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In many applications, conservation organizations depend on one species to indicate the presence of another. While extensive research has gone into methods for selecting these indicator species, few studies have directly measured the performance of indicator species in guiding conservation actions. Here, we evaluated whether a small number of indicator species could be used to efficiently select barrier removal projects to restore breeding habitat access for many other Great Lakes migratory fishes in the highly fragmented tributaries of the North American Great Lakes. First, we used a dataset of the historical distributions of 35 species of native migratory fishes to identify four clusters of co-occurring species, and then selected an indicator species for each cluster based on within-group co-occurrence or range width. We evaluated the utility of these indicator species by using upstream habitat and removal costs for 103,894 dams and road culverts across 1800 tributaries of the Great Lakes. We compared the potential increase in accessible tributary habitat for each species when barrier removals were prioritized to maximize benefits for (1) each species itself, versus (2) possible indicator species. We found that for 80% of the species, habitat gains from indicator-based project selection were at least 75% of the maximum gains possible under species-specific planning. However, a small subset of species would receive few habitat gains under indicator-directed project selection. Overall, our findings suggest that a suite of indicator species could be an efficient basis for planning restoration efforts for a majority of native migratory fishes in the Great Lakes.

International audience; Environmental flows (e-flows) are powerful tools for sustaining freshwater biodiversity and ecosystem services, but their widespread implementation faces numerous social, political, and economic barriers. These barriers are amplified in water-limited systems where strong trade-offs exist between human water needs and freshwater ecosystem protection. We synthesize the complex, multidisciplinary challenges that exist in these systems to help identify targeted solutions to accelerate the adoption and implementation of environmental flows initiatives. We present case studies from three water-limited systems in North America and synthesize the major barriers to implementing environmental flows. We identify four common barriers: (a) lack of authority to implement e-flows in water governance structures, (b) fragmented water governance in transboundary water systems, (c) declining water availability and increasing variability under climate change, and (d) lack of consideration of non-biophysical factors. We then formulate actionable recommendations for decision makers facing these barriers when working towards implementing environmental flows: (a) modify or establish a water governance framework to recognize or allow e-flows, (b) strive for collaboration across political jurisdictions and social, economic, and environmental sectors, and (c) manage adaptively for climate change in e-flows planning and recommendations.

Water scarcity during severe droughts has profound hydrological and ecological impacts on rivers. However, the drying dynamics of river surface extent during droughts remains largely understudied. Satellite remote sensing enables surveys and analyses of rivers at fine spatial resolution by providing an alternative to in-situ observations. This study investigates the seasonal drying dynamics of river extent in California where severe droughts have been occurring more frequently in recent decades. Our methods combine the use of Landsat-based Global Surface Water (GSW) and global river bankful width databases. As an indirect comparison, we examine the monthly fractional river extent (FrcSA) in 2071 river reaches and its correlation with streamflow at co-located USGS gauges. We place the extreme 2012–2015 drought into a broader context of multi-decadal river extent history and illustrate the extraordinary change between during- and post-drought periods. In addition to river extent dynamics, we perform statistical analyses to relate FrcSA with the hydroclimatic variables obtained from the National Land Data Assimilation System (NLDAS) model simulation. Results show that Landsat provides consistent observation over 90% of area in rivers from March to October and is suitable for monitoring seasonal river drying in California. FrcSA reaches fair (&gt, 0.5) correlation with streamflow except for dry and mountainous areas. During the 2012–2015 drought, 332 river reaches experienced their lowest annual mean FrcSA in the 34 years of Landsat history. At a monthly scale, FrcSA is better correlated with soil water in more humid areas. At a yearly scale, summer mean FrcSA is increasingly sensitive to winter precipitation in a drier climate, and the elasticity is also reduced with deeper ground water table. Overall, our study demonstrates the detectability of Landsat on the river surface extent in an arid region with complex terrain. River extent in catchments of deficient water storage is likely subject to higher percent drop in a future climate with longer, more frequent droughts.

Despite increasing efforts globally to remove dams and construct fish passage structures, broad-scale analyses balancing tradeoffs between cost and habitat gains from these mitigations infrequently consider invasive species. We present an optimization-based approach for prioritizing dam mitigations to restore habitat connectivity for native fish species, while limiting invasive species spread. Our methodology is tested with a case study involving 240 dams in the Upper Mississippi River, USA. We integrate six native migratory fish species distribution models, distributions of two invasive fishes, and estimated costs for dam removal and construction of fish passes. Varying budgets and post-mitigation fish passage rates are analyzed for two scenarios: ‘no invasives’ where non-selective mitigations (e.g., dam removal) are used irrespective of potential invasive species habitat gains and ‘invasives’ where a mixture of selective (e.g., lift-and-sort fish passage) and non-selective mitigations are deployed to limit invasive species range expansion. To achieve the same overall habitat connectivity gains, we find that prioritizations accounting for invasive species are 3 to 6 times more costly than those that do not. Habitat gains among native fish species were highly variable based on potential habitat overlap with invasive species and post-mitigation passabilities, ranging from 0.4–58.9% (‘invasives’) and 7.9–95.6% (‘no invasives’) for a $50M USD budget. Despite challenges associated with ongoing nonnative fish invasions, opportunities still exist to restore connectivity for native species as indicated by individual dams being frequently selected in both scenarios across varying passabilities and budgets, however increased restoration costs associated with invasive species control indicates the importance of limiting their further spread within the basin. Given tradeoffs in managing for native vs. invasive species in river systems worldwide, our approach demonstrates strategies for identifying a portfolio of candidate barriers that can be investigated further for their potential to enhance native fish habitat connectivity while concurrently limiting invasive species dispersal.

