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Transcript
Unit 2: Ecosystems Feedback loops: All systems on Earth are linked Feedback loop = A system structure that causes output from one node to eventually influence input to that node Negative feedback loop = output from a system moving in one direction acts as input Stabilizes the system, ie. predator – prey interactions Positive feedback loop = instead of stabilizing a system, it drives it further toward one extreme or another o Exponential growth in human population, erosion, melting sea ice o Rare in nature, but common in natural systems altered by humans Major components of Ecosystems Abiotic: nonliving components (water, air, nutrients, solar energy) Zone of tolerance: min. & max range of environmental factors that organism can survive in (optimal range can be small) o Most organisms are least tolerant during juvenile or reproductive stages Limiting factor:single factor that can limit or prevent growth of a population (too much or too little) o Examples: nutrients, space, mate competition, net primary productivity Biotic: living components (plants, animals, microbes) Biodiversity: different life forms Ecosystem = all organisms and nonliving objects that occur and interact in a particular area at the same time o It includes abiotic and biotic components Ecotones = transitional zones between two ecosystems. Elements of each ecosystem mix Patches = form the landscape. Example: forested patches within an agricultural landscape o Widely spaced patches endanger organisms NPP Ecosystem Productivity: The amount of photosynthesis that takes place is one indicator of an ecosystem’s productivity Primary productivity: amount of biomass produced by photosynthetic organisms How much solar energy is converted into chemical energy through photosynthesis Net Primary Productivity (NPP): the left-over remains of biomass available to use as food for other consumers after the producer has used some for their own respiration A measure of the rate at which an ecosystem incorporates carbon from the atmosphere into biomass in a given length of time (day, week, month, etc. Secondary productivity: amount of biomass produced by organisms that eat photosynthetic organisms Most productive ecosystems 1. algal beds and reefs 2. tropical rain forests 3. swamps and marshes Least productive ecosystems 1. desert 2. open ocean 3. tundra Loss of Biodiversity 21% of mammals, 12% of birds & 30% of amphibian species are threatened with extinction In the past 500 years (in the US) 237 animal species & 30 plant species have become extinct Extirpation: the disappearance of a population from a given area, but not the entire species globally Habitat loss Disturbed or degraded 40-50% of earth’s land surface o 95-98% of all virgin forests in US have been destroyed since 1620 Fragmentation: gradual destruction of a habitat Causes of habitat loss Overuse - poaching Climate Change pollution; introduced species; Nonnative (exotic) species (Biological Pollution) 49% of all US endangered species are caused by nonnative species many introduced species have no natural predators, competitors, or pathogens to control numbers ex. Kudzu vine(SE US for erosion control), Brown Tree Snake (kills birds in Guam) Zebra mussels (from E. Europe threaten native mussels in Great Lakes) Gypsy moth (eat American forests), Brazilian pepper (in Everglades) Rosy tree snail (introduced in Hawaii to kill the giant African tree snail) Feral & outdoor pet cats—kill 568 million birds annually Endangered and extinct species Endangered Species: any organism (plant or animal) whose population has dropped drastically Major causes (human): poaching, habitat destruction, climate change Extinction Endangered species: has so few individual survivors that the species could soon be extinct Threatened species: still abundant, but declining in #’s & is likely to become endangered Background Extinction (Natural rate of extinction) natural, low level of species extinction each year, 3-14/ yr. based on fossil record estimate 99% of all species that have ever existed are now extinct Mass extinction catastrophic, widespread event kills many existing species Earth has experienced five mass extinctions (20-60 million years apart) o some biologists believe we are experiencing the sixth mass extinction o rise today in extinction rates above background level = 3-200 species/day Characteristics that make a species more vulnerable to biological extinction Low reproductive rate ex. blue whales, giant pandas Not adaptive to environmental changesex. giant pandas, Everglades kite Not many mates ex. many island species Feeds at high trophic level (less diversity of food) ex. Bengal tiger, bald eagle, grizzly bear Fixed migratory patterns (development