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PubMed1995

Preferences for fixed and variable food sources: variability in amount and delay.

Much research has focused on the effects of environmental variability on foraging decisions. However, the general pattern of preference for variability in delay to reward and aversion to variability in amount of reward remains unexplained a either a mechanistic or a functional level. Starlings' preferences between a fixed and a variable option were studied in two treatments, A and D. The fixed option was the same in both treatments (20-s fixed-interval delay, five units food). In Treatment A the variable option gave two equiprobable amounts of food (20-s delay, three or seven units) and in D it gave two equiprobable delays to food (2.5-s or 60.5-s delays, five units). In both treatments the programmed ratio [amount/(intertrial interval+latency+delay)] in the fixed option equaled the arithmetic mean of the two possible ratios in the variable option (ITI = 40 s, latency = 1 s). The variable option was strongly preferred in Treatment D and was weakly avoided in Treatment A. These results are discussed in the light of two theoretical models, a form of constrained rate maximization and a version of scalar expectancy theory. The latter accommodates more of the data and is based on independently verifiable assumptions, including Weber's law.

Animals↗
PubMed2003

Risk mapping of visceral leishmaniasis: the role of local variation in rainfall and altitude on the presence and incidence of kala-azar in eastern Sudan.

Visceral leishmaniasis (VL) is a vector-borne disease highly influenced by environmental factors. A model was developed for mapping the distribution and incidence of VL in Gedaref State, eastern Sudan, in relation to different environmental factors. Geographical information systems (GIS) were used to extract and map regression results for environmental variables of 190 villages in Gedaref State, including rainfall, vegetation status, soil type, altitude, distance from river, topography, wetness indexes, and average rainfall estimates. VL incidence in each village was calculated from hospital records. By use of logistic and linear multivariate regression analyses, models were developed to determine which environmental factors explain variability in VL presence and incidence. We found that average rainfall and the altitude were the best predictors of VL incidence. The resulting models were mapped by GIS software predicting both VL presence or absence and incidence at any locality in Gedaref State. The results are discussed in relation to VL control.

Altitude↗
PubMed2000

Aquatic fate assessment of the polycyclic musk fragrance HHCB. Scenario and variability analysis in accordance with the EU risk assessment guidelines.

By means of the environmental fate and distribution models laid down in the Technical Guidance Documents (TGD) and implemented in the European Union System for the Evaluation of Substances (EUSES) environmental concentrations of the polycyclic musk fragrance HHCB (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta-[g]-2- benzopyrane; trade name: e.g. Galaxolide) were calculated for the aquatic environment under consideration of various scenarios. The results were then compared to monitoring data from the region of North Rhine-Westphalia (River Ruhr). An uncertainty analysis was carried out to determine sensitive parameters, to integrate environmental variability and to confirm the model's calculations. The standard scenario of EUSES overestimates the measured concentrations, which confirms the conservative nature of the calculations. The regional-specific scenarios lead to lower deviations from the measured values than the standard scenario. Deviations range from one to two orders of magnitude in the effluent of sewage treatment plants; they amount to one order of magnitude for surface water concentrations on a local scale and conform to monitoring data on a regional scale. The use of measured bioconcentration factors for fish instead of estimated ones reduces deviations remarkably. The investigation reveals that unrealistic worst-case calculations of HHCB can at best be ameliorated by the application of more realistic emission rates and measured bioconcentration factors. The use of regional-specific parameters also diminishes the deviations of the calculations from the measured concentrations.

Benzopyrans↗
PubMed1983

Effects of nutrition and environment on brain biochemistry and behavior.

A factorial design was used to explore the influence of malnutrition and environmental enrichment on brain development and adult behavior. Malnutrition in suckling rats was produced by restricting the intake of their dams to 40% of normal food consumption. Environment was enriched using combined preweaning handling and a postweaning complex environment treatment. Malnutrition produced lasting effects upon brain biochemical composition and behavior. The environmental manipulation had no ameliorative effect on the brain parameters measured but it had pronounced effects on behavior, decreasing latency to move in the open field and increasing some measures of activity while it enhanced passive-avoidance performance. There was little evidence for any interaction between the nutritional and environmental variables, but all trends were in the direction of the environmental treatment having more effect on the well-nourished rats.

Animals↗
PubMed2003

Year class coexistence or competitive exclusion for strict biennials?

We consider a discrete time model of semelparous biennial population dynamics. Interactions between individuals are modelled with the aid of an "environmental" variable I. The impact on and the sensitivity to the environmental condition is age specific. The main result is that competitive exclusion between the year classes is possible as is their coexistence. For moderate values of the basic reproduction ratio R(0) there is a strict dichotomy: depending on the other parameters we either find competitive exclusion or coexistence. We characterize rather precisely the patterns of age specific impact and sensitivity that lead to either of these outcomes.