Conceptual models underpin river ecosystem research. However, current models focus on continuously flowing rivers and few explicitly address characteristics such as flow cessation and drying. The applicability of existing conceptual models to nonperennial rivers that cease to flow (intermittent rivers and ephemeral streams, IRES) has not been evaluated. We reviewed 18 models, finding that they collectively describe main drivers of biogeochemical and ecological patterns and processes longitudinally (upstream‐downstream), laterally (channel‐riparian‐floodplain), vertically (surface water‐groundwater), and temporally across local and landscape scales. However, perennial rivers are longitudinally continuous while IRES are longitudinally discontinuous. Whereas perennial rivers have bidirectional lateral connections between aquatic and terrestrial ecosystems, in IRES, this connection is unidirectional for much of the time, from terrestrial‐to‐aquatic only. Vertical connectivity between surface and subsurface water occurs bidirectionally and is temporally consistent in perennial rivers. However, in IRES, this exchange is temporally variable, and can become unidirectional during drying or rewetting phases. Finally, drying adds another dimension of flow variation to be considered across temporal and spatial scales in IRES, much as flooding is considered as a temporally and spatially dynamic process in perennial rivers. Here, we focus on ways in which existing models could be modified to accommodate drying as a fundamental process that can alter these patterns and processes across spatial and temporal dimensions in streams. This perspective is needed to support river science and management in our era of rapid global change, including increasing duration, frequency, and occurrence of drying.

Societies around the world face difficult choices in allocating fresh water between human uses and environmental flows for freshwater ecosystems. In many regions, policy makers are developing water conservation plans that set ambitious targets for reduced water consumption. These plans often rely on incentives, rather than regulation, to achieve water savings. However, water managers and conservation groups lack guidance on the most cost-effective locations and times for incentivizing water conservation. Here, we develop a spatial planning framework that enables conservation practitioners to strategically allocate incentives for water conservation actions to balance ecosystem and societal needs for water. We apply this model to the Red River (USA) and draw three main conclusions. First, even optimal allocation of water across the network cannot simultaneously meet societal and environmental flow targets given current water availability and societal usage. Second, modest reductions in societal water usage (e.g., 1–3%) can significantly reduce water conflicts in the basin, but only when these water conservation actions are strategically allocated in time and space. Third, however, substantial reduction in societal water usage (>21%) is needed to fully satisfy societal and environmental flow goals. We discuss future research directions in the Red River and the transferability of our results to other drought-prone river networks worldwide.

Rivers and streams worldwide are highly fragmented by dams and road crossings, and there is a pressing need to retrofit the most problematic structures to ensure aquatic organism passage. At the same time, a majority of the transportation infrastructure within developed nations is beyond its projected lifespan and significant investments will be needed to ensure that this transportation infrastructure remains safe and functional. Historically, these two problems have been addressed separately. Here, we use a rapid survey methodology to identify road-stream crossings that are likely high-priority projects for both conservation and infrastructure agencies. We conducted a field assessment of more than 700 road-stream crossings across Oklahoma to determine if they blocked fish movements and to determine their physical condition. We then developed an index of ecological impact, and an index of infrastructure condition, based on physical variables measured at each crossing. This survey revealed a subset of crossings that are both fragmenting the river network and in poor physical condition. These crossings are high-priority locations where culvert replacement may have both high ecosystem benefit and would eliminate a piece of transportation infrastructure with a high risk of failure. We discuss opportunities for cost-sharing between conservation and transportation agencies.

Controlling invasive species is critical for conservation but can have unintended consequences for native species and divert resources away from other efforts. This dilemma occurs on a grand scale in the North American Great Lakes, where dams and culverts block tributary access to habitat of desirable fish species and are a lynchpin of long-standing efforts to limit ecological damage inflicted by the invasive, parasitic sea lamprey (Petromyzon marinus). Habitat restoration and sea-lamprey control create conflicting goals for managing aging infrastructure. We used optimization to minimize opportunity costs of habitat gains for 37 desirable migratory fishes that arose from restricting sea lamprey access (0-25% increase) when selecting barriers for removal under a limited budget (US$1-105 million). Imposing limits on sea lamprey habitat reduced gains in tributary access for desirable species by 15-50% relative to an unconstrained scenario. Additional investment to offset the effect of limiting sea-lamprey access resulted in high opportunity costs for 30 of 37 species (e.g., an additional US$20-80 million for lake sturgeon [Acipenser fulvescens]) and often required ≥5% increase in sea-lamprey access to identify barrier-removal solutions adhering to the budget and limiting access. Narrowly distributed species exhibited the highest opportunity costs but benefited more at less cost when small increases in sea-lamprey access were allowed. Our results illustrate the value of optimization in limiting opportunity costs when balancing invasion control against restoration benefits for diverse desirable species. Such trade-off analyses are essential to the restoration of connectivity within fragmented rivers without unleashing invaders.

Conservation practitioners face difficult choices in apportioning limited resources between rare species (to ensure their existence) and common species (to ensure their abundance and ecosystem contributions). We quantified the opportunity costs of conserving rare species of migratory fishes in the context of removing dams and retrofitting road culverts across 1,883 tributaries of the North American Great Lakes. Our optimization models show that maximizing total habitat gains across species can be very efficient in terms of benefits achieved per dollar spent, but disproportionately benefits common species. Conservation approaches that target rare species, or that ensure some benefits for every species (i.e., complementarity) enable strategic allocation of resources among species but reduce aggregate habitat gains. Thus, small habitat gains for the rarest species necessarily come at the expense of more than 20 times as much habitat for common ones. These opportunity costs are likely to occur in many ecosystems because range limits and conservation costs often vary widely among species. Given that common species worldwide are declining more rapidly than rare ones within major taxa, our findings provide incentive for triage among multiple worthy conservation targets.

