Showing papers by "Julian D. Olden published in 2008"

Assessing the effects of climate change on aquatic invasive species.

Abstract: Different components of global environmental change are typically studied and managed independently, although there is a growing recognition that multiple drivers often interact in complex and nonadditive ways. We present a conceptual framework and empirical review of the interactive effects of climate change and invasive species in freshwater ecosystems. Climate change is expected to result in warmer water temperatures, shorter duration of ice cover, altered streamflow patterns, increased salinization, and increased demand for water storage and conveyance structures. These changes will alter the pathways by which non-native species enter aquatic systems by expanding fish-culture facilities and water gardens to new areas and by facilitating the spread of species during floods. Climate change will influence the likelihood of new species becoming established by eliminating cold temperatures or winter hypoxia that currently prevent survival and by increasing the construction of reservoirs that serve as hotspots for invasive species. Climate change will modify the ecological impacts of invasive species by enhancing their competitive and predatory effects on native species and by increasing the virulence of some diseases. As a result of climate change, new prevention and control strategies such as barrier construction or removal efforts may be needed to control invasive species that currently have only moderate effects or that are limited by seasonally unfavorable conditions. Although most researchers focus on how climate change will increase the number and severity of invasions, some invasive coldwater species may be unable to persist under the new climate conditions. Our findings highlight the complex interactions between climate change and invasive species that will influence how aquatic ecosystems and their biota will respond to novel environmental conditions.

Machine Learning Methods Without Tears: A Primer for Ecologists

Abstract: Machine learning methods, a family of statistical techniques with origins in the field of artificial intelligence, are recognized as holding great promise for the advancement of understanding and prediction about ecological phenomena. These modeling techniques are flexible enough to handle complex problems with multiple interacting elements and typically outcompete traditional approaches (e.g., generalized linear models), making them ideal for modeling ecological systems. Despite their inherent advantages, a review of the literature reveals only a modest use of these approaches in ecology as compared to other disciplines. One potential explanation for this lack of interest is that machine learning techniques do not fall neatly into the class of statistical modeling approaches with which most ecologists are familiar. In this paper, we provide an introduction to three machine learning approaches that can be broadly used by ecologists: classification and regression trees, artificial neural networks,...

Dam invaders: impoundments facilitate biological invasions into freshwaters

Abstract: Freshwater ecosystems are at the forefront of the global biodiversity crisis, with more declining and extinct species than in terrestrial or marine environments. Hydrologic alterations and biological invasions represent two of the greatest threats to freshwater biota, yet the importance of linkages between these drivers of environmental change remains uncertain. Here, we quantitatively test the hypothesis that impoundments facilitate the introduction and establishment of aquatic invasive species in lake ecosystems. By combining data on boating activity, water body physicochemistry, and geographical distribution of five nuisance invaders in the Laurentian Great Lakes region, we show that non-indigenous species are 2.4 to 300 times more likely to occur in impoundments than in natural lakes, and that impoundments frequently support multiple invaders. Furthermore, comparisons of the contemporary and historical landscapes revealed that impoundments enhance the invasion risk of natural lakes by increasing their...

A management framework for preventing the secondary spread of aquatic invasive species

Abstract: Biological invasions continue to accelerate, and there is a need for closer integration between invasive species research and on-the-ground management. In many regions, aquatic invasive species hav...

Surface geosciences (hydrology-hydrogeology) Flow variability and the biophysical vitality of river systems

