Albia Dugger Miami Dade College Cecie Starr Christine Evers Lisa Starr Chapter 44 Human Effects on the Biosphere (Sections )

4.1 A Long Reach In the Arctic, unusually warm temperatures are affecting the seasonal cycle of sea ice melting and formation This is bad news for polar bears, which can only reach their main prey by traveling across ice Polar bears face other threats as well – their tissues contain high amounts of mercury and organic pesticides from pollutants produced by humans and carried to polar regions by winds and ocean currents

Biosphere at Risk All over the world, humans are replacing wildlife habitat with our dwellings, factories, and farms We also put species at risk by competing with them for resources, overharvesting them, and introducing non-native competitors The rate of species extinctions is on the rise and many types of biomes are threatened

Polar Bears on Ice

44.2 A Global Extinction Crisis Extinction (permanent disappearance of a species) is a natural process, but human activities are raising the rate at which other species disappear We are currently in the midst of a mass extinction event (many kinds of organisms in many different habitats becoming extinct in a relatively short period) caused by humans

Threatened and Endangered Species A species is considered endangered when one or more of its populations have declined or are declining endangered species A species that faces extinction in all or a part of its range threatened species Species likely to become endangered in the near future

Causes of Species Declines Overharvesting directly reduces population sizes Heavy harvesting of white abalone reduced the population to levels too low for effective reproduction

Causes of Species Declines (cont.) Habitat destruction especially threatens endemic species, such as the panda endemic species Species that remains restricted to the area where it evolved

Causes of Species Declines (cont.) Logging is a major cause of habitat destruction (know deforestation, or removal of plant cover) Some species endangered by logging: Ivory-billed woodpeckers Harlequin frog Gorillas

Endangered by Logging Harlequin frog Gorilla

Causes of Species Declines (cont.) Pollution!

Causes of Species Declines (cont.) Destruction of the Indonesian rain forest endangers the world’s largest flowers (Rafflesia) (Removal of plant cover)

Causes of Species Declines (cont.) Habitat degradation, such as excessive water withdrawals and aquifer pollution, threatens Texas blind salamanders

Causes of Species Declines (cont.) Beach development interferes with reproduction of leatherback sea turtles

Causes of Species Declines (cont.) Florida manatees are injured by motor boat propellers and get tangled in fishing line

Other Threats to Species Survival Deliberate or accidental species introductions Exotic species that outcompete native ones Declines or losses of one species that endanger others Most endangered species face a number of simultaneous threats

Biological Controls Gone Awry The Hawaiian koa bug is threatened by an exotic parasitoid fly introduced to attack another bug that is an agricultural pest

The Unknown Losses Of 47,677 species assessed by the International Union for Conservation of Nature and Natural Resources (IUCN), 36% were threatened or endangered The threat level for the other 1.8 million named species (including essential bacteria), and for millions of species yet to be discovered, is unknown

Key Concepts An Extinction Crisis Extinction is a natural process, but human activities have increased the frequency of extinction events Species go extinct when they are adversely affected by habitat destruction, degradation, and fragmentation The extent of species losses is not fully known

ANIMATION: Five Major Extinctions To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

ABC Video: Bald Eagle Off Endangered List

ABC Video: Whaling

BBC Video: Darwin’s Galapagos under Threat

BBC Video: Are We Facing an Extinction Crisis?

44.3 Harmful Land Use Practices Human activities threaten other species by destroying or degrading habitat Around the globe, alteration of habitats by farming, grazing, and logging are major contributors to species loss

Deforestation Tropical forests continue to disappear at an alarming rate In addition to immediate destruction of forest organisms, deforestation encourages flooding, and raises risk of landslides in hilly areas Deforestation also affects local weather – temperatures rise, and reduced transpiration results in less rainfall Forests take up and store huge amounts of carbon, so deforestation also contributes to global climate change

Deforestation (cont.) Deforested areas also become nutrient-poor Experimental deforestation increased runoff of essential topsoil nutrients such as calcium (compared with undisturbed forest)

Key Concepts Harmful Land Uses Plowing under grasslands and cutting down forests can have long-term and long-range effects Loss of plants allows topsoil erosion, raises soil temperature, and affects rainfall patterns in ways that make it difficult to restore plant cover

ANIMATION: Effects of Deforestation To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE