Evaluating the performance of temporal and spatial early warning statistics of algal blooms.

Regime shifts have large consequences for ecosystems and the services they provide. However, understanding the potential for, causes of, proximity to, and thresholds for regime shifts in nearly all settings is difficult. Generic statistical indicators of resilience have been proposed and studied in a wide range of ecosystems as a method to detect when regime shifts are becoming more likely without direct knowledge of underlying system dynamics or thresholds. These early warning statistics (EWS) have been studied separately but there have been few examples that directly compare temporal and spatial EWS in ecosystem-scale empirical data. To test these methods, we collected high-frequency time series and high-resolution spatial data during a whole-lake fertilization experiment while also monitoring an adjacent reference lake. We calculated two common EWS, standard deviation and autocorrelation, in both time series and spatial data to evaluate their performance prior to the resulting algal bloom. We also applied the quickest detection method to generate binary alarms of resilience change from temporal EWS. One temporal EWS, rolling window standard deviation, provided advanced warning in most variables prior to the bloom, showing trends and between-lake patterns consistent with theory. In contrast, temporal autocorrelation and both measures of spatial EWS (spatial SD, Moran's I) provided little or no warning. By compiling time series data from this and past experiments with and without nutrient additions, we were able to evaluate temporal EWS performance for both constant and changing resilience conditions. True positive alarm rates were 2.5-8.3 times higher for rolling window standard deviation when a lake was being pushed towards a bloom than the rate of false positives when it was not. For rolling window autocorrelation, alarm rates were much lower and no variable had a higher true positive than false positive alarm rate. Our findings suggest temporal EWS provide advanced warning of algal blooms and that this approach could help managers prepare for and/or minimize negative bloom impacts.

Early warnings of regime shifts: a whole-ecosystem experiment.

Catastrophic ecological regime shifts may be announced in advance by statistical early warning signals such as slowing return rates from perturbation and rising variance. The theoretical background for these indicators is rich, but real-world tests are rare, especially for whole ecosystems. We tested the hypothesis that these statistics would be early warning signals for an experimentally induced regime shift in an aquatic food web. We gradually added top predators to a lake over 3 years to destabilize its food web. An adjacent lake was monitored simultaneously as a reference ecosystem. Warning signals of a regime shift were evident in the manipulated lake during reorganization of the food web more than a year before the food web transition was complete, corroborating theory for leading indicators of ecological regime shifts.

Leading indicators of trophic cascades.

Regime shifts are large, long-lasting changes in ecosystems. They are often hard to predict but may have leading indicators which are detectable in advance. Potential leading indicators include wider swings in dynamics of key ecosystem variables, slower return rates after perturbation and shift of variance towards lower frequencies. We evaluated these indicators using a food web model calibrated to long-term whole-lake experiments. We investigated whether impending regime shifts driven by gradual increase in exploitation of the top predator can create signals that cascade through food webs and be discerned in phytoplankton. Substantial changes in standard deviations, return rates and spectra occurred near the switch point, even two trophic levels removed from the regime shift in fishes. Signals of regime shift can be detected well in advance, if the driver of the regime shift changes much more slowly than the dynamics of key ecosystem variables which can be sampled frequently enough to measure the indicators. However, the regime shift may occur long after the driver has passed the critical point, because of very slow transient dynamics near the critical point. Thus, the ecosystem can be poised for regime shift by the time the signal is discernible. Field tests are needed to evaluate these indicators.

Prevalence of occupational allergy due to live fish bait.

BACKGROUND: Larvae of insects and worms, used as live fish bait (LFB), are a common source of allergy in anglers and occupationally exposed workers, but the prevalence and predictors have not yet been investigated. OBJECTIVE: This study assessed the prevalence and associated factors of occupational allergy in workers exposed to LFB. METHODS: We assessed the prevalence of sensitization to LFB and work-related symptoms (WRS) in 76 workers occupationally exposed to it. All workers completed a case history questionnaire and underwent skin prick tests (SPT) for common aeroallergens and bluebottle (Calliphora vomitoria), bee moth (Galleria mellonella), mealworm (Tenebrio molitor), and gusano rojo (Cilecomadia moorei). Specific IgE were tested in 64 subjects. Two-thirds of the workers had a high level of LFB exposure. RESULTS: Sensitization to LFB was found in 24 workers (31.6%). Seven subjects (9.2%) reported WRS (asthma in 3, rhinoconjunctivitis in 5, and contact urticaria in 1), and 5 were positive for SPT and serum IgE to one or more LFB extracts. One was also exposed to LFB while fishing. Sensitization to LFB extracts and WRS were strongly associated (Odds Ratio = 6.6, P < 0.05). The 7 subjects with WRS had been exposed longer than asymptomatic subjects with positive skin tests to LFB (P < 0.05). No differences in sex, age, smoking habit, duration or level of exposure, and atopy were detected in symptomatic or in sensitized subjects, compared with normal workers. CONCLUSION: Sensitization to LFB and WRS are relatively frequent in occupationally exposed workers. No associated factors of occupational allergy to LFB could be detected.

[Clinical and functional course of occupational asthma in pharmacologic treatment and during persistent exposure. A 3-year follow-up]. / Andamento clinico e funzionale dell'asma professionale in trattamento farmacologico e durante il persistere dell'esposizione. Follow-up di tre anni.

According to act 626/1994, employers have the duty to inform and train workers and their representatives. The implementation of training activities requires the following points: planning the training progra according to the needs of the target population, use of the methods aimed at promoting learning and the adoption of safe behaviour, setting-up of evaluation tools. The disciplines of risk perception and communication and adult training may provide useful contribution in this frame. At the light of the preliminary experiences in this field, the importance of the following items for workers, workers representatives and employers is emphasized: probabilistic causality models, role of cognitive and emotional factors in the learning process, definition of carcinogenic according to national and internationals organisation, meaning of TLV with respect to carcinogenic exposure, interaction between carcinogens in the case of multiple exposition, risk evaluation, preventive measures, transfer of carcinogen risk from workplace to domestic environment, due to lack of compliance with basic hygienic rules such proper use of work clothes.

[Occupational asthma and rhinitis caused by colophony among linoleum production workers]. / Asma e rinite professionale da colofonia negli addetti alla produzione del linoleum.

According to act 626/1994, employers have the duty to inform and train workers and their representatives. The implementation of training activities requires the following points: planning the training progra according to the needs of the target population, use of the methods aimed at promoting learning and the adoption of safe behaviour, setting-up of evaluation tools. The disciplines of risk perception and communication and adult training may provide useful contribution in this frame. At the light of the preliminary experiences in this field, the importance of the following items for workers, workers representatives and employers is emphasized; probabilistic causality models, role of cognitive and emotional factors in the learning process, definition of carcinogenic according to national and internationals organisation, meaning of TLV with respect to carcinogenic exposure, interaction between carcinogens in the case of multiple exposition, risk evaluation, preventive measures, transfer of carcinogen risk from workplace to domestic environment, due to lack of compliance with basic hygienic rules such proper use of work clothes.

Occupational rhinitis.

Occupational rhinitis (OR), a very frequent disease caused by several occupations, tends to share etiological agents and to be three times more prevalent than occupational asthma (OA). Exposure, which can be reliably estimated by means of job description or mean week exposure, may be the single most important determinant of occupational sensitization and OR. Atopy is a controversial risk factor for OR and a major risk factor for occupational sensitization when high molecular weight agents are involved. The role of smoking in OR and occupational sensitization is not clear and has yet to be explained in full.

[Prevalence of occupational allergy to laboratory animals in two towns of northern and central Italy]. / Prevalenza dell'allergia professionale agli animali di laboratorio in due città del nord e del centro Italia.

BACKGROUND: Laboratory animal allergy (LAA) is a well known occupational hazard for workers employed in biological and medical research institutes, but few Italian data on this disease exist. OBJECTIVES: The aim of our study was to evaluate the prevalence of LAA in 45 workers in Trieste (NE-Italy) and in 80 workers in Perugia (Central Italy) and to assess factors predisposing to sensitisation among subjects occupationally exposed to animals. METHODS: All subjects underwent a physical examination and responded to a standardized questionnaire for the evaluation of allergic respiratory symptoms and exposure data. Skin prick tests with common allergens and with hair extract from laboratory animals were performed and specific IgE was measured. Atopy was defined as positive skin prick test to common allergens. RESULTS: There were 60% atopic subjects in Trieste and 55% in Perugia and sensitisation to laboratory animal hair was found in 24.4% subjects in Trieste and in 35% in Perugia. The prevalence rates of LLA were respectively 11.1% and 11.2%; 2.3% and 3.7% complained of asthma while 8.9% and 7.5% complained of rhinitis. The resulting symptoms were significantly related to skin prick tests that were positive to laboratory animal hair (odds ratio (OR) = 7.64; 1.83-44.5), to skin prick test positivity to common inhalant allergens (OR = 5.29; 1.09-50.2), to common allergic symptoms (OR = 3.95; 1.05-18.2) and to exposure time exceeding 5 hours per day (OR = 5.45; 1.31-22.0). CONCLUSION: The role of atopy and of exposure time in causing LLA was confirmed and the need of prevention measures to reduce exposure in people at risk was discussed.

Ecosystem size determines food-chain length in lakes.

