Apex Predators—Lions and Wolves and Sharks, Oh My!
We often hear of large predators both on land and in water—like bears, lions, killer whales and sharks. But what does ‘apex’ predator mean? It simply means that these animals are at the top of the food chain and they have no natural predators—they are the top dogs in their environment. (Of course, until humans came along and changed the game)
Interactions between species at different levels of the food chain are called ‘trophic’ interactions—and altering one part of the food chain can affect plants and animals at other trophic levels.
Aside from being featured as the majestic, often terrifying villains in many movies (think, Jaws), these apex predators are actually essential for the health of the ecosystems that they live in. Here’s why:
1. They keep mesopredator populations under control.
In 2014, the IUCN (International Union for Conservation of Nature) determined that a quarter of the world’s sharks are threatened with extinction. Why? Primarily due to overfishing. As shark populations decline, their prey (also known as mesopredators, or medium-sized predators) including smaller sharks, rays and some marine mammals, increase. In turn, the mesopredators' prey, such as smaller fish, shellfish and other invertebrates—many which are important fisheries for humans—decrease.
2. Apex predators indirectly influence their prey’s habitat use— their prey adapt their lifestyles to avoid getting eaten by the big guys, so they have special feeding and foraging strategies. For example, zebra must focus on not getting eaten by lions, so they move from place to place and can’t spend all their time leisurely overgrazing vegetation in the open. This determines how these animals use the land/sea, which is crucial to the maintaining a balanced state of the natural environment.
3. Ultimately, the decline in an apex predator can lead to collapses in entire ecosystems. Here is an example:
Perhaps one of the most well-known examples of a trophic cascade is the story about wolves in Yellowstone. About 100 years ago, people hunted all the wolves in Yellowstone, resulting in their complete disappearance. As a result, elk populations skyrocketed in absence of their main predator, the wolf. Previously, the elk wouldn’t spend much time by the river because there they were exposed to the wolves’ predation. But without the wolves, the elk spent a lot of time drinking water and grazing along the river, which resulted in the erosion of the river banks. The water where fish thrived became muddled with sediment. The elk continued to overgraze the land, eating young willow, aspen and cotton plants. Grizzly bears had fewer berries to eat. Without the willow, songbirds lost their habitats and beavers lost their main source of lumber to build their dams. No dams? Fish, otters and amphibians suffer even more. All of this simply due to the disappearance of one top predator.
In 1995, 41 wolves were reintroduced into Yellowstone, to restore the natural balance of the ecosystem. Now the elk populations have leveled off, there are more trees, cleaner water, dams built by beavers again, more fish, more grizzly bears, more songbirds, etc.
Unfortunately, the science of ecological interactions is not as simple as I am alluding to. As you can see with the example of Yellowstone, it is hard to fully predict the large-scale effects of removing or adding one predator to an ecosystem— food webs and trophic interactions are incredibly complicated.
Which is why perhaps the most important lesson is: affecting one level of the food chain can have a huge ripple effect on the whole ecosystem. Our role as humans—as these ‘super apex predators’ that we have become—have been shown to have profound impacts on the environment, as we wipe out species at lower trophic levels. The effects are cascading and alarming. But we have also seen that ecosystems can recover—if we stop overfishing, overhunting and let the natural world rebound.
Trophic interactions are fascinating, complex and indubitably important to the health of the environment and the livelihood of our own species. And while you might be afraid of seeing a shark while surfing or running into a bear while hiking—hopefully now you have a greater appreciation for these amazing animals that keep the environment thriving.
Cheers,
AT
Sources:
https://www.iucn.org/content/quarter-sharks-and-rays-threatened-extinction
https://www.yellowstonepark.com/things-to-do/wolf-reintroduction-changes-ecosystem
https://www.nationalgeographic.org/media/wolves-yellowstone/
https://themysteriousworld.com/top-9-apex-predators/
Really interesting article:
https://www.conservationmagazine.org/2015/08/what-made-humans-into-global-super-predators/