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Michigan’s water-quality standards specify that E. coli concentrations at bathing beaches must not exceed 300 E. coli per 100 mL, as determined by the geometric mean of culture-based concentrations in three or more representative samples from a given beach on a given day. Culture-based analyses require 18–24 h to complete, so results are not available for issuing beach notifications (advisories or closings) until the day following collection. This one-day delay is problematic because E. coli concentrations at beaches can change markedly from one day to the next. qPCR-based E. coli concentrations, by contrast, can be obtained in only 3–4 h, making same-day beach notifications possible. Michigan has proposed a qPCR threshold value (qTV) for E. coli of 1.863 log10 gene copies per reaction as a potential equivalent value to the state standard, based on statistical analyses of a set of training data from 2016–2018. The main purpose of the present study is to assess the validity of the proposed qTV by determining whether the implied qPCR-based beach notification decisions agree well with culture-based decisions on two sets of test data (from 2016–2018 and 2019–2020), and whether performance of the proposed threshold is similar on the test and training data. The results show that performance of the proposed qTV on both sets of test data was consistently good (e.g., 95% agreement with culture-based beach notification decisions during 2019–2020) and was at least as good as its performance on the training data set, supporting its use as an equivalent value to the state standard.

Fecal pollution is one of the most prevalent forms of pollution affecting waterbodies worldwide, threatening public health, and negatively impacting aquatic environments. Microbial source tracking (MST) applies polymerase chain reaction (PCR) technology to help identify the source of fecal pollution. In this study, we combine spatial data for two watersheds with general and host-specific MST markers to target human, bovine, and general ruminant sources. Two different PCR technologies were applied for quantifying the targets: quantitative PCR (qPCR) and droplet digital PCR (ddPCR). We found that ddPCR had a higher detection rate (75%) of quantifiable samples compared to qPCR (27%), indicating that ddPCR is more sensitive than qPCR. The three host-specific markers were detected at all sites (n=25), suggesting that humans, cows, and ruminants are contributing to fecal contamination in these watersheds. MST results, combined with watershed characteristics, suggest that streams draining areas with low-infiltration soil groups, high septic system prevalence, and high agricultural land use are at an increased risk for fecal contamination. Microbial source tracking has been applied in numerous studies to aid in identifying the sources of fecal contamination, however these studies usually lack information on the involvement of watershed characteristics. Our study combined watershed characteristics with MST results, applying more sensitive PCR techniques, in addition to watershed characteristics to provide more comprehensive insight into the factors that influence fecal contamination in order to implement the most effective best management practices.Abstract FigureHighlightsddPCR provided higher sensitivity over qPCR when analyzing environmental samplesHuman markers had an association with the number of septic systems in a watershedEvery site had positive detections for all FIB markersBoth ruminant markers were associated with low infiltration hydrologic soil groupsCombining watershed characteristics with MST testing improved source identification

While many watershed models estimate overland flow-related soil loss, streambank erosion is often overlooked even though it can be the dominant source of sediment in a catchment. We used the enhanced generalized watershed loading functions (GWLF-E) model to simulate the water budget, field erosion from the landscape, and streambank erosion along a gradient of agricultural to urban land cover from 1997 to 2015 in the Indian Mill Creek watershed of Michigan, USA. We evaluated discharge simulations using in-streamflow measurements and evaluated streambank erosion simulations using field-collected erosion pin measurements from a previous study. Annual water budget results suggest the creek is primarily groundwater fed, but that a per-subbasin average of 6–15% of precipitation becomes runoff. Field erosion contributed a per-subbasin average of 0.5–2.5 Mg ha−1 year−1 of sediment, while streambank erosion accounted for 0.2–50.1% of the subbasins’ total sediment yields. Average lateral erosion rate of streambanks in subbasins ranged from 0.04 to 7.37 cm year−1, with four subbasins exceeding 1.0 cm year−1. Evaluation with field-collected discharge data suggest that GWLF-E may have been overestimating discharge in the subbasins. Evaluation with streambank erosion data found that GWLF-E may have difficulty capturing the complexity of erosion rates, including instances where sediment is deposited on streambanks from upstream sources, and that it underestimates streambank erosion in headwater catchments sometimes over an order of magnitude. Our findings are important for watershed managers to evaluate modeling approaches and highlight the importance of modeling both field and streambank erosion.

Baby’s breath (Gypsophila paniculata L.) is an invasive species in Michigan’s northern lower peninsula and is a problem in much of northern North America. It is of particular concern in coastal dune habitats of northwest Michigan, because the areas where it is most dense are also populated by several endemic and threatened species. Current removal methods include manual removal with a spade and directed spray-to-wet foliar application of glyphosate to individual plants using backpack sprayers. We assessed these methods by measuring G. paniculata density and presence–absence frequency before and after treatment using a point-intercept grid, establishing how type and timing of treatment within the growing season influences treatment efficacy and determining the proportion of plants that resprout after treatment. Our results show a consistent reduction in G. paniculata density after treatment with herbicide or manual removal (P < 0.001) but minimal impact on presence–absence frequency. These results indicate a need for quantitative data in the assessment of management efficacy to show a clearer picture of density reduction when extirpation is no longer a viable outcome of management. Through the assessment of treatment timing of manual removal and glyphosate treatments over time, we found no evidence that either treatment type was effective at reducing density when applied before plants flowered, but there was evidence that both treatments were effective when applied later in the growing season when plants were flowering. Resprouting of marked plants occurred in 14% of manually removed plants and 2% of herbicide-treated plants. Our results suggest that managers should treat G. paniculata infestations for consecutive years to remove regrowth and focus treatment during flowering for best control.

