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Coexistence of species requires equalizing mechanisms that minimize fitness differences, which are balanced by stabilizing mechanisms that enhance negative intraspecific interactions versus interspecific ones. Here, we develop a simple theoretical framework that allows measuring the relative strength of intraspecific versus interspecific competition in dominance hierarchies. We use it to evaluate mechanisms promoting coexistence between two congeneric charr that compete for foraging positions, which strongly influence density-dependent growth and survival. Agonistic interactions (n = 761) among 71 Dolly Varden Salvelinus malma and whitespotted charr Salvelinus leucomaenis were measured by snorkelling in two pools in the sympatric zone of a Hokkaido stream during two summers. Interspecific dominance hierarchies, analysed using three methods, were closely correlated with fish length but the species treated each other equally. Ranks for the most dominant fish in each pool, determined directly by knockout experiments, were also virtually identical to ranks by length. Similarly, exponential random graph modelling of the social networks provided no evidence that either species was dominant over the other. Instead, larger fish were more likely to win contests, especially over fish of the next lower ranks. These results demonstrated that the two species were nearly ecological equivalents in accessing key resources in this sympatric zone. Nearly identical growth and stable densities over 4 years further supported this inference, although Dolly Varden were a minority (29% of the assemblage), a sign of some fitness difference. Detailed foraging observations coupled with two concurrent studies revealed an effective stabilizing mechanism. Dolly Varden shifted to feeding directly from the benthos when drifting invertebrates declined, a behaviour enhanced by morphological character displacement, thereby partitioning food resources and enhancing intraspecific competition while avoiding agonistic encounters with whitespotted charr. The plurality of evidence indicates that fitness differences between these ecologically equivalent species are small in this local assemblage, and balanced by resource partitioning, a modest stabilizing mechanism that promotes coexistence. The theoretical framework presented here is a useful tool to evaluate the strength of interspecific versus intraspecific competition, which combined with information on trade-offs in ecological performance can contribute to a mechanistic understanding of species coexistence.1. 複数種の共存には適応度の種間差を最小にする均等化機構が必要だが、これは負の種間相互作用と比べて負の種内相互作用を相対的に強める安定化機構と相補的に働く．我々は種間順位制における種内競争と種間競争の相対的強度を測定する理論的な枠組みを構築し，北海道の河川に同所的に生息するイワナ属２種 (オショロコマ Salvelinus malmaおよびアメマス S. leucomaenis) に適用した．両種は流下する水生昆虫類を摂食するための定位場所をめぐって争い，密度依存的な成長率と生存率を示すことが知られている. これら２種のイワナが同所的に生息する北海道幌尻沢の２つの淵において、２年にわたりシュノーケリングによる潜水観察を行い，両種合計71個体による761回の攻撃行動を記録した．3つの手法で推定した個体の順位はいずれも魚種には影響を受けず，ほぼ体サイズによって決まっていた．この結果は各淵における最優位個体の除去実験によっても支持された. 同様に指数的ランダムグラフモデル (exponential random graph modeling) によるソーシャルネットワーク分析でも、一方の魚種が優位という結果は得られなかった．一方、体サイズで上回る上位の個体は、次の順位の個体を頻繁に攻撃する傾向が認められた. これらの結果は、同所的空間スケールでの餌資源をめぐる争いにおいて両種が生態的に同等な関係にあることを示す．同じ場所での４年にわたる調査でも、両種の生息密度は比較的安定で成長速度も類似しており、この事実もこの推論を支持する．ただし，混生域のオショロコマ個体数の比率は29 %とアメマスよりも少ないことは適応度に種間差があることを意味するかもしれない. 同時に行った形態計測と摂食行動の詳細な観察によって、両種の適応度を均衡させるメカニズムも明らかになった．つまりオショロコマは下顎形態を変化させる適応（形質置換）により，流下昆虫の減少期には底生動物を直接ついばむ摂食スタイルに容易にシフトし，アメマスとの直接的な攻撃を回避しつつ餌資源を効率的に利用していた. これらの複数の証拠は、局所的な空間スケールにおいて生態的に同等な２種の適応度の差はわずかで，この均等化機構と資源分割が生む適度な安定化機構とが相まって共存が促進されていることを示している．この研究で提唱した理論的枠組みは，種間競争と種内競争の相対的な強さを評価する際に有用であり，生態学的なトレードオフに関する情報と併せることで複数種の共存メカニズム解明がさらに進むことが期待される.

Similar species that overlap in sympatry may diverge in characters related to resource use as a result of evolution or phenotypic plasticity. Dolly Varden charr (Salvelinus malma) and whitespotted charr (S. leucomaenis) overlap along streams in Hokkaido, Japan, and compete by interference for invertebrate drift-foraging positions. Previous research has shown that as drift declines during summer, Dolly Varden shift foraging modes to capture benthic prey, a behaviour facilitated by their subterminal jaw morphology. We compare body and jaw morphology of Dolly Varden in sympatry vs. allopatry in two locations to test for character displacement. Statistical analysis showed significant divergence in characters related to foraging, which was correlated with variation in individual charr diets. Dolly Varden in sympatry had shorter heads and lower jaws than in allopatry, and even within sites charr with these characteristics fed less on drifting terrestrial invertebrates but more on benthic aquatic invertebrates. Those in allopatry had longer heads and lower jaws, and fed more on terrestrial invertebrates. The close proximity of sites in one stream suggests that Dolly Varden may display phenotypic plasticity similar to other charr, allowing rapid responses in morphology to the presence of competitors. These morphological shifts probably help them maintain positive fitness when competing with whitespotted charr in Hokkaido streams.

Networks of direct and indirect biotic interactions underpin the complex dynamics and stability of ecological systems, yet experimental and theoretical studies often yield conflicting evidence regarding the direction (positive or negative) or magnitude of these interactions. We revisited pioneering data sets collected at the deciduous forested Horonai Stream and conducted ecosystem-level syntheses to demonstrate that the direction of direct and indirect interactions can change depending on the timescale of observation. Prior experimental studies showed that terrestrial prey that enter the stream from the adjacent forest caused positive indirect effects on aquatic invertebrates during summer by diverting fish consumption. Seasonal and annual estimates of secondary production and organic matter flows along food web pathways demonstrate that this seasonal input of terrestrial invertebrate prey increases production of certain fish species, reversing the indirect effect on aquatic invertebrates from positive at the seasonal timescale to negative at the annual timescale. Even though terrestrial invertebrate prey contributed 54% of the annual organic matter flux to fishes, primarily during summer, fish still consumed 98% of the aquatic invertebrate annual production, leading to top-down control that is not revealed in short-term experiments and demonstrating that aquatic prey may be a limiting resource for fishes. Changes in the direction or magnitude of interactions may be a key factor creating nonlinear or stabilizing feedbacks in complex systems, and these dynamics can be revealed by merging experimental and comparative approaches at different scales.

