte surveys. We cored littoral-zone sediments at sediment depths of 0–5, 5–10, and 10–15 cm to test whether deeper layers hold viable seeds that can be used to restore macrophytes. The seed bank in uninvaded lakes contained a higher number and richness of viable seeds than did the seed bank in invaded lakes. Number and richness of viable seeds decreased with sediment depth in all lake categories, and most seeds were found in the top 10 cm. Among all lakes, at most, 33% of the species recorded in field surveys of standing vegetation were represented in the seed bank. We conclude that the seed bank has only modest potential to contribute to natural recovery. Natural regeneration of the macrophyte community is more likely to rely upon vegetative propagules from remnant stands in invaded lakes, especially from very soft-bottom areas avoided by crayfish. Our results emphasize the importance of preventing destruction of macrophytes, especially in lakes without habitats likely to constitute a refuge for macrophytes.

Stream functioning includes simultaneous interaction among solute transport, nutrient processing, and metabolism. Metabolism is measured with methods that have limited spatial representativeness and are highly uncertain. These problems restrict development of methods for up-scaling biological processes that mediate nutrient processing. We used the resazurin—resorufin (Raz-Rru) tracer system to estimate metabolism at different spatial scales (habitat, subreach, and reach) in 2 headwater streams of the H. J. Andrews Experimental Forest (Oregon, USA), and present a mathematical framework for its application. We investigated the relationship between metabolism and hydrodynamics, i.e., geomorphic units (e.g., pool—riffle, pool—cascade), bed materials (i.e., alluvium vs bedrock channels), and type of transient storage (i.e., pure hyporheic exchange, pure surface transient storage, and a combination of both). The metabolic hotspots detected by the Raz-Rru system in both watersheds were related to hydrodynamic conditions known to increase biological processing. Higher respiration rate coefficients were found in subreaches with extensive hyporheic flow and flow through large woody-debris complexes, and higher reaeration rate coefficients were found in subreaches with intensive respiration activity and higher flow velocities. Because such hydrodynamic conditions and their effects on stream processing are difficult to quantify in headwater streams without the use of tracer techniques, the Raz-Rru system proved to be a good integrator of solute transport and stream metabolism processes.

Resources that cross ecosystem boundaries (subsidies) are common in nature, but we have little knowledge of how such resources affect individual traits and, consequently, ecological interactions. In wetlands, leaf litter is an important resource subsidy that regulates ecological processes including the production of consumer biomass. However, litter quality is highly variable and depends on local plant species diversity. Many aquatic consumers are highly nutrient limited, so differences in nutrients and other chemical components in litter are likely to affect numerous individual traits of consumers including life-history and sexually selected traits. We tested whether the species of tree leaf litter consumed by freshwater amphipods affected survival, growth, and development of sexually selected traits. Amphipods had higher survival, attained larger body sizes, and had larger male sexual traits when reared on litter that was relatively nutritious and low in plant secondary and structural compounds. Such widespread trait changes suggest that changing forest composition could have substantial effects on wetland ecology and the evolution of sexual traits over ecological time scales.

The theory of ecological stoichiometry holds that heterotrophs are mostly homeostatic and exhibit less variation in body stoichiometry than do autotrophs. Most studies of stream foodweb stoichiometry have been done in low-nutrient environments. Little is known about foodweb stoichiometry in nutrient-rich streams, in which a higher level of stoichiometric homeostasis should be expected, mainly because imbalances between resources and consumers are low and nutrient availability may meet biotic requirements. We analyzed elemental content (C, N, P) and stoichiometric ratios (C:N, C:P, N:P) of basal resources, macroinvertebrates, and fishes in a nutrient-rich Pampean stream and compared these values to those from other studies. We manipulated P and N in a 1-y fertilization experiment to analyze biotic stoichiometric responses to additional nutrient input to this naturally enriched system. Soluble reactive P concentration in the treatment reach was doubled relative to the background concentration. Consumers had lower C:P and N:P than those in other lotic systems, whereas P content and C:P and N:P of basal resources were within the ranges observed for other systems. Most components of the trophic web were not affected by fertilization, and only epiphyton, fine benthic organic matter, and 2 macroinvertebrate species (Palaemonetes argentinus and Pomacea canaliculata) changed their nutrient content or stoichiometric ratios. Imbalances in C:N and C:P occurred between primary consumers and their resources, particularly among macroinvertebrate collectors and detritivorous fishes feeding on FBOM. Most basal resources and consumers were strictly homeostatic for P content and the stoichiometric ratios, but a lower degree of homeostasis occurred in the epiphyton, P. canaliculata, and collectors feeding on epiphyton. A high degree of stoichiometric homeostasis exists across the various components of the food web in this nutrient-rich stream, regardless of their trophic position.