Abstract: Weillustratethefundamentalimportanceofsuctuationsinnaturalwatersowstothelong-termsustainabilityandproductivityofriverineecosystemsandtheirriparianareas.Naturalsowsarecharacterizedbytemporalandspatialheterogeneityinthemagnitude,frequency, duration, timing, rate of change, and predictability of discharge. These characteristics, for a speciÞc river or a collectionof rivers within a deÞned region, shape species life histories over evolutionary (millennial) time scales as well as structure theecological processes and productivity of aquatic and riparian communities. Extreme events– uncommon soods or droughts– areespecially important in that they either reset or alter physical and chemical conditions underpinning the long-term development ofbiotic communities. We present the theoretical rationale for maintaining sow variability to sustain ecological communities andprocesses, and illustrate the importance of sow variability in two case studies– one from a semi-arid savanna river in South Africaand the other from a temperate rainforest river in North America. We then discuss the scientiÞc challenges of determining thedischarge patterns needed for environmental sustainability in a world where rivers, increasingly harnessed for human uses, areexperiencing substantially altered sow characteristics relative to their natural states.To cite this article: R.J. Naiman et al., C. R.Geoscience 340 (2008).# 2008 AcadŽmie des sciences. Published by Elsevier Masson SAS. All rights reserved.ResumeVariabilite des debits et vitalite biophysique des systemes uviaux.Nous illustrons lOimportance fondamentale des suxhydriques naturels pour la permanence ˆ long terme et la productivitŽ des Žcosystmes lotiques et riverains. Les sux naturels sontcaractŽrisŽs par une hŽtŽrogŽnŽitŽ temporelle et spatiale des dŽbits, de par leur ampleur, frŽquence, durŽe, calendrier, vitesse dechangement et prŽdictibilitŽ. Ces caractŽristiques, pour une rivire ou lOensemble des rivires dOune rŽgion donnŽe, faonnent leshistoires de vie des espces sur des Žchelles de temps millŽniales, de mme quOelles structurent les processus Žcologiques et laproductivitŽ des communautŽs aquatiques et riveraines. Les ŽvŽnements extrmes– crues ou sŽcheresses inhabituelles– sontparticulirementimportants,enceciquOilsrŽtablissentoumodiÞentlesconditionsphysiquesetchimiquesdudŽveloppementˆlongterme des communautŽs biotiques. Nous prŽsentons les bases thŽoriques dOune prŽservation des rŽgimes de dŽbit, dans le butdOentretenir les communautŽs et les processus Žcologiques. Nous illustrons lOimportance de lavariabilitŽ des dŽbits par deux Žtudesde cas– une rivire de savane semi-aride en Afrique du Sud et une rivire de fort pluvieuse tempŽrŽe en AmŽrique du Nord. Nousdiscutons ensuite la question des rŽgimes de dŽbit nŽcessaires ˆ la permanence des Žcosystmes dans un monde o les rivires, de

Trait synergisms and the rarity, extirpation, and extinction risk of desert fishes

Abstract: Understanding the causes and consequences of species extinctions is a central goal in ecology. Faced with the difficult task of identifying those species with the greatest need for conservation, ecologists have turned to using predictive suites of ecological and life-history traits to provide reasonable estimates of species extinction risk. Previous studies have linked individual traits to extinction risk, yet the nonadditive contribution of multiple traits to the entire extinction process, from species rarity to local extirpation to global extinction, has not been examined. This study asks whether trait synergisms predispose native fishes of the Lower Colorado River Basin (USA) to risk of extinction through their effects on rarity and local extirpation and their vulnerability to different sources of threat. Fish species with "slow" life histories (e.g., large body size, long life, and delayed maturity), minimal parental care to offspring, and specialized feeding behaviors are associated with smaller geographic distribution, greater frequency of local extirpation, and higher perceived extinction risk than that expected by simple additive effects of traits in combination. This supports the notion that trait synergisms increase the susceptibility of native fishes to multiple stages of the extinction process, thus making them prone to the multiple jeopardies resulting from a combination of fewer individuals, narrow environmental tolerances, and long recovery times following environmental change. Given that particular traits, some acting in concert, may differentially predispose native fishes to rarity, extirpation, and extinction, we suggest that management efforts in the Lower Colorado River Basin should be congruent with the life-history requirements of multiple species over large spatial and temporal scales.

Integrated Monitoring and Information Systems for Managing Aquatic Invasive Species in a Changing Climate

Abstract: Changes in temperature, precipitation, and other climatic drivers and sea-level rise will affect populations of existing native and non-native aquatic species and the vulnerability of aquatic environments to new invasions. Monitoring surveys provide the foundation for assessing the combined effects of climate change and invasions by providing baseline biotic and environmental conditions, although the utility of a survey depends on whether the results are quantitative or qualitative, and other design considerations. The results from a variety of monitoring programs in the United States are available in integrated biological information systems, although many include only non-native species, not native species. Besides including natives, we suggest these systems could be improved through the development of standardized methods that capture habitat and physiological requirements and link regional and national biological databases into distributed Web portals that allow drawing information from multiple sources. Combining the outputs from these biological information systems with environmental data would allow the development of ecological-niche models that predict the potential distribution or abundance of native and non-native species on the basis of current environmental conditions. Environmental projections from climate models can be used in these niche models to project changes in species distributions or abundances under altered climatic conditions and to identify potential high-risk invaders. There are, however, a number of challenges, such as uncertainties associated with projections from climate and niche models and difficulty in integrating data with different temporal and spatial granularity. Even with these uncertainties, integration of biological and environmental information systems, niche models, and climate projections would improve management of aquatic ecosystems under the dual threats of biotic invasions and climate change.