Shigeru Nakano was a Japanese ecologist whose work crossed boundaries among subdisciplines in ecology, between aquatic and terrestrial habitats, and between different languages and cultures. He published his first paper in 1985 while still an undergraduate, and is well known for his early research on the individual behavior of stream salmonids in dominance hierarchies. Shortly after completing his Master’s degree in 1987 he began collaborating with many graduate students and other scientists, including those from the US, and expanded his research to include factors controlling stream salmonid distribution and abundance across spatial scales ranging from local to landscape levels. In 1995 he moved to a research station in southwestern Hokkaido and began new collaborative research on interactions between forest and stream food webs. Nakano pioneered large-scale field experiments using greenhouses to sever the reciprocal fluxes of invertebrate prey between stream and riparian food webs. The strong direct and indirect effects of isolating these food webs from each other on organisms ranging from stream algae to fish, riparian spiders, and bats have revealed new linkages and explained phenomena that were previously unexplained. When combined with similar results from other investigators, they have created a paradigm shift in ecology. Shigeru Nakano was lost at sea in Baja California on March 27, 2000 at the age of 37, but key papers from his 15-year career set new standards for rigor, detail, and synthesis. They continue to be highly cited and inspire new research, and to foster new collaborations among Japanese and western scientists.

Water flow is a fundamental characteristic required for the ecological integrity of stream ecosystems. However, populations of many freshwater fishes in the Mediterranean region are threatened by man-induced drought due to water diversion. Mark-recapture methodology is an effective tool for estimating fish abundance and survival probability, but it has been seldom used with Mediterranean freshwater fish. We tagged over 2,400 individuals of two threatened cyprinids (Mediterranean barbel Barbus meridionalis and Catalan chub Squalius laietanus) inhabiting an Iberian stream affected by water diversion, and used mark-recapture methods to evaluate the effects of flow, temperature and depth on their apparent survival and abundance at hydrologically altered and perennial reaches. Based on estimates over the summer drying season, survival of Mediterranean barbel was more than six times higher in an upstream reach with permanent flow than a middle reach impacted by water diversion. Water depth was the most important habitat feature accounting for differences in survival, with both barbel and chub exhibiting higher survival and abundance at permanent sites farther downstream where flow had been restored and in an unaltered tributary. Our results show clear negative impacts of water diversion on fish populations. Both species, but particularly barbel, have life-cycle characteristics that may allow populations to recover quickly if natural streamflow was restored by conserving water and reducing water diversion.

Intact native fish assemblages—those with all or most historical taxa present and a strong numerical dominance of native species—are rare in streams and other aquatic systems worldwide. Our sampling during four intervals from 1983 to 2007 showed that the Purgatoire River, a Great Plains stream in eastern Colorado, supported an assemblage that was 99.6% native taxa, and all but one rare species persisted through time. An additional rare Arkansas River native fish colonized the Purgatoire River and was widespread in 2006–2007, and only three nonnative taxa were detected. The perennial Purgatoire River supported all native fishes in the basin, while tributaries supported mainly native fishes that were tolerant of intermittent, harsh habitat. In the Purgatoire River, frequency and abundance of dominant species varied spatially during 2006–2007. Persistence of native fishes was unchanged over time in the Pinon Canyon reach of the river even though abundance varied substantially. Despite the presence of...

Effective conservation of Cutthroat Trout Oncorhynchus clarkii lineages native to the Rocky Mountains will require estimating effects of multiple stressors and directing management toward the most important ones. Recent analyses have focused on the direct and indirect effects of a changing climate on contemporary ranges, which are much reduced from historic ranges owing to past habitat loss and nonnative trout invasions. However, nonnative trout continue to invade Cutthroat Trout populations in the southern Rocky Mountains. Despite management to isolate and protect these native populations, nonnatives still surmount barriers or are illegally stocked above them. We used data on the incidence of invasions by nonnative Brook Trout (BT) Salvelinus fontinalis and the rate of their invasion upstream to simulate effects on a set of 309 conservation populations of Colorado River Cutthroat Trout (CRCT) O. c. pleuriticus isolated in headwater stream fragments. A previously developed Bayesian network model w...

The natural wood regime forms the third leg of a tripod of physical processes that supports river science and management, along with the natural flow and sediment regimes. The wood regime consists of wood recruitment, transport, and storage in river corridors. Each of these components can be characterized in terms of magnitude, frequency, rate, timing, duration, and mode. We distinguish the natural wood regime, which occurs where human activities do not significantly alter the wood regime, and a target wood regime, in which management emphasizes wood recruitment, transport, and storage that balance desired geomorphic and ecological characteristics with mitigation of wood-related hazards. Wood regimes vary across space and through time but can be inferred and quantified via direct measurements, reference sites, historical information, and numerical modeling. Classifying wood regimes with respect to wood process domains and quantifying the wood budget are valuable tools for assessing and managing rivers.

Pacific trout Oncorhynchus spp. in western North America are strongly valued in ecological, socioeconomic, and cultural views, and have been the subject of substantial research and conservation efforts. Despite this, the understanding of their evolutionary histories, overall diversity, and challenges to their conservation is incomplete. We review the state of knowledge on these important issues, focusing on Pacific trout in the genus Oncorhynchus. Although most research on salmonid fishes emphasizes Pacific salmon, we focus on Pacific trout because they share a common evolutionary history, and many taxa in western North America have not been formally described, particularly in the southern extent of their ranges. Research in recent decades has led to the revision of many hypotheses concerning the origin and diversification of Pacific trout throughout their range. Although there has been significant success at addressing past threats to Pacific trout, contemporary and future threats represented by nonnativ...

Instream and floodplain wood can provide many benefits to river ecosystems, but can also create hazards for inhabitants, infrastructure, property, and recreational users in the river corridor. We propose a decision process for managing large wood, and particularly for assessing the relative benefits and hazards associated with individual wood pieces and with accumulations of wood. This process can be applied at varying levels of effort, from a relatively cursory visual assessment to more detailed numerical modeling. Decisions to retain, remove, or modify wood in a channel or on a floodplain are highly dependent on the specific context: the same piece of wood that might require removal in a highly urbanized setting may provide sufficient benefits to justify retention in a natural area or lower-risk urban setting. The proposed decision process outlined here can be used by individuals with diverse technical backgrounds and in a range of urban to natural river reaches so that opportunities for wood retention or enhancement are increased.

