Overexploitation - Introduction to Conservation Biology - Lecture Slides, Slides of Biology

Download Overexploitation - Introduction to Conservation Biology - Lecture Slides and more Slides Biology in PDF only on Docsity! Overexploitation • Exploitation involves living off the land or sea, using plant and animal products for food, medicine, shelter, fiber, and other products • It is the second most important threat to the survival of birds, plants, and mammals • It is also the 3rd most important threat to freshwater fish extinctions Docsity.com History of Overexploitation • Humans have always been ‘extractive’ by nature and ‘primitive’ societies still largely follow this MO • While much of this appears sustainable, archaeological and paleontological evidence suggests premodern people have been driving species to extinction for 1,000’s of years Docsity.com History of Overexploitation • Impacts of Exploitation • Most activities are directed at a single target species Docsity.com Exploitation of Target Species • Tropical Terrestrial Ecosystems • Timber extraction is a major threat • Approximately 5.8M ha of tropical forests logged each year (25% world) • Single species approaches (e.g. mahogany) are difficult to compare to other methods, but it is better than clear cutting Docsity.com Exploitation of Target Species • A discrepancy between high inflation and slow growth rate of tree value creates the situation where cutting all trees irrespective of age is the best economic plan Docsity.com Exploitation of Target Species • Subsistence game hunting affects the structure of tropical forest mammal assemblages, as well as other groups through potential cascading effects Docsity.com Exploitation of Target Species • Nontimber forest products (NTFP) • E.g. fruits, nuts, oil seeds, latexes, resins, gums, medicinal plants, spices, dyes, fibers, and may others • The ethnobotanical studies have catalogued the wide variety of plants used by different groups (e.g. India, 6Kof 16K angiosperms used for traditional medicines, 79% of trees in 1ha of Amazon utilized) Docsity.com Exploitation of Target Species • The traditional view of NTFP is usually assumed to be sustainable and is viewed as a promising alternative to exploitive practices and/or landclearing • Extractive reserves are one of the of the fastest growing categories of protected areas in tropical forests • The sustainability of these areas is not fully understood at this time Docsity.com Exploitation of Target Species • Forestry • Only 22% of the world’s original forest remain in large, relatively natural ecosystems • Most are either boreal (48%) or tropical (44%), with only a fraction of temperate forests remaining (3%) • Many are currently threatened from increased pressure from logging Docsity.com Exploitation of Target Species • When commercial forestry expands into previously remote, roadless areas, it typically results in high levels of fragmentation of remaining stands • A study of postlogging silviculture on wildlife suggests loss of structure (i.e. snags, woody debris) is particularly important to many species Docsity.com Exploitation of Target Species • In Fennoscandia, 50% of the red-listed species are threatened because of forestry • In WA, actively managed forests could support 100% of biodiversity whereas timber management on a 50-yr rotation at the landscape level could support a maximum of 87% • Why? Largely structural simplification Docsity.com Exploitation of Target Species • Aquatic systems, especially marine fisheries, have been well monitored • Since the 1990’s global catches have leveled off for the first time in history, despite better technology being constantly developed and utilized Docsity.com Exploitation of Target Species • Trends have leveled off (and fallen) with aquaculture increasing in importance Docsity.com Exploitation of Target Species • Wild stocks continue to decline due to poor management • E.g. A recent survey of 232 stocks showed 83% over the past 25yrs are on the decline • E.g. Canadian cod 99.9% since 1960’s • By the way, are fish farms a good alternative to wild caught? Are they more productive? Docsity.com Exploitation of Target Species • Some of these same traits apply to other groups that make species vulnerable • E.g. abalone occur in shallow waters and species have been harvested from most valuable to least…densities have changed from 1- 5K/acre to <1/acre Docsity.com Exploitation of Target Species • Many freshwater taxa are subject to exploitation for food and other reasons • In 2000, estimated 8.8M tons of inland fish caught (22.4M ton aquaculture) • Economics: in US, estimated 35M spent $38B spent fishing/yr • Europe, estimate 21.3M anglers Docsity.com Exploitation of Target Species • Populations of 4/7 sp of salmon (Onchorhyncus) listed as endangered • Problem?: • Problem: this may be the most visible fish species in the world • While wild populations are supplemented with hatchery fish, they quickly show divergence (genetically, phenotypically) from wild populations Overfishing and dams Docsity.com