Key plant species and detritivores drive diversity effects on instream leaf litter decomposition more than functional diversity: A microcosm study

Anthropogenic impacts on freshwater ecosystems cause critical losses of biodiversity that can in turn impair key processes such as decomposition and nutrient cycling. Forest streams are mainly subsidized by terrestrial organic detritus, so their functioning and conservation status can be altered by changes in forest biodiversity and composition, particularly if these changes involve the replacement of functional groups or the loss of key species. We examined this issue using a microcosm experiment where we manipulated plant functional diversity (FD) (monocultures and low-FD and high-FD mixtures, resulting from different combinations of deciduous and evergreen Quercus species) and the presence of a key species (Alnus glutinosa), all in presence and absence of detritivores, and assessed effects on litter decomposition, nutrient cycling, and fungal and detritivore biomass. We found (i) positive diversity effects on detritivore-mediated decomposition, litter nutrient losses and detritivore biomass exclusively when A. glutinosa was present; and (ii) negative effects on the same processes when microbially mediated and on fungal biomass. Most positive trends could be explained by the higher litter palatability and litter trait variability obtained with the inclusion of alder leaves in the mixture. Our results support the hypothesis of a consistent slowing down of the decomposition process as a result of plant biodiversity loss, and hence effects on stream ecosystem functioning, especially when a key (N-fixing) species is lost; and underscore the importance of detritivores as drivers of plant diversity effects in the studied ecosystem processes.

Effect of sublethal concentrations of waterborne copper on lipid peroxidation and enzymatic antioxidant response in Gambusia holbrooki

The aim of the current research was to assess the possible influence of copper sulphate contamination on the antioxidant enzymatic defenses and lipid peroxidation (LPO) in the mosquitofish (Gambusia holbrooki). Quadruplicated lots of this fish were exposed to three increasing sub-lethal concentrations of Cu (0.10; 0.17 and 0.25mgCu/L) and a control without Cu for 20 days. Previous to laboratory acclimation, 8 fish were taken to define the initial population. At the end of the trials, 12 fish/sex/treatment were sampled for the determination of levels of copper in gills, metallothioneins (MTs) content, total lipids, fatty acids profiles and antioxidant enzymatic activity, as well as lipid peroxidation. Most of the antioxidant enzymatic defenses assayed were not activated and lipid peroxidation decreased significantly in fish exposed to any concentration of copper applied. This leads us to presume the existence of a protective mechanism against peroxidation other than the enzymatic antioxidant defense, which could be related to the observed increase of copper content in the gills.

Prevalence of eating disorders in a Spanish school-age population

PURPOSE

To determine the prevalence of eating disorders (anorexia nervosa, bulimia, and partial syndromes) in students in a Madrid school district during the 1993-1994 academic period. The results were compared with those of an earlier study performed in 1985-1986 and with findings in other countries.

METHODS

In the first phase, 1314 adolescents (731 girls and 583 boys) with a mean age of 15.05 +/- 0.98 years were surveyed according to the Eating Disorder Inventory (EDI) and a psychosocial data survey. Of these, 1281 (97.48%) [724 girls (99.04%) and 557 boys (95.54%)] were considered appropriate for the study. The risk population included individuals with a total EDI score over 50, plus a drive for thinness (DT) score over 10; 180 girls (24.86%) and 19 boys (3.41%) were identified on this basis. To reduce possible false negatives, those whose score on the bulimia scale was over 5, with amenorrhea of more than 3 months duration and a body mass index (weight in kilograms per height in square meters) under 18 were also considered to be at risk. The total risk population thus defined consisted of 293 adolescents (22.87%): 67 boys (12.02%) and 226 girls (31.21%). In the second phase, all risk subjects were reevaluated with a semistructured interview for ED, and they were also weighed and measured. In all, 156 adolescents (53.24%)[103 girls (45.57%) and 53 boys (79.10%)] participated in person. The remaining 137 subjects completed the interview by telephone. Diagnostic and Statistical Manual (DSM)-III-R diagnostic criteria were applied.

RESULTS

Five girls (0.69% of the total study population) fulfilled the DSM-III-R criteria for anorexia nervosa, and nine (1.24%), for bulimia nervosa. Two boys (0.36%) had bulimia. Twenty girls (2.76%) and three boys (0.54%) represented partial syndromes. The results of adding the full and partial syndromes showed that 4.7% of the girls and 0.9% of the boys had eating disorders.

CONCLUSIONS

This study demonstrates an increase in the prevalence of eating disorders in Madrid, reaching similar levels to those reported in the literature for other developed countries.