The Columbia Basin once supported a diversity of native fishes and large runs of anadromous salmonids that sustained substantial fisheries and cultural values. Extensive land conversion, watershed disruptions, and subsequent fishery declines have led to one of the most ambitious restoration programs in the world. Progress has been made, but restoration is expensive (exceeding US$300M/year), and it remains unclear whether habitat actions, in particular, can be successful. A comprehensive approach is needed to guide cost-effective habitat restoration. Four elements that must be addressed simultaneously are (1) a scientific foundation from landscape ecology and the concept of resilience, (2) broad public support, (3) governance for collaboration and integration, and (4) a capacity for learning and adaptation. Realizing these in the Columbia Basin will require actions to rebalance restoration goals to include diversity, strengthen linkages between science and management, increase public engagement, work acros...

Anthropogenic climate change is causing a wide range of stresses in aquatic ecosystems, primarily through warming thermal conditions. Lakes, in response to these changes, are experiencing increases in both summer temperatures and ice-free days. We used continuous records of lake surface temperature and air temperature to create statistical models of daily mean lake surface temperature to assess thermal changes in mountain lakes. These models were combined with downscaled climate projections to predict future thermal conditions for 27 high-elevation lakes in the southern Rocky Mountains. The models predict a 0.25°C·decade-1 increase in mean annual lake surface temperature through the 2080s, which is greater than warming rates of streams in this region. Most striking is that on average, ice-free days are predicted to increase by 5.9 days ·decade-1, and summer mean lake surface temperature is predicted to increase by 0.47°C·decade-1. Both could profoundly alter the length of the growing season and potentially change the structure and function of mountain lake ecosystems. These results highlight the changes expected of mountain lakes and stress the importance of incorporating climate-related adaptive strategies in the development of resource management plans.

Groundwater pumping for agriculture is a major driver causing declines of global freshwater ecosystems, yet the ecological consequences for stream fish assemblages are rarely quantified. We combined retrospective (1950–2010) and prospective (2011–2060) modeling approaches within a multiscale framework to predict change in Great Plains stream fish assemblages associated with groundwater pumping from the United States High Plains Aquifer. We modeled the relationship between the length of stream receiving water from the High Plains Aquifer and the occurrence of fishes characteristic of small and large streams in the western Great Plains at a regional scale and for six subwatersheds nested within the region. Water development at the regional scale was associated with construction of 154 barriers that fragment stream habitats, increased depth to groundwater and loss of 558 km of stream, and transformation of fish assemblage structure from dominance by large-stream to small-stream fishes. Scaling down to subwatersheds revealed consistent transformations in fish assemblage structure among western subwatersheds with increasing depths to groundwater. Although transformations occurred in the absence of barriers, barriers along mainstem rivers isolate depauperate western fish assemblages from relatively intact eastern fish assemblages. Projections to 2060 indicate loss of an additional 286 km of stream across the region, as well as continued replacement of large-stream fishes by small-stream fishes where groundwater pumping has increased depth to groundwater. Our work illustrates the shrinking of streams and homogenization of Great Plains stream fish assemblages related to groundwater pumping, and we predict similar transformations worldwide where local and regional aquifer depletions occur.

Thirty years ago, Fausch (Can J Zool 62:441–451, 1984) proposed a simple model of optimal positions for drift-feeding salmonids in streams, whereby fish maximize their net energy intake (NEI) by selecting focal points in low water velocity near faster currents that deliver abundant drifting invertebrates. The theory was based on earlier observations in artificial and natural streams describing characteristics of salmonid positions and a conceptual model by Chapman (Am Nat 100:345–357, 1966). A test of this simple drift foraging model in a laboratory stream showed that the growth rate of juvenile trout and salmon increased with NEI, and that the rank of NEI at positions held by coho salmon (Oncorhynchus kisutch) correlated nearly perfectly with their rank in the dominance hierarchy. Fausch (1984) inferred from these findings that positions that optimize NEI, within the constraints of the dominance hierarchy, are the resource for which these stream salmonids compete. In turn, the model was used to test the effects of interspecific competition by coho salmon on the foraging positions held by brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta), and these results were used to infer potential effects of the introduced salmon on resident trout in Lake Michigan tributaries. Though the goals for this model were originally modest, it was tested in the field and further refined by Hughes and Dill (Can J Fish Aquat Sci 47:2039–2048, 1990) and others. During the last 20 years, the general theory has been incorporated into other models, which have been applied widely to analyze salmonid distribution and abundance in streams and rivers and used for management and restoration of habitat and flow regimes to benefit these fishes.

Summary Non-native species can affect food web and community structure, including the flow of resources from one habitat to another. In many streams of western North America, non-native brook trout (Salvelinus fontinalis) have replaced native cutthroat trout (Oncorhynchus clarkii). Because brook trout naturally occur at higher densities and exhibit different feeding habits, this replacement may have consequences for a range of organisms in stream-riparian food webs. We conducted a large-scale, 2-month field experiment to test whether, compared with cutthroat trout, brook trout reduce benthic insects, cause an increase in stream algae, and reduce emerging adult aquatic insects as well as riparian spiders that rely on emergence as prey. Twenty enclosed reaches from which trout were removed were treated by adding age-1 and older: (i) cutthroat trout at natural density (0.15 fish m−2); (ii) brook trout at a natural density (0.40 fish m−2); (iii) brook trout at a low density equal to the cutthroat trout treatment (0.15 fish m−2) or (iv) no trout added. Brook trout reduced the flux of emerging insects by 55% compared with cutthroat trout, but, surprisingly, only at the lower density. This reduction in emergent insects was predicted to reduce spider abundance by 20%, provided that sufficient branches were available to support riparian spider webs. We also detected an effect of trout on large-bodied benthic and emerging insects, but not on the entire assemblage of benthic insects, or periphyton. We hypothesise that our results were influenced by trout foraging behaviour mediated by their density and size structure. Regardless of the mechanisms responsible, our results indicate that non-native brook trout can reduce the flux of emerging insects, and further analysis showed that this could reduce riparian spiders and birds that prey on them. Similar effects of non-native fish are likely to occur in lotic and lentic waters beyond the western United States.