Explaining spatiotemporal variability in metacommunities is challenging because conducting empirical studies that link mechanisms across scales is difficult. We developed a stochastic model of epilithic algal succession in streams to better understand the underlying interactions that drive patch dynamics at three levels of spatial hierarchy: patch, channel habitat, and reach. The state of an algal patch is specified by one of nine community types, which are defined by growth form. Ninety‐two empirical data sets of epilithic succession were used to estimate Markov transition probabilities among patch types as functions of inputs for light, nutrients, and current. Two additional probability matrices determine the effects of herbivory and disturbance based on user inputs. Testing model predictions of patch composition against independent empirical data indicated good correspondence based on resemblance metrics. Early in succession, most patches were occupied by prostrate and erect diatoms. These persisted under low light and nutrient conditions. Motile and stalked diatom patches characterized later stages when resources were moderate. Succession proceeded to mostly filamentous green algal patches under high resource levels. Sensitivity simulations indicated light most affected succession. Herbivory and disturbance increased the probability of prostrate diatom patches. We then used the model to examine how changes in abiotic and biotic parameters affect patch dynamics at different scales. Changes in nutrients or light affected patch diversity differently at the habitat vs. reach scale. Interactions with local resource levels within a channel habitat determined its alpha diversity. The proportion of channel habitat types within a reach, and their collective response to changes, determined beta diversity. Patch diversity within channel habitats generated by herbivory followed the predation hypothesis only when nutrients were low. At the reach scale, herbivory always increased patch similarity among channel habitats, lowering beta diversity. Diversity within channel habitats followed the intermediate disturbance hypothesis for a variety of habitats. Effects of disturbance on beta diversity at the reach scale depended on channel habitat heterogeneity. The stability of patches at the reach scale was highest when disturbance created high patch diversity, supporting the insurance hypothesis. The ideas generated can improve stream bioassessment methods and provide insight into mechanisms underlying patch dynamics in other ecosystems.

Babysbreath or perennial babysbreath (Gypsophila paniculata L.) is an aggressive invasive plant in large parts of southern Canada and the northern and western United States. It reproduces and disperses by seed, so the phenology of seed maturation is important in designing management programs. The present study provides the first quantitative assessment of G. paniculata seed-maturation phenology in a field population, as well as the first quantitative assessment of how the efficacy of herbicide treatment in preventing production of germinable seeds depends on the timing of treatment in relation to this phenology. Seeds were collected from untreated plants on five dates during July and August in both 2016 and 2017 and tested for germinability. Percent germination increased from 20% to 81% between July 22 and 28 and exceeded 90% by August 4, 2016. The seed-maturation phenology in 2017 was similar but delayed by about 4 d. On a growing degree-day scale, seed-maturation phenologies for the 2 yr were nearly identical. We also tested germinability of seeds from plants sprayed with glyphosate (23.4 ml ae L−1) on July 11, 18, and 25, 2016 (one date per plant). Percent germination increased from 0% to 13% to 20% over successive treatment dates, highlighting the importance of completing treatment early in the growing season.

We evaluated data from 10 laboratories that analyzed water samples from 82 recreational water sites across the state of Michigan between 2016 and 2018. Water sample replicates were analyzed by experienced U.S. Environmental Protection Agency (EPA) analysts and Michigan laboratories personnel, many of whom were newly trained, using EPA Draft Method C—a rapid quantitative polymerase chain reaction (qPCR) technique that provides same day Escherichia coli (E. coli) concentration results. Beach management decisions (i.e. remain open or issue an advisory or closure) based on E. coli concentration estimates obtained by Michigan labs and by the EPA were compared; the beach management decision agreed in 94% of the samples analyzed. We used the Wilcoxon one-sample signed rank test and nonparametric quantile regression to assess (1) the degree of agreement between E. coli concentrations quantified by Michigan labs versus the EPA and (2) Michigan lab E. coli measurement precision, relative to EPA results, in different years and water body types. The median quantile regression curve for Michigan labs versus EPA approximated the 1:1 line of perfect agreement more closely as years progressed. Similarly, Michigan lab E. coli estimates precision also demonstrated yearly improvements. No meaningful difference was observed in the degree of association between Michigan lab and EPA E. coli concentration estimates for inland lake and Great Lakes samples (median regression curve average slopes 0.93 and 0.95, respectively). Overall, our study shows that properly trained laboratory personnel can perform Draft Method C to a degree comparable with experienced EPA analysts. This allows health departments that oversee recreational water quality monitoring to be confident in qPCR results generated by the local laboratories responsible for analyzing the water samples.

Draft method C is a standardized method for quantifying E. coli densities in recreational waters using quantitative polymerase chain reaction (qPCR). The method includes a Microsoft Excel workbook that automatically screens for poor-quality data using a set of previously proposed acceptance criteria, generates weighted linear regression (WLR) composite standard curves, and calculates E. coli target gene copies in test samples. We compared standard curve parameter values and test sample results calculated with the WLR model to those from a Bayesian master standard curve (MSC) model using data from a previous multi-lab study. The two models&rsquo, mean intercept and slope estimates from twenty labs&rsquo, standard curves were within each other&rsquo, s 95% credible or confidence intervals for all labs. E. coli gene copy estimates of six water samples analyzed by eight labs were highly overlapping among labs when quantified with the WLR and MSC models. Finally, we compared multiple labs&rsquo, 2016&ndash, 2018 composite curves, comprised of data from individual curves where acceptance criteria were not used, to their corresponding composite curves with passing acceptance criteria. Composite curves developed from passing individual curves had intercept and slope 95% confidence intervals that were often narrower than without screening and an analysis of covariance test was passed more often. The Excel workbook WLR calculation and acceptance criteria will help laboratories implement draft method C for recreational water analysis in an efficient, cost-effective, and reliable manner.