Aging↗
PubMed1993

Neurotoxicity screening methods are sensitive to experimental history.

Toxicity studies commonly include unavoidable environmental differences (experimental history) among test groups, such as chemical taste, odor and irritation. The influence of environmental variables on USEPA guideline neurotoxicity tests was evaluated using an environmental enrichment model. 6-week-old male Fischer 344 rats were housed for 13 weeks in pairs with access to an exercise wheel, trained to run on a rotating rod and handled frequently. Control animals were housed singly, lacked the exercise wheel and rotating rod training, and had only routine interaction with caretakers. At the end of 13 weeks, flash evoked potentials (FEPs), somatosensory evoked potentials (SEPs), auditory brainstem responses (ABRs), grip performance, motor activity (MA), elements of the functional observational battery (activity and reactivity to handling/restraint) and brain histopathology with glial fibrillary acidic protein immunohistochemistry (GFAP IHC) were evaluated. Animals from the enriched group demonstrated changes (P < 0.05) in FEPs, SEPs and grip performance. Enriched animals were more active and reactive to their surroundings, and were highly reactive to physical restraint. Control (unenriched) animals showed little to no exploratory behavior and were more tolerant of restraint. Differences in experimental history can be detected using elements of standard guideline tests and may confound interpretation of such data if not taken into consideration.

Analysis of Variance↗
PubMed1994

Chitinolytic properties of Bacillus pabuli K1.

The chitinolytic properties of Bacillus pabuli K1 isolated from mouldy grain was studied. Chitinase activity was measured as the release of p-nitrophenol from p-nitrophenyl-N,N'-diacetylchitobiose. Influences of substrate concentration and different environmental variables on growth and chitinase activity were determined. The optimum environmental conditions for chitinase production were: 30 degrees C, initial pH 8, initial oxygen 10% and aw > 0.99. Chitinase production was induced when B. pabuli K1 was grown on colloidal chitin. The smallest chito-oligosaccharide able to induce chitinase production was N,N'-diacetylchitobiose, (GlcNAc)2. Production was also induced by (GlcNAc)3 and (GlcNAc)4. When the bacterium was grown on glucose or N-acetylglucosamine, no chitinases were formed. The highest chitinase production observed was obtained with colloidal chitin as substrate. The production of chitinases by B. pabuli K1 growing on chitin was repressed by high levels (0.6%) of glucose. The production was also repressed by 0.6% starch, laminarin and beta-glucan from barley and by glycerol. The addition of pectin and carboxymethyl cellulose increased chitinase production.

Bacillus↗
PubMed1979

Comparative effects of Aroclor 1254 (polychlorinated biphenyls) and phenanthrene on glucose uptake by freshwater microbial populations.

The effects of polychlorinated biphenyl (PCB) and phenanthrene stress on glucose uptake by natural microbial populations were examined by the heterotrophic potential technique. Temporal and spatial distributions in glucose uptake velocities were examined for natural samples as well as PCB- and phenanthrene-stressed samples. Statistical analysis indicated significant variability among the various samples. It was demonstrated that the environmental variables contributed significantly to the variability in uptake kinetics. Although general trends indicated a PCB-induced stimulation in uptake velocities, these trends were in part masked by sample variability. Data analysis indicated no statistically significant PCB or phenanthrene effect on either total glucose uptake velocities or the proportion of 14CO2 evolved, as compared to natural unstressed samples.

Aroclors↗
PubMed2001

Predicting spoken language level in children with autism spectrum disorders.

Thirty-five children who received an autism spectrum diagnosis at the age of 2 years (24 with autism, 11 with PDD-NOS) were re-evaluated 2 years later to examine factors related to the development of spoken language. Child variables (play level, motor imitation ability and joint attention) and environmental variables (socioeconomic status and hours of speech/language therapy between ages 2 and 3) were used to predict an aggregate measure of language outcome at age 4. After controlling for age 2 language skills, the only significant predictors were motor imitation and number of hours of speech/language therapy. Implications of these results for understanding the early developmental course of autism spectrum disorders and the effects of intervention are discussed.

Autistic Disorder↗
PubMed2004

Sibling effects, environmental influences, and university attendance: a follow-up study.

In 2002 Marjoribanks examined relations among sibling variables, environmental influences, and school dropout. In this follow-up study, relations were examined between sibling variables (number of children in the family, birth order position) and university attendance. Data were collected from 8,005 (4,116 women, 3,889 men) Australian young adults (M age=20.1 yr., SD=0.5). Logistic regression analyses in the two studies indicated that (a) young adults from Asian, Middle Eastern, and middle-class families were less likely to drop out of school and more likely to attend a university than were young Australians from Anglo-Australian, English, European, and working-class backgrounds, and (b) after taking into account differences in family background and learning environment measures, there continued to be small but significant relations between the number of children in families, birth-order position, and the likelihood that young people would drop out of school or attend a university.

