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Transcript
Conservation biology Chapter 60 Extinction All species become extinct eventually More than 99% of species known to science are now extinct Current accelerating loss of habitat 20% of present day species will be extinct by the middle of this century 2000 of the world’s 8600 species of birds could go extinct The evolutionary history of extinction Almost 99% of the species that one time existed have become extinct Mass extinctions Extinction is usually compensated for by the creation of new species Overall diversity has increased Extinction now Extinction rates are currently 1,000 to 10,000 times “background” extinction rates As much as 20% of current biodiversity may be lost by 2050 Humans are primary cause of extinctions today Anthropogenic extinctions In recent history, extinction is almost invariably associated with human colonization of unoccupied areas Human-caused extinction Members of Homo sapiens caused extinction even in prehistoric times Mammoths and mastodons, giant sloths, saber-toothed tigers 74% - 86% of mega fauna thought to have been caused by human hunting Why have African megafauna survived ? Perhaps because animals coevolved with humans there Animals evolved counteradaptations to human predation Island extinction Majority of extinctions have occurred on islands 85 species of mammals; 60% lived on islands Why are islands so vulnerable ? Evolved in the absence of predators Humans introduced competitors, diseases Island populations are usually small which increases their risk for extinction Sixth mass extinction Current mass extinctions are notable because It is the only such event triggered by a single species (Homo sapiens) A few million years is a long time to wait for recovery It is not clear that biodiversity will rebound this time Humans are utilizing resources that new species would need to evolve Endemism Endemic: a species found in a particular region and nowhere else Levels of endemism high for areas that have been isolated for long periods of time, especially islands 18 regions of high endemism Some species under imminent extinction threat Hotspots World Conservation Monitoring Network assessed geographical regions according to: total species richness (biodiversity) proportion of endemic species extinction risk Hotspots Identified “hotspots” contain: 44% of the world’s known species of plants 35% of terrestrial mammals 28% of the birds 30% of mammals 38% of reptiles 54% of amphibian species All in an area of 1.4% of the world’s total land surface Biodiversity hotspots Population density exceeds world average Growth rate exceeds world average Why do we care about losing biodiversity? Direct economic value Indirect economic value Ethical and aesthetic values Benefits of biodiversity Food As many as 80,000 edible wild plant species could be utilized by humans Agriculture Benefits of biodiversity Drugs and medicines 40% of all prescriptions contain some natural product Pharmaceutical companies actively prospect tropical countries for products Rosy periwinkle Use fees USFWS estimates Americans spend $104 billion annually on wildliferelated recreation Ecotourism can be an important form of sustainable economic development Value of Biodiversity Indirect economic value is derived from ecosystem services Maintain chemical quality of natural water, buffer against storms and droughts Prevent loss of minerals and nutrients Moderate local and regional climate Absorb pollution Promote breakdown of organic wastes and cycling of minerals Mangroves Tropical rainforests To build plants cost $6 billon Operating cost $300 million/year Spend $1 billion over 10 years to preserve the ecosystem Benefits of biodiversity Aesthetic and cultural benefits Cultural diversity inextricably linked to biodiversity Existence (intrinsic) value