Streambank erosion is difficult to quantify, models and field methods are needed to assess this important sediment source to streams. Our objectives were to (1) evaluate and compare three techniques for quantifying streambank erosion: erosion pins, total station, and laser scanning, (2) spatially assess streambank erosion rates in the Indian Mill Creek watershed of Michigan, USA, and (3) relate results with modeling of nonpoint source pollution. We found large absolute and relative errors between the different measurement techniques. However, we were unable to determine any statistically significant differences between techniques and only observed a correlation between total station and laser scanner. This suggests that the three methods have limited comparability and differences between measurements were largely not systemic. Further, the application of each technique should be dependent on site conditions, project goals, desired resolution, and resources. The laser scanner collected high-resolution data on clear, barren streambanks, but the erosion pin and total station were more representative of complex vegetated banks. Streambank erosion rates varied throughout the watershed and were influenced by fluvial processes. We estimate that streambank erosion contributed 28.5% of the creek&rsquo, s total sediment load. These findings are important to address sources of watershed impairments related to sedimentation, as choosing an applicable technique for individual purposes can help reduce the challenges and costs of a streambank erosion study.

Parks SR, McNair JN, Hausler P, Tyning P, Thum RA. 2016. Divergent responses of cryptic invasive watermilfoil to treatment with auxinic herbicides in a large Michigan lake. Lake Reserve Manage. 32:366–372.Invasive plants are a major concern for environmental managers around the world. Cryptic invasive taxa present additional challenges because of their potential to respond differently to management efforts while being difficult to distinguish morphologically. Here, we consider the potential for different responses of Eurasian watermilfoil (Myriophyllum spicatum) and hybrid watermilfoil (Myriophyllum spicatum x Myriophyllum sibiricum), which cannot be reliably distinguished based on morphological characters. Laboratory studies show that hybrid watermilfoil genotypes can grow faster, branch more, and be less responsive to herbicide control methods designed for Eurasian watermilfoil. To date, however, there have been no statistical comparisons of the responses of hybrid versus Eurasian watermilfoil u...

The 2-sample mark-recapture method with Chapman’s estimator is often used by inland fishery managers to estimate the reach-scale abundance of stream fish. An important assumption of this method is that no dispersal into or out of the study reach occurs between the two samples. Violations of this assumption are probably common in practice, but their effect on bias (systematic error) of abundance estimates is poorly understood, especially in small populations. Estimation methods permitting dispersal exist but, for logistical reasons, often are infeasible for routine assessments in streams. The purpose of this paper is to extend available results regarding effects of dispersal on the bias of Chapman’s estimator as applied to reach-scale studies of stream fish abundance. We examine for the first time the joint effects of dispersal and sampling variation on the bias of this estimator. To reduce the bias effects of dispersal, we propose a modified sampling scheme in which the original study reach is expanded, a central subreach is sampled during the mark session (sample 1), and the entire reach is sampled during the recapture session (sample 2). This modified sampling scheme can substantially reduce bias effects of dispersal without requiring unique marking of individual fish or additional site visits. Analytical and simulation results show that sampling variation tends to create negative bias with respect to study-reach abundance, while dispersal tends to create positive bias; the net effect can be positive, negative, or zero, depending on the true abundance, capture probabilities, and amount and nature of dispersal. In most cases, simply expanding the study reach is an effective way to reduce dispersal-related bias of Chapman’s estimator, but expanding the study reach and employing the modified sampling scheme we propose is a better alternative for accurately estimating abundance with the same level of sampling effort.

Most studies that investigate biases in stream fish abundance estimators focus on salmonines, yet nongame species comprise a major portion of fish assemblages. We evaluated mark–recapture (the Lincoln–Petersen estimator with Chapman correction) and removal (constant capture probability and generalized removal estimators) methods for estimating abundance of Mottled Sculpin Cottus bairdii, and we tested whether assumptions of the abundance estimators (i.e., the population is closed during sampling; and marks are detected) were reasonable. Over 2-d periods, fish in eight streams were sampled by using backpack electrofishing in 90-m reaches (each divided into three 30-m subreaches) to assess movement. Removal abundance estimates were significantly lower than mark–recapture estimates. Moreover, removal estimates were 52% lower than the known number of marked individuals, likely because capture probability (q) was low and declined with subsequent sampling passes. Survival of fish held in cages was 100%;...

A novel lateral flow immunochromatographic device (LFD) was evaluated in several veterinary diagnostic laboratories. It was confirmed to be specific for Mycobacterium bovis and M. caprae cells. The performance of the novel LFD was assessed relative to the confirmatory tests routinely applied after culture (spoligotyping or quantitative PCR [qPCR]) in each laboratory; liquid (MGIT or BacT/Alert) and/or solid (Stonebrink, Coletsos, or Lowenstein-Jensen) cultures were tested. In comparison to spoligotyping of acid-fast-positive MGIT cultures, percent agreement between positive LFD and spoligotyping results was excellent in two United Kingdom laboratories (97.7 to 100%) but lower in the Spanish context (76%), where spoligotyping was applied to MGIT cultures previously confirmed to be positive for M. tuberculosis complex (MTBC) by qPCR. Certain spoligotypes of M. bovis and M. caprae were not detected by the LFD in Spanish MGIT cultures. Compared to qPCR confirmation, the agreement between positive LFD and qPCR results was 42.3% and 50% for BacT/Alert and MGIT liquid cultures, respectively, and for solid cultures, it ranged from 11.1 to 89.2%, depending on the solid medium employed (Coletsos, 11.1%; Lowenstein-Jensen, 55.6%; Stonebrinks, 89.2%). Correlation between the novel LFD and BD MGIT TBc Identification test results was excellent when 190 MGIT cultures were tested ( r = 0.9791; P < 0.0001), with the added benefit that M. bovis was differentiated from another MTBC species in one MGIT culture by the novel LFD. This multilaboratory evaluation demonstrated the novel LFD's potential utility as a rapid test to confirm isolation of M. bovis and M. caprae from veterinary specimens following culture.

