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Exam #4 W 4/23 in class (bring cheat sheet) Review T 4/22 at 5pm in PAI 3.02 How many tigers does the world need? Human Population Growth CB 52.22 What happens as populations approach their carrying capacity? CB 52.13 What happens as populations approach their CB 52.13 carrying capacity? What happens as populations approach their CB 52.13 carrying capacity? CB 52.13 What happens as populations approach their carrying capacity? 36.4 9 2.3 UN Department of Economic and Social Affairs Population Division (2004) How much of our society is based on continuing population increases? 36.4 9 2.3 UN Department of Economic and Social Affairs Population Division (2004) CB 55.2 Genetic Diversity Biodiversity- number of species within an area Ecosystem Diversity Ecosystems on Earth CB 50.19 Larger areas can support more biodiversity CB 53.28 Islands CB 53.25 Water is critical for biodiversity Removing resources reduces biodiversity 1/10th 1/100th Australian tree hole communities (leaf litter supports bugs etc) CB 53.15 CB 53.19 Juncus, increases marshland biodiversity New England marine grass; shades soil decreasing evaporation and salinity New predators can have an affect throughout the ecosystem CB 53.17 Different types of biodiversity Biodiversity and Abundance CB 53.11 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% 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. 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. Extra information about invasive species that was NOT covered in class 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 Caulerpa Seaweed (Caulerpa taxifolia) Slide 37 • Introduced into Mediterranean by Monaco Aquarium in 1984 by dumping aquarium waste into the sea. • Hardier clone than the tropical species which seemed to have developed in the aquarium. • Smothers natural seagrass beds while being toxic to herbivores. • By 2000 covered 131km2 in several Mediterranean countries. Extra information about invasive species that was NOT covered in class Extra information about invasive species that was NOT covered in class 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 Extra information about invasive species that was NOT covered in class 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. Extra information about invasive species that was NOT covered in class Extra information about invasive species that was NOT covered in class 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 Why are species going extinct? 2% 36% 39% Species introductions Hunting Habitat Destruction Other 23% Exam #4 W 4/23 in class (bring cheat sheet) Review T 4/22 at 5pm in PAI 3.02 How many tigers does the world need?