When top predators and large herbivores are weakened, the animals and plants they eat usually thrive because they're no longer actively killed. Their overpopulation, and the ripple effect throughout the ecosystem, is throwing ecosystems out of balance.
The impacts of this phenomenon on the planet include changes in soil, water, vegetation, and the atmosphere. The phenomenon also increases human contact with invasive and disease-carrying species.
The study provided the following examples:
-The reduction of lions and leopards from areas of sub-Saharan Africa caused the baboon population to swell. This unexpectedly increased transmission of intestinal parasites from baboons to humans as the primates were forced to forage closer to human settlements.
-As large ungulates recovered from a devastating rinderpest epidemic in the Serengeti in Africa, herbivory increased, and the frequency of wildfire declined in that region. Wildfire frequency increased following the late Pleistocene/early Holocene decline of megaherbivores in Australia and the northeastern United States.
-Industrial whaling in the 20th century resulted in the loss of large numbers of plankton-consuming great whales, which are now known to sequester carbon into the deep sea through deposition of feces. The result has been the transfer of approximately 105 million tons of carbon into the atmosphere that would have been absorbed by whales, contributing to climate change.
The study said previous research of ecosystems focused on species on the bottom of the food chain partly because it was easier to do so. Contrastingly, apex consumers are usually large, long-lived, and not amenable to laboratory experiments.
There is an urgent need for interdisciplinary research to forecast how a continued loss of top level consumers will further harm the planet's ecosystems, said Dr. James A. Estes of University of California at Santa Cruz, the lead author of the paper.
It was co-authored by Dr. Ellen K. Pikitch of the Institute for Ocean Conservation Science at Stony Brook University.