Drought-escape behaviors of aquatic insects may be adaptations to highly variable flow regimes characteristic of desert rivers

Abstract: We document how two species of desert aquatic insects use positive rheotaxis to escape drought in desert rivers. We observed ca. 3,600 adults of the long-toed water beetle Postelichus immsi (Coleoptera: Dryopidae) crawling upstream concurrent with upstream recession of surface water in the Santa Maria River, La Paz and Mohave counties, Arizona. At the same time, we observed larvae of the gray sanddragon Progomphus borealis (Odonata: Gomphidae) burrowing and swimming upstream in large densities (690 larvae/m2). Both taxa moved with sufficient speed to arrive at perennial reaches of the river before being overtaken by drought.

Do schools and golf courses represent emerging pathways for crayfish invasions

Abstract: Prevention is frequently promoted as the most desirable management strategy for biological invasions. Crayfish introductions are typically associated with aquaculture and bait bucket releases, but here we report two alternate pathways that may be responsible for the recent invasion of Procambarus clarkii (Girard, 1852) and Orconectes virilis (Hagen, 1870) in Washington State, U.S.A. Using distributional data and personal interviews we identified (1) school science programs, which use crayfish as laboratory organisms, as a likely pathway of introductions, and (2) golf courses bordering lakes, in which ponds have been constructed and are suspected to be stocked with O. virilis to control aquatic macrophytes. Particularly concerning, we found the highly invasive crayfish Orconectes rusticus (Girard, 1852) in use as a laboratory organism at multiple schools, although this species is not known to be established in the region. Vector management is critical for interrupting the transfer of invasive species, and our study has identified two emerging pathways that require greater research attention and stricter regulation.

The varying role of population abundance in structuring indices of biotic homogenization

Abstract: Aim An important component of human-induced global change is the decrease or increase in community distinctiveness (taxonomic homogenization or differentiation, respectively) that follows the loss of native species and gain of non-native species. We use simulation approaches to assess the extent to which conclusions about the outcome of the homogenization process depend on whether or not abundance data are incorporated. Location Data were produced through computer simulation. Methods The frequency with which occurrence-based similarity indices and abundance-based similarity indices give different views of changes in community similarity, and the conditions under which such differences occurred were assessed using both deterministic and stochastic modelling approaches to simulate species assemblage states. Results Occurrence-based and abundance-based indices were positively correlated across the set of simulations for both the deterministic and stochastic models. However, in both situations approximately one quarter (25%) of models resulted in contrasting outcomes for the two approaches of calculating changes in compositional similarity; that is, one data type showed a positive value (homogenization), whereas the other showed a negative value (differentiation). Main conclusions In the majority of cases, species abundances will not change drastically enough after perturbation to produce large differences between homogenization scores measured using occurrence versus abundance information. However, in cases where these changes are large, it is important to recognize that the choice of metric to analyse homogenization trends will influence the qualitative and quantitative conclusions drawn. Studies of real assemblages are therefore necessary to evaluate the role of species abundance in defining the magnitude and direction of changes in community composition across space, and the implications of these changes for native biodiversity.

Ecologically sustainable water management in Washington State, USA: Developing flow management tools for watershed planning

Abstract: Washington’s streams and rivers are naturally dynamic and complex ecological systems that provide significant economic, social, spiritual, and recreational value. Despite Washington's reputation as a perpetually rainy place, the water needs of people and natural ecosystems are increasingly in conflict. Century-long decline of Pacific salmon, degraded water quality of rivers flowing into the Puget Sound, and continued loss of wildlife habitat are all strong signals of current water demand stress in this region. Water managers are becoming increasingly cognizant of these pressures, yet there remains a critical knowledge gap of the ecological tradeoffs associated with various flow management practices, including instream flows as presently mandated in Washington. Here, we introduce a new research initiative to advance the science and develop the tools required for ecologically sustainable water management in Washington. Our approach follows the Ecological Limits of Hydrologic Alteration (ELOHA) framework by synthesizing the knowledge and data collected from individual rivers into a scientific framework that supports and guides the development of environmental flow standards at the regional scale. We present a state-wide hydrologic classification of unregulated rivers and quantify the range of natural flow variation that regulates characteristic ecological processes and habitat characteristics for distinct hydrologic types. This provides a baseline or reference condition against which ecological responses to alteration can be measured across multiple river segments falling along a gradient of hydrologic alteration. As an example, we develop flow-ecology relationships for hydrologic types according to population patterns of life history diversity for Chinook salmon (Oncorhynchus tshawytscha) throughout the Puget Sound. These results highlight the ecological effects of hydrologic alteration and help form the basis of flow management for both river ecosystem protection (proactive flow management) and sustainable restoration (reactive flow management) for salmon life history diversity.