Destructive primate-palm interactions: predation by capuchin monkeys causes local extinction of a vulnerable palm species

Abstract

Defaunation causes the loss of top predators, increases the abundance of herbivores, and has impacts on plant populations. Forest herbivores commonly consume small plant individuals, reducing regeneration. Yet, some herbivores target large, reproductive individuals, with potentially more detrimental demographic consequences. In Atlantic Forest fragments in Brazil, abundant capuchin monkeys ( Sapajus nigritus ) consume the apical meristem of mature Juçara palms ( Euterpe edulis ), inflicting adult mortality of this vulnerable palm species. Utilizing four years of demographic monitoring of Juçara palms in four populations differing in monkey predation, we constructed Integral Projection Models to assess the effects of herbivory. Populations experiencing more intense predation exhibited consistent declines, with population growth rate (λ) ranging from 0.6 (95% CI: 0.5740–0.6340) to 0.9 (95% CI: 0.8921–0.9159), the lowest λ (λ = 0.6042 and λ = 0.6396) values were observed in the most intensively predated populations. The size structures of the most impacted populations become dominated by smaller-sized individuals, as the large ones are decimated. Projections for the future of these populations indicate local extinction, where the population size reaches zero, within 15 years. Such low population growth rates are unprecedented in the studies on demographic effects of herbivory and predation, showcasing the possible dramatic impacts of multi-trophic interactions. Although capuchin monkeys are a native species that can thrive in the defaunated and deforested context of the Atlantic Forest, their foraging behavior threatens an already vulnerable palm species. These impacts extend further than the palm populations because Juçara fruits are a key resource for frugivorous species in certain communities in the Atlantic Forest.