Rivers are among the most dynamic components in Earth's terrestrial water cycle and provide critical ecosystem services. Yet, the spatiotemporal variability of river surface extents remains largely unquantified at the global scale. Satellite remote sensing provides a promising alternative to in-situ observations, which can enable a more comprehensive survey and systematic analysis of global rivers at fine spatial resolutions. The study examines the spatiotemporal variability of river surface extent globally and its natural driving factors, by combining the use of Landsat-based Global Surface Water (GSW) and Global River Widths from Landsat (GRWL) databases. In addition to examining the long-term mean river surface extent in various climate zones, we perform statistical analyses to correlate monthly times series of fractional river extent with the terrestrial water storage (TWS) components obtained from the Gravity Recovery and Climate Experiment (GRACE) satellite observation and the Global Land Data Assimilation System (GLDAS) model simulations. Results show that the spatiotemporal variability of water presence in rivers can be explained well via differentiating climate zones. The analysis also shows that 52.7% of the global maximum river extent is covered by water less than half of time. Changes of fractional river extent are found to be highly correlated with groundwater storage in low- and mid-latitudes, whereas snow melting dominates the river dynamics in high latitudes. By examining the extremes of fractional river extent, we found that the abrupt changes of fractional river extent are well linked to precipitation anomalies in the equatorial, arid, and warm temperate areas. This study offers an innovative perspective to study spatiotemporal dynamics of rivers by combining optical remote sensing (Landsat), gravimetry observations (GRACE), and land surface simulations; and it highlights the significant role of low-flow-generating processes (snow melting, infiltration, and recharge-discharge) in controlling river dynamics in certain regions, which warrants future investigation.

Dams and road culverts fragment river ecosystems worldwide by restricting the movement of aquatic species. In many watersheds, a diverse set of actors coordinates the removal of these barriers. Non-governmental organizations often focus on small dams and road culverts, while large dam removal projects are coordinated by federal agencies or coalitions of partners. Here we evaluate the return-on-investment of these strategies by exploring a continuum of methods for selecting barrier removal projects, ranging from a focus on many small barrier removal projects to a few large ones. We used estimated removal costs of more than 100,000 barriers in the North American Great Lakes to construct economically realistic barrier removal scenarios. We then simulated the movement of stream-resident and anadromous fishes through model river networks with a few large dam removals, many road culvert retrofits, or a mix of both. We found that the strategy of removing both dams and road culverts had the greatest potential to benefit both stream-resident and anadromous fishes, but only when projects were aligned longitudinally within the river network. Our results demonstrate the importance of allocating conservation resources to both small and large restoration projects, and highlight a need for increased coordination and communication among the many different organizations investing in barrier removals. Our findings complement optimization approaches to prioritizing barrier removals by providing general guidelines for practitioners to follow when project selection must depart from a prescribed portfolio of projects.

More than half of all streams globally are non-perennial, and thus dynamic due to their expanding and retracting nature. Field mapping in conjunction with observational data from gauges and/or in-situ loggers is a typical approach for studying non-perennial stream dynamics, but these approaches underrepresent their spatiotemporal variability. High-resolution distributed hydrological modeling promises to bridge this gap, thanks to advances in model physics, remote sensing, and computational power. As the first step towards this goal, we investigate the capability of distributed hydrologic modeling to capture stream dynamics in Upper Blue River Basin, OK. Coupled Routing and Excess STorage (CREST), a distributed hydrological model, is used to simulate spatiotemporally varied streamflow at 10-meter spatial resolution and daily time steps. USGS stream gauge data and in-situ state logger data are used to calibrate and validate the simulation at the watershed outlet and small headwater tributaries, respectively. Dynamic Surface Water Estimate (DSWE), a LANDSAT product is also compared with simulated water presence in high-order streams. Results show that the CREST model can capture low-moderate streamflow values at the watershed outlet with a log-NSE value over 0.7 in the validation period, while underestimating high flow values due to the daily time step. Also, the calibrated model can accurately estimate wet/dry status as monitored by in-situ state loggers in nine headwater catchments. The dynamic stream networks are mapped over 2510 stream segments using the CREST simulation. Non-perennial streams are the most dynamic in small headwater tributaries (contributing area

In this paper, a multi-objective, multi-period, and stochastic mathematical model is developed to identify drought-resilient strategies for balancing human and environmental water needs given uncertainty about future water availability. The model makes sustainable water withdrawal/distribution decisions for the interconnected water reservoirs of a river network through balancing societal and environmental water needs. These decisions are restricted by the storage capacities of reservoirs and fluctuations of water availability over the planning horizon. The model relies on interval estimation of stochastic hydrological factors, which may be drawn from historical data or future climate projections. The model finds a compromise between drought resilience and satisfaction of water needs through a reliability level that represents the risk attitude of water decision-makers. Finally, the model is extended to include water conservation options. The extended model determines the spatial and temporal prioritization of water reservoirs for water conservation. The proposed models are tested on the Red River of the south-central United States. We quantify tradeoffs between human and environmental water needs and identify water sustainability strategies that are resilient to stochastic drought events. Our model is applicable to drought-prone river basins around the world where water managers seek to balance environmental and human water needs while remaining resilient to unexpected fluctuations in water availability.

