Change in dominance determines herbivore effects on plant biodiversity.

Herbivores alter plant biodiversity (species richness) in many of the world's ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet, empirical support for the importance of site productivity as a mediator of these herbivore impacts is equivocal. Here, we synthesize data from 252 large-herbivore exclusion studies, spanning a 20-fold range in site productivity, to test an alternative hypothesis-that herbivore-induced changes in the competitive environment determine the response of plant biodiversity to herbivory irrespective of productivity. Under this hypothesis, when herbivores reduce the abundance (biomass, cover) of dominant species (for example, because the dominant plant is palatable), additional resources become available to support new species, thereby increasing biodiversity. By contrast, if herbivores promote high dominance by increasing the abundance of herbivory-resistant, unpalatable species, then resource availability for other species decreases reducing biodiversity. We show that herbivore-induced change in dominance, independent of site productivity or precipitation (a proxy for productivity), is the best predictor of herbivore effects on biodiversity in grassland and savannah sites. Given that most herbaceous ecosystems are dominated by one or a few species, altering the competitive environment via herbivores or by other means may be an effective strategy for conserving biodiversity in grasslands and savannahs globally.

Evaluation of in vitro Antioxidant Activities of Ethanol Extracts of Datura innoxia Mill. Leaves and Seeds Harvested in Mali

Aims: The purpose of this study was to evaluate the in vitro antioxidant activities of Datura innoxia Mill. leaves and seeds harvested in Mali. Place and Duration of Study: Collection of plant materials were done at Kolondieba (Mali) in june 2016. Evaluation of polyphenols and flavonoids contents, determination of antioxidant activities were done at Laboratory of Plant and Food Biochemistry and Biotechnology of University of Sciences, Techniques and Technologies of Bamako (Mali) between august 2016 and March 2017. Methodology: The leaves and seeds were collected in Kolondieba, Mali. The phytochemical screening based on the standard methods of tube reactions has been performed with ethanol extracts. The quantitative estimation of total polyphenols was made by the Folin-Ciocalteu method and that of flavonoids by the use of aluminum trichloride. The in vitro antioxidant activities of the ethanol extracts was determined by three methods: the 1,1- diphenyl - 2- picrylhydrazyl (DPPH) test, the ferric reducing ability power (FRAP) test and the Phosphomolybdate test (PPM). Results: The phytochemical screening revealed that leaves and seeds of this plant contains alkaloids, polyphenols, flavonoids, coumarins, tannins, triterpenes and saponin. Phenolic contents of ethanol extracts are 30.97 ± 0.33 mg equivalent gallic acid / g in leaves and 14.02 ± 0.15 mg equivalent gallic acid / g in seeds; those of flavonoids are 15.13 ± 0.2 mg equivalent of quercetin / g in the leaves and 4.93 ± 0.41 mg equivalent of quercetin / g in the seeds. The three tests showed that the leaves have a higher level of antiradical activity in vitro than seeds. Conclusion: The results of this work showed that Datura innoxia Mill. has a good antioxidant activity which would justify its use as a potential source of natural antioxidants.