Exchange of carbon between the biosphere and atmosphere is dominated by rates of photosynthetic CO2 uptake and respiratory CO2 release by aquatic and terrestrial ecosystems worldwide. Obtaining accurate estimates of these rates is therefore important. In lakes, the most common estimation method is based on a model of dissolved-oxygen (DO) dynamics and a corresponding time series of DO concentrations measured in freely moving lake water. O2 production and consumption are inferred from changes in DO concentration, then converted to estimates of carbon uptake and release using photosynthetic and respiratory quotients. The traditional method of this type uses a simple accounting procedure to estimate daily gross primary production (GPP), total respiration (R), and net production (NP). Assuming that measured DO concentrations contain no error, it attempts to back-calculate GPP, R, and NP from an observed time series without using statistical techniques. This method produces valid estimates of GPP and the nighttime component of R, but it is unable to estimate the daytime component of R and hence cannot estimate R or NP for a complete dark–light cycle. To obtain estimates of these quantities, one must subjectively assume a value for daytime respiration. We present three new methods for estimating GPP, R, and NP that resolve this problem and also facilitate assessment of model adequacy. We illustrate use of the methods and compare their parameter estimates by applying them to monitoring data from Muskegon Lake, Michigan (USA).

A field study assessing the sustainability and efficacy of 55 biosand filters installed during 1999–2010 was conducted in the Artibonite Valley, Haiti during 2011. Twenty-nine filters were still in use. Duration of filter use ranged from < 1 to 12 years. Water quality, microbial analysis, and flow rate were evaluated for each functioning filter. Kaplan-Meier analysis of filter lifespans showed that filter use remained high (> 85%) up to seven years after installation. Several filters were still in use after 12 years, which is longer than documented in any previous study. Filtered water from 25 filters (86%) contained Escherichia coli concentrations of < 10 most probable number of coliforms/100 mL. Recontamination of stored filtered water was negligible. Bacterial removal efficiency was 1.1 log10. Comparable results from previous studies in the same region and elsewhere show that biosand filter technology continues to be an effective and sustainable water treatment method in developing countries worldwide.

Natural rates of straying are difficult to quantify over large spatial scales using direct observations, particularly for long-lived fish species characterized by delayed sexual maturity and long interspawning intervals. Using multilocus microsatellite genotypes and likelihood-based statistical methods, we quantified rates of immigration and emigration for six genetically differentiated (mean F ST = 0.041) lake sturgeon Acipenser fulvescens populations in Lake Michigan based on adults (n = 437) captured in tributaries during the spawning season. Estimated rates of straying were high (mean = 0.105), asymmetrical, and highly variable across populations. We found no significant association between the total length (a surrogate measure of age) of individuals that strayed and those that did not. Linear distance between streams was more predictive of straying rates and F ST than least-cost distances estimated based on lakescape features (bathymetry and lake current patterns). Historical rates of gene f...

Seed germination experiments are conducted in a wide variety of biological disciplines. Numerous methods of analysing the resulting data have been proposed, most of which fall into three classes: intuition-based germination indexes, classical non-linear regression analysis and time-to-event analysis (also known as survival analysis, failure-time analysis and reliability analysis). This paper briefly reviews all three of these classes, and argues that time-to-event analysis has important advantages over the other methods but has been underutilized to date. It also reviews in detail the types of time-to-event analysis that are most useful in analysing seed germination data with standard statistical software. These include non-parametric methods (life-table and Kaplan–Meier estimators, and various methods for comparing two or more groups of seeds) and semi-parametric methods (Cox proportional hazards model, which permits inclusion of categorical and quantitative covariates, and fixed and random effects). Each method is illustrated by applying it to a set of real germination data. Sample code for conducting these analyses with two standard statistical programs is also provided in the supplementary material available online (athttp://journals.cambridge.org/). The methods of time-to-event analysis reviewed here can be applied to many other types of biological data, such as seedling emergence times, flowering times, development times for eggs or embryos, and organism lifetimes.

The tuberculin skin test has been used for the diagnosis of bovine and human tuberculosis (TB) for over a hundred years. However, the specificity of the test is compromised by vaccination with theMycobacterium bovis-derived vaccine strain bacille Calmette-Guérin (BCG). Since current promising vaccines against bovine TB are based on heterologous prime-boost combinations that include BCG, there is a need for diagnostic tests for differentiating infected from vaccinated animals (DIVA). The application of antigens such as ESAT-6 and CFP-10 for DIVA has so far been realized largely through their application in the blood-based gamma interferon release assay. In the current study, we have reassessed the potential of such antigens as skin test reagents for DIVA in cattle. A cocktail of theMycobacterium tuberculosiscomplex recombinant protein antigens ESAT-6, CFP-10, MPB70, and MPB83 elicited delayed-type hypersensitivity (DTH) skin test responses in 78% of naturally infected tuberculin-positive cattle. Importantly, this cocktail induced no skin responses in BCG-vaccinated cattle despite them being sensitized for strong tuberculin responses. Further optimization of skin test antigen combinations identified that the inclusion of Rv3615c (Mb3645c) enhanced skin test sensitivity in naturally infected cattle without compromising specificity. In addition, we demonstrate for the first time the utility of synthetic peptides as promising skin test antigens for bovine TB for DIVA. Our data provide a promising basis for the future development of skin tests for DIVA with practical relevance for TB diagnosis in both veterinary and clinical settings.