Adolescent↗
PubMed2002

Geomagnetics and society interact in weekly and broader multiseptans underlying health and environmental integrity.

Evidence for the ubiquity and partial endogenicity of about-weekly (circaseptan) components and multiples and/or submultiples thereof (the multiseptans) accumulates as longer and denser records become available. Often attributed to a mere response to the social schedule, circaseptan components now have been documented to characterize environmental variables related to primarily non-photic solar effects. Plausibly, like circadians, circaseptans are anchored in genomes, from bacteria to humans, via both an internal and external evolution. If so, circaseptans, like circadians, may be found in the absence of a 7-day schedule, whereas the social schedule may play a synchronizing role and be responsible for the detection of prominent weekly variations in population statistics. The wobbliness of multiseptans and other components of some environmental time structures (chronomes) may correspond to the wobbliness of multiseptans found in cardiovascular morbidity statistics. Here, the latter stem primarily, but not exclusively, from an extensive database on the incidence of daily calls for an ambulance in Moscow, Russia from 1979-1981. A modulation of multiseptans and other chronome components of both environmental and biological variables by the about 11-year solar activity cycle (and of other low-frequency signals reviewed elsewhere) may account for prior controversies and scepticism about a variety of non-photic effects on biota. This is notably the case when relatively short series are analyzed without consideration of effects of unassessed long-term variations; this is the task of the new field of chronomics. In the spectral element of the chronomes of geophysical and biospherical variability, there are natural near weeks,apart from any precise 7-day periodicity.

Analysis of Variance↗
PubMed2006

Removal of selenate from sulfate-containing media by sulfate-reducing bacterial biofilms.

A biofilm-selected strain of a Desulfomicrobium sp. removed selenate from solution to sub-micromolar concentrations during growth on lactate (or hydrogen) and sulfate. Under sulfate-limited growth conditions, selenium was enzymatically reduced to selenide. Under excess sulfate conditions, selenate removal was primarily by enzymatic reduction to elemental selenium. Sequestration by biofilms was greater under the latter condition. Experiments with washed cell suspensions showed that high sulfate concentrations inhibited cell-specific selenate reduction, but when growing cells were exposed to selenate, the biomass increase achieved during incubations with abundant sulfate resulted in more rapid selenate removal. The addition of small amounts of sulfite, or thiosulfate, ameliorated this inhibition. Nitrate also inhibited selenate reduction in washed cell suspensions, apparently due to a general oxidizing effect. These results suggest that where biofilm-based sulfate-reducing bacteria (SRB) bioreactors are considered for the treatment of mixed metalliferous wastes that contain selenium oxyanions, adequate selenate removal should be achievable under a range of environmental conditions. The form and fate of the precipitated product will, however, be influenced by the dominant reduction pathway, which is controlled by environmental variables.

Biodegradation, Environmental↗
PubMed1979

Variability of Temperature, pH, and Moisture in an Aerobic Composting Process.

This study measured the environmental variability which exists in a commercial aerobic composting process. The specific process studied is carried out in six decomposition cells which present six different phases of the process. Temperature, pH, and moisture content were determined in several randomly chosen sample sites in each cell, both at the beginning and at the end of the time the material was left in the cell. Temperature and pH varied greatly from one sample site to another in each cell, whereas moisture content was less varied. A significant rise in both temperature and pH was observed at two stages of degradation.

Journal Article↗
PubMed2001

Spatial and temporal co-structure analyses between ichthyofauna and environment: an example in the tropics.

Ichthyofauna distribution and habitat characteristics of Thalassia beds in the Grand Cul-de-Sac marin lagoon in Guadeloupe were studied during a one-year survey. Environmental variables (9) were measured monthly in ten sites along with collection of fish communities. The environmental data set, analysed alone through between-within group 'principal component analysis' (PCA), exhibited a significant spatial and temporal variability. The fish data set, however, presented only a significant spatial structure, stable over the year. Given the lack of temporal variability in fish distribution, a 'between-site co-structure analysis' (BSCA) was used to compare the faunistic and environmental structures in space. The co-inertia structure was reduced to one axis representing a strong coast-reef gradient, the major common phenomena to both data sets. Environment and fish distribution allowed to distinguish sites directly under mangrove influence (characterised by high seagrasses, high concentration of chlorophyll a and high densities of zooplankton), to sites under reef influence (with short but dense seagrasses, clear water, and poor nutriments). For that purposes, the BSCA summarised efficiently what in common the fauna spatial structure and the environment spatial structure may present.