The combination of changing climate and anthropogenic activities is increasing the probability of wildfire around the world. When fires occur in riparian zones, associated tree mortality can add wood directly to streams or wood may fall to the forest floor and remain there for some time before being transported into stream channels. Wood provides critical structure for aquatic macroinvertebrates, so our objectives were to assess the effects of wood burn status, conditioning, and their interaction on macroinvertebrate community composition, taxon and functional diversity, and trait affinities. We conducted a field experiment with pieces of freshly cut wood (length = 10 cm, diameter ≈ 7.5 cm) for which we first manipulated burn status (burned, unburned) and then, conditioned by placing burned and unburned wood directly into streams (no conditioning) or by leaving pieces in streams (water conditioning) or on the forest floor (soil conditioning) for a year before submergence. We used distance-based redundancy analysis to assess community structure by wood treatments and linear mixed-effects modeling to assess effects of wood treatments on taxon and functional diversity and trait affinity. Changes in wood quality resulting from fire may not alter macroinvertebrate community structure. Taxonomic and functional patterns of stream invertebrate colonization did not differ between burned and unburned wood, even after a year of incubation in the stream or on the forest floor. Conditioning status affected taxonomic composition, taxon and functional diversity, and trait affinities of wood invertebrate communities. The terrestrial legacy of soil conditioning was clearly important in structuring macroinvertebrate assemblages. Our results suggest that macroinvertebrate communities may be more sensitive to fire effects on the dynamics of wood input than to effects of fires on the wood itself.

Small, permanent streams are at risk of becoming stagnant or intermittent because of hydrological changes induced by climate change, which can be further intensified by anthropogenic disruptions, such as water abstraction. Macroinvertebrate communities are vulnerable to such changes because they depend on stream hydromorphological regime. We conducted a fully controlled field experiment in 1 impacted and 1 unimpacted Danish lowland stream with contrasting nutrient availability. We used dams and diversions to create short-term (2–10 wk) stagnant and drought conditions, and we installed pools in the drought area to test their value as refugia for benthic macroinvertebrates. After 2 wk, community composition had changed significantly in all treatments in both streams. The abundance of Chironomidae increased and the abundance of mayflies (Baetis rhodani), stoneflies (Amphinemura standfussi, Leuctra nigra), caddisflies (Silo pallipes, Sericostoma personatum), the amphipod Gammarus pulex, and some Diptera taxa (Simuliidae, Dicranota sp.) decreased relative to the control. Diversity and total abundance did not change in the stagnant or drought treatments, so we do not consider these variables sensitive to effects of short-term flow reductions. Diversity decreased (unimpacted stream) or was not affected (impacted stream) in pools relative to the drought treatment. Thus, pools did not act as a substantial refugium for macroinvertebrates under extreme low-flow conditions. Current velocity and amount of deposited organic material explained most of the change in the macroinvertebrate community. Nutrient availability did not influence the response of the macroinvertebrate community to the treatments, probably because the physicochemical changes were exacerbated in the impacted stream and outweighed the expected higher resilience of this community. Our results clearly demonstrate that short-term stagnation and droughts in lowland streams can cause strong alteration of species composition.

An understanding of the interactions among local environmental factors (e.g., physical habitat and water quality) and aquatic assemblages is essential to conserve biodiversity in tropical and subtropical headwater streams. We evaluated the relative importance of multiple physical and chemical habitat variables that influence the richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT) assemblages in wadeable Brazilian Cerrado (savanna) streams. We sampled macroinvertebrate assemblages and quantified physical and chemical habitat in 79 randomly selected sites in 2 Cerrado basins in southeastern Brazil. The environmental variables selected by multiple regression models (MLRs) via corrected Akaike Information Criteria (AICc) contributed significantly to variation in EPT taxon richness. The variance explained by physical-habitat variables was slightly greater in the Upper São Francisco Basin (adjusted R² = 0.53) than in the Upper Araguari Basin (adjusted R² = 0.46), and both were greater than the variance explained by a combined basin model (adjusted R² = 0.39). Physical-habitat variables were more important than water-quality variables in structuring EPT genera in streams with catchments dominated by agriculture or pasture land uses. Regional models can be improved by incorporating basin-specific information to refine biological assessments and to provide better understanding of the interactions that maintain biodiversity in stream networks.

Nonnative fishes have been linked to the decline of native fishes and may affect aquatic food webs through direct and indirect pathways. These concerns have led to efforts to remove nonnative Brown and Rainbow Trout, which are abundant in tributaries of the Colorado River, to enhance native fish communities. We sampled fish, benthic, and drifting macroinvertebrates in November 2010, January 2011, June 2011, and September 2011 to assess resource availability and to evaluate the effects of nonnative Brown and Rainbow Trout in a tributary of the Colorado River in the Grand Canyon. We evaluated trout diets from stomach samples collected during macroinvertebrate sampling periods, and we estimated annual consumption with bioenergetics models. We used ¹³C and ¹⁵N stable isotopes to examine potential diet overlap between native and nonnative fishes. Contributions to benthic biomass varied among megalopterans (16–35%), trichopterans (19–28%), and ephemeropterans (9–32%), whereas ephemeropterans dominated biomass (44–64%) in drift samples. Ephemeropterans were dominant in diets of small (<150 mm total length [TL]) trout, whereas Corydalus and native fish dominated diets of large (>150 mm TL) Brown Trout, and Corydalus and algae dominated diets of large Rainbow Trout. Annual resource consumption was 6× higher for large trout than small trout. Stable isotopes suggested diet overlap between native and nonnative fishes. Large nonnative trout occupied the highest trophic positions. Our results suggest that suppression of nonnative trout may have a positive effect on native fishes via reduced predation and resource competition.

The benthic foodweb structure of Lake Võrtsjärv, a large (270 km²), shallow, and turbid Estonian lake, was evaluated based on C and N stable-isotope signatures (δ¹³C, δ¹⁵N). Variation in δ¹³C between sampling sites was not related to site proximity to the littoral zone or the more vegetated southern part of the lake, but rather appeared to be influenced by in-situ site peculiarities. δ¹³C was stable temporally and between functional feeding groups, a result implying that the whole benthic food web of the lake relies largely on the same C source admixture, essentially particulate organic matter (POM). Thus, the foodweb composition of Lake Võrtsjärv is remarkably homogeneous given the lake's large surface area. Apparent trophic-level δ¹⁵N fractionation between total collectors and total predators (mean 1.7‰) was lower than the value of 3.4‰ generally adopted in foodweb studies, but the higher value was valid for specific prey—predator links. The low δ¹³C signature of some chironomid samples indicated probable assimilation of methane-oxidizing bacteria (MOB) by these sediment-dwelling invertebrates. However, the lack of similar ¹³C depletion in benthic filterers (mussels) indicated that the MOB layer is essentially confined to the sediments and does not reach the water column, which probably constrains transfer of methane-derived C through the food web to fish in this lake. Our study demonstrates that the benthic food web of shallow turbid lakes like Võrtsjärv is simplified and is mostly sustained by phytoplanktonic C sources.