Power scaling relationships between body mass and organismal traits are fundamental to biology. Compilations of mammalian masses and basal metabolic rates date back over a century and are used both to support and to assail the universal quarter-power scaling invoked by the metabolic theory of ecology. However, the slope of this interspecific allometry is typically estimated without accounting for intraspecific variation in body mass or phylogenetic constraints on metabolism. We returned to the original literature and culled nearly all unique measurements of body mass and basal metabolism for 695 mammal species and (1) phylogenetically corrected the data using the fullest available phylogeny, (2) applied several different regression analyses, (3) resampled regressions by drawing randomly selected species from each of the polytomies in the phylogenetic hypothesis at each iteration, and (4) ran these same analyses independently on separate clades. Overall, 95% confidence intervals of slope estimates frequently did not include 0.75, and clade-specific slopes varied from 0.5 to 0.85, depending on the clade and regression model. Our approach reveals that the choice of analytical model has a systematic influence on the estimated allometry, but irrespective of the model applied, we find little support for a universal metabolic rate-body mass scaling relationship.

Effective landuse planning to protect stream ecosystems requires quantitative tools that link catchment landuse to stream biotic integrity. This study explores two practical catchment-scale modeling approaches to this problem. Both predict levels of sediment or nutrient stressors in stream reaches based on landcover and other geospatial data, then predict impacts of these stressor levels on metrics of stream biotic integrity using fitted stressor-response functions (SRFs). Both approaches can be applied to large numbers of catchments using only readily available geospatial data and types of biological data commonly collected by state environmental agencies. The two approaches differ in the types of stressors they address and in details of how stressor loads of catchments are predicted. Stressor variables include total sediment and dissolved, particulate, and total nitrogen and phosphorus. Biological response variables include various metrics of community structure and pollution tolerance or sens...

The toxicity of three common antibiotics (streptomycin sulfate, tetracycline hydrochloride, and tylosin tartrate) to the freshwater rotifer Brachionus calyciflorus and brackish-water rotifer B. plicatilis was investigated using full-lifespan exposure durations. Effects of each antibiotic on lifespan, lifetime reproduction, and Malthusian parameter were assessed at seven nominal concentrations (ranging from 5.6 mg l−1 to 2,000 mg l−1) and a negative control. Lowest Observed Effect Concentrations (LOECs) were determined for reproduction and lifespan, while 1%, 10%, 25%, and 50% Inhibitory Concentrations (IC1, IC10, IC25, IC50) and 95% confidence intervals were estimated for all three endpoints. LOECs ranged from 5.6 mg l−1 to 90 mg l−1, with all LOECs less than 90 mg l−1 occurring in B. calyciflorus. The lowest IC1 concentrations were 3.91 mg l−1 for the effect of tetracycline on lifetime reproduction in B. calyciflorus and 4.06 mg l−1 for the effect of tylosin on lifetime reproduction in B. plicatilis. Overall, lifetime reproduction was the most sensitive endpoint and the Malthusian parameter was the least sensitive. IC1 values for lifetime reproduction were roughly one to two orders of magnitude lower than the corresponding IC50 values.

The recently proposed metabolic theory of ecology (MTE) claims to provide a mechanistic explanation for long known allometric relationships between mass and metabolic rate. The MTE postulates that these patterns of allometry are driven by the primary selective constraint of transport of energy and materials. However, recent evidence along several different lines has called into question both the adequacy and the universality of this mechanism. We review the accumulating body of literature on this subject, adding our own concerns and criticisms. In addition to other difficulties, we argue that MTE fails as a mechanistic explanation of mass versus metabolic rate allometries because: 1) circulatory cost minimization is not a tenable criterion for evolutionary optimization, 2) the Boltzmann type relationships on which MTE depends are inadequate descriptors of complex metabolic pathways, and 3) most of the hypotheses advanced by the MTE do not, in fact, depend on the proposed mechanism and therefore cannot be used to test the theory. We conclude that the MTE should be abandoned as a monolithic explanation for allometric patterns, and that a more realistic path toward a better understanding of allometry would be to consider multiple explanatory mechanisms for physiological allometries.

Summary 1. The restoration of native, forested riparian habitats is a widely accepted method for improving degraded streams. Little is known, however, about how the width, extent and continuity of forested vegetation along stream networks affect stream ecosystems. 2. To increase the likelihood of achieving restoration goals, restoration practitioners require quantitative tools to guide the development of restoration strategies in different catchment settings. We present an empirically based model that establishes a relationship between a ‘stress’ imposed at different locations along a stream by the spatial pattern of land cover within catchments, and the response of biologically determined ecosystem characteristics to this stress. The model provides a spatially explicit, quantitative framework for predicting the effects of changes in catchment land cover composition and spatial configuration on specific characteristics of stream ecosystems. 3. We used geospatial datasets and biological data for attached algae and benthic macroinvertebrates in streams to estimate model parameters for 40 sites in 33 distinct catchments within the mid-Atlantic Piedmont region of the eastern U.S. Model parameters were estimated using a genetic optimisation algorithm. R2 values for the resulting relationships between catchment land cover and biological characteristics of streams were substantially improved over R2 values for spatially aggregated regression models based on whole-catchment land cover. 4. Using model parameters estimated for the mid-Atlantic Piedmont, we show how the model can be used to guide restoration planning in a case study of a small catchment. The model predicts the quantitative change in biological characteristics of the stream, such as indices of species diversity and species composition, that would occur with the implementation of a hypothetical restoration project.

