Biodiversity is the variability of life on Earth, a concept that encompasses the totality of genes, species, and ecosystems within a region. It is not merely a count of animals and plants but a complex web of genetic variability, species diversity, ecosystem diversity, and phylogenetic diversity. This variability is not distributed evenly across the globe; instead, it follows a distinct pattern known as the latitudinal gradient, where diversity increases from the poles toward the equator. Tropical forest ecosystems, which cover less than one-fifth of Earth's terrestrial area, contain about 50% of the world's species, creating a stark contrast with the polar regions. The warm climate and high primary productivity near the equator drive this concentration of life, making these regions the engine of global biological variety. The study of this spatial distribution is the science of biogeography, which reveals how temperature, precipitation, altitude, and soil interact to shape the living world. Even within these hotspots, local factors create unique pockets of life, such as the Cape Floristic Region or the rainforests of Yasuní National Park in Ecuador, which have maintained wet climates for millions of years, fostering an extraordinary density of species.
Echoes of Extinction
Since life began on Earth, the history of biodiversity has been punctuated by six major mass extinctions and several minor events that led to large and sudden drops in life forms. The Phanerozoic aeon, spanning the last 540 million years, marked a rapid growth in biodiversity via the Cambrian explosion, a period during which the majority of multicellular phyla first appeared. However, the next 400 million years included repeated, massive biodiversity losses classified as mass extinction events. The worst of these was the Permian, Triassic extinction event, which occurred 251 million years ago, causing vertebrate recovery to take 30 million years. Another significant loss occurred when rainforests collapsed in the Carboniferous, leading to a great loss of plant and animal life. The most recent major mass extinction event, the Cretaceous, Paleogene extinction event, occurred 66 million years ago, resulting in the extinction of the dinosaurs and many marine taxa such as ammonites. These events have shaped the evolutionary trajectory of life, creating periods of diversification followed by periods of recovery and reorganization. The fossil record suggests that the last few million years featured the greatest biodiversity in history, though some scientists argue that corrected for sampling artifacts, modern biodiversity may not be much different from biodiversity 300 million years ago.The Sixth Mass Extinction
Human activities have led to an ongoing biodiversity loss and an accompanying loss of genetic diversity, a process often referred to as the Holocene extinction or the sixth mass extinction. It was estimated in 2007 that up to 30% of all species will be extinct by 2050, with about one eighth of known plant species threatened with extinction. The rate of species loss is greater now than at any time in human history, with extinctions occurring at rates hundreds of times higher than background extinction rates. As of 2012, some studies suggest that 25% of all mammal species could be extinct in 20 years. In absolute terms, the planet has lost 58% of its biodiversity since 1970 according to a 2016 study by the World Wildlife Fund. The Living Planet Report 2014 claims that the number of mammals, birds, reptiles, amphibians, and fish across the globe is, on average, about half the size it was 40 years ago. Biodiversity took the biggest hit in Latin America, plummeting 83 percent, while high-income countries showed a 10% increase in biodiversity, which was canceled out by a loss in low-income countries. This disparity highlights how wealthy nations are outsourcing resource depletion to poorer nations, which are suffering the greatest ecosystem losses. A 2017 study published in PLOS One found that the biomass of insect life in Germany had declined by three-quarters in the last 25 years, suggesting that humans are making vast tracts of land inhospitable to most forms of life.