Bioclimatic models predict large reductions in native trout across the Rocky Mountains in the 21st century but lack details about how changes will occur. Through five case histories across the region, we explore how a changing climate has been affecting streams and the potential consequences for trout. Monitoring records show trends in temperature and hydrographs consistent with a warming climate in recent decades. Biological implications include upstream shifts in thermal habitats, risk of egg scour, increased wildfire disturbances, and declining summer habitat volumes. The importance of these factors depends on the context, but temperature increases are most relevant where population boundaries are mediated by thermal constraints. Summer flow declines and wildfires will be important where trout populations are fragmented and constrained to small refugia. A critical information gap is evidence documenting how populations are adjusting to long-term habitat trends, so biological monitoring is a pr...

Non-native brook trout (Salvelinus fontinalis) have replaced native cutthroat trout (Oncorhynchus clarkii) in streams across the western USA. Brook trout have been assumed to be functionally equivalent to cutthroat trout, which could argue against extensive control of this species by government agencies. This assumption was assessed by comparing the diets of the two trout species and their effects on benthic invertebrates in a large-scale field experiment. Within a Rocky Mountain stream where brook trout had already become established, trout species and density were manipulated in 20 fenced sections to create four treatments: cutthroat trout at a density natural for un-invaded streams, brook trout at two densities, natural for invaded streams or reduced to match the natural density of cutthroat trout, and areas depleted of most trout. By the end of the experiment, populations of brook trout at natural density consumed seven times more benthic invertebrates than cutthroat trout. Brook trout also consumed more Apatania caddisflies and Heterlimnius riffle beetles per capita than cutthroat trout. However, the greater consumption did not cause detectable reductions in benthic invertebrate densities. A large-scale experiment of trout removal like this may be inherently limited in its ability to detect effects on benthic invertebrate densities. However, this and several companion studies indicate that stream ecosystems would not function in the same way if cutthroat trout are replaced by brook trout. Sustaining these functions, as well as biodiversity and socioeconomic values, are important reasons to conserve native cutthroat trout. Copyright © 2012 John Wiley & Sons, Ltd.

Summary 1. Research in forest and grassland ecosystems indicates that terrestrial invertebrates that fall into streams can be an important prey resource for fish, providing about 50% of their annual energy and having strong effects on growth and abundance. However, the indirect effects of land uses like cattle grazing on this important prey subsidy for stream salmonids are unclear. 2. During summer 2007, we compared the effects of three commonly used grazing systems on terrestrial invertebrate inputs to streams in northern Colorado and their use by trout. Cattle graze individual pastures for about 120 days under traditional season-long grazing (SLG), about 35–45 days under simple rotational grazing and 10–20 days under intensive rotational grazing in this region. We also compared these effects to a fourth group of sites grazed only by wildlife (i.e. no livestock use). 3. Overall, rotational grazing management (either simple or intensive), resulted in more riparian vegetation, greater inputs of terrestrial invertebrates, greater biomass of terrestrial invertebrate prey in trout diets, a higher input compared to trout metabolic demand and more trout biomass than SLG. However, these differences were frequently not statistically significant owing to high variability, especially for trout diets and biomass. 4. Despite the inherent variability, riparian vegetation and terrestrial invertebrates entering streams and in trout diets at sites managed for rotational grazing were similar to sites managed for wildlife grazing only. 5. These results indicate that rotational grazing systems can be effective for maintaining levels of terrestrial invertebrate subsidies to streams necessary to support robust trout populations. However, factors influencing the effect of riparian grazing on stream subsidies are both spatially variable and complex, owing to differences in microclimate, invertebrate and plant populations and the efforts of ranchers to tailor grazing systems to specific riparian pastures.

Like many fishes native to western Great Plains streams, the Arkansas darter Etheostoma cragini has declined, apparently in response to changes in flow regimes and habitat fragmentation. We investigated the effectiveness of translocation as a management strategy to conserve this threatened species in the Arkansas River basin of southeastern Colorado. We used a multiscale design to sample the darter and several attributes of its habitat at the local 10-m site scale, the 3.25-km translocation segment scale, and the 10-km riverscape scale in all 19 streams where it had been previously translocated. The darter was captured in 11 of the 19 streams, although 5 were completely dry when visited. Arkansas darters had reproduced in 10 of the 11 streams (one criterion in the state recovery plan), and 6 streams also met a second criterion for abundance (>500 individuals). However, the populations in only two streams unequivocally met a third criterion of being self-sustaining, because the other four streams ...

Replacement of a native species by a nonnative can have strong effects on ecosystem function, such as altering nutrient cycling or disturbance frequency. Replacements may cause shifts in ecosystem function because nonnatives establish at different biomass, or because they differ from native species in traits like foraging behavior. However, no studies have compared effects of wholesale replacement of a native by a nonnative species on subsidies that support consumers in adjacent habitats, nor quantified the magnitude of these effects. We examined whether streams invaded by nonnative brook trout (Salvelinus fontinalis) in two regions of the Rocky Mountains, USA, produced fewer emerging adult aquatic insects compared to paired streams with native cutthroat trout (Oncorhynchus clarkii), and whether riparian spiders that depend on these prey were less abundant along streams with lower total insect emergence. As predicted, emergence density was 36% lower from streams with the nonnative fish. Biomass of brook trout was higher than the cutthroat trout they replaced, but even after accounting for this difference, emergence was 24% lower from brook trout streams. More riparian spiders were counted along streams with greater total emergence across the water surface. Based on these results, we predicted that brook trout replacement would result in 6-20% fewer spiders in the two regions. When brook trout replace cutthroat trout, they reduce cross-habitat resource subsidies and alter ecosystem function in stream-riparian food webs, not only owing to increased biomass but also because traits apparently differ from native cutthroat trout.

Recent and projected climate warming trends have prompted interest in impacts on coldwater fishes. We examined the role of climate (temperature and flow regime) relative to geomorphology and land use in determining the observed distributions of three trout species in the interior Columbia River Basin, USA. We considered two native species, cutthroat trout ( Oncorhynchus clarkii ) and bull trout ( Salvelinus confluentus ), as well as nonnative brook trout ( Salvelinus fontinalis ). We also examined the response of the native species to the presence of brook trout. Analyses were conducted using multilevel logistic regression applied to a geographically broad database of 4165 fish surveys. The results indicated that bull trout distributions were strongly related to climatic factors, and more weakly related to the presence of brook trout and geomorphic variables. Cutthroat trout distributions were weakly related to climate but strongly related to the presence of brook trout. Brook trout distributions were related to both climate and geomorphic variables, including proximity to unconfined valley bottoms. We conclude that brook trout and bull trout are likely to be adversely affected by climate warming, whereas cutthroat trout may be less sensitive. The results illustrate the importance of considering species interactions and flow regime alongside temperature in understanding climate effects on fish.