Many aquatic organisms need to settle in suitable benthic habitats while being transported via water currents. Such settlement is especially challenging for organisms that encounter complex benthic topography and lack the ability to move easily from the water column to the bed (e.g., via swimming). We conducted flume studies to examine whether the settlement of drifting stream insects is facilitated by adhesive filaments that extend from their bodies. Using a new tripwire visualization technique, we found that neonatal black flies (Simulium tribulatum) drifted with silk threads averaging six times their body length. These threads allowed larvae to contact or snag the bed from a greater height than would be possible through direct body-to-bed contact alone, and instantly arrested their downstream movement. Thus, silk increased their probability of settlement. We then performed an experiment to examine how settlement varied with bed topography and velocity. We tested whether settlement rate differed between a flat bed and an irregular bed that mimicked key aspects of their natural cobble-bed habitat. Velocities were similar for both bed treatments. Settlement on the irregular bed was 40 times greater than on the flat bed due to silk use. Settlement rate also exhibited a marginally significant decline with increasingly velocity on the flat bed, but not on the irregular bed. Silk threads should greatly increase the settlement rate of these nonswimming larvae on coarse-grained stream beds. Thus, silk snagging can potentially reduce the downstream distance that individuals are transported during a drift event, although the effects of silk on other phases of larval dispersal may differ.

The performance of the Soil and Water Assessment Tool (SWAT) and artificial neural network (ANN) models in simulating hydrologic response was assessed in an agricultural watershed in southeastern Pennsylvania. All of the performance evaluation measures including Nash-Sutcliffe coefficient of efficiency (E) and coefficient of determination (R2) suggest that the ANN monthly predictions were closer to the observed flows than the monthly predictions from the SWAT model. More specifically, monthly streamflow E and R2 were 0.54 and 0.57, respectively, for the SWAT model calibration period, and 0.71 and 0.75, respectively, for the ANN model training period. For the validation period, these values were −0.17 and 0.34 for the SWAT and 0.43 and 0.45 for the ANN model. SWAT model performance was affected by snowmelt events during winter months and by the model's inability to adequately simulate base flows. Even though this and other studies using ANN models suggest that these models provide a viable alternative approach for hydrologic and water quality modeling, ANN models in their current form are not spatially distributed watershed modeling systems. However, considering the promising performance of the simple ANN model, this study suggests that the ANN approach warrants further development to explicitly address the spatial distribution of hydrologic/water quality processes within watersheds.

Sexual reproduction is known to be an important means of propagation for native Japanese knotweed populations in Asia. For naturalized populations in the United States, however, its relative importance compared with propagation by rhizome and stem fragments has not been established. This article presents two related studies that address two basic questions regarding the potential for propagation by seed: (1) are seeds that are produced by Japanese knotweed in areas of Philadelphia, PA, capable of germinating in the field? If so, (2) when and how rapidly during the year do these seeds acquire germinability? Field germination experiments assessed germination of planted seeds at intervals during the growing season at two different study sites (one in 2000 and the other in 2002) and showed that germination was common at both sites. The 2002 experiment also demonstrated that germination occurred both within existing stands of Japanese knotweed and in areas well removed from existing stands, and that b...

Fine particles suspended in turbulent water exhibit highly irregular trajectories as they are buffeted by fluid eddies. The Local Exchange Model provides a stochastic diffusion approximation to the randomlike motion of such particles (e.g. dispersing benthic organisms in a stream). McNair et al. (1997, J. theor. Biol.188, 29) used this model to derive equations governing the mean hitting time, which is the expected time until a particle hits bottom for the first time from a given initial elevation. The present paper derives equations governing the probability distribution of the hitting time, then studies the distribution's dependence on a particle's initial elevation and two dimensionless parameters. The results show that for fine particles suspended in moderately to highly turbulent water, the hitting-time distribution is strongly skewed to the right, with mode

Turbulence plays an important role in the transport of particles in many aquatic systems. In addition to various types of inorganic sediment (silt, sand, etc.), these particles typically include bacteria, algae, invertebrates, and fine organic debris. In this paper, we focus on one aspect of turbulent particle transport; namely, the average time required for a suspended particle to reach the bottom of a waterbody from a specified initial elevation. This is the mean hitting-time problem, and it is important in determining, for example, the effect of turbulence on downstream transport of organic particles, dispersal times and dispersal propagules. We approach this problem by developing a stochastic diffusion model of particle transport called the Local Exchange Model, which is an extension of a model posed by Denny & Shibata (1989) in an earlier study of the same problem. We show how the mean hitting-time of the Local Exchange Model varies with factors such as a particle's fall velocity an the shape of the vertical profile in turbulent mixing. We also show how the mean hitting-time is related to both the vertical profile in current velocity and the vertical profile in concentration of suspended particles, and how these relationships can be exploited in testing the model. Among other things, our results predict that, with the sole exception of neutrally buoyant particles that do not swim downward, there is always a region of the water-column in which turbulence increases rather than decreases the mean hitting-time. We discuss the significance of this and other results for dispersal by benthic organisms.

