EXTINCTIONS AND HUMANS 

Extinctions caused by humans are generally considered to be a recent, modern  phenomenon. However, humanity's first significant contribution to the rate of 

global extinction may have occurred during the past 100,000 years, when North and South America and Australia lost 74 to 86% of the genera of "megafauna" -mammals greater than 44 kg.  In Australia, where the earliest human remains are dated to approximately 64,000  years, the great majority of the 22 identified genera of large land animals  disappeared between 30,000 and 60,000 years ago.  In the Americas, almost 80% of large-bodied genera became extinct. Extraordinary creatures, such as sabre-toothed cats, mammoths, giant armoured glyptodonts and  giant ground-sloths, all disappeared some time between 11,000 and 13,000 years  ago, coinciding with the dates of the first clear evidence of a human presence  there. 

Island megafaunas - like giant birds known as moas in New Zealand, the dodo on  Mauritius, giant lemurs and the extraordinary elephantbird in Madagascar, or large rodents and ground-sloths in the Caribbean - survived until much more recently  than the continental faunas. All seem to have disappeared within a few hundred  years after the arrival of humans - in the case of the moas within the last 300 years.

 

 

THE “SIXTH WAVE”

The rapid loss of species that we are witnessing today is estimated by some  xperts to be between 1,000 and 10,000 times higher than the “background” 

or expected natural extinction rate (estimated at one species every four years).  Natural extinction rate is between 11- 24 spices per year. Unlike the mass-extinction events of geological history, the current extinction phenomenon is one for which a single species - ours - appears to be almost wholly responsible. Such a deteriorating situation is being referred to as “the 

sixth extinction crisis”, after the five known extinction waves in the Ordovican,  Devonian, Permian, Triassic and Cretaceous Periods. 

The frequently asked question of “how many species have gone extinct in the last  100 years” is difficult to answer because of problems in recording contemporary 

extinction events. Decline and eventual extinction may take place over many  years, or even centuries in the case of very long-lived organisms like some of the 

large mammal and tree species.  The final stages of extinction are seldom observed except those caused by extreme  events such as the excessive hunting of the passenger pigeon Ectopistes  migratorius or the mass extinction of native snails in French Polynesia and Hawaii  following the introduction of the predatory snail Euglandina rosea to Pacific  Islands. Since 1500 AD, 820 extinctions have been recorded. 

 

 

PROFILES IN RED

The 2004 IUCN Red List of Threatened Species tells us that the global extinction  crisis is as bad, or worse, than we believed.  A total of 15,589 species of plants and animals are known to face a  high risk of extinction in the near future, in almost all cases as a  result of human activities. This includes 32% (one in three) of 

amphibian species, 24% (one in four) of mammal species, 12% (one in eight) of bird species, 25% (one in four) of conifers and 52% of cycads 

(an ancient group of plants).  Indonesia, India, Brazil and China are among the countries with the most  threatened mammals and birds, while plant species are declining rapidly in South  and Central America, Central and West Africa, and Southeast Asia. 

The IUCN Red List highlights the plight of a range of animals and  plants, from the Pemba flying fox to the King Pilly pine.

Aders duiker (Cephalophus adersi). This antelope which occurs in Kenya and  Tanzania moved from Endangered to Critically Endangered since 2003 because of 

substantial population declines caused by declining habitat and illegal hunting.  The state of the world’s threatened bird species is worse than ever. 

Since 1994 the number of bird species threatened with global  extinction has risen to 12%. Of the new total, 1,175 (99%) are at risk 

of extinction from human activities.  Sao Tome free-tailed bat (Chaerephon tomensis). This bat has moved up the  threatened scale from Vulnerable to Critically Endangered. It is known to occur in  only two sites, despite extensive searches. Its coastal forest and savanna habitats  are being destroyed through tourism and agricultural development.  The number of threatened reptiles increased from 253 in 1996 to  304 in 2004. The number of Critically Endangered species has  increased from 41 to 64 and Endangered from 59 to 79 species.  St Helena olive (Nesiota elliptica). Listed in 2003 as Extinct in the Wild, this  symbolic species is now Extinct. The last known tree surviving in the wild died in 1994 and the only known plant still in cultivation died in November 2003. No other  live material (plants, seeds or tissues) remain in local or international collections.  A total of 8,321 threatened plants are listed. This is around 2% of the  world’s described plants, but as only approximately 4% of the world's  described plants have been evaluated, the true percentage of  threatened plant species is much higher. 

Giant Hispaniolan galliwasp (Celestus warreni). Moving from Near Threatened to  Critically Endangered, this lizard is thought to have declined by at least 80% over  the last 20 years. It is threatened by habitat loss, especially deforestation for  agricultural activities (planting crops and creating pastures). The galliwasp is also 

killed by local people who mistakenly consider it to be venomous. Galliwasps are  also killed by dogs, cats and mongooses. 

 

 

A CATEGORICAL THREAT

Almost all the factors that have led to the extinction of species in the modern  era continue to operate, many with ever-increasing intensity. While these  factors vary in intensity and relative importance in the three major biomes (the land, inland waters and the seas), certain common threads emerge.

Major threats to ecosystems and biological diversity (biodiversity) are: 

• Habitat loss and fragmentation 

• Over exploitation (extraction, hunting, fishing etc.) 

• Pollution 

• Invasions of alien species (e.g. cats and rats on Ascension island)

• Global climate change (changes in migratory species patterns, coral bleaching, 

etc.)

Habitat Loss and Degradation is the most pervasive threat to birds, mammals and amphibians, affecting 86% of all threatened birds, 86% of the threatened mammals  assessed and 88% of the threatened amphibians.  Exploitation, including hunting, collecting, fisheries and fisheries by-catch, and 

the impacts of trade in species and species' parts, constitutes a major threat for  birds (30% of threatened birds), mammals (33% of threatened mammals), 

amphibians (6% of threatened amphibians), reptiles and marine fishes.  Alien Invasive Species are a significant threat, affecting 326 (30%) of all 

threatened birds, and 212 threatened amphibian species (11%). The commonest cause of extinction of bird species since 1800, especially those on islands, is the  introduction of alien invasive species such as the black rat. 

 

 

WHY SHOULD WE CARE?

Living organisms keep the planet habitable. Plants and bacteria carry out  photosynthesis, which produces oxygen. Trees absorb carbon dioxide, which can 

help in the fight against global warming.  The monetary value of goods and services provided by natural  ecosystems (including gas regulation, waste treatment, and nutrient  recycling) is estimated to amount to some 33 trillion dollars per year –  nearly twice the global production resulting from human activities. 

Many species are of immense value to humans as sources of food,  medicines, fuel and building materials. Between 10,000 and 20,000 plant 

species are used in medicines worldwide.  Currently about 100 million metric tons of aquatic organisms, including  fishes, molluscs, and crustaceans, are taken from the wild every year and  represent a vital contribution to world food security. Meat from wild animals (wild meat) forms a critical contribution to food 

sources and livelihoods in many areas particularly in countries with high  levels of poverty and food insecurity. A huge range of species are involved 

including monkeys, tapirs, antelopes, pigs, pheasants, turtles and snakes.  The diversity of nature helps meet the recreational, emotional, cultural, 

spiritual and aesthetic needs of people. - IUCN Species Survival Commission