Feeding behavior in sexual and clonal strains of Poeciliopsis

Summary Sexual and clonal fish of the genus Poeciliopsis occur together in desert streams of Sonora, Mexico. Their coexistence has been explained in terms of niche partitioning for food and space. We examined predatory behavior that might influence niche relationships, and found significant differences among two coexisting sperm-dependent clonal strains and their two sexual progenitors. Handling time and prey manipulation of free-swimming (Artemia) and benthic (chironomid larvae) prey differed significantly among sexual and clonal strains. Analyses of gut contents from field-collected fish revealed that the laboratory estimates of predatory efficiency were related to their feeding behavior in nature. Behavior differences, such as those described herein, contribute to our understanding of the mechanisms of unisexual/bisexual coexistence in Poeciliopsis. Offprint requests to: R.C. Vrijenhoek     

“Applicability of the t-Test for Detecting Trends in Water Quality Variables,” by Robert H. Montgomery and Jim C. Loftis2

Montgomery and Loftis (1987) have listed several situations for which the t-test does not accurately reproduce Type I errors, and should therefore be avoided. Characteristics common to water quality data (skewness or other non-normality, presence of outliers and less-thans) also reduce the power of the t-test, in relation to nonparametric alternatives. Thus if one is interested in reaching correct decisions when trends or differences exist, and not just when they do not, the t-test should not be considered “robust” (in the sense of being generally applicable) when its assumptions are violated. Further, t-tests assume that differences in means are relevant (the mean is a good measure of central tendency), and that data groups differ by some additive amount. When all of these assumptions are recognized, and in light of the availability of truly robust and comparatively powerful non-parametric alternatives, we believe there is little applicability of the t-test for detecting trends or differences in water quality variables.     

Towards a national reference center for environmental information in The Netherlands: A review

For improvement of the accessibility and use of environmental information a prototype national reference center (CIMI) was constructed in the Netherlands in 1986. Target groups were identified on the basis of an analysis of the demand side. They were questioned about their needs in the field of environmental information. On the basis of these experiences an automated integrated system has been built that is composed of subsystems for reference to expertise in organizations (specialisms), literature, research, and databases of site-specific data. This system is also equipped with a thesaurus. The system has been tested and examined in several ways. The outcome of these independent tests and investigations confirm the usefulness of this center for information transfer. The reference center can be helpful in providing overviews on and structuring of environmental information in the Netherlands. The results of the activities have been presented in several ways and were described extensively in a number of reports.     

Lower health risk with increased job control among white collar workers

Associations between increased job control and health status were tested with questionnaire data from a random sample of full-time workers (n = 8504) from the national Swedish white collar labor federation, TCO (representing 25 per cent of the Swedish work force). Of these subjects, 1937 had undergone a company-initiated job reorganization during the previous several years. Workers in the job reorganization group who had influence in the reorganization process and obtained increased task control as a result had lower levels of illness symptoms on 11 of 12 health indicators controlling for age and sex (11 of 12 associations significant for males, four of 12 associations significant for females). A previously validated measure of coronary heart disease was significantly lower in circumstances of increased job control for males (8.6 per cent symptom frequency with decreased control versus 3.4 per cent with increased control; p = 0.05). Absenteeism was lower: 10.7 per cent versus 5.0 per cent (0.01). Depression was lower 27.8 per cent to 13.7 per cent (0.001). However, smoking was significantly higher for women 11.0 per cent versus 23.5 per cent (0.01). All illness indicators showed that the process of job reorganization itself was associated with significantly higher symptoms (‘change stress’). However for males (only) symptoms levels when reorganization was accompanied by increased control were often as low or lower than symptom levels for no reorganization at all. Unfortunately, job reorganizations involving employee influence and increased task control were less frequent than job reorganizations involving reduced influence and no increased control, especially for women and older workers.