Societies worldwide make large investments in the sustainability of integrated human-freshwater systems, but uncertainty about water supplies under climate change poses a major challenge. Investments in infrastructure, water regulation, or payments for ecosystem services may boost water availability, but may also yield poor returns on investment if directed to locations where water supply unexpectedly fluctuates due to shifting climate. How should investments in water sustainability be allocated across space and among different types of projects? Given the high costs of investments in water sustainability, decision-makers are typically risk-intolerant, and considerable uncertainty about future climate conditions can lead to decision paralysis. Here, we use mathematical optimization models to find Pareto-optimal satisfaction of human and environmental water needs across a large drought-prone river basin for a range of downscaled climate projections. We show how water scarcity and future uncertainty vary independently by location, and that joint consideration of both factors can provide guidance on how to allocate water sustainability investments. Locations with high water scarcity and low uncertainty are good candidates for high-cost, high-reward investments; locations with high scarcity but also high uncertainty may benefit most from low regret investments that minimize the potential for stranded assets if water supply increases. Given uncertainty in climate projections in many regions worldwide, our analysis illustrates how explicit consideration of uncertainty may help to identify the most effective strategies for investments in the long-term sustainability of integrated human-freshwater systems.

Structures that block movement of fish through river networks are built to serve a variety of societal needs, including transportation, hydroelectric power, and exclusion of exotic species. Due to their abundance, road crossings and dams reduce the amount of habitat available to fish that migrate from the sea or lakes into rivers to breed. The benefits to fish of removing any particular barrier depends on its location within the river network, its passability to fish, and the relative position of other barriers within the network. Balancing the trade-offs between ecological and societal values makes choosing among potential removal projects difficult. To facilitate prioritization of barrier removals, we developed an online decision support tool (DST) with three functions: (1) view existing barriers at various spatial scales; (2) modify information about barriers, including removal costs; and (3) run optimization models to identify portfolios of removals that provide the greatest amount of habitat access for a given budget. A survey of available DSTs addressing barrier removal prioritization indicates that barrier visualization is becoming widespread but few tools allow dynamic calculation of connectivity metrics, scenario analysis, or optimization. Having these additional functions, our DST enables organizations to develop barrier removal priorities based on\ud cost-effectiveness in restoring aquatic connectivity.

Most ecosystems are impacted by multiple local and long-distance stressors, many of which interact in complex ways. We present a framework for prioritizing ecological restoration efforts among sites in multi-stressor landscapes. Using a simple model, we show that both the economic and sociopolitical costs of restoration will typically be lower at sites with a relatively small number of severe problems than at sites with numerous lesser problems. Based on these results, we propose using cumulative stress and evenness of stressor impact as complementary indices that together reflect key challenges of restoring a site to improved condition. To illustrate this approach, we analyze stressor evenness across the world's rivers and the Laurentian Great Lakes. This exploration reveals that evenness and cumulative stress are decoupled, enabling selection of sites where remediating a modest number of high-intensity stressors could substantially reduce cumulative stress. Just as species richness and species evenness are fundamental axes of biological diversity, we argue that cumulative stress and stressor evenness constitute fundamental axes for identifying restoration opportunities in multi-stressor landscapes. Our results highlight opportunities to boost restoration efficiency through strategic use of multi-stressor datasets to identify sites that maximize ecological response per stressor remediated. This prioritization framework can also be expanded to account for the feasibility of remediation and the expected societal benefits of restoration projects.

Rivers worldwide are fragmented by transportation infrastructure that blocks the movements of aquatic organisms. To assess the effects of road culverts on stream fishes in the Ozark and Ouachita Mountains regions of Oklahoma, we surveyed 39 free-flowing sites, 29 sites upstream and 29 sites downstream of culverts. We observed differences in species richness and abundance between free-flowing sites, sites upstream of a culvert, and downstream sites. We also found that the degree to which a culvert affected richness and abundance depended on culvert type and length. Furthermore, the culverts in the poorest condition had the greatest effects on abundance and richness. Replacement of these poor condition culverts is likely a high priority for both conservation groups and infrastructure agencies. Our findings enable conservation practitioners to identify structures that may be high priorities for aquatic organism passage projects, including those that may benefit from cost-sharing or collaboration with infrastructure agencies.

In a multireservoir system, ensuring adequate water availability while managing conflicting goals is critical to making the social–ecological system sustainable in the presence of considerable uncertainty. The priorities of multiple user groups and availability of the water resource vary with time, weather, and other factors. Uncertainties such as variations in precipitation can intensify the discrepancies between water supply and water demand. To reduce such discrepancies, we seek to satisfice conflicting goals, considering typical uncertainties. We observe that models are incomplete and inaccurate, which calls into question using a single point solution and suggests the need for solutions, which are robust to uncertainties. So, we explore satisficing solutions that are relatively insensitive to uncertainties, by incorporating different design preferences, identifying sensitive segments, and improving the design accordingly. In this article, we present an example of the exploration of the solution space to enhance sustainability in multidisciplinary systems, when goals conflict, preferences are evolving, and uncertainties add complexity, which can be applied in mechanical design. In this paper, we focus on the method rather than the results.

