This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Chapter 27 Chapter
Biodiversity In Perspective Impacts, Issues: The Human Touch Touch 165 km island in 2 Polynesia Easter Island, 3501400 A.D. 15,000 people totally destroyed the biodiversity upon which they depended Today, there are six billion people on Earth and global biodiversity is declining A worldwide extinction crisis is in the making Hundreds of massive stone statues When Europeans first visited in 1722, the population was small and there was little vegetation There have been five great mass extinctions Causes of mass extinctions are not always clear Asteroid hit Earth at the KT boundary, but many species were already in decline Mass Extinctions Mass Slow Recoveries Slow Each mass extinction has been followed by an adaptive radiation Biodiversity recovers very slowly It takes 20 million to 100 million years to reach the premass extinction level of diversity Biodiversity & Extinction Biodiversity 90 percent of all species that have ever lived are now extinct Current range of biodiversity is the result of past extinctions and recoveries it took 3.8 billion years to get to this point Biodiversity is greater than ever So, What is the Problem? The domino effect:Dead as a Dodo The The flightless Dodo bird once lived on the island of Mauritius Killed off by Europeans Once the dodo was extinct, a native tree stopped reproducing May have coevolved with dodo The extinction of one species can lead to the unexpected extinction of one to a multitude of other species Endangered Species Endangered An endemic species that is extremely vulnerable to extinction
• Endemic means a species originated in one geographic region and is found nowhere else Critically endangered species Threatened species
Stable species Populations intact People versus Biodiversity People The main threat to biodiversity is growth of human populations People will sustain biodiversity when they can make a living by doing so Due to limited space and/or resources, many people must now choose between the good of endangered species and the good of their families San Francisco 1900>1990 Contributions to the accelerating rates of extinction rates Habitat Loss Habitat fragmentation Pollution,hazardous chemicals/poison Introduction of exotics/alien species Over harvesting Over hunting and illegal wildlife trading Habitat Loss Habitat Physical reduction of suitable places to live, as well as loss of habitat as a result of chemical pollution In the U.S.:
• 98 percent of tall grass prairies are gone • 50 percent of wetlands have been destroyed Island Biogeography Island Study of the factors affecting diversity on islands Has implications for predicting extinction of nonisland species Isolated patches of habitat are like islands MacArthur-Wilson Model MacArthur-Wilson Uses island biogeography to estimate future extinctions Model predicts
• Destruction of 50 percent of a habitat island will drive 10 percent of endemic species to extinction • Destruction of 90 percent of a habitat island will drive 50 percent of species to extinction Habitat Fragmentation Habitat Habitats are chopped up into patches Three effects: • Increases habitat edges • Decreases number of individuals that can be supported; may be too few to allow breeding • Decreases the area in which individuals can find food or other resources Indicator Species Indicator Species that provide warning of changes in habitat and impending widespread loss of biodiversity Example: • Migratory birds that breed in N. America and winter over in tropical forests • Study found populations are plummeting as a result of deforestation, habitat fragmentation Rachel Carson Rachel Oceanographer and marine biologist Published Silent Spring in 1962
• Described the harmful effects of pesticides on songbirds and other species Book helped launch the environmental movement Threats to Coral Reefs Threats Natural threats, such as hurricanes Manmade threats
and cyanide fishing,Coral bleaching Water pollution, oil spills, Dredging, Dynamite Coral Bleaching Coral Reefbuilding corals have photosynthetic, dinoflagellate symbionts When stressed, corals expel the protistans If the stress persists, the coral dies, leaving its bleached hard parts behind Coral bleaching may be an effect of global warming and increased sea temperatures Species that have been introduced into a habitat, either deliberately or accidentally Exotic species often have characteristics that allow them to outcompete endemic species Exotic Species Exotic ie:Purple loosestrife, Kudzu in U.S, Rabbits in Australia Play a role in 70 percent of cases where endemic species are threatened Humans and Mammalian Diversity Mammalian Humans began hunting mammals about 2 million years ago About 11,000 years ago, they began to drastically reduce mammalian habitat Of the 4,500 living mammal species, 300 (6.7 percent) are endangered Hunting and Whales humpback whale sperm whale sei whale fin whale blue whale other species Illegal Hunting of Endangered Animals Animals Identifying Hot Spots Identifying A global survey of biodiversity is impossible Researchers are identifying habitats where many endemic species are facing extinction Regional data is pooled to create a global inventory of biodiversity Conservation Biology Conservation Systematic study of biodiversity Works to elucidate the evolutionary and ecological origins of biodiversity Attempts to identify ways to maintain biodiversity for the good of human populations What’s It Worth? What’s Economic analysis can assign future value to ecoregions Successful conservation requires that sustaining biodiversity have greater economic value than destruction Biodiversity may have future economic value as a source of medications or chemical products ...
View Full Document