We examined the hypothesis that direct predation is part of the explanation for the displacement of zebra (Dreissena polymorpha) by quagga mussels (Dreissena rostriformis bugensis) in North America. We investigated selectivity and feeding rates by 3 predators (Round Goby, Pumpkinseed Sunfish, rusty crayfish) using 2 or 3 size classes of predators feeding on different size classes of both mussel species. Round Goby, the predator with a long evolutionary history with dreissenids, consumed a larger range of dreissenid sizes than the other 2 predators. Pumpkinseed Sunfish did not show a preference for either mussel species, but both rusty crayfish and gobies preferred quagga mussels over zebra mussels. The size of mussels vulnerable to these predators increased with predator size, but all predators preferred the smallest mussels (4–8 mm). Medium (105–125 mm) and large (135–155 mm) Round Gobies consumed the largest size class (16–20 mm) of quagga mussels, but only large Round Gobies were able to consume 16–20-mm zebra mussels. Crayfish consumed a higher number of quagga than zebra mussels in both the 8–12-mm and 12–16-mm size classes. Large Pumpkinseed Sunfish (170–185 mm) were able to consume the largest size class of quagga but not zebra mussels. Our results do not support direct predation as the cause for quagga mussels replacing zebra mussels. However, predation may affect mussel size structure because small mussels were more vulnerable to predation than larger mussels.

Resource availability and quality determine the distribution and community structure of animals in ecosystems. However, the balance between energy supply and energy consumption of species has received little attention because of the difficulty of estimating these factors. We measured the carrying capacity of a stream ecosystem in relation to the metabolic demands of Banded Kokopu (Galaxias fasciatus), a drift-feeding fish, to investigate the proportion of their energy budget met by the supply of their primary prey, drifting invertebrates. We sampled drifting invertebrates from multiple pools in 2 freshwater streams once a month over 1 y and measured their energy content. We used the energy content of individual invertebrates to estimate the total energy available in the form of drifting invertebrates in each pool. We measured fish O₂ consumption rate (mg O₂ kg¹ h¹) and converted it to metabolic demand (cal/h). Drifting aquatic invertebrates alone appear to be insufficient to meet Banded Kokopu energetic requirements in most seasons because the fish could obtain up to only 60% of their total energy expenditure from this food source. This result indicates that Banded Kokopu must access other sources of energy, such as benthic food items or terrestrial invertebrate inputs, especially during episodic events, and highlights the potential importance of terrestrial-aquatic exchange and other energetic subsidies. Our results suggest that food supply is likely to limit assemblages of drift-feeding fish and plays a key role in determining the outcome of intraspecific interactions, growth, movement, and the distribution of individuals within streams.

Mountaintop mining (MTM) affects chemical, physical, and hydrological properties of receiving streams, but the long-term consequences for fish-assemblage structure and function are poorly understood. We sampled stream fish assemblages using electrofishing techniques in MTM exposure sites and reference sites within the Guyandotte River basin, USA, during 2010–2011. We calculated indices of taxonomic diversity (species richness, abundance, Shannon diversity) and functional diversity (functional richness, functional evenness, functional divergence) to compare exposure and reference assemblages between seasons (spring and autumn) and across years (1999–2011). We based temporal comparisons on 2 sites that were sampled during 1999–2001 by Stauffer and Ferreri (2002). Exposure assemblages had lower taxonomic and functional diversity than reference assemblages or simulated assemblages that accounted for random variation. Differences in taxonomic composition between reference and exposure assemblages were associated with conductivity and aqueous Se concentrations. Exposure assemblages had fewer species, lower abundances, and less biomass than reference assemblages across years and seasons. Green Sunfish (Lepomis cyanellus) and Creek Chub (Semotilus atromaculatus) became numerically dominant in exposure assemblages over time because of their persistence and losses of other taxa. In contrast, species richness increased over time in reference assemblages, a result that may indicate recovery from drought. Mean individual biomass increased as fish density decreased and most obligate invertivores were apparently extirpated at MTM exposure sites. Effects of MTM were not related to physical-habitat conditions but were associated with water-quality variables, which may limit quality and availability of benthic macroinvertebrate prey. Simulations revealed effects of MTM that could not be attributed to random variation in fish assemblage structure.