A hallmark of industrialization is the construction of dams for water management and roads for transportation, leading to fragmentation of aquatic ecosystems. Many nations are striving to address both maintenance backlogs and mitigation of environmental impacts as their infrastructure ages. Here, we test whether accounting for road repair needs could offer opportunities to boost conservation efficiency by piggybacking connectivity restoration projects on infrastructure maintenance. Using optimization models to align fish passage restoration sites with likely road repair priorities, we find potential increases in conservation return-on-investment ranging from 17% to 25%. Importantly, these gains occur without compromising infrastructure or conservation priorities; simply communicating openly about objectives and candidate sites enables greater accomplishment at current funding levels. Society embraces both reliable roads and thriving fisheries, so overcoming this coordination challenge should be feasible. Given deferred maintenance crises for many types of infrastructure, there could be widespread opportunities to enhance the cost effectiveness of conservation investments by coordinating with infrastructure renewal efforts.

This paper describes a process of ‘open’ interdisciplinary scholarship. Researchers from across the University of Oklahoma blogged about a recent paper by ecologist Erle Ellis, and met in person to discuss posts. They then hosted Ellis for a seminar on questions that emerged, and for a public panel discussion.

Limited resources and taxonomic expertise in biodiversity surveys often lead to the application of the higher taxa approach (HTA),i.e., the identification of specimens to genus or higher taxonomic levels rather than to species. The reliability of the HTA varies significantly among studies, yet the factors underlying this variability have rarely been investigated. Bees are an ideal model taxon for testing the HTA because they are highly diverse, challenging to identify, and there is widespread interest in their role as native pollinators, driving demand for efficient diversity assessment tools. Using extensive bee data sets collected across three biomes and various habitats, we assessed the performance of the HTA in reflecting bee species richness and composition patterns at local scales, factors affecting this performance, and ways to improve it. The performance of the HTA varied considerably among biomes, taxonomic levels (genera and subfamilies), and diversity measures (species richness and composition); genus and subfamily richness accounted for 55-77% and 32-61% of the variation in species richness, respectively; genus and subfamily composition accounted for 28-87% and 26-80% of the variation in species composition, respectively. The number of species per higher taxon was a main factor influencing this performance (accounting for 63% of the variation), while the co-occurrence of taxonomically related species had no significant influence on the performance of the HTA. Further subdividing genera by body size contributed to the performance of the HTA and increased its accuracy in representation of compositional patterns by ~16%. Our results have several practical implications. The considerable variability found in the performance of the HTA in representing local-scale richness and composition patterns of bee species dictates caution in implementing this tool in bee surveys. When possible, an a priori evaluation of the expected performance of the HTA should be done, focusing on species distributions within higher taxonomic levels and the species: higher taxa ratio. Integrating morphological characteristics (such as body size) that consistently subdivide genera will improve the HTA's performance. Our results are likely applicable to the implementation of the HTA in other small-bodied and species-rich groups and may contribute to the cost-effectiveness of biodiversity surveys.

The concept of shifting baselines in conservation science implies advocacy for the use of historical knowledge to inform these baselines but does not address the feasibility of restoring sites to those baselines. In many regions, conservation feasibility varies among sites due to differences in resource availability, statutory power, and land-owner participation. We used zooarchaeological records to identify a historical baseline of the freshwater mussel community's composition before Euro-American influence at a river-reach scale (i.e., a kilometer stretch of river that is abiotically similar) in the Leon River of central Texas (U.S.A.). We evaluated how the community reference position and the feasibility of conservation might enable identification of sites where conservation actions would preserve historically representative communities and be likely to succeed. We devised a conceptual model that incorporated community information and landscape factors to link the best conservation areas to potential cost and conservation benefits. Using fuzzy ordination, we identified modern mussel beds that were most like the historical baseline. We then quantified housing density and land use near each river reach identified to estimate feasibility of habitat restoration. Using our conceptual framework, we identified reaches of high conservation value (i.e., contain the best mussel beds) and where restoration actions would be most likely to succeed. Reaches above Lake Belton were most similar in species composition and relative abundance to zooarchaeological sites. A subset of these mussel beds occurred in locations where conservation actions appeared most feasible. Our results show how to use zooarchaeological data (biodiversity data often readily available) and estimates of conservation feasibility to inform conservation priorities at a local spatial scale.

One of the most important ecological relationships between any two species is the degree of overlap in their distributions, i.e., their co-occurrence. Quantifying this relationship is a key step in the selection of indicator species and many other analyses in conservation biology and ecology. We derived a measure of the co-occurrence of two species based on the relative mutual information (RMI) of their distributions, and then compared its performance to three existing statistics: bivariate or binary covariance (BC), mean pairwise index (MPI), and proportional similarity (PS). To make this comparison, we measured co-occurrence values for all pairwise combinations of species collected from three communities (ground-dwelling beetles, moths, and vascular plants) in the Jerusalem Mountains and Judean Foothills, central Israel. We then used these co-occurrence values to address two different ecological problems: the challenge of identifying good indicator species, and the question of whether congeneric species co-occur more than species from different genera. We found that PS and RMI were the most reliable basis for choosing indicator species, but these two statistics differed in their error structures: PS had lower rates of type I errors (false positives), while RMI had lower rates of type II errors (false negatives). We also found that congeneric species co-occurred more often than species from different genera, but this pattern was statistically significant for only some of the measures of co-occurrence. In our analysis, then, the conclusion that we reached regarding the co-occurrence of congeneric species depended on which co-occurrence statistic was used. We therefore caution that available co-occurrence statistics should not be used interchangeably, because the ecological inferences drawn from a study may depend on the choice of co-occurrence statistic. In summary, we recommend PS and RMI as pairwise measures of species co-occurrence for investigating the reliability of biodiversity indicators and other applications in conservation biology and ecology.