Animals↗
PubMed2005

Applying a large, statewide database to the assessment, stressor diagnosis, and restoration of stream fish communities.

In this report, predictions of the species that were expected to occur at stream sites were generated and probable stressors to fish species that were predicted to occur but were absent were diagnosed. Predictions were generated based on the hierarchical screening method of Smith and Powell (1971, Am. Mus. Novit. 2458, 1-30), using fish abundance in conjunction with 25 environmental variables at 895 sites. The sites were sampled throughout Maryland and represent the entire range of environmental quality from severely degraded to minimally degraded. Stressor variable values that exceeded tolerance thresholds for species that were expected to occur, but were absent, were considered to be probable stressors. This method was tested for efficacy in stream site assessments and stressor diagnosis using an independent data set. Sites that were classified as degraded according to the IBI and to non-biological criteria had fewer predicted species present compared to minimally influenced sites, indicating that the proportion of predicted species present accurately represents the biological integrity of a stream site. The nine stressors that were applied to the test data set accounted for species absences in 43.7% of degraded sites. Impervious land cover was the most common stressor identified. In addition to assessing stream biological integrity and identifying stressors to fish species, this approach also provides tolerance thresholds for predicted fish species that are useful endpoints necessary to plan effective restoration of fish species in Maryland.

Animals↗
PubMed1982

Social networks and psychiatric clients: the personal and environmental context.

The study examines the extent to which characteristics of psychiatric clients (interpersonal problem-solving) and their families (family climate and family social resources) are associated with dimensions of clients' social networks (size and support). Respondents were 35 clients recruited from outpatient psychiatric clinics and the family members with whom they resided. The results revealed that individual and environmental variables were significant correlates of social network dimensions. For example, client problem-solving was positively related to the number of intimates cited by the client, while level of independence was positively related to the degree of support clients reported receiving from their peers. Level of client psychopathology partially moderated the effects of some of the predictor variables. The results highlight the need to examine the individual and environmental processes that shape and are shaped by social network patterns.

Adaptation, Psychological↗
PubMed1998

HLA-DR gene frequencies in a Zaïrean population with particular reference to rheumatic diseases.

Epidemiological studies have shown that rheumatic diseases such as rheumatoid arthritis and systemic lupus erythematosus are uncommon in black Africans, and in this population the prevalence and the clinical features of these rheumatic diseases are variable. Environmental and genetic factors have been pointed out to explain this variability. In the present study, HLA-DR genes have been determined in a Zaïrean population in order to compare our results with those found elsewhere in other black populations of the same Bantu origin. Our results show that the frequency of HLA-DR1 is higher than in Nigerians, Zimbabweans and Xhosas, the decrease in Xhosas being statistically significant (p < 0.006). The HLA-DR3 frequency is higher in Zaïreans than in Nigerians but not significantly, while it is lower than in Xhosas (p < 0.003) and in Zimbabweans (not significant). The HLA-DR4 frequency is higher in Zaïreans than in Nigerians but it is lower than in Xhosas and Zimbabweans; the differences are not statistically significant. The HLA-DR8 frequency is lower in Zaïreans than in Nigerians while it is higher than in Xhosas (p < 0.002) and in Zimbabweans (not significant). These data suggest that genetic factors partly explain the clinical and epidemiological variability of rheumatic diseases in black Africans.

Adult↗
PubMed1998

Habitat dependence of a parasite-host relationship: flea (Siphonaptera) assemblages in two gerbil species of the Negev Desert.

Flea assemblages of Meriones crassus Sundevall and Gerbillus dasyurus Wagner in different habitats in the Negev Highlands of Israel were studied to determine how flea abundance and species composition on the same host change among habitats, and the environmental parameters determining specific composition of flea assemblage. Fleas of the same species parasitizing different hosts responded differently to the same set of environmental variables. Spatial distribution of fleas on M. crassus was determined by environmental parameters significantly stronger than those on G. dasyurus. Flea abundance and species composition on both host species changed among habitats. Indirect ordination of flea assemblages produced axes that presented spatial components of change in flea composition (for M. crassus--Xenopsylla conformis Rothschild versus Xenopsylla ramesis Rothschild; for G. dasyurus--Xenopsylla dipodilli Smit versus X. conformis and X. ramesis versus X. conformis). Discriminant analyses of flea assemblage on M. crassus demonstrated that fleas were segregated along 2 discriminant axes that reflected a soil structure and productivity gradient and a contrast between dry riverbeds and watershed plains. Ordination of flea assemblages on G. dasyurus produced 2 discriminant axes, both presenting a complex gradient of the soil structure and the level of primary production.

Animals↗