Spiny plants, mammal browsers, and the origin of African 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. We investigated whether mammals could also have contributed to savanna expansion by using spinescence as a marker of mammal herbivory. Looking at the present distribution of 1,852 tree species, we established that spinescence is mainly associated with two functional types of mammals: large browsers and medium-sized mixed feeders. Using a dated phylogeny for the same tree species, we found that spinescence evolved at least 55 times. The diversification of spiny plants occurred long after the evolution of Afrotherian proboscideans and hyracoids. However, it is remarkably congruent with diversification of bovids, the lineage including the antelope that predominantly browse these plants today. Our findings suggest that herbivore-adapted savannas evolved several million years before fire-maintained savannas and probably, in different environmental conditions. Spiny savannas with abundant mammal herbivores occur in drier climates and on nutrient-rich soils, whereas fire-maintained savannas occur in wetter climates on nutrient-poor soils.
Department of Biological Sciences, University of Cape Town, Rondebosch 7701, South Africa; Department of Botany and Zoology, Stellenbosch University, Matieland 7602, South Africa; tristancd1@gmail.com william.bond@uct.ac.za.
Tristan
T
Charles-Dominique
African Centre for DNA Barcoding, Department of Botany and Plant Biotechnology, University of Johannesburg, Johannesburg 2006, South Africa; Department of Biology, McGill University, Montreal, QC, H3A 0G4 Canada;
T Jonathan
TJ
Davies
School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits 2050, South Africa;
Gareth P
GP
Hempson
African Centre for DNA Barcoding, Department of Botany and Plant Biotechnology, University of Johannesburg, Johannesburg 2006, South Africa;
Bezeng S
BS
Bezeng
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138; Department of Plant Sciences, University of Pretoria, Pretoria 0028, South Africa;
Barnabas H
0000-0002-2115-0257
BH
Daru
African Centre for DNA Barcoding, Department of Botany and Plant Biotechnology, University of Johannesburg, Johannesburg 2006, South Africa;
Ronny M
RM
Kabongo
African Centre for DNA Barcoding, Department of Botany and Plant Biotechnology, University of Johannesburg, Johannesburg 2006, South Africa;
Olivier
O
Maurin
Department of Biological Sciences, University of Cape Town, Rondebosch 7701, South Africa;
A Muthama
AM
Muasya
African Centre for DNA Barcoding, Department of Botany and Plant Biotechnology, University of Johannesburg, Johannesburg 2006, South Africa;
Michelle
M
van der Bank
Department of Biological Sciences, University of Cape Town, Rondebosch 7701, South Africa; South African Environmental Observation Network, National Research Foundation, Claremont 7735, South Africa tristancd1@gmail.com william.bond@uct.ac.za.
William J
WJ
Bond
D000349:Africa; D000818:Animals; D017753:Ecosystem; D005390:Fires; D065948:Grassland; D060434:Herbivory / Q000235:genetics; D008322:Mammals; D010802:Phylogeny; D010944:Plants / Q000235:genetics*; D006109:Poaceae / Q000235:genetics / Q000254:growth & development*; D012987:Soil
D012987:Soil
Africa; Bovidae; coevolution; mammalian herbivory; savanna