Most animals forage in nutritionally complicated environments in which the densities of complementary foods vary in space and time. Locally rare foods can lead to nutritional deficiencies in consumers, yet there has been little consideration of the influence of nutritional deficits, and consumers’ efforts to redress these deficits, on population and community dynamics. A taxonomically and trophically diverse group of animals can redress accumulated deficits using nutrient-specific foraging, defined here as the ability of an animal to bias its foraging effort towards certain foods on the basis of its own nutritional state. We focus on the true omnivores, because they feed on vastly different nutrient sources, animals and plants. We use an ordinary differential equation model to show that nutrient-specific foraging may destabilize omnivore–prey population dynamics, depending on the degree to which the omnivore alters its foraging in an attempt to balance its nutritional state. In particular, a high behavioral sensitivity to nutritional imbalances led to a novel type of Allee effect driven by the interaction between prey density and nutritional deficiencies in the omnivore. Our model overall is characterized by a causal loop between the omnivore's nutritional state, food preferences and population dynamics. Consequently, the omnivore exhibited a dynamic functional response, in which the relationship between prey density and omnivore per capita consumption of prey was influenced by the current nutritional state of the omnivore. With regards to omnivory in general, our results reinforce the idea that statements about the effects of omnivory on population or community stability are not possible without a consideration of the behavioral mechanisms of diet mixing.

Human activity causes abrupt changes in resource availability across the landscape. In order to persist in human-altered landscapes organisms need to shift their habitat use accordingly. Little is known about the mechanisms by which whole communities persist in human-altered landscapes, including the role of complementary habitat use. We define complementary habitat use as the use of different habitats at different times by the same group of species during the course of their activity period. We hypothesize that complementary habitat use is a mechanism through which native bee species persist in human-altered landscapes. To test this idea, we studied wild bee communities in agro-natural landscapes and explored their community-level patterns of habitat and resource use over space and time. The study was conducted in six agro-natural landscapes in the eastern United States, each containing three main bee habitat types (natural habitat, agricultural fields, and old fields). Each of the three habitats exhibited a unique seasonal pattern in amount, diversity, and composition of floral resources, and together they created phenological complementarity in foraging resources for bees. Individual bee species as well as the bee community responded to these spatiotemporal patterns in floral availability and exhibited a parallel pattern of complementary habitat use. The majority of wild bee species, including all the main crop visitors, used fallow areas within crops early in the season, shifted to crops in mid-season, and used old-field habitats later in the season. The natural-forest habitat supported very limited number of bees, mostly visitors of non-crop plants. Old fields are thus an important feature in these arable landscapes for maintaining crop pollination services. Our study provides a detailed examination of how shifts in habitat and resource use may enable bees to persist in highly dynamic agro-natural landscapes, and points to the need for a broad cross-habitat perspective in managing these landscapes.

Habitat mapping is a common and often useful tool in the ecological management of rivers. The complex nature of fluvial processes, however, makes it difficult to predict the reach-scale distribution of substrate habitat from landscape-scale covariates. An option is to identify and partition a data set on boundaries of geomorphic process domains, within which the globally complex relationships between landscape, climate, and instream habitat may potentially be approximated by a simpler model. In this study, we used regression trees as a machine learning method for partitioning and identifying useful strata in a geographically extensive substrate habitat model for larvae of the sea lamprey Petromyzon marinus, an invasive and economically harmful species in the Laurentian Great Lakes. We used field survey data from over 5,000 substrate habitat transects collected in 43 watersheds of the Lower Peninsula of Michigan, and we created a geographic database of geographical information systems-derived cova...

The spatial dynamics of many populations are highly contextual in that they depend on the structure of the environment at specific locations or scales. In this paper, we asked how the unique geomorphic structure of each river system might shape the spatial dynamics of larvae of sea lamprey (Petromyzon marinus), an anadromous fish species that is invasive and ecologically harmful in the Laurentian Great Lakes. We developed an individual-based model and conducted a series of simulations in which we varied geomorphic structure at two spatial scales (local habitat substrate composition and basin-wide river network shape). We observed three main results: (1) Larval distribution depended on both river network structure and the distribution of larval habitat, but the relative importance of these two factors depended on the basin-wide abundance of larval habitat. (2) Larvae in the model became spatially aggregated over time, and the degree and rate of this aggregation depended on river network structure and the amount and distribution of larval habitat. Larvae aggregated most quickly, and eventually into the smallest number of reaches, in elongated river networks with abundant larval habitat. (3) Total larval population size in a watershed varied with factors that control larval aggregation, i.e. river network structure and amount and distribution of larval habitat, but relationships were strongly nonlinear. In summary, we found that the population dynamics of anadromous lampreys in Great Lakes tributary rivers constitute an interesting and complex ecological system in which some perennial themes of landscape ecology emerge: connectivity, historical process, and the importance of spatial arrangement. Our results overall suggest that the spatial dynamics of larval lampreys might be highly varied from river system to river system across the Great Lakes basin. We discuss how the unique geomorphic structure of each river might inform adaptive management strategies at specific locations and scales.