Estimation of stream fish abundance using removal electrofishing is common and allows sampling of fish populations during a single site visit. However, recent evaluations have demonstrated that removal estimators can substantially underestimate fish abundance, raising concerns about using this method. We evaluated removal estimates of trout (family Salmonidae) abundance using night electrofishing in 200–300-m reaches of 8 Rocky Mountain streams and analyzed the data using new methods in Program MARK to account for potential sources of bias. The removal estimates were validated using populations of previously captured and marked resident fish. Overall, removal estimates were accurate estimates of the number of marked fish in study reaches (mean bias, −2.4% [

Knowledge of basic life-history attributes, paired with unbiased estimates of species distribution, is critical for the effective conservation of sensitive fish species. We quantified the spawning phenology, habitat use, and detectability for larvae of an assemblage of threatened Great Plains, USA, stream fishes using new occupancy estimation methods. Spawning by six Great Plains fish species occurred from April through July, and was likely initiated by changes in water temperature and photoperiod. Habitat size and type were important factors influencing the occupancy of larvae in spawn- ing habitats. Detectability of larvae differed among species and over time, and was influenced by habitat depth and fish size. Our models indicated that multiple samples from individual habitats within a season are needed to adequately detect and predict occupancy by stream fish larvae. Conservation efforts for imperiled Great Plains fish assemblages should focus on sustaining flows that maintain a sufficient density and size of habitats needed for successful spawning and recruitment. The occupancy estimation and modeling methods employed here will be useful in developing comprehensive, unbiased programs to monitor the reproductive success of Great Plains stream fishes. Resume´ : La conservation efficace des especes sensibles de poissons requiert une connaissance des caracteristiques fonda- mentales de leur cycle biologique, de meme que des estimations non faussees de leur repartition. Nous avons determinela phenologie de la reproduction, l'utilisation de l'habitat et la detectabilitedes larves dans des peuplements de poissons me- naces des Grandes Plaines, E ´ .-U., a l'aide de nouvelles methodes d'estimation de l'occupation. La fraie de six especes de poissons des plaines a lieu d'avril ala fin de juillet et est vraisemblablement declenchee par la temperature de l'eau et la photoperiode. La taille et le type de l'habitat sont des facteurs importants qui influencent l'occupation des habitats de fraie par les larves. La detection des larves varie d'une espece al'autre dans le temps et est influencee par la profondeur de l'habitat et la taille des poissons. Notre modelisation indique qu'il faut de multiples echantillons provenant de chaque habi- tat au cours d'une saison pour detecter adequatement et predire l'occupation du cours d'eau par les larves de poissons. Les efforts de conservation des peuplements de poissons menaces des Grandes Plaines devraient se concentrer sur le maintien de debits qui assurent une densiteet une taille d'habitats suffisantes pour une fraie et un recrutement reussis. Les methodes d'estimation de l'occupation et de modelisation que nous avons employees pourront servir amettre sur pied des program- mes complets et non fausses de surveillance du succes reproductif des poissons des eaux courantes dans les plaines. (Traduit par la Redaction)

Flow alterations caused by reservoir storage, groundwater pumping, diversions, and drought are widespread in North American Great Plains streams and have altered and fragmented habitats and reduced native fish biodiversity. Early life stages of fish are particularly sensitive to altered flow regimes, and reduced growth and survival may negatively affect the persistence of native species and assemblages. We investigated how growth and survival of brassy minnow Hybognathus hankinsoni larvae in the Arikaree River, Colorado, varied among three 6.4-km river segments that differed in hydrology and how climate influenced drying rates of spawning and rearing habitats in these segments over 3 years. We found that brassy minnow spawned in backwater habitats within a discrete period from mid-April to late May, based on otolith increment analysis. The timing of spawning and growth of larvae were influenced by climate and the hydrologic context of the river segment. Brassy minnow spawned 2 weeks earlier under...

SUMMARY 1. Streams are highly connected to their landscapes and so are easily altered by multiple stressors that affect both uplands and riparian zones, and the streams themselves. These include dams and diversions, channelisation, deforestation, water pollution, biological invasions and climate change. 2. We review research conducted in Hokkaido Island, northern Japan, which measured the effects of many of these stressors on both stream food webs and fluxes of invertebrates to and from the riparian zone that feed aquatic and terrestrial consumers. About half the energy that sustains fish falls directly into streams as terrestrial invertebrates, and a quarter of the energy needs for riparian birds is supplied by adult aquatic insects emerging from the stream. 3. Single stressors in these Hokkaido streams, including deforestation, channelisation, erosion-control dams, biological invasions and climate change, have drastic effects on stream food webs, the fishes they support and riparian predators (spiders, birds, and bats). Most stressors caused 30–90% declines in foraging, growth, or abundance of aquatic or terrestrial predators. Indirect effects of stressors also cascaded throughout stream food webs and across the aquatic–terrestrial boundary. 4. Effects of individual stressors were largely concordant across spatial scale, through time during years of different productivity and among different food web components. 5. Two studies of multiple stressors revealed that each stressor alone reduced food web components like abundance of stream benthos or riparian spiders to low levels (35–83% reduction; mean 59%), beyond which an additional stressor had little effect. Synergism and antagonism are less relevant when individual stressors have such large effects. 6. Thematic implications: small streams in Hokkaido are highly sensitive to many individual stressors and have little resistance or resilience to their effects. Moreover, each stressor alone can reduce biota strongly, indicating that restoration will need to consider all simultaneously to protect biotic diversity.

Conservation biologists often face the trade-off that increasing connectivity in fragmented landscapes to reduce extinction risk of native species can foster invasion by non-native species that enter via the corridors created, which can then increase extinction risk. This dilemma is acute for stream fishes, especially native salmonids, because their populations are frequently relegated to fragments of headwater habitat threatened by invasion from downstream by 3 cosmopolitan non-native salmonids. Managers often block these upstream invasions with movement barriers, but isolation of native salmonids in small headwater streams can increase the threat of local extinction. We propose a conceptual framework to address this worldwide problem that focuses on 4 main questions. First, are populations of conservation value present (considering evolutionary legacies, ecological functions, and socioeconomic benefits as distinct values)? Second, are populations vulnerable to invasion and displacement by non-native salmonids? Third, would these populations be threatened with local extinction if isolated with barriers? And, fourth, how should management be prioritized among multiple populations? We also developed a conceptual model of the joint trade-off of invasion and isolation threats that considers the opportunities for managers to make strategic decisions. We illustrated use of this framework in an analysis of the invasion-isolation trade-off for native cutthroat trout (Oncorhynchus clarkii) in 2 contrasting basins in western North America where invasion and isolation are either present and strong or farther away and apparently weak. These cases demonstrate that decisions to install or remove barriers to conserve native salmonids are often complex and depend on conservation values, environmental context (which influences the threat of invasion and isolation), and additional socioeconomic factors. Explicit analysis with tools such as those we propose can help managers make sound decisions in such complex circumstances.

