The Sixth Extinction
The dinosaurs didn’t know it was coming. We do.
While life has existed on Earth for 3.5 billion years, the first animals only evolved 540 mya (million years ago). Since then, there have been five major extinction events. An extinction event is an engulfing global death wave that snuffs out most of Earth’s plant and animal species. It occurs when the extinction rate dramatically exceeds the speciation rate (the formation of new species).
The last mass extinction ended the reign of the dinosaurs and the existence of 75% of all other plant and animal species on Earth. However, that was 65 million years ago, before the rise of Man and the start of the current extinction. Today, we live through the 6th biodiversity crisis, the Anthropocene. It is the only mass extinction resulting from a single species – Homo sapiens.
Early humans established themselves as the ultimate global superpredator, preying on large groups of marine and terrestrial apex predators alike. With our colonization of the world, the biodiversity of large animals began to plummet. The biodiversity of a region refers to the variety and variability of native plants and animals within the ecosystems of that region.
It encompasses the number of species, population density and genomics, and interactions within biological communities and the environment. The health of an ecosystem is directly linked to its biodiversity because biological interactions act like threads in food chains and webs to create an interconnected life-sustaining balance. The extinction of a single species causes ecological imbalances throughout its ecosystem, resulting in the ‘co-extinction’ of other species.
For example, when gray wolves were exterminated from Yellowstone National Park, the population of their main prey species – the elk exploded. Overpopulation of elk resulted in extreme overgrazing of willow and aspen trees and other plant life that support riverbanks. As a result, rivers widened, and the water temperature increased, impacting fish, amphibians, and reptiles.
Beavers use the branches of the same trees the elk feeds on to build dams that create wetland habitats utilized by many species. The reintroduction of wolves as apex predators has stabilized the elk population and as a result, riverine plant life and animal populations (e.g. beaver & songbirds) have recovered. The remains from wolf kill provide food for bald – and golden eagles, sustaining their populations through winter.
The biodiversity of Earth is unevenly distributed in species-rich hotspots, the majority of which lies within forest ecosystems and the tropics.
A biodiversity hotspot is a region with a variety of unique ecosystems, an extraordinary number of species, and a high level of endemic species (found only in a single region) that have suffered habitat loss.
For example, over 95% of Madagascar island’s amphibians, reptiles, and mammals are endemic species; of these, 166 species are critically endangered. The Atlantic forest of South America has lost over 85% of its original area, and 40% of plants and 60% of vertebrate species that live in the Atlantic forest are endemic.
Biodiversity hotspots cover just 2.4% of the planet’s surface but are home to 60% of the world’s terrestrial animal species. In essence, biodiversity hotspots are the last safe havens for many wild animals and must be conserved.
The living organisms of Earth are extraordinary because of their diversity. Approximately 9 million different species inhabit the Earth; however, this number is steadily dropping. Extinction rates have accelerated in the 21st century to an estimated 1000x greater rate than the rate of natural extinction due to human population growth, overconsumption, and habitat degradation.
Since 1970, wildlife populations across the globe have been decimated by 68%. Migratory fish populations have declined by 76% since 1970, and freshwater’ megafish’ populations have fallen by 94%. Currently, 1 in 4 of the world’s mammals, 1 in 6 bird species, and 40% of amphibians are at risk of extinction.
In 1992, the first Earth Summit was held because human actions were dismantling the Earth’s ecosystems, eliminating genes, species, and biological traits at an alarming rate. We are the undeniable cause of the 6th mass extinction, but if we reduce anthropogenic pressures and manage resources wisely, in time, the diversity of our natural world will recover.
The best time to act has passed, but we might not be too late if we act now.