Urban areas are increasing in size and human population density. The implications of widespread urbanization are apparent for a wide variety of stream organisms, but the responses of stream-dwelling salamanders to urbanization have been understudied historically. Studies on this assemblage have increased sufficiently over the last decade to warrant a review and synthesis of current knowledge. Our survey of the literature indicates a research bias toward species within the Piedmont ecoregion of the USA and a strong emphasis on changes in species richness, relative abundance, and occupancy along an urbanization gradient. Very few investigators have examined vital rates for specific life stages, population dynamics over extended periods, or mechanistic explanations for the specific aspects of urbanization that drive species loss and decline. We reviewed a broad array of literature on stream salamanders to identify the key abiotic and biotic drivers that explain species responses in urban watersheds. Based on these findings and the applied ecological literature, we identified conservation options for urban areas where decision makers and stakeholders wish to preserve stream salamanders and their habitats. We have listed 7 future research priorities that will further efforts to conserve stream salamanders in rapidly urbanizing regions.

Hydroperiod strongly influences the breeding period and development time of many amphibians, and larvae of various species display developmental plasticity in response to habitat drying. Hydrologic alterations associated with anthropogenic activities potentially can influence host—parasite interactions in humans and wildlife, but few investigators have examined this possibility. Pathogens can delay amphibian development, so infections could constrain the ability of parasitized larvae to respond to a shortened hydroperiod under drying conditions. We examined the individual and joint effects of hydroperiod and infection with a pathogenic trematode parasite (Ribeiroia ondatrae) on larval development of Pacific chorus frogs (Pseudacris regilla) in mesocosms. Tadpoles subjected to accelerated drying were twice as likely to emerge early. However, this tendency was most pronounced among uninfected individuals (96% of early-emerging individuals) and may have arisen from differences in competitive ability between infected and uninfected conspecifics in mesocosms. Our findings indicate the importance of investigating hydrologic variables associated with environmental perturbations, such as climate change, particularly as they relate to the ability of organisms to respond to multiple stressors that include diseases.

In ephemeral streams, floods can temporarily connect isolated pools and provide otherwise spatially restricted organisms with the option to stay in or leave a pool. A field survey of the middle-eastern fire salamander (Salamandra infraimmaculata) larvae demonstrated that 18% disappeared from pools during high-discharge events, and ∼2% were found subsequently in downstream pools.We conducted indoor experiments to test whether larvae alter drift rate in response to different velocities and perceived risk of predation. We manipulated flow velocities within the range of natural ephemeral streams during floods. Anesthetized larvae (passive drifters) drifted out of a central pool faster than conscious larvae at low velocities but not at high velocities, suggesting that conscious larvae actively resisted hydraulic pressures. Drift of small larvae out of a pool in the presence of a caged, larger cannibalistic conspecific was faster than in the absence of a predator, indicating that the larvae perceived and attempted to avoid the predator. Our findings confirm that larval drift that occurs from normally isolated temporary pools in ephemeral streams, is in part behaviorally controlled, and can be mediated by predation risk. We suggest that larval drift can serve as a dispersal pathway for amphibians and may be of particular importance at local spatial scales when the terrestrial habitat surrounding breeding sites is fragmented and movement of terrestrial stages is restricted.