Subspecies of inland cutthroat trout Oncorhynchus clarkii occupy a fraction of their historic ranges, and displacement by nonnative brook trout Salvelinus fontinalis is among the greatest threats to existing populations in small, headwater streams. Electrofishing is often used to suppress brook trout and enhance cutthroat trout populations, but these efforts are labor intensive and costly. To help managers more effectively plan and implement brook trout control programs, we used survival estimates from a field experiment to construct matrix population models for both species and linked the models by making the vital rates of young cutthroat trout a function of brook trout density to represent the effect of invasion. We then explored the response of cutthroat trout populations (growth rate [λ] and probability of persistence for 50 years) to brook trout suppression across various levels of electrofishing frequency, sampling intensity, capture efficiency, and brook trout immigration rate. Cutthroat ...

We review the ecology and conservation of three lesser-known chars (genus Salvelinus): Dolly Varden (S. malma), white-spotted char (S. leucomaenis), and bull trout (S. confluentus). Dolly Varden is distributed across the northern Pacific Rim and co-occurs with bull trout and white-spotted char at the southern extremes of its range. In contrast, bull trout and white-spotted char are naturally isolated, with the former restricted to North America and the latter distributed in northeastern Asia. Though the range of Dolly Varden overlaps with the two other chars, it is most closely related to Arctic char (S. alpinus), whereas bull trout and white-spotted char are sister taxa. Each species exhibits diverse life histories with respect to demographic characteristics, trophic ecology, and movement. This diversity appears to be tied to environmental variability (e.g., temperature, habitat connectivity), resource availability (e.g., food), and species interactions. Increasingly, these interactions involve ...

Lake Superior once supported abundant lake-dwelling brook trout Salvelinus fontinalis called coasters; however, only scattered remnant populations remained by the early 20th century. Owing to their early decline, there is little information about their ecology and life history, yet such information is vital for the ecologically based rehabilitation and management of coasters. This study reviews the ecology of coaster brook trout from a life history perspective and presents quantitative data on the biology and status of the few populations that have been studied. Within the Lake Superior basin, some brook trout are stream residents while others are lacustrine or adfluvial. Although the variation in migratory behavior may be related to individual energetics, the role of evolution and the proximate factors triggering specific life histories remain uncertain. Comparisons of recent biological data from populations in the Lake Superior basin show that the northern populations have longer lengths at age...

Native salmonid fishes often face simultaneous threats from habitat fragmentation and invasion by nonnative trout species. Unfortunately, management actions to address one may create or exacerbate the other. A consistent deci- sion process would include a systematic analysis of when and where intentional use or removal of barriers is the most appropriate action. We developed a Bayesian belief network as a tool for such analyses. We focused on native westslope cutthroat trout (Oncorhynchus clarkii lewisi) and nonnative brook trout (Salvelinus fontinalis) and considered the environmental factors influencing both species, their potential interactions, and the effects of isolation on the persis- tence of local cutthroat trout populations. The trade-offs between isolation and invasion were strongly influenced by size and habitat quality of the stream network to be isolated and existing demographic linkages within and among populations. An application of the model in several sites in western Montana (USA) showed the process could help clarify management objectives and options and prioritize conservation actions among streams. The approach can also facilitate communication among parties concerned with native salmonids, nonnative fish invasions, barriers and inten- tional isolation, and management of the associated habitats and populations. Resume : Les poissons salmonides indigenes font souvent face simultanement a une double menace representee par la fragmentation des habitats et l'invasion de salmonides non indigenes. Malheureusement, les amenagements faits pour regler un de ces problemes peuvent faire surgir ou exacerber le second. Un processus de decision coherent devrait inclure une analyse systematique du moment et de l'endroit les plus appropries pour l'erection ou le retrait de barrie- res. Nous avons mis au point un reseau de croyance bayesien pour servir d'outil pour ces analyses. Nous nous sommes interesses specifiquement a la truite fardee (Oncorhynchus clarkii lewisi) indigene du versant occidental et a l'omble de fontaine (Salvelinus fontinalis) non indigene; nous avons tenu compte des facteurs du milieu qui influencent les deux especes, de leurs interactions potentielles et des effets de l'isolement sur la persistance des populations locales de trui- tes fardees. Les compromis entre l'isolement et l'invasion sont fortement influences par la taille et la qualite des habi- tats du reseau de cours d'eau a isoler, ainsi que par les liens demographiques etablis a l'interieur des populations et entre elles. L'utilisation du modele dans plusieurs sites de l'ouest du Montana (E.-U.) montre que le processus peut servir a eclaircir les objectifs et les options de l'amenagement et a etablir les priorites des initiatives de conservation dans les differents cours d'eau. Cette methode peut aussi faciliter la communication entre les divers intervenants preoc- cupes par les salmonides indigenes, les invasions de poissons non indigenes, les barrieres et l'isolement delibere, ainsi que par l'amenagement des habitats et des populations associes.

Salmonids like rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis and brown trout Salmo trutta are potent invaders in various regions throughout the world, but non-native rainbow trout have become established in only a few locations in the U.K. to date. Salmonid invasions in other regions are often driven by repeated authorized introductions of large numbers of fish, escapees from fish culture and illegal introductions by anglers. Their spread can be rapid within catchments via long-distance movements. Currently, large numbers of all-female diploid rainbow trout are released in the U.K., the eggs of which could be fertilized by relatively few mature males, thereby increasing the risk of invasion. If reproducing fish began to spread, especially by anadromy, then eradication could be difficult due to angler interest and logistical constraints. Establishment of non-native salmonids can be limited by abiotic factors such as flow and temperature regimes, and biotic resistance from competition, predation and parasites or diseases, which often affect early life stages most strongly. Moreover, these factors can also interact with the zoogeography and evolutionary history of the native and introduced salmonids to make explanation and prediction complex. Although flow and temperature regimes in the U.K. are broadly suitable for rainbow trout, and biotic resistance by brown trout has been overcome in other regions, resistance from native diseases and angling mortality appear to be plausible hypotheses for lack of rainbow trout invasion in the U.K. Invading salmonids can have both direct effects on native salmonids and other fishes via biotic interactions, and indirect effects by fragmenting their habitat and isolating native populations. In addition, invaders can have indirect effects on entire aquatic food webs (e.g. invertebrates and algae) that cascade throughout ecosystems, or even cross boundaries into adjacent ecosystems. Evidence from other regions indicates that rainbow trout could have negative effects on brown trout or Atlantic salmon Salmo salar in U.K. waters, but this probably depends on the context set by other factors. Overall, primary factors to consider in any risk analysis of rainbow trout invasion in the U.K. include the decline of native salmonid populations due to degradation or overexploitation, the evolutionary history of newly introduced rainbow trout stocks, local or global influences that change aquatic environments and reduce biotic resistance by native parasites or diseases, and rapid evolution of local adaptations by new or marginally established populations of rainbow trout that makes them more invasive.