Several stage-structured population models are considered in which fecundity, mortality, and maturation to the next stage are allowed to depend on stage and within-stage age, and in which adults are assumed to be the dominant consumers of limiting resources. Local stability effects of changing the strength of regulation about a fixed equilibrium point are examined. The main result is that shifting the principal target of strongly density-dependent mortality from adults to progressively earlier phases of juvenile development reverses the stability effect of such mortality from locally stabilizing to destabilizing. This result holds for all the models studied and therefore appears to be fairly robust to the pattern of age-dependence in adult fecundity and the shape of the juvenile period’s durational distribution. A simple intuitive interpretation is developed which can account for these and several related results in the literature. The necessity of distinguishing between life-historical delays and regulatory delays is also discussed.

BACKGROUND:Early secretory antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) are co-secreted proteins of Mycobacterium tuberculosis complex mycobacteria (includes M. bovis, the zoonotic agent of bovine tuberculosis) involved in phagolysosome escape of the bacillus and, potentially, in the efficient induction of granulomas. Upon tuberculosis infection, multi-nucleate giant cells are elicited, likely as a response aimed at containing mycobacteria. In tissue culture models, signal regulatory protein (SIRP)alpha (also referred to as macrophage fusion receptor or CD172a) is essential for multi-nucleate giant cell formation. METHODOLOGY/PRINCIPAL FINDINGS:In the present study, ESAT-6/CFP-10 complex and SIRPalpha interactions were evaluated with samples obtained from calves experimentally infected with M. bovis. Peripheral blood CD172a(+) (SIRPalpha-expressing) cells from M. bovis-infected calves proliferated upon in vitro stimulation with ESAT-6/CFP-10 (either as a fusion protein or a peptide cocktail), but not with cells from animals receiving M. bovis strains lacking ESAT-6/CFP-10 (i.e, M. bovis BCG or M. bovis DeltaRD1). Sorted CD172a(+) cells from these cultures had a dendritic cell/macrophage morphology, bound fluorescently-tagged rESAT-6:CFP-10, bound and phagocytosed live M. bovis BCG, and co-expressed CD11c, DEC-205, CD44, MHC II, CD80/86 (a subset also co-expressed CD11b or CD8alpha). Intradermal administration of rESAT-6:CFP-10 into tuberculous calves elicited a delayed type hypersensitive response consisting of CD11c(+), CD172a(+), and CD3(+) cells, including CD172a-expressing multi-nucleated giant cells. CONCLUSIONS/SIGNIFICANCE:These findings demonstrate the ability of ESAT-6/CFP-10 to specifically expand CD172a(+) cells, bind to CD172a(+) cells, and induce multi-nucleated giant cells expressing CD172a.

We pose and analyze a new demographic model which includes embryo abundance and a gestation period. All vital rates are fully age-dependent but do not depend on population density. We demonstrate convergence to a stable age configuration, characterize that configuration, and derive expressions for important population attributes such as the Malthusian parameter and net reproductive rate. We then use the model in two ways. First we examine effects of a gestation period on the population growth rate and the nature of population waves. Then we deduce a variety of simple birth rate estimators which can be applied to field populations. These include nearly all the existing egg ratio methods, and several new ones, as well.

The Local Exchange Model (LEM) is a stochastic diffusion model of particle transport in turbulent flowing water. It was developed mainly for application to particles of near-neutral buoyancy that are strongly influenced by turbulent eddies. Turbulence can rapidly transfer such particles to the bed, where settlement can then occur by, for example, sticking to biofilms (e.g., fine particulate organic matter, or FPOM) or attaching to the substrate behaviorally (e.g., benthic invertebrates). Previous papers on the LEM have addressed the problems of how long (time) and far (distance) a suspended particle will be transported before hitting the bed for the first time. These are the hitting-time and hitting-distance problems, respectively. Hitting distances predicted by the LEM for FPOM in natural streams tend to be much shorter than the distances at which most particles actually settle, suggesting that particles usually do not settle the first time they hit the bed. The present paper extends the LEM so it can address probabilistic settling, where a particle encountering the bed can either remain there for a positive length of time (i.e., settle) or immediately reflect back into the water column, each with positive probability. Previous results for the LEM are generalized by deducing a single set of equations governing the probability distribution and moments of a broad class of quantities that accumulate during particle trajectories terminated by hitting or settling on the bed (e.g., transport time, transport distance, cumulative energy expenditure during transport). Key properties of the settling-time and settling-distance distributions are studied numerically and compared with the observed FPOM settling-distance distribution for a natural stream. Some remaining limitations of the LEM and possible means of overcoming them are discussed.

Zooplankton accumulate large amounts of lipids, as much as 40-70% of the dry mass of their body (Goulden and Henry, 1985; Lee et al., 1972) ome polyunsaturated fatty acids and sterols are essential but required in trace amounts. By contrast, storage and membrane lipids are generally composed of nonessential lipids and make up an important energy reserve.

The classical chemostat models of Monod and others were designed for unicellular organisms. We summarize evidence that these models are not adequate for the rotifer chemostat, then propose a new, physiologically structured model that resolves some of their key problems yet remains biologically simple. The new model includes separate ontogenetic stages for eggs and free-swimming rotifers, with generalized age structure in the egg stage and body mass structure in the free-swimming stage. We present several numerical examples to illustrate the model’s behavior, and we compare these in a preliminary way with experimental evidence from the literature.