The conservation of ecologically and economically important species, as well as the management of invasive species, benefits from the ability to make broad-scale predictions of habitat. In this paper, we revised an existing substrate size model based upon stream power to include variables that are readily-quantifiable in a Geographic Information System (GIS) (i.e. stream slope and drainage area). We found no significant difference between slopes measured in the field using surveying techniques and slopes measured in a GIS using a 10 m digital elevation model and high resolution stream dataset. GIS-derived drainage areas and those measured with hand-delineations were also statistically similar. The revised model can be applied using both GIS and field-derived variables to predict median particle sizes from stream power in northeastern Ohio streams draining to Lake Erie. Integration of such models into a GIS could result in regional estimates of the amount and location of preferred fish habitat, which has important applications in fisheries management. In particular, we provide examples of how the predictive substrate model could improve assessment methodologies for invasive sea lamprey, thereby improving eradication measures, and how we may better understand geographic linkages between walleye spawning and nursery habitats.

a b s t r a c t Adult sea lampreys (Petromyzon marinus) migrating upstream to spawn follow a pheromone released by instream larvae. The size (i.e. flow) of a tributary dilutes the concentration of this pheromone, such that the downstream propagation pattern of larval pheromone must be influenced by patterns in the relative sizes and numbers of confluent tributaries. We developed an individual-based model to explicitly test the resulting hypothesis that river network structure influences the migration decisions of adult lampreys following the larval pheromone, and in turn the distribution of larvae. First, we initialized the model using randomly generated river networks, and found a strong positive relationship between network diameter and larval aggregation. Larvae aggregated over time, and the degree and rate of this aggregation depended on network diameter. Second, we initialized the model using a river network based on the Muskegon River, Michigan, and compared model-generated larval distribution to available field survey data. We found a significant correlation between model-generated larval abundance and field-measured larval densities (r2 = 0.54; p < 0.0001). We also found an inverse relationship between subwatershed area and the degree to which path-dependent effects influenced larval abundance in that subwatershed. Our results overall suggest that larval distribution across a watershed results from a system of context-dependent interannual feedbacks shaped by network structure and the past migratory and spawning behavior of adults.

Stream channel slope is often a critical component of geographical information systems (GIS)-based models of preferred habitat of aquatic species, but the relative accuracy of various GIS slope derivation methods is not well established. We examined the accuracy of GIS-derived stream slopes for a set of stream reaches in Idaho and Ohio. We also used the Ohio data set to examine in more detail the effects of stream reach length, source of GIS file representing the stream path (“shapefile”), and digital elevation model (DEM) resolution on the accuracy of GIS-derived slopes. The accuracy of GIS-derived slopes in the Ohio dataset improved with increasing reach length, but we could not draw any consistent conclusions about the effect of DEM resolution or shapefile. We present a simple and efficient method for improving GIS-derived slopes by identifying probable elevation errors in the GIS-derived longitudinal stream profiles. The resulting derived slopes were improved in all cases; the slopes derived ...

Rapid and ongoing change creates novelty in ecosystems everywhere, both when comparing contemporary systems to their historical baselines, and predicted future systems to the present. However, the level of novelty varies greatly among places. Here we propose a formal and quantifiable definition of abiotic and biotic novelty in ecosystems, map abiotic novelty globally, and discuss the implications of novelty for the science of ecology and for biodiversity conservation. We define novelty as the degree of dissimilarity of a system, measured in one or more dimensions relative to a reference baseline, usually defined as either the present or a time window in the past. In this conceptualization, novelty varies in degree, it is multidimensional, can be measured, and requires a temporal and spatial reference. This definition moves beyond prior categorical definitions of novel ecosystems, and does not include human agency, self-perpetuation, or irreversibility as criteria. Our global assessment of novelty was based on abiotic factors (temperature, precipitation, and nitrogen deposition) plus human population, and shows that there are already large areas with high novelty today relative to the early 20th century, and that there will even be more such areas by 2050. Interestingly, the places that are most novel are often not the places where absolute changes are largest; highlighting that novelty is inherently different from change. For the ecological sciences, highly novel ecosystems present new opportunities to test ecological theories, but also challenge the predictive ability of ecological models and their validation. For biodiversity conservation, increasing novelty presents some opportunities, but largely challenges. Conservation action is necessary along the entire continuum of novelty, by redoubling efforts to protect areas where novelty is low, identifying conservation opportunities where novelty is high, developing flexible yet strong regulations and policies, and establishing long-term experiments to test management approaches. Meeting the challenge of novelty will require advances in the science of ecology, and new and creative. conservation approaches.

In many large ecosystems, conservation projects are selected by a diverse set of actors operating independently at spatial scales ranging from local to international. Although small-scale decision making can leverage local expert knowledge, it also may be an inefficient means of achieving large-scale objectives if piecemeal efforts are poorly coordinated. Here, we assess the value of coordinating efforts in both space and time to maximize the restoration of aquatic ecosystem connectivity. Habitat fragmentation is a leading driver of declining biodiversity and ecosystem services in rivers worldwide, and we simultaneously evaluate optimal barrier removal strategies for 661 tributary rivers of the Laurentian Great Lakes, which are fragmented by at least 6,692 dams and 232,068 road crossings. We find that coordinating barrier removals across the entire basin is nine times more efficient at reconnecting fish to headwater breeding grounds than optimizing independently for each watershed. Similarly, a one-time pulse of restoration investment is up to 10 times more efficient than annual allocations totaling the same amount. Despite widespread emphasis on dams as key barriers in river networks, improving road culvert passability is also essential for efficiently restoring connectivity to the Great Lakes. Our results highlight the dramatic economic and ecological advantages of coordinating efforts in both space and time during restoration of large ecosystems.

