Impacts of large herbivores on spinescence and abundance of palms in the Pantanal, Brazil

Abstract

South America harboured a rich megafauna for millions of years, but most of it was lost during the latest Pleistocene and early Holocene. However, human-introduced livestock is a potential partial ecological replacement, with livestock having been present in many areas of the Brazilian Pantanal for > 200 years. We tested the impact of cattle on spinescence and abundance of four common palm species (three armed: Acrocomia aculeata, Bactris glaucescens, Copernicia alba; one unarmed: Attalea phalerata), comparing areas with cattle to areas free of cattle for 30 years. We measured spine length and density on leaves and stems and the abundances of different life stages. In all armed species, leaf spine length and density increased with cattle presence, suggesting strong responses to megafauna herbivory by increasing investment in anti-herbivory defence. Weaker non-significant trends were observed for stem spinescence, perhaps reflecting a lower susceptibility of stems to herbivore damage. In three of four species, the abundances of seedlings and juveniles (but not adults) were reduced in areas with cattle. We conclude that armed palm species have most probably retained an adaptive capacity to respond to megafauna herbivory and trampling despite the extinction of native megafauna. Nevertheless, livestock at high densities can still have negative impacts on palm recruitment.