A large number of studies show that apex predators such as pumas fulfill fundamental functions of the ecosystems they inhabit. Apex predators help to maintain the abundance and diversity of mammals, birds, reptiles, and invertebrates, in some cases regulating the populations of herbivores, which would otherwise overgraze vegetation, leading to a simplification of the landscape. Grazing intensity can be controlled by decreasing the number of herbivores by predation (trophic cascades). This includes the herbivores’ behavior, as they avoid grazing in areas where they could more easily be hunted. These types of trophic cascades are called “behavior-mediated.” For example in the Andes mountain range in San Juan, Argentina, vicuñas avoid certain areas where the risk of being preyed upon by pumas is high. In these areas, the vegetation prospers and the grasses produce more biomass and seeds, with potential beneficial effects on organisms such as small mammals, birds, and insects who seek shelter and food in this well-preserved vegetation.
Apex predators also regulate the populations of medium-sized predators. When apex predators disappear a phenomenon known as mesopredator release occurs: medium-sized predators such as foxes, Geoffroy’s cats, raccoons, and coatis proliferate the the absence of large carnivores such as pumas and jaguars, applying tremendous predation pressure on their prey, some of which may even disappear. For example, it has been suggested that in Iberá the absence of the jaguar led to the increase in fox population, which over-predated grassland bird nests, such as those of the strange-tailed tyrant.
In addition, apex predators subsidize other animals’ diets, as with scavengers. In areas of the Andes with little human impact, condors feed in large part on the carcasses of vicuñas and guanacos that have been hunted by pumas. Without the availability of carrion, the condor could not subsist, or its population numbers would decline.
At the same time, apex predators are involved in limiting the spread of pathogens, such as viruses and bacterias, and thereby, the diseases they cause. In the eastern United States, the disappearance of apex predators such as pumas and wolves has led to an increase in the coyote population and therefore a decrease in the amount of their prey, including foxes. At the same time, the decreased number of foxes has led to an overproliferation of small mammals that are hosts to the ticks that cause Lyme disease in humans, which can be fatal.
Apex predators’ effect on the trophic cascade also increases vegetation and soil carbon sequestration, and therefore helps to mitigate global climate change. Moose predation by wolves in the northern forests of North America reduces the rate at which the vegetation is grazed. Therefore, trees fix more carbon through photosynthesis and the dead leaves fall to the ground, where microbial activity is slow due to low temperatures. In this way, the organic material decomposes slowly and the carbon is stored in the ground rather than returning to the atmosphere.
It is evident that recovering ecologically effective densities of apex predators is essential to maintain the structure and functioning of ecosystems and to cope with the three major climate crises ravaging the earth, which are biodiversity loss, the emergence of pandemics, and global climate change. It is therefore clear that we must undertake every necessary effort to restore and maintain apex predator populations in their respective habitats.
