The current rate of species loss has significantly accelerated over the past century. This rapid decline raises concerns about the health of ecosystems and the planet’s biodiversity. Exploring the animals that have vanished in the last 100 years reveals a pattern of profound environmental change and highlights the impact of human activities on the natural world.
Defining Recent Extinction
In biology, extinction refers to the permanent disappearance of a species. It occurs when a species can no longer adapt to environmental changes. While extinction is a natural part of evolution, the “last 100 years” timeframe is notable because it largely reflects extinctions driven by human influence. The current rate of human-induced extinctions is estimated to be significantly higher than natural background rates.
Notable Extinction Cases
The last century has witnessed the loss of numerous animal species, each with a unique story of decline. These extinctions span various taxonomic groups, illustrating the widespread nature of the biodiversity crisis.
The thylacine, also known as the Tasmanian tiger, was a carnivorous marsupial native to mainland Australia, New Guinea, and Tasmania. The last known individual died in captivity at Hobart Zoo on September 7, 1936, though the species was officially declared extinct in 1986. Overhunting, driven by bounty systems established due to perceived threats to livestock, was a primary factor in its demise. Habitat destruction and introduced diseases also contributed to its population decline.
The Caribbean monk seal, once abundant in the Caribbean Sea, was last sighted in 1952 at Serranilla Bank. It was officially declared extinct in 2008 after extensive searches found no evidence of its survival. Overhunting for oil and meat by European explorers and settlers, coupled with overfishing of its primary food sources, were the main reasons for its disappearance. The seals’ docile nature made them easy targets for hunters.
The golden toad, a small, brightly colored amphibian, was endemic to a cloud forest region in Monteverde, Costa Rica. This species was last observed in May 1989, and the International Union for Conservation of Nature (IUCN) declared it extinct in 2004. Its rapid disappearance is largely attributed to climate change, which altered the delicate balance of its cloud forest habitat by reducing mist levels and rainfall. The emergence of chytrid fungus, a pathogen affecting amphibians globally, also likely played a role.
The Baiji, or Yangtze River dolphin, was a freshwater dolphin unique to the Yangtze River system. It was the first dolphin species declared functionally extinct due to human activities, in 2007, after surveys found no individuals. Its population plummeted due to intense fishing pressure, particularly bycatch in methods like rolling hook long-lines and electric fishing, which was outlawed but continued. Increased shipping traffic, noise pollution, and extensive habitat degradation from industrial development further impacted the species.
Underlying Causes of Loss
The extinctions observed over the last century are largely a consequence of several interconnected human-induced factors. These drivers exert immense pressure on animal populations, pushing them beyond their capacity to adapt and survive.
Habitat destruction and fragmentation stand as the leading causes of biodiversity loss. As human populations expand, natural landscapes are converted for agriculture, urbanization, and resource extraction, directly eliminating animal habitats. This process isolates remaining populations, making them more vulnerable to other threats.
Overexploitation, including unsustainable hunting and fishing, has directly decimated numerous species. Historically, commercial interests have driven intense harvesting of animals for their meat, oil, or other products, without considering sustainability. This pressure can rapidly deplete species, especially those with slow reproductive rates or those easily targeted.
The introduction of invasive species poses a significant threat to native wildlife. Non-native organisms, introduced to new environments, can outcompete native species for resources, prey upon them, or introduce new diseases. Native species often lack defenses against these invaders, leading to steep population declines and sometimes extinction.
Pollution from industry, agriculture, and waste contaminates air, water, and soil, creating toxic environments for animals. Chemicals like pesticides and industrial waste disrupt ecosystems, impairing animal health, reproduction, and survival. This widespread contamination can weaken immune systems and accumulate in food chains, affecting top predators.
Climate change is a major driver of extinctions. Rising global temperatures alter habitats, shift climatic conditions, and increase the frequency of extreme weather events. Many species struggle to adapt to these rapid changes or migrate to suitable new areas, leading to reduced ranges and increased vulnerability.
Confirming Extinction
Officially declaring a species extinct is a rigorous scientific process, often overseen by organizations like the IUCN. It involves evaluating comprehensive data and evidence to determine if any living individuals remain. Scientists typically conduct extensive, systematic surveys of known and potential habitats over many years.
Despite thorough efforts, confirming extinction presents significant challenges. Species in remote or inaccessible areas may evade detection, leading to prolonged uncertainty. The “Lazarus effect” describes rare instances where species presumed extinct are unexpectedly rediscovered, though these cases are exceptional. Genuine extinctions represent an irreversible loss of biodiversity.