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How many tigers does the world need? Human Population Growth CB 52.22 CB 55.2 Genetic Diversity Biodiversity- number of species within an area Ecosystem Diversity Ecosystems on Earth CB 50.19 Have we overstated the tropical biodiversity crisis? William F. Laurance Trends in Ecology & Evolution Vol. 22: 65-70 February 2007 Are we on the verge of a massive die-off of tropical species? Changes in Extinctions and Diversity Are we on the verge of a massive die-off of tropical species? Increased rural density leads to decreased forest. This is because rural slash-andburn farmers cause most forest loss. The good news? About 21–24% of species in the Asian tropics and 16–35% of species in the African tropics are threatened with possible extinction. Rural populations are expected to decline. Substantial areas of agricultural land are likely to be abandoned, because the population growth rates of many developing nations are slowing and because of increasing urbanization. This could enable significant forest regeneration, which could help buffer species losses from deforestation. CB 55.21 Human vs Natural Disturbances Extinction rates are likely to be higher in biodiversity hotspots CB 55.17 Terrestrial Biodiversity Hotspots the 16 hotspots that sustain tropical forest have already lost, on average, 90% of their forest cover Rainforest clear cutting CB 55.15 CB 55.13 Not all habitats are equal A third to a half of all old-growth species avoid younger (<30-year-old) regrowth. In many tropical regions, future pressures on forests will be determined more strongly by industrial drivers, globalization and macroeconomic forces than by local population density. Rural populations are expected to decline, but increased urban population will demand more resources. The precautionary principle maintains that one should err on the side of caution in conservation matters. We need to evaluate critically the degree to which regenerating and degraded habitats, which are increasing dramatically at the expense of old-growth forests, can sustain tropical biodiversity Why are species going extinct? 2% 36% 39% Species introductions Hunting Habitat Destruction Other 23% Nearly Extinct Species: maybe only 100 individuals exist CB 55.3 Extinction Vortex Attwater Prairie Chicken As population declined, genetic diversity declined CB 55.10 Attwater Prairie Chicken Individuals brought from other populations increased reproduction and population CB 55.10 Why are species going extinct? 2% 36% 39% Species introductions Hunting Habitat Destruction Other 23% Ecosystem Fragmentation Habitat loss and fragmentation has been extensive in the US due to human modification of the environment Many human tragedies have been a boon for native animal species: http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=15362 Science v. 269 pg. 304 7/21/1995 Korean DMZ: Among the species making their homes in the DMZ are endangered Asian cranes, black-faced spoonbills, angora goats, Amur leopards, and even bears. http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=15362 Savanah River nuclear site in Georgia: forest remnant Why are species going extinct? 2% 36% 39% Species introductions Hunting Habitat Destruction Other 23% Invasive species can disrupt an ecosystem by outcompeting native species for resources CB 55.6 Nile Perch (Lates niloticus) • Introduced to Lake Victoria in 1954 to increase fish yield • Caused extinction of 200+ endemic fish species through predation, and competition • Fish caused indirect increased erosion on land, causing higher nutrient levels in the lake. Water Hyacinth (Eichhornia crassipes) • Introduced as ornamental plant around the world • Now in 50 countries on 5 continents including US • In California it replaced the native pennywort (Hydrocotyle umbellata) which occupies a similar habitat, leading to a marked decrease in invertebrate communities • Limits water transport, reduces oxygen and light levels in the water Zebra mussel (Dreissena polymorpha) • Spread from its native range in the Baltic Sea via ballast water • Spreads in Europe and North America • Kills native molluscs, changes ecosystems, and damages infrastructure • Estimated annual damage in US $3 billion The brown tree snake (Boiga irregularis) • Its native in Australia and was introduced to Guam accidentally in the 1950’s • Overall responsible for the extinction of 3 out of 4 seabirds; 9 out of 13 forest birds; 3-5 out 12 reptile species on the Island of Guam. • This snake caused the extirpation or serious reduction of most of the island's 25 resident bird species on the main island of Guam. How Many Invasive Species Are There in Texas? 67 terrestrial plants 12 aquatic/wetland plants 10 mammals 4 birds 7 fishes 11 insects 11 mollusks and crustaceans QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Hydrilla verticillata Aquatic invader covering nearly 100,000 surface acres of water in Texas. Spreads rapidly, in one Texas lake it covered 23 acres in 1999 but over 200 in 2000. Depletes water of oxygen and blocks sunlight killing off many native plants and animal species. Hydrilla on Longhorn dam over Town Lake QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Why are species going extinct? 2% 36% 39% Species introductions Hunting Habitat Destruction Other 23% For Th, 6/26, please bring a laptop if possible. How many tigers does the world need?