* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Biodiversity Crisis
Unified neutral theory of biodiversity wikipedia , lookup
Restoration ecology wikipedia , lookup
Biogeography wikipedia , lookup
Occupancy–abundance relationship wikipedia , lookup
Conservation biology wikipedia , lookup
Introduced species wikipedia , lookup
Biodiversity wikipedia , lookup
Theoretical ecology wikipedia , lookup
Decline in amphibian populations wikipedia , lookup
Molecular ecology wikipedia , lookup
Latitudinal gradients in species diversity wikipedia , lookup
Overexploitation wikipedia , lookup
Holocene extinction wikipedia , lookup
Island restoration wikipedia , lookup
Extinction debt wikipedia , lookup
Biological Dynamics of Forest Fragments Project wikipedia , lookup
Biodiversity action plan wikipedia , lookup
EXTINCTION & THE BIODIVERSITY CRISIS Biodiversity: All the variety of life, at every level of organization... Genetic diversity Species diversity Ecosystem diversity • According to the U.S. Endangered Species Act: – An endangered species is “in danger of becoming extinct throughout all or a significant portion of its range” – A threatened species is “likely to become endangered in the foreseeable future” Extinction: The death of the last surviving individual of a species, population, or gene, locally or globally. The Biodiversity Synthesis Report KEY FINDINGS: • Decline in biodiversity due to human activities more rapid in past 50 yrs than at any time in human history • Over last 100 yrs, human-caused species extinctions have multiplied ~ 1,000 times • 12 % of birds, 23% of mammals, and 32% of amphibians are threatened with extinction Current estimates of species loss range between 10-50% over next 20-50 years. This current rapid decline in biodiversity is known as the “Biodiversity Crisis” What makes a species vulnerable to extinction? • Vulnerability to introduced exotics • Overexploitation • Rarity • Habitat loss / Fragmentation Introduced Exotics • Species that humans have moved from native locations to new geographic regions • In absence of their native competitors, predators, parasites, and pathogens, introduced species may spread rapidly • Introduced species that become established in a new habitat usually disrupt the community European Starling Fig. 56-8 Brown tree snake introduced accidentally to Guam has caused extinction of 12 species of birds and 6 species of lizards. (a) Brown tree snake (b) Kudzu Asian plant kudzu introduced by USDA to control erosion; now choking out native plant species. Overexploitation • Human harvesting of wild plants or animals at rates exceeding ability of populations of those species to rebound • Large organisms with low reproductive rates are especially vulnerable • Overexploitation by the fishing industry has greatly reduced populations of some game fish, such as blue-fin tuna • World’s fish stocks have been reduced by 90% since the start of industrial fishing Rarity • Rare species are the most vulnerable to extinction, though common species can also become extinct. Three ways a species can be rare... 1. Cave Salamander 2. 3. Maned Wolf 4. Proboscis Monkey 5. Hawaiian Hawk 6. Dwarf Naupaka • A small population is prone to positive-feedback loops that draw it down an extinction vortex • The key factor driving the extinction vortex is loss of the genetic variation necessary to enable evolutionary responses to environmental change Fig. 56-10 Small population Inbreeding Genetic drift Lower reproduction Higher mortality Reduction in individual fitness and population adaptability Smaller population Loss of genetic variability Case Study: The Greater Prairie Chicken and the Extinction Vortex • Populations fragmented by agriculture and later found to exhibit decreased fertility • Scientists imported genetic variation by transplanting birds from larger populations • Population rebounded, confirming that low genetic variation had been causing an extinction vortex Habitat Loss Estimates of current rates of extinction worldwide are based primarily on speciesarea relationships and rates of tropical deforestation. Habitat Fragmentation • The fragmentation of habitats into patches that are too small to support populations is a major cause of extinction... Problems due to fragmentation: • edge effects • small area • isolation Fig. 56-14 (a) Natural edges (b) Edges created by human activity Edge Effects Problems due to fragmentation: • edge effects • small area • isolation Island Biogeography: Species richness on islands depends on island size and distance from mainland. Equilibrium Model Explains variation in species richness on different islands by considering effects of isolation and area on rates of immigration and extinction. Removal Experiment - Mangrove Islands Arthropods removed from islands of equal size, near and far from mainland. Number of species on each island at end of expt matched number at start (at least on near island), though the species differed. The equilibrium species number is dynamic: species composition constantly changes due to immigration and extinction. Today, the equilibrium model of island biogeography is being applied to conservation issues… Smaller fragments have: • fewer habitat types • fewer species • smaller populations • higher extinction rates Area-sensitive species with large home ranges are especially vulnerable to small area effects... Jaguar Spider Monkey White-plumed Antbird Isolation • Rates of extinction are much higher on islands than on the mainland... ...problematic if species are not immigrating due to isolation. Habitat fragments are habitat “islands”... Bogor Botanical Garden, Java A possible solution? Habitat (Movement) Corridors: -links between fragmented habitats -allow species movement between habitats Fig. 56-15 Advantages of Habitat Corridors - increased species richness - “rescue effect” - maintain genetic variation - altitudinal migration Three-wattled Bellbird - altitudinal migrant Disadvantages of Habitat Corridors - increased disease transmission - increase predation risk - increased spread of fire - reduced genetic variation between fragments Biodiversity ‘Hot Spot’: A relatively small ecosystem with a high concentration of species, many of which are endemics. Terrestrial biodiversity hot spots Marine biodiversity hot spots Equator Hotspots of biodiversity are also hotspots of extinction… Video Topics Population Ecology: life history strategies parental care / fecundity Community Ecology: biodiversity mutualisms, competition, predation Ecosystem Ecology: primary producers (plants) primary, secondary, tertiary consumers water cycle Conservation Biology: hot spot, endemic species, rarity, habitat fragmentation, extinction