interferes – dams, windmills, powerlines) ex. whooping crane, sea turtles Rare (not many to begin with) ex. many island species, some orchids Commercially valuable (poachers more likely to kill them) ex. tiger, elephants, rhinoceros Large territories (hard to find a mate, habitat fragmentation) ex. California condor, Florida panther Causes of Species Extinction Habitat Loss (#1 cause) tropical deforestation is greatest eliminator of species followed by: destruction of coral reefs & wetlands c. plowing of grasslands pollution of freshwater & marine habitats Greatest threats in US are: Agriculture, Commercial development, hydroelectric development, Outdoor recreation (off-road vehicles), Livestock grazing, Pollution Commercial hunting & poaching trade in wild plants & animals generates $10-20 billion annually o Gorilla ($150,000), elephant & rhino ivory ($?), Amazon macaw ($20,000) for every live animal sold as a pet in US, 50 other animals were killed sale of bushmeat (gorilla meat) by local people Over-harvesting of commercial fisheries Predators & Pest Control extinction of Carolina parakeet by US fruit farmers prairie dog holes break cattle’s legs African farmers kill elephants that trample their food crops Loss of Genetic Diversity limits ability to survive by limiting phenotype outcome possibilities, less chance of having right combination if environment changes Inbreeding allows recessive genes to accumulate Maintenance through conservation Strategies Conservation Biology:studies the factors behind the loss, protection, and restoration of biodiversity Captive breeding Cloning (not helpful large scale) Forensics (increase genetic diversity) Umbrella/flagship species (protects other species) Protect biodiversity hotspots Debt for nature swaps Restoration Ecology o Combine with local community-based conservation Species Approach involves identifying which species are at greatest risk of becoming extinct, gaining understanding of the species, & legally protect them & their habitats o problem = we protect only “cute animals” propagate endangered species in captivity reintroduce species into sustainable habitats Ecosystem Approach (National Parks, etc.) more effective than species approach focuses on ensuring that enough land and aquatic areas are protected to provide habitat for the majority of terrestrial and aquatic wild species eliminate or reduce populations of alien species from protected areas restore degraded ecosystems saves multiple species o Problems: mostly scenic areas protected, poor countries don’t enforce Reasons for preservation Intrinsic value & preserving genetic diversity Economic goods (species provide food, fuel, lumber, medicines, etc.) Ecosystem services (photosynthesis, pollination of crops, soil formation, nutrient cycling, pest control, climate regulation, flood control, waste decomposition, etc.) Recreation—ecotourism (generates $500 billion worldwide) o Ex. Male lion in Kenya generates $515,000 in tourist dollars but only $1000 if killed for its skin. Relevant laws and treaties International treaties International Union for Conservation of Nature (IUNC) Red List list of species at high risk of extinction Convention on International Trade in Endangered Species (CITES)-1975 lists more than 800 species that cannot be traded lists 29,000 species whose international trade is monitored & regulated limited effectiveness (difficult to enforce, convicted violators pay small fines, member countries can exempt themselves, much illegal trade occurs in countries that have not signed the treaty-152 have signed) National Laws Lacey Act (1900)-prohibits transport of live or dead wild animals across state lines without federal permit Endangered Species Act (1973)-makes it illegal for Americans to import or trade any product made from an endangered species forbids federal agencies & private land owners to carry out, fund, or authorize development that would jeopardize endangered species Fish & Wildlife service must design a recovery plan for all endangered Zoos & Game parks Egg pulling-collect wild eggs of endangered species & hatch them in zoos or research centers Captive breeding-wild animals are captured and bred in captivity, or artificially inseminated, then reintroduce the offspring into the wild (ex. Peregrine falcon & black-footed ferret) Seed Banks – stores seeds of plants as a reference for the future Wildlife Management manipulating wildlife populations and their habitats for their welfare & for human benefit uses laws to regulate hunting & fishing plant vegetation that is preferred food for wild species sport hunting is allowed only during certain seasons and is limited to size, number, and sex of animals killed major flyways for migratory waterfowl are managed by international treaties