An apex predator is a predator (usually a carnivorous animal) at the top of a food chain that normally has no natural enemies of its own in that ecosystem. It occupies the highest trophic level in its food web.
Apex predators are often considered keystone species because their influence on ecosystems is far greater than their numbers suggest. By controlling prey populations and affecting the balance of species in their habitat, they stabilize ecosystems and prevent overgrazing or unchecked predation lower in the food chain. Their presence balances species interactions and helps maintain healthy, resilient environments.
On land, apex predators include wolves, lions, leopards, tigers and large birds of prey such as eagles. In the oceans, killer whales (orcas), great white sharks, and other large predatory sharks fulfill similar roles, keeping the population sizes of prey and other predator species in check.
By limiting the most abundant prey species and removing weak and sick individuals, apex predators support biodiversity and reduce the spreading of disease. Their victims also feed scavengers and enrich soils, creating nutrient hotspots that promote plant growth and a diversity of plant and animal species in the area. Through these processes, apex predators indirectly sustain the diversity and productivity of entire ecosystems.
Removing apex predators typically disrupts ecosystems, leading to surges in the prey population, habitat damage and biodiversity loss. Without them, herbivores may multiply and overbrowse vegetation, thinning plant cover, eroding soils, and degrading habitats for many species.
These disruptions can set off trophic cascades in which rapidly increasing numbers of prey and mid-sized predators reshape food webs, alter nutrient cycles and destabilize entire ecosystems. Overcrowded prey populations without natural predators often grow stressed and malnourished, increasing disease and mortality while reducing overall ecosystem health.
One of the best-known examples occurred in Yellowstone National Park in the U.S. After wolves were eliminated by 1926, elk overbrowsed riparian (adjacent to rivers, ponds, etc.) areas, reducing tree and shrub growth and degrading habitats for beavers, birds and aquatic species. The resulting habitat loss diminished shade, root stability, and wetland formation, affecting everything from amphibians to scavengers.
After wolves were reintroduced in 1995, the Yellowstone ecosystem began to recover. Elk became more mobile, allowing willows, aspens and cottonwoods to regenerate. This vegetation growth supported the return of beavers and birds and restored stream habitats. As beaver dams created ponds and slow-water zones, amphibians and fish also increased in abundance and diversity, reflecting a renewed ecological equilibrium.