A paradox of invasion biology is that even though native species are locally adapted to environmental conditions, nonnative species without this advantage often invade. Ecologists have advanced four main theories to explain why invaders are successful in some places and not others: biotic resistance, environmental resistance, human disturbance, and natural enemies. However, none of these theories alone can account for invasions by two trout species outside their native ranges in North America. Brook trout (Salvelinus fontinalis) are able to displace native cutthroat trout (Oncorhynchus clarkii) in the inland western US, but are themselves displaced by nonnative rainbow trout (O. mykiss) in the southeastern US. An alternative hypothesis is that an interaction among zoogeography, evolutionary history, and environmental resistance from the natural flow regimes can account for this paradox. The nonnative species invade successfully at the southern edge of the ranges of the native species, which are farthest from their ancestral origins. Due to their evolutionary history, the native species are poorly adapted to the natural disturbance regime at the southern limit of their ranges, but the nonnative species are preadapted by chance due to theirs. This alternative hypothesis about the interaction between the historical contingency of evolution and environmental resistance should be more widely tested, to inform both invasion biology and the conservation of native trout.

Translocation is a key strategy for conserving native subspecies of cutthroat trout Oncorhynchus clarkii that have declined markedly throughout their native range. Previous research showed that successful translocations of cutthroat trout in high-elevation southern Rocky Mountain streams were more likely in streams with warm summer water temperature and led to the hypothesis that cold summer temperatures govern translocation success by limiting recruitment. We tested this by measuring the density and size of age-0 cutthroat trout (greenback cutthroat trout O. c. stomias and Colorado River cutthroat trout O. c. pleuriticus) in six headwater streams in north-central Colorado that varied in thermal characteristics. Surveys were conducted at peak emergence during 3 years in two widely spaced study reaches in each stream. Fry density increased with Celsius degree-days accumulated during the growing season but did not vary significantly among years. We used laboratory data on the growth and survivorshi...

Movements of prey organisms across ecosystem boundaries often subsidize consumer populations in adjacent habitats. Human disturbances such as habitat degradation or non-native species invasions may alter the characteristics or fate of these prey subsidies, but few studies have measured the direct effects of this disruption on the growth and local abundance of predators in recipient habitats. Here we present evidence, obtained from a combined experimental and comparative study in northern Japan, that an invading stream fish usurped the flux of allochthonous prey to a native fish, consequently altering the diet and reducing the growth and abundance of the native species. A large-scale field experiment showed that excluding terrestrial invertebrates that fell into the stream with a mesh greenhouse reduced terrestrial prey in diets of native Dolly Varden charr (Salvelinus malma) by 46-70%, and reduced their growth by 25% over six weeks. However, when nonnative rainbow trout (Oncorhynchus mykiss) were introduced, they monopolized these prey and caused an even greater reduction of terrestrial prey in charr diets of 82-93%, and reduced charr growth by 31% over the same period. Adding both greenhouse and rainbow trout treatments together produced similar results to adding either alone. Results from a comparative field study of six other stream sites in the region corroborated the experimental findings, showing that at invaded sites rainbow trout usurped the terrestrial prey subsidy, causing a more than 75% decrease in the biomass of terrestrial invertebrates in Dolly Varden diets and forcing them to shift their foraging to insects on the stream bottom. Moreover, at sites with even low densities of rainbow trout, biomass of Dolly Varden was more than 75% lower than at sites without rainbow trout. Disruption of resource fluxes between habitats may be a common, but unidentified, consequence of invasions, and an additional mechanism contributing to the loss of native species.

Native salmonids are increasingly restricted to upstream habitats that may be too cold to sustain recruitment, and recruitment limitation owing to cold temperatures is a main hypothesis to explain translocation failures of native cutthroat trout Oncorhynchus clarkii in high-elevation streams in the southern Rocky Mountains. We subjected Colorado River cutthroat trout O. c. pleuriticus fry to one of three temperature regimes (cold, intermediate, or warm), which averaged 7.0, 8.5, and 10.0°C during the warmest summer month, in each of 2 years. The regimes mimicked those of natural streams where translocated fish had died out or produced populations of cutthroat trout of low or high abundance. The mean fry survival rate from hatching through swim-up was high during both experiments, ranging from 97% in the warm regime to 85% in the cold. After swim-up, fry in the warm regime grew more than 60% more on average than those in the cold regime by the onset of winter in 2003 during a 22-week period. Survi...

Removal of riparian vegetation and straightening of stream channels (channelization) are the most prevalent forms of habitat degradation in streams and their riparian zones. Both have direct effects on organisms in the habitats where they occur, but also have potential to cause indirect effects by interrupting the flux of invertebrate prey between the two adjacent ecosystems. We measured abundance of web-building riparian spiders along four types of streams in Hokkaido, Japan: relatively undisturbed streams, streams where riparian vegetation had been removed, previously channelized streams where the banks had revegetated, and streams that had been both channelized and had the vegetation removed. Spider abundance was reduced by 70% or more by either habitat disturbance alone, or both combined, and the number of spider families was also reduced. Spiders of the family Tetragnathidae, which specialize in capturing adult insects emerging from streams, were strongly reduced by either form of habitat degradation alone, or in combination. In contrast, abundance of spiders in other families that capture prey from both terrestrial and aquatic sources was reduced more strongly by vegetation loss than channelization. These results indicate that riparian vegetation loss has strong direct effects on spiders by reducing habitat for web sites. They also suggest that channelization can have strong indirect effects on riparian-specialist tetragnathid spiders, probably by reducing the flux of adult aquatic insects from the stream to the riparian zone.

