8.10 Extinction

Extinction shapes biodiversity by removing less adapted species and allowing others to thrive. Natural causes like climate change and asteroid impacts, as well as human activities like habitat destruction, drive species to extinction. This process has occurred throughout Earth's history.

Mass extinctions, like the one that wiped out the dinosaurs, dramatically reshape life on Earth. Today, we're facing a biodiversity crisis called the Sixth Mass Extinction, driven by human activities. Conservation efforts aim to slow this trend and protect vulnerable species.

Extinction and Biodiversity

The Role of Extinction in Shaping Biodiversity

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• Extinction terminates a species lineage due to the death of the last individual organism of that species
• Extinction occurs gradually or rapidly depending on environmental pressures and the species' ability to adapt
• Extinction is a natural process that has occurred throughout Earth's history, shaping the diversity and distribution of life over time
• Background extinction refers to the continuous low rate of species extinctions
• Mass extinctions are relatively short periods of geologic time during which a high percentage of species go extinct
• Extinction plays a crucial role in the evolution of life by removing less adapted species and allowing better-adapted species to thrive and diversify (survival of the fittest)

Causes of Extinction

Natural Causes of Extinction

• Climate change alters habitats and environmental conditions, forcing species to adapt, migrate, or face extinction
• Volcanic eruptions can cause widespread habitat destruction and alter atmospheric composition (Siberian Traps, Deccan Traps)
• Asteroid impacts can trigger global environmental changes and mass extinctions (Chicxulub asteroid impact)
• Disease outbreaks can decimate populations and lead to extinctions (amphibian chytridiomycosis)
• Competition from other species can lead to the decline and extinction of less adapted species (Neanderthals outcompeted by Homo sapiens)

Anthropogenic Causes of Extinction

• Habitat loss and fragmentation due to human land use changes are major drivers of species extinctions (deforestation, urbanization, agriculture)
• Overexploitation through hunting, fishing, and harvesting can deplete species populations and lead to extinction (passenger pigeon, dodo)
• Pollution, such as chemical contamination, plastic waste, and nutrient runoff, can degrade habitats and directly harm species (DDT, marine plastic pollution)
• The introduction of invasive species can disrupt ecosystems and outcompete native species (Burmese pythons in Florida Everglades, brown tree snakes in Guam)
• Human-induced climate change is altering habitats and environmental conditions, forcing species to adapt, migrate, or face extinction (coral bleaching, Arctic sea ice loss)

Impacts of Mass Extinctions

Characteristics and Causes of Mass Extinctions

• Mass extinctions are characterized by the rapid loss of a significant portion of Earth's biodiversity over a geologically short period
• There have been five major mass extinctions in Earth's history: End-Ordovician, Late Devonian, End-Permian, End-Triassic, and End-Cretaceous
• Mass extinctions can be caused by a combination of factors, such as climate change, volcanic activity, asteroid impacts, and changes in ocean chemistry

Evolutionary Consequences of Mass Extinctions

• Mass extinctions can reshape the evolutionary trajectory of life by eliminating dominant species and allowing previously minor groups to diversify and occupy new niches
• The End-Permian extinction, the most severe mass extinction, saw the loss of an estimated 95% of marine species and 70% of terrestrial vertebrate species
• The End-Cretaceous extinction, famously associated with the demise of non-avian dinosaurs, allowed for the radiation of mammals and the eventual rise of human beings
• Mass extinctions can lead to the emergence of novel adaptations and the diversification of surviving lineages, shaping the composition of Earth's biosphere (mammalian diversification after the End-Cretaceous extinction)

Biodiversity Crisis and Conservation

The Sixth Mass Extinction

• The current biodiversity crisis, often referred to as the Sixth Mass Extinction, is characterized by an unprecedented rate of species extinctions driven primarily by human activities
• The current extinction rate is estimated to be 100 to 1,000 times higher than the background extinction rate, with many species facing imminent extinction (IUCN Red List)
• The Sixth Mass Extinction is a result of the combined effects of habitat loss, overexploitation, pollution, invasive species, and climate change

Strategies for Preventing Species Extinctions

• Habitat conservation and restoration protect and recover critical habitats for endangered species (rainforest conservation, wetland restoration)
• Establishing protected areas, such as national parks and wildlife reserves, safeguards biodiversity hotspots and threatened ecosystems (Yellowstone National Park, Great Barrier Reef Marine Park)
• Implementing sustainable land use practices, such as agroforestry and sustainable forestry, can balance human needs with biodiversity conservation
• Reducing overexploitation through regulations on hunting, fishing, and trade in endangered species helps protect vulnerable populations (CITES, marine protected areas)
• Mitigating pollution and improving waste management reduce the negative impacts on species and their habitats (plastic bag bans, wastewater treatment)
• Controlling the introduction and spread of invasive species through biosecurity measures and eradication programs protects native biodiversity (inspection of imported goods, island restoration projects)
• Addressing climate change by reducing greenhouse gas emissions and promoting ecosystem resilience helps species adapt to changing environmental conditions (Paris Agreement, ecosystem-based adaptation)
• Increasing public awareness, education, and engagement in conservation efforts fosters support for biodiversity protection and sustainable practices (citizen science projects, eco-tourism)