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[QUOTE]Originally posted by DD'eDeN: [QB] Spiny plants, mammal browsers, and the origin of African savannas Tristan Charles-Dominique cs 2016 PNAS doi 10.1073/pnas.1607493113 Africa hosts contrasting communities of mammal browsers: it is the ideal background for testing their effect on plant communities & evolution. In this study at the continental scale, we reveal which mammal browsers are most closely associated with spiny communities of trees. We then show a remarkable convergence between the evolutionary histories of these browsers (the bovids) & spiny plants. Over the last 16 Ma, plants from unrelated lineages developed spines 55 times. These convergent patterns of evolution suggest that the arrival & diversification of bovids in Africa changed the rules for persisting in woody communities. Our data suggest that browsers predate fire by millions of years as agents driving the origin of savannas. Savannas first began to spread across Africa during the Miocene. A major hypothesis for explaining this vegetation change is the increase in C4 grasses, promoting fire. Did mammals contribute to savanna expansion, by using spinescence as a marker of mammal herbivory? Looking at the present distribution of 1852 tree spp, we established that spinescence is associated with 2 functional types of mammals: - large browsers & - medium-sized mixed feeders. Using a dated phylogeny for the same tree spp, we found that spinescence evolved at least 55 times. The diversification of spiny plants - occurred long after the evolution of Afrotherian proboscideans & hyracoids, - is remarkably congruent with diversification of bovids (incl.the antelope that predom.browse these plants today). Our findings suggest that herbivore-adapted savannas evolved several million years before fire-maintained savannas, probably in different environments: - Spiny savannas with abundant mammal herbivores occur in drier climates & on nutrient-rich soils. - Fire-maintained savannas occur in wetter climates on nutrient-poor soils. - - - Afrotherians = elephants etc. are native to Africa. Antelopes etc. are not from Africa, they moved in after the tectonic plate collision of Africa and EurAsia, along with many other taxa. I claim that Homo sapiens originated in the tropical rainforest belt, mainly living along feeder streams (shallow tributaries which flowed into larger rivers or coastal estuaries) that did not have large predators (except leopards, which KhoiSan claim are the most dangerous animals to humans). Today's Congo Pygmies live in this way, choosing to camp in small forest openings which are surrounded by thickets (which grow fast when large old trees are felled by high winds above the canopy, same in temperate forest - blackberry thickets full of thorns grow quickly). While rainforest soils are generally poor in nutrients and are kept constantly moist, forest openings created by fallen trees are microclimates which have relatively rich soil (temporarily) and sun-dried surface, encouraging 'micro-savanna' conditions desirable to forest antelope seeking low-hanging foliage to browse. Similarly, in temperate forests that are logged, deer quickly invade to browse on the fallen vegetation and the new ground growth. DDeden [/QB][/QUOTE]
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