Immunomagnetic separation (IMS) can selectively isolate and concentrate Mycobacterium bovis cells from lymph node tissue to facilitate subsequent detection by PCR (IMS-PCR) or culture (IMS-MGIT). This study describes application of these novel IMS-based methods to test for M. bovis in a survey of 280 bovine lymph nodes (206 visibly lesioned (VL), 74 non-visibly lesioned (NVL)) collected at slaughter as part of the Northern Ireland bovine TB eradication programme. Their performance was evaluated relative to culture. Overall, 174 (62.1%) lymph node samples tested positive by culture, 162 (57.8%) by IMS-PCR (targeting IS6110), and 191 (68.2%) by IMS-MGIT culture. Twelve (6.9%) of the 174 culture positive lymph node samples were not detected by either of the IMS-based methods. However, an additional 79 M. bovis positive lymph node samples (27 (13.1%) VL and 52 (70.3%) NVL) were detected by the IMS-based methods and not by culture. When low numbers of viable M. bovis are present in lymph nodes (e.g. in NVLs of skin test reactor cattle) decontamination prior to culture may adversely affect viability, leading to false negative culture results. In contrast, IMS specifically captures whole M. bovis cells (live, dead or potentially dormant) which are not subject to any deleterious treatment before detection by PCR or MGIT culture. During this study only 2.7% of NVL lymph nodes tested culture positive, whereas 70.3% of the same samples tested M. bovis positive by the IMS-based tests. Results clearly demonstrate that not only are the IMS-based methods more rapid but they have greater detection sensitivity than the culture approach currently used for the detection of M. bovis infection in cattle. Adoption of the IMS-based methods for lymph node testing would have the potential to improve M. bovis detection in clinical samples.

Host-parasite interactions may lead to a variety of outcomes. Trematode infection of pulmonate snails is often associated with increased growth and/or survivorship of snail hosts. We use the freshwater pulmonate Lymnaea elodes and its trematode parasites to test whether this increase is a parasite adaptation, a host adaptation, or a side effect that serves no adaptive function for either participant. Field experiments indicate that trematode parasitism significantly reduces host fecundity and causes a temporary elevation and subsequent reduction in host growth. A 2-yr field survey of the prevalence of trematode infection in three snail populations revealed a significant positive relationship between shell size and prevalence. Apparently, L. elodes does not outlive its trematode infections. When survey data are compared with theoretical curves generated from a simple model of the system, it appears that trematode parasitism increases the survivorship of infected snails. Overall, the results suggest that in...

Prey refuges are widely believed to prevent prey extinction and damp predator-prey oscillations. A review of the empirical evidence suggests that refuges are indeed capable of playing the former role. But the conditions under which they do so are not understood, nor is there any solid evidence for an effect on population fluctuations. The intuitive view that refuges act to stabilize equilibria and damp predator-prey oscillations is based in several theoretical studies of extremely simple models. Using a more realistic model, I show that several kinds of refuges can exert a locally destabilizing effect and create stable, large-amplitude oscillations which would damp out if no refuge was present. This finding contrasts sharply with the usual view. I argue that current evidence is tol weak, and the range of theoretically possible effects is too broad, to justify any simple characterization of refuge effects in nature. Manipulative empirical studies are an important first step toward correcting this situation, and I discuss some important factors to consider in their design.

Standard optimal diet models require that a predator's behavior while searching for food does not change in response to experiences with individual prey. There is evidence for rapid and reversible changes in feeding behavior caused by as few as one or two prey encounters. When these “training effects” occur, a given prey type is more likely to be captured next if it was the last type with which the predator had experience. This is not compatible with the standard foraging model. I present a stochastic model which incorporates predator training effects, and three types of training are explored: training in the ability to detect prey (search image formation), training in the probability of succeeding in an attempted capture, and training in the time to pursue, capture, and eat prey. The main result is that all three types of training can result in optimal diets which do not obey the standard optimal diet rules. Conditions under which these rules will suffice are discussed.

Prior theoretical studies have shown that the juvenile period's length is an important determinant of local stability in age-structured population dynamics. For example, both short and long periods produce stability, but intermediate lengths can cause instability. Short juvenile periods significantly increase stability (compared to no juvenile period) if fecundity is independent of adult age. Here I re-examine these and other patterns, using a model which includes a variable juvenile period, juvenile mortality, density-dependent fecundity and adult mortality, and age-dependence is adult fecundity. Among other things, the results confirm the stable-unstable-stable pattern with increasing juvenile period length, but show that the stabilizing effect of short periods disappears when fecundity varies with adult age. Broadly speaking, the results suggest that age-dependence in adult fecundity has important dynamical consequences, and that models assuming that fecundity is independent of adult age may be unreliable guides to the dynamics of populations for which this assumption is not reasonably accurate.

Synopsis. Previous empirical and theoretical work has focused on how feeding territory size is governed by average levels of food availability and intrusion pressure; the potentially important effects of variability have not yet been studied in detail. Here I incorporate variation in food availability and intrusion pressure in some simple optimality models of territory size. The results show that the possible effects of variability are diverse, including both increase and decrease in territory size. And in some cases, variation in food availability produces qualitatively different effects than variation in intrusion pressure.

Prey refuges are widely believed to be important components of natural communities. Conventional wisdom holds that damping predator-prey oscillations is one of their most significant roles. Refuges are thus thought to reduce fluctuation and foster stable coexistence of prey and predator populations. Here I examine this view using a model which explicitly incorporates the process by which prey enter and leave their refuge, a process which nearly all previous models have ignored. Contrary to conventional wisdom, the results indicate that a prey refuge with legitimate entry-exit dynamics is quite capable of amplifying rather than damping predator-prey oscillations. Some simple conditions are identified which ensure that a refuge will act as (a) a damper and (b) an antidamper, and these are exploited in proposing a strategic way to test the model experimentally.