SUMMARY 1. Streams and their adjacent riparian zones are closely linked by reciprocal flows of invertebrate prey. We review characteristics of these prey subsidies and their strong direct and indirect effects on consumers and recipient food webs. 2. Fluxes of terrestrial invertebrates to streams can provide up to half the annual energy budget for drift-feeding fishes such as salmonids, despite the fact that input occurs principally in summer. Inputs appear highest from closed-canopy riparian zones with deciduous vegetation and vary markedly with invertebrate phenology and weather. Two field experiments that manipulated this prey subsidy showed that it affected both foraging and local abundance of stream fishes. 3. Emergence of adult insects from streams can constitute a substantial export of benthic production to riparian consumers such as birds, bats, lizards, and spiders, and contributes 25–100% of the energy or carbon to such species. Emergence typically peaks in early summer in the temperate zone, but also provides a low-level flux from autumn to spring in ice-free streams. This flux varies with in-stream productivity, and declines exponentially with distance from the stream edge. Some predators aggregate near streams and forage on these prey during periods of peak emergence, whereas others rely on the lower subsidy from autumn through spring when terrestrial prey are scarce. Several field experiments that manipulated this subsidy showed that it affected the short-term behaviour, growth, and abundance of terrestrial consumers. 4. Reciprocal prey subsidies also have important indirect effects on both stream and riparian food webs. Theory predicts that allochthonous prey should increase density of subsidised predators, thereby increasing predation on in situ prey and causing a negative indirect effect via apparent competition. However, short-term experiments have produced either positive or negative indirect effects. These contrasting results may be due to characteristics of the subsidies and individual consumers, but could also result from differences in experimental designs. 5. New study approaches are needed to better determine the direct and indirect effects of reciprocal prey subsidies. Experiments coupled with comparative research will be required to measure their effects on individual consumer fitness and population demographics. Future work should investigate whether reciprocal prey fluxes stabilise linked stream–riparian ecosystems, explore how landscape context affects the magnitude and importance of subsidies, and determine how impacts of human disturbance can propagate between streams and riparian zones via these trophic linkages. Study of these

We conducted two types of experiments in the upper Sacramento River, California, to test the effects of hatchery-reared juvenile Chinook salmon Oncorhynchus tshawytscha on the emigration, growth, and survival of their wild counterparts. In 3 years of displacement experiments, emigration rates from 8-m2 enclosures into downstream traps were similar between control enclosures that contained 40 wild fish and treatment enclosures to which 33 or 40 hatchery fish were also added. The mean number of wild fish in enclosures at the end of experiments differed by less than one fish between treatments and controls during all 3 years, indicating that hatchery fish prompted few wild fish to emigrate. In 2 years of competition experiments wherein fish could not emigrate, the enclosures contained wild fish (40 fish), wild fish plus hatchery fish (40 wild fish plus 33 or 40 hatchery fish), or wild fish at the same total density as the treatment with wild plus hatchery fish (73 or 80 wild fish). During 2001, surv...

If hatchery-reared salmon delay emigration after release, they may compete with wild salmon in freshwater rearing habitat. We measured the densities and size distributions of ocean-type juvenile Chinook salmon Oncorhynchus tshawytscha in two rearing areas downstream of a hatchery in the Sacramento River, California, before, during, and after two large releases in both 2001 and 2002. Densities of juvenile salmon followed a unimodal trend through time, peaking at about 0.5–1.5 fish/m2 during late March or early April but declining by the time hatchery fish were released in mid to late April. Hatchery releases did not increase densities above the underlying trend, except after one release at one site. Density increased by 0.83 fish/m2 (SE, 0.30 fish/m2) after this release but returned to the baseline level within 3 d. Although hatchery fish were much larger than most wild fish, the mean size of fish captured did not increase appreciably after hatchery releases, even after the release when density in...

Habitat alteration and biotic invasions are the two leading causes of global environmental change and biodiversity loss. Recent innovative experiments have shown that habitat disturbance can have drastic effects that cascade to adjacent ecosystems by altering the flow of resource subsidies from donor systems. Likewise, exotic species in- vasions could alter subsidies and affect distant food webs, but very few studies have tested this experimentally. Here we report evidence from a large-scale field experiment in northern Japan that invasion of nonnative rainbow trout (Oncorhynchus mykiss) interrupted reciprocal flows of invertebrate prey that drove stream and adjacent riparian forest food webs. Rainbow trout usurped terrestrial prey that fell into the stream, causing native Dolly Varden charr (Salvelinus malma) to shift their foraging to insects that graze algae from the stream bottom. This indirectly increased algal biomass, but also decreased biomass of adult aquatic insects emerging from the stream to the forest. In turn, this led to a 65% reduction in the density of riparian-specialist spiders in the forest. Thus, species invasions can interrupt flows of resources between interconnected ecosystems and have effects that propagate across their boundaries, effects that may be difficult to anticipate without in-depth understanding of food web relationships.

Invasion by nonnative brook trout (Salvelinus fontinalis) often results in replacement of cutthroat trout (Oncorhynchus clarki) in the inland western United States, but the underlying mechanisms are not well understood. We conducted a four-year removal experiment to test for population-level mechanisms (i.e., changes in recruitment, survival, emigration, and immigration) promoting invasion success of brook trout and causing decline of native Colorado River cutthroat trout (O. c. pleuriticus). We chose 700–1200 m segments of four small mountain streams where brook trout had recently invaded cutthroat trout populations, two each at mid elevation (2500–2700 m) and high elevation (3150–3250 m), and annually removed brook trout from two streams (treatments), but not the other two (controls). We used depletion electrofishing, two-way fish weirs, and mark–recapture methods to estimate abundance, movement, and survival of trout. At mid elevation, age-0 and age-1 cutthroat trout survived at 13 times and two times ...

Biotic homogenization, the gradual replacement of native biotas by locally expanding non-natives, is a global process that diminishes floral and faunal distinctions among regions. Although patterns of homogenization have been well studied, their specific ecological and evolutionary consequences remain unexplored. We argue that our current perspective on biotic homogenization should be expanded beyond a simple recognition of species diversity loss, towards a synthesis of higher order effects. Here, we explore three distinct forms of homogenization (genetic, taxonomic and functional), and discuss their immediate and future impacts on ecological and evolutionary processes. Our goal is to initiate future research that investigates the broader conservation implications of homogenization and to promote a proactive style of adaptive management that engages the human component of the anthropogenic blender that is currently mixing the biota on Earth.