Large herbivores favour species diversity but have mixed impacts on phylogenetic community structure in an African savanna ecosystem

There has been much debate on the impact of large herbivores on biodiversity, especially given that large mammals are becoming locally extinct in many places. The use of evolutionary information on community structure has typically been limited to evaluating assembly processes, for example, competition or habitat filtering, whereas a lack of long-term experiments has precluded the test of predictions considering more complex biotic interactions. Reconstructing the complete phylogeny of the trees and shrubs of the Kruger National Park from DNA data, we tested for phylogenetic signal in antiherbivory traits and compared the phylogenetic structure of communities under various degrees of herbivore pressure using experimental plots spanning several decades. We show that all antiherbivory traits examined demonstrated weak but significant phylogenetic signal, and that exclusion of large herbivores results in impoverished species diversity in restructured communities. Surprisingly, we also show that reduction in species diversity coupled with community reorganization does not necessarily result in a decrease in phylogenetic diversity, and that community responses to herbivore exclusion depend on initial structure. Synthesis. Extinction of large mammal herbivores will have cascading effects on plant diversity; however, impacts on plant community structure are contingent on initial conditions. This research has implications for best practice when managing large herbivores and natural habitats. Extinction of large mammal herbivores will have cascading effects on plant diversity; however, impacts on plant community structure are contingent on initial conditions. This research has implications for best practice when managing large herbivores and natural habitats.