Forest fragmentation and defaunation drive an unusual ecological cascade: Predation release, monkey population outburst and plant demographic collapse

摘要

Anthropogenic habitat fragmentation combined with differential defaunation triggers complex trophic cascades. Here we test a Fragmentation-Defaunation Cascade Hypothesis by examining how a medium-sized monkey population outbreak, occurring in a predator-free forest fragment, lead to the decline of a dominant plant. We computed long-term population dynamics of Euterpe edulis ("palmito") plants in a Brazilian Atlantic Forest landscape, where the palmito predator, capuchin monkey, becomes hyper-abundant in fragments devoid of monkey predators. Palmito plants (N = 1193) were marked and measured to define stage (height and diameter) categories in 2005, and then annually censused (2006-2015). Newly recruited plants within plots were marked and monitored throughout the 10-year period. Lefkovitch matrices for each transition year, population growth rate (lambda), elasticity, and plant stage distribution showed a strong trend of demographic decline due to monkey lethal consumption of palm hearts. Indeed, lambda calculations revealed that, by the end of the study period, palmito population was decreasing by 34% annually. A major shift in plant stage distribution occurred, in which the population became increasingly dominated by infants, while reproductives continuously declined, indicating that palmito will soon become extinct in this predator-free fragment. We conclude that differential defaunation in a forest fragment resulted insmalland medium-sized mammal outbreaks negatively impacting the demography of a previously dominant host plant population. We posit that fragmentation-selective defaunation can disrupt animal communities, driving cascading effects which include plant demographic collapse and, potentially, severely altered forest community structure.