Regular ship-board monitoring of oxygen in the hypolimnion of Lake Erie has been established to monitor the status of the lake and determine if the water quality is meeting the terms of the Great Lakes Water Quality Agreement (GLWQA). However, lake-wide monitoring is expensive and there is a difference of opinion on whether dissolved oxygen depletion rate is a good indicator of the condition of Lake Erie. One the most poorly known components of the Lake Erie oxygen budget is the sediment-oxygen demand (SOD). In this work, vertical oxygen concentration profiles in Lake Erie sediments are measured by incrementally inserting a micro-oxygen electrode. The SOD is the flux of oxygen across the sediment-water interface and is calculated from the oxygen profiles assuming Fickian diffusion at the sediment-water interface. Oxygen consumption was measured in sediments collected on four dates from 3, 13, and 5 stations in the western, central, and eastern basins, respectively. Oxygen concentration profiles in the sediment and the SOD are well described by a diffusion/reaction transport model where oxygen diffuses into the sediment and is consumed by reactions that follow Michaelis-Menten kinetics. The flux of oxygen into the sediment in the central basin in August 2002 was 1.03 ± 0.271 × 10−11 mol O2/cm2/sec, within about 30% of the hypolimnetic oxygen depletion rate derived from monitoring. These results suggest that modeling of oxygen profiles hold promise as an alternative technique to regular monitoring for determining hypolimnetic oxygen depletion rates.

Migratory fishes are natural wonders. For many people, the term migratory fish evokes images of salmon audaciously jumping at waterfalls as they return to their own riverine birthplace to spawn after years of growth in the ocean, but freshwater fishes actually show a broad spectrum of migration strategies. Migratory fishes include small species – three-spined sticklebacks that spawn in coastal streams around the northern Pacific and gobies that move from the ocean into tropical island streams by climbing waterfalls (McDowall, 1988) – as well as some of the largest freshwater fishes in the world, such as the Mekong dog-eating catfish and the Chinese paddlefish (Stone, 2007). Aside from migratory habits, these species have few shared characteristics; they encompass numerous evolutionary lineages, enormous differences in life history, and every possible direction and distance of migration. Biologists treat migratory freshwater fishes as a functional group because their life-history strategy revolves around long-distance movement between ecosystems in a perilous quest to take advantage of both high-quality breeding sites and bountiful feeding areas. As humans have physically blocked fish migrations, degraded breeding and feeding grounds and relentlessly harvested migrants for their flesh and roe, many populations have declined or been extirpated. This chapter will provide an overview of fundamental and applied research that is helping to guide efforts to conserve migratory freshwater fishes. For practical purposes, we define migratory behaviour as the synchronized movement of a substantial proportion of a population between distinct habitats, which is repeated through time within or across generations. Modern definitions of fish migrations typically recognise both the adaptive benefits of migrating and individual variation in executing the general strategy (see McDowall, 1988; Lucas & Baras, 2001). Not every individual must move, the timing may vary somewhat from year to year, and the motive for migrating may include seeking refuge from harsh conditions in addition to breeding and feeding. Nonetheless, in most cases, migration is critical to individual fitness and population persistence because it enables specialised use of different habitats for growth and reproduction. Where their migration routes are blocked or key habitats are lost, migratory fishes often suffer rapid and catastrophic losses. Human appropriation and degradation of the Earth's freshwater ecosystems (Vorosmarty et al. , 2010; Carpenter et al. , 2011) have transformed this reliance on multiple habitats into a detriment for many migratory fishes.

Ecologists and paleontologists often rely on higher taxon surrogates instead of complete inventories of biological diversity. Despite their intrinsic appeal, the performance of these surrogates has been markedly inconsistent across empirical studies, to the extent that there is no consensus on appropriate taxonomic resolution (i.e., whether genus- or family-level categories are more appropriate) or their overall usefulness. A framework linking the reliability of higher taxon surrogates to biogeographic setting would allow for the interpretation of previously published work and provide some needed guidance regarding the actual application of these surrogates in biodiversity assessments, conservation planning, and the interpretation of the fossil record. We developed a mathematical model to show how taxonomic diversity, community structure, and sampling effort together affect three measures of higher taxon performance: the correlation between species and higher taxon richness, the relative shapes and asymptotes of species and higher taxon accumulation curves, and the efficiency of higher taxa in a complementarity-based reserve-selection algorithm. In our model, higher taxon surrogates performed well in communities in which a few common species were most abundant, and less well in communities with many equally abundant species. Furthermore, higher taxon surrogates performed well when there was a small mean and variance in the number of species per higher taxa. We also show that empirically measured species-higher-taxon correlations can be partly spurious (i.e., a mathematical artifact), except when the species accumulation curve has reached an asymptote. This particular result is of considerable practical interest given the widespread use of rapid survey methods in biodiversity assessment and the application of higher taxon methods to taxa in which species accumulation curves rarely reach an asymptote, e.g., insects.

The sea lamprey (Petromyzon marinus) is an invasive, parasitic species with a long history of decimating fisheries in the Laurentian Great Lakes. The sea lamprey life cycle consists of stream larval ammocoete, open water parasitic, and adult spawning phases. Population control of sea lamprey is achieved mainly through the application of chemical lampricides that target the sedentary larval stage. The physical characteristics of preferred ammocoete habitat are well defined at the sub-reach scale (< 50 m). We tested whether the spatial distribution of beds of preferred ammocoete habitat depends upon a specific set of geomorphic variables (field-measured slope, and geographic information system (GIS)-derived curvature, radius of curvature, presence of a confluence, and valley wall type). We tested for this relationship at several spatial scales of stream length ranging from 50 m to 300 m, on the East Branch of the Chagrin River, Ohio, USA, a tributary stream to Lake Erie. Of the five geomorphic vari...