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The unresolved question of what causes the observed positive relationship between large-scale productivity and species richness has long interested ecologists and evolutionists. Here we examine a potential explanation that we call the biogeographic affinity hypothesis, which proposes that the productivity-richness relationship is a function of species' climatic tolerances that in turn are shaped by the earth's climatic history combined with evolutionary niche conservatism. Using botanical data from regions and sites across California, we find support for a key prediction of this hypothesis, namely, that the productivity-species richness relationship differs strongly and predictably among groups of higher taxa on the basis of their biogeographic affinities (i.e., between families or genera primarily associated with north-temperate, semiarid, or desert zones). We also show that a consideration of biogeographic affinity can yield new insights on how productivity-richness patterns at large geographic scales filter down to affect patterns of species richness and composition within local communities.

Fire and herbivory are important determinants of nutrient availability in savanna ecosystems. Fire and herbivory effects on the nutritive quality of savanna vegetation can occur directly, independent of changes in the plant community, or indirectly, via effects on the plant community. Indirect effects can be further subdivided into those occurring because of changes in plant species composition or plant abundance (i.e., quality versus quantity). We studied relationships between fire, herbivory, rainfall, soil fertility, and leaf nitrogen (N), phosphorus (P), and sodium (Na) at 30 sites inside and outside of Serengeti National Park. Using structural equation modeling, we asked whether fire and herbivory influences were largely direct or indirect and how their signs and strengths differed within the context of natural savanna processes. Herbivory was associated with enhanced leaf N and P through changes in plant biomass and community composition. Fire was associated with reduced leaf nutrient concentrations through changes in plant community composition. Additionally, fire had direct positive effects on Na and nonlinear direct effects on P that partially mitigated the indirect negative effects. Key mechanisms by which fire reduced plant nutritive quality were through reductions of Na-rich grasses and increased abundance of Themeda triandra, which had below-average leaf nutrients.

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Antioxidants are vital substances that have an ability to protect the body from various damages caused by free radical-induced oxidative stress. Plants are the source of a wide variety of natural free radical scavenging antioxidants. The objective of the present study is to carry out in vitro antioxidant tests to evaluate the antioxidant ability of Methanolic extracts of selected mangrove plans i.e., Aegiceras corniculatum, Excoecaria agallocha and Lumnitzera racemosa. In this study, In vitro antioxidant activity was estimated by assays like DPPH, Reducing power assay and total antioxidant activity methods. The in vitro antioxidant studies revealed that, the extract of Lumnitzera racemosa has the highest phenolic content (38.80 ± 0.19 µg GAE/ 100 µg) and highest antioxidant potential. This is followed by Aegiceras corniculatum (24.06 ± 0.79 µg GAE/100 µg) and, Excoecaria agallocha (20.56 ± 0.58 µg GAE/100 µ). This study provides the preliminary data that can pave the way for further studies to validatee their medicinal uses and focus on bioassay guided fractionation and isolation of active compounds from the extracts.