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Mazor R.D.,Southern California Coastal Water Research Project | Mazor R.D.,Aquatic Bioassessment Laboratory | Rehn A.C.,Aquatic Bioassessment Laboratory | Ode P.R.,Aquatic Bioassessment Laboratory | And 6 more authors.
Freshwater Science | Year: 2016

Regions with great natural environmental complexity present a challenge for attaining 2 key properties of an ideal bioassessment index: 1) index scores anchored to a benchmark of biological expectation that is appropriate for the range of natural environmental conditions at each assessment site, and 2) deviation from the reference benchmark measured equivalently in all settings so that a given index score has the same ecological meaning across the entire region of interest. These properties are particularly important for regulatory applications like biological criteria where errors or inconsistency in estimating site-specific reference condition or deviation from it can lead to management actions with significant financial and resource-protection consequences. We developed an index based on benthic macroinvertebrates for California, USA, a region with great environmental heterogeneity. We evaluated index performance (accuracy, precision, responsiveness, and sensitivity) throughout the region to determine if scores provide equivalent ecological meaning in different settings. Consistent performance across environmental settings was improved by 3 key elements of our approach: 1) use of a large reference data set that represents virtually all of the range of natural gradients in the region, 2) development of predictive models that account for the effects of natural gradients on biological assemblages, and 3) combination of 2 indices of biological condition (a ratio of observed-to-expected taxa [O/E] and a predictive multimetric index [pMMI]) into a single index (the California Stream Condition Index [CSCI]). Evaluation of index performance across broad environmental gradients provides essential information when assessing the suitability of the index for regulatory applications in diverse regions. © 2016 by The Society for Freshwater Science.

Deiner K.,University of California at Davis | Deiner K.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Knapp R.A.,Morrison University | Boiano D.M.,Sequoia and Kings Canyon National Parks | May B.,University of California at Davis
Molecular Ecology Resources | Year: 2013

The first step in many community ecology studies is to produce a species list from a sample of individuals. Community ecologists now have two viable ways of producing a species list: morphological and barcode identification. In this study, we compared the taxonomic resolution gained by a combined use of both methods and tested whether a change in taxonomic resolution significantly impacted richness estimates for benthic macroinvertebrates sampled from ten lakes in Sequoia National Park, USA. Across all lakes, 77 unique taxa were identified and 42% (32) were reliably identified to species using both barcode and morphological identification. Of the 32 identified to species, 63% (20) were identified solely by comparing the barcode sequence from cytochrome oxidase I to the Barcode of Life reference library. The increased resolution using a combined identification approach compared to identifications based solely on morphology resulted in a significant increase in estimated richness within a lake at the order, family, genus and species levels of taxonomy (P < 0.05). Additionally, young or damaged individuals that could not be identified using morphology were identified using their COI sequences to the genus or species level on average 75% of the time. Our results demonstrate that a combined identification approach improves accuracy of benthic macroinvertebrate species lists in alpine lakes and subsequent estimates of richness. We encourage the use of barcodes for identification purposes and specifically when morphology is insufficient, as in the case of damaged and early life stage specimens of benthic macroinvertebrates. © 2013 John Wiley & Sons Ltd.

Smith T.C.,University of California at Santa Barbara | Knapp R.A.,Morrison University | Briggs C.J.,University of California at Santa Barbara
Ecosphere | Year: 2016

Species extinctions have the potential to dramatically reshape ecological communities. In the Sierra Nevada mountains of California, the emergence of a lethal amphibian pathogen (Batrachochytrium dendrobatidis) drives mountain yellow-legged frog (Rana muscosa and Rana sierrae) populations to local extinction. Prior to population declines, these frogs and their tadpoles were abundant, high-level predators and grazers with high trophic connectance. To quantify how these low diversity aquatic macroinvertebrate communities respond to nonrandom single-species local extinctions, we quantified aquatic macroinvertebrate communities using two approaches: a natural experiment ("Resurveys") and a large-scale synoptic observational study ("Snapshot" surveys). In the Resurveys, we compared benthic macroinvertebrate communities in 22 Sierra Nevada alpine lakes that we categorized as either having extant frog populations, experiencing ongoing disease-driven frog declines, or having previously experienced local disease-driven frog extirpation. In the Resurveys, taxonomic richness was about one taxa (17%) higher in lakes where frogs were declining or extinct, compared to lakes where frogs were extant. However, multivariate analyses revealed no strong dissimilarities among Resurvey communities, and there were no differences in the abundances of individual taxa between lakes in the frogs extant, declining, or extinct categories. In the Snapshot surveys, we reanalyzed previously collected data from a large-scale survey of 157 lakes with and without frogs. In the Snapshot survey, invertebrate taxonomic richness was less than one taxa (9%) lower in lakes without frogs, and multivariate analyses again indicated only small differences between lakes with and without frogs. Overall, disease-driven mountain yellow-legged frog extinctions had small effects on lake benthic macroinvertebrate communities, with no large changes in invertebrate abundance, richness or evenness, no clear secondary extinctions or invasions, and few taxa showing distinct responses to frog extinctions. Our study highlights how even for conspicuous, highly connected, omnivorous taxa that are experiencing large, rapid, and widespread declines and extinctions, the ecological effects of extinctions will sometimes be small and subtle. © 2016 Smith et al.

Reiter M.J.,Morrison University | Stromberg K.D.,Medtronic | Whitman T.A.,Medtronic | Adamson P.B.,Oklahoma Foundation for Cardiovascular Research | And 2 more authors.
Circulation: Arrhythmia and Electrophysiology | Year: 2013

Background-The implantation of a combination hemodynamic monitor-cardioverter-defibrillator in the Reducing Decompensation Events Utilizing Intracardiac Pressures in Patients with Chronic Heart Failure (REDUCEhf) study allowed assessment of the relationship between daily intracardiac pressure and occurrence of ventricular arrhythmic (VT/VF) events. Methods and Results-Median estimated pulmonary artery diastolic pressures (ePAD) were calculated every 24 hours in 378 subjects with New York Heart Association functional class II-III heart failure who had at least 60 days of hemodynamic data. Forty-six subjects experienced 140 VT/VF events on 80 unique study days in which daily median ePAD was available. The incidence of days with VT/VF events was significantly higher when the daily median ePAD for a subject was elevated, defined as >1 SD above that subject's average median ePAD for the whole study: (2.8 episode days per patient-year compared with 1.7 episode days per patient-year; P=0.040). However, the incidence of days with VT/VF events was not significantly different on days when ePAD was >25 mm Hg compared with days when ePAD was <25 mm Hg. For all 378 subjects, the risk of VT/VF increased with average median ePAD calculated over the whole follow-up period (odds ratio, 1.072 for a 1-mm Hg increase; 95% confidence interval, 1.023-1.124; P=0.003). Conclusions-There is significant positive association between average daily median ePAD and risk for VT/VF. Among patients with VT/VF, elevated intracardiac pressures are associated with higher VT/VF risk only when the definition of increased pressure is subject specific. © 2013 American Heart Association, Inc.

Herbst D.B.,Morrison University | Roberts S.W.,Morrison University | Medhurst R.B.,Morrison University
Journal of Insect Conservation | Year: 2013

Walker Lake, Nevada, a saline desert lake, has been undergoing loss of stream inflows, lowering of lake level, and concentration of dissolved salts for over a century due to agricultural diversions of water. This lake is or has been inhabited by native fish and visited by many species of waterbirds that depend on productive invertebrate life for food resources. The extent to which salinity limits the present and future viability of resident invertebrate fauna was evaluated using salt-tolerance bioassays and studies of salinity effects on growth and behavior in larval stages of the midges Cricotopus ornatus and Tanypus grodhausi, and nymphs of the damselfly Enallagma clausum. We found that salinities into and above a range of 20-25 g/L present either lethal limits or sublethal inhibitions to survival and growth that will eliminate or substantially reduce the current community of common benthic invertebrates. All species survived best at salinities below the current ambient level, suggesting these populations are already under stress. The 72-h LC-50 for Cricotopus was 25 g/L, and while mature damselfly nymphs were somewhat more tolerant, early instars survived for only short times in increased salinity. Damselflies also grew more slowly and fed less when salinity increased from 20 to 30 g/L. A conservation level for the lake that incorporates survival of native fish and recovers diversity and viability of invertebrate life should be within the range of 10-15 g/L salinity of Walker Lake water. © 2013 Springer Science+Business Media Dordrecht.

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