Extinction and Mass Extinctions

Extinction

• A species becomes extinct when it no longer has any living representation on Earth.
• Extinction is suggested when a species goes unrecorded for 50 years by many conservation organizations.
• The Vaquita is functionally extinct because there are so few left in the Sea of Cortez.
• The background extinction rate is the rate at which species are expected to disappear, roughly 10% every million years.

Mass Extinctions

• The Permian extinction was the most severe, with more than 85% of marine fossilizable genera disappearing.
• At the end of the Cretaceous period, half of Earth's species vanished, including most dinosaurs.
• The present mass extinction, known as the Anthropocene, is potentially the largest yet.
• Human degradation of the environment causes this extinction.
• The rates are 100-1000 times higher than background rates.

Dinosaurs: A Most Notable Extinction Event

• The extinction at the end of the Cretaceous period is thought to have been caused by an asteroid impact.
• Dust clouds from the impact blocked sunlight, disrupting photosynthesis.
• Chain reaction of extinctions started with microscopic marine organisms and ended with dinosaurs, birds, and mammals.
• Dinosaurs disappeared approximately 65.5 million years ago.

Human Impact

• Most known extinctions can be attributed to human activities.
• An example is the Australian gastric brooding frog which went extinct in the 1980s.
• The Australian gastric brooding frog incubated pre-juvenile frogs in its stomach.
• Destruction/degradation of stream habitats, pollution, and disease caused their extinction.

Vulnerable Species

• Species, especially flightless birds, that are confined to islands are particularly vulnerable.
• Species with smaller populations face a higher risk of extinction
• Species not accustomed to terrestrial predators or wildfire are vulnerable.
• Expanding human populations increase the vulnerability of species to extinction.

Introduced and Invasive Species

• Humans contribute to extinction through overhunting, habitat destruction, and the introduction of other species.
• Moving species to different parts of the world can have disastrous consequences.
• The Stephens Island Wren of New Zealand is an example where a species was exterminated by a new species (the domestic cat).
• Dodos were native to Mauritius in the Indian Ocean.
• Humans decimated dodos for ship provisions, destroyed their habitats, and introduced dogs, pigs, cats, rats, and monkeys, leading to their extinction.
• The last dodo was seen in 1662.
• The arrival of zebra mussels (originally from Russia) in the Great Lakes is a primary factor in the decline of eastern pond mussels.
• Zebra mussels have outcompeted pond mussels from 90% of their habitat since the mid 1980s.
• Since 1880, ballast water has been regularly used by ships to stabilize and balance.
• A survey of ballast water in 159 ships found 367 species representing 19 animal phyla and 3 plant divisions.
• Ballast stowaways can result in hull fouling.
• The American chestnut tree, once widespread from southern Ontario to Alabama, is now endangered.
• These trees reached heights of 30 m.
• Chestnut blight (ascomycete) introduction around 1904 from Asian nursery stock decimated the trees.
• By 2000, only scattered trees remained.
• Invasive species often perform better than native species due to lack of predators or diseases.
• Invasive plants of Hawaii thrive do to there being no predators or diseases in that region

The Case of the Black Rhino

• By 1987, black rhino populations in the wild were reduced to 3500.
• There are only a few black rhinos in protected African parks.
• Species almost exterminated in less than 30 years (dropped by 95% between 1960 and 1995).
• In 1960, black rhinos were one of the "big five" animals to shoot for trophies.

White Nose Syndrome in Bats

• White-nose syndrome in bats was first discovered in New York State in hibernating bats in 2006.
• As of the time of writing, the syndrome is in 33 states and 7 Canadian provinces.
• 12 species and 6 million deaths have occurred between 2007-2021.
• Some bat species populations have declined by 90%.

Downside of Being Rare

• Endangered animals become commodities in high demand due to their rarity.
• These animals become status symbols.
• Bali starlings and tortoises are often poached as pets; pangolins are poached for their meat, scales, and blood for traditional uses.

Current Trends Against Background Extinctions

• Vertebrate extinction rates have increased since the year 1500.
• The amount of extinction caused by humans has increased over time.
• The amount of extinction caused by humans is several times larger than the background extinction rate.

The Root Problem in the Fight for Conservation

• The root problem in the fight for conservation is expanding human populations and development.
• A major threat is waste that comes from overconsumption.

Conservation Development

• The International Union for Conservation of Nature (IUCN) formed in 1948, and is a global organization in Gland, Switzerland.
• IUCN established objective criteria identifying at-risk species.
• The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) formed in 1977, and is located in Gatineau, QC.
• COSEWIC recognizes seven categories for assessing species at risk.
• The Species at Risk Act (SARA) was passed in 2002.
• SARA is Canadian Federal Legislation to prevent species from disappearing.
• SARA helps recover extirpated, endangered, threatened, or special concern species.

Categories for Species at Risk

• Extinct: A wildlife species that no longer exists.
• Extirpated: A species no longer exists in one location in the wild but can still be found elsewhere (BC Red List).
• Endangered: A species facing imminent extirpation or extinction (BC Red List).
• Threatened: A species likely to become endangered if the factors causing it are not reversed (BC Red List).
• Special concern: A species that may become threatened or endangered due to biological issues (BC Blue List).
• Data deficient: When available information is insufficient.
• Not at Risk: A species is evaluated and found not to be at risk for extinction (BC Yellow List).

Challenges - Habitat and Caribou

• Caribou habitats have been extirpated from 45% of their historical range.
• This extirpation is due to habitat loss and altered predator-prey dynamics from human activity.
• 9 populations are decreasing, 7 are stable, and 2 are increasing.

Challenges - Habitat and Northern BC Moose

• Northern BC Moose populations are down 70%.
• Ultimate causes for the decline are habitat destruction, climate change, and imbalanced sex ratios.
• These causes reduce productivity of the species.
• Proximate causes are predation, hunting, poaching, cars, and trains.
• IUCN (2018) considers a taxon to become "vulnerable" when an observed, estimated, inferred, or suspected reduction of at least 50% over the last 10 years.
• This determination relies on if numbers are observed or reported in a specific area of occupancy.