Biological attributes of ecosystems often change nonlinearly as a function of anthropogenic and natural stress. Plant and animal communities may exhibit zones of change along a stressor gradient that are disproportionate relative to the incremental change in the stressor. The ability to predict such transitions is essential for effective management intervention because they may indicate irreversible changes in ecological processes. Despite the importance of recognizing transition zones along a stressor gradient, few, if any, investigators have examined these responses across multiple taxa, and no community threshold studies have been reported at large geographic scales. We surveyed benthic macroinvertebrate, fish, bird, diatom, and plant communities in coastal wetlands across a geospatially referenced gradient of anthropogenic stress in the Laurentian Great Lakes. We used Threshold Indicator Taxon Analysis (Baker and King 2010) to analyze each community's response to identify potential zones of disproportionate change in community structure along gradients of major watershed-scale stress: agriculture and urban/suburban development. Our results show surprising congruence in community thresholds among different taxonomic groups, particularly with respect to % developed land in the watershed. We also analyzed uncertainty associated with the community-specific thresholds to understand the ability of different assemblages to predict stress. The high and congruent sensitivity of assemblages to development demonstrates that watershed-scale stress has discernible effects on all biological communities, with increasing potential for ecosystem-scale functional changes. These findings have important implications for identifying reference-condition boundaries and for informing management and policy decisions, in particular, for selecting freshwater protected areas.

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 different directions to enable quantification of insect flight direction. After sampling, Petri dishes can be taped closed, packed in boxes, and stored indefinitely. Petri traps are comparable in price to standard acetate sheet traps at ∼US$0.50/directional deployment, but they require more space for storage than acetate sheet traps. However, a major benefit of Petri traps is that field deployment times are those of acetate traps. Our study demonstrated that large Petri dishes are an ideal platform for sampling postemergent adult aquatic insects, particularly when the study design involves estimating flight direction and when rapid deployment and recovery of traps is critical.

Body shapes of aquatic insect larvae reflect phenotypic responses to complex environmental conditions and can be used to infer habitat properties and indicate natural and anthropogenic perturbations in river ecosystems. Investigation of relationships between body shape and physical-habitat characteristics has been restricted by a lack of an objective schema for quantitative characterization of body-shape variation. We present a functional ecological framework for body-shape classification based on defined criteria. We applied a geometric morphometric (GM) approach to the general classification of body shape in 4 morphologically diverse orders, Ephemeroptera (E), Plecoptera (P), Trichoptera (T), and Odonata (O) collected from 3 sites with contrasting hydrological and hydraulic characteristics. We describe a robust classification of body shapes for E, P, and O, which possess a compartmentalized body plan, and suggest a preliminary classification for T. We compared GM body shapes with body-shape trait states available in trait databases and found discordance between the 2 classifications. We explored the value of GM body shapes to describe taxon shape structure of reference sites and to detect variation reflecting physical properties of the sites. GM body-shape classes can augment the trait states already available and enhance inference regarding habitat status. Patterns in the shape strategies of aquatic insects, particularly EPO taxa, can be used to extrapolate shape information for other taxonomic groups. GM provides a stable shape classification that can contribute to the description of different ecological strategies of aquatic insects. Expanding the scope of shape information available for many taxonomic groups can improve our understanding of how organism phenotype relates to environmental conditions and supports traits-based assessment.

The chironomid Benthic Quality Index (BQI) is a widely used metric in assessments of lake status. The BQI is based on 7 indicator taxa, which like most profundal fauna, often occur sporadically in low densities. Hence, a major weakness of the index is that it cannot be calculated when indicator taxa are not captured. Thus, an extension of the BQI that incorporates more macroinvertebrate taxa is desirable. We used 2 statistical approaches (Detrended Correspondence Analysis and Weighted Averaging) to estimate new benthic quality indicator scores for profundal macroinvertebrate taxa and to construct modified BQIs called Profundal Invertebrate Community Metrics (PICMs). We calibrated the PICMs and evaluated their bioassessment performance with macroinvertebrate and environmental data from 735 lake basins in Finland. Both PICMs included 70 taxa and could be calculated for a substantially greater proportion (99.5%) of sites than the original BQI (83.5%). Compared to the BQI, the PICMs were more strongly correlated with whole-community variation and were more predictable from environmental factors independent of human activities in undisturbed reference lakes. PICMs were more specific in identifying undisturbed lakes and more sensitive in discriminating nonreference from reference lakes. The strength of relationships to total P concentration was equal among indices. These results suggest that the extension of BQI to incorporate more taxa will increase generality, accuracy, and representativeness of lake profundal macroinvertebrate assessment.