Food-chain length is an important characteristic of ecological communities: it influences community structure, ecosystem functions and contaminant concentrations in top predators. Since Elton first noted that food-chain length was variable among natural systems, ecologists have considered many explanatory hypotheses, but few are supported by empirical evidence. Here we test three hypotheses that predict food-chain length to be determined by productivity alone (productivity hypothesis), ecosystem size alone (ecosystem-size hypothesis) or a combination of productivity and ecosystem size (productive-space hypothesis). The productivity and productive-space hypotheses propose that food-chain length should increase with increasing resource availability; however, the productivity hypothesis does not include ecosystem size as a determinant of resource availability. The ecosystem-size hypothesis is based on the relationship between ecosystem size and species diversity, habitat availability and habitat heterogeneity. We find that food-chain length increases with ecosystem size, but that the length of the food chain is not related to productivity. Our results support the hypothesis that ecosystem size, and not resource availability, determines food-chain length in these natural ecosystems.

Regulation of planktonic bacterial growth rates: The effects of temperature and resources.

We examined the potential limitation of bacterial growth by temperature and nutrients in a eutrophic lake. Dilution cultures from winter and summer were incubated at both high (>20°C) and low (4°C) temperatures and enriched with various combinations of organic carbon (C), inorganic nitrogen (N), and inorganic phosphorus (P). Bacterial abundance, (3)H-thymidine incorporation, and (3)H-leucine incorporation were measured over the growth cycle. For both winter and summer assemblages, low temperature limited growth even when resources (C, N, and P) were added. When temperature was adequate, bacterial growth in dilution cultures was co-limited by C, N, and P Additions of either C, P, or N and P alone provide little or only modest stimulation of growth, suggesting that under in situ conditions both nutrients and organic carbon limit bacterial growth. Our results provide little evidence of seasonal adaptation to low temperatures for bacterial communities in temperate lakes. Instead, bacterial growth appears to be temperature limited during winter and resource limited during summer. We propose that, in general, bacterial growth rates are temperature dependent up to a threshold, but that the patterns of change across temperature gradients are resource dependent, such that temperature has little effect on growth in resource-rich environments but a strong effect in resource-poor environments.

Comparative and experimental approaches to top-down and bottom-up regulation of bacteria.

The regulation of bacterial community biomass and productivity by resources and predators is a central concern in the study of microbial food webs. Resource or bottom-up regulation refers to the limitation of bacteria by carbon and nutrients derived from allocthonous inputs, primary production, and heterotrophic production. Predatory or top-down regulation refers to the limitation of bacteria below levels supportable by resources alone. Large scale comparative studies demonstrate strong correlations between bacterial productivity and biomass, suggesting significant resource regulation. Comparisons of the abundances of heterotrophic flagellates and bacteria, however, imply that in some cases there may be top-down regulation of bacteria in eutrophic environments. Experimental studies in lakes support the importance of resource regulation and reveal little top-down control from protozoans. Increases in bacterial abundance and production with nutrient enrichment were limited in enclosure experiments with high abundances of the cladoceran, Daphnia. Regulation of bacteria by Daphnia may occur in many lakes seasonally and prevail in some lakes throughout the year where these animals sustain dense populations. In most situations, however, bacteria appear to be limited primarily by resources.

Validity of eucaryote inhibitors for assessing production and grazing mortality of marine bacterioplankton.

Application of eucaryote inhibitors to the estimation of production and grazing mortality of bacterioplankton was evaluated. Exposure to a range of concentrations of thiram, cycloheximide, and neutral red (0.4 to 210, 36 to 1,777, 4 to 346 muM, respectively) was 98 to 100% effective at inhibiting growth of a chrysomonad in culture. Exposure to colchicine and griseofulvin (50 to 1,000 muM for both) yielded only 24 to 94 and 53 to 79% inhibition, respectively. Exposures to thiram, neutral red, and griseofulvin were 90 to 100% effective at inhibiting growth in culture of a ciliate, Cyclidium sp., and the responses to colchicine and cycloheximide were variable (64 to 100 and 0 to 100% inhibition, respectively). Thiram and neutral red inhibited field populations of nanozooplankton more effectively than cycloheximide and colchicine. Direct effects of eucaryote inhibitors on growing cultures of bacterioplankton varied with parameters measured and duration of exposure. After 3-day exposures, specific growth rates and "instantaneous" heterotrophic potential ([C]glucose uptake) were not consistently affected, but biosynthetic activity (RNA and DNA syntheses) was depressed. The degree of inhibition of isolates and field populations of phytoplankton depended upon type of inhibitor and phytoplankton species. In field experiments, it was possible to calculate rates of bacterioplankton production and grazing mortality for only 16 of 29 inhibitor experiments and for 4 of 10 size fractionation experiments. Bacterioplankton production and mortality estimates varied greatly with the eucaryote inhibitor used, and those derived from inhibition techniques were substantially different from those derived from fractionation techniques. The poor performances of both techniques are attributed to the following: (i) effects of inhibitors on phytoplankton, (ii) indirect effects of the inhibitors on bacterioplankton, and (iii) insufficient separation of grazers from prey by filtration techniques. Because of the inconsistent results obtained in this investigation, we strongly recommend exercising caution in the application of inhibitor techniques to ecological problems, especially in phototrophically dominated systems.