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Transcript
Biodiversity Chapters 5 and 11 and not in exact order Striking gold in Costa Rica • Golden toads were discovered in 1964, in Monteverde, Chile • The mountainous cloud forest has a perfect climate for amphibians • Unfortunately, they became extinct within 25 years – Due to global warming’s drying effect on the forest Central Case: Saving the Siberian tiger • The largest cat in the world • The Russian Far East mountains house the last remaining tigers • Nearly became extinct due to hunting, poaching and habitat destruction • International conservation groups saved the species from extinction – Research, education, zoos, and captive breeding programs Evolution: the source of Earth’s biodiversity • Biological evolution = genetic change in populations of organisms across generations • May be random or directed by natural selection – Natural Selection = the process by which traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not New Species arise from old species • It alters the genetic makeup of a population • It is important for understanding antibiotic and pesticide resistance, agricultural issues, production, medicines, etc. • Organisms adapt to their environment and change over time Natural selection shapes organisms • In 1858, Darwin and Wallace both proposed natural selection as the mechanism of evolution – Organisms face a constant struggle to survive and reproduce – Organisms tend to produce more offspring than can survive – Individuals of a species vary in their characteristics due to genes and the environment – Some individuals are better suited to their environment and will survive and pass their genes on in their offspring Genetic variation • Adaptive Trait (Adaptation) = a trait that promotes reproductive success • Mutations = accidental changes in DNA that may be passed on to the next generation – Non-lethal mutations provide the genetic variation on which natural selection acts • Sexual reproduction also leads to variation Natural selection acts on genetic variation • Directional selection = drives a feature in one direction • Stabilizing selection = produces intermediate traits, preserving the status quo • Disruptive selection = traits diverge in two or more directions If the environment changes, a trait may no longer be adaptive Evidence of natural selection is everywhere • It is evident in every adaptation of every organism • Evident in bacteria and fruit flies in laboratories • Selective breeding of animals Artificial selection • Artificial Selection = the process of selection conducted under human direction – For example, artificial selection has led to the great variety of dog breeds Evolution generates biodiversity • Biological Diversity = An area’s sum total of all organisms – The diversity of species – Their genes – Their populations – Their communities • Species = a population or group of populations whose members share characteristics and can freely breed with one another and produce fertile offspring • Population = a group of individuals of a species that live in the same area Speciation produces new types of organisms • The process of generating new species – A single species can generate multiple species • Allopatric speciation = species formation due to physical separation of populations – Can be separated by glaciers, rivers, mountains – The main mode of species creation Another type of speciation • Sympatric speciation = species form from populations that become reproductively isolated within the same area – Feed in different areas, mate in different seasons – Hybridization between two species – Mutations • Speciation results in diverse life formspatterns of diversity Speciation generates complex above the species level • Phylogenetic trees (Cladograms) = Represents the history of species divergence – Scientists can trace when certain traits evolved – Show relationships between species Extinction • Species generally evolve from simple to complex and small to big, but the opposite can occur, and some even disappear • Extinction = the disappearance of a species from Earth – Occurs when a species cannot adapt quickly enough to a changing environment – Speciation and extinction affect species numbers Extinction is a natural process • Extinction is irreversible: once a species is lost, it is lost forever • Humans profoundly affect rates of extinction Some species are more vulnerable to extinction • Extinction occurs when the environment changes too rapidly for natural selection to keep up • Endemic species = a species only exists in a certain, specialized area – Very susceptible to extinction – These species usually have small populations • Many other factors also cause extinction – Severe weather – New species – Specialized species Earth has had several mass extinctions • Background extinction rate = extinction usually occurs one species at a time • Mass extinction events = five events in Earth’s history that killed off massive numbers of species at once – 50-95% of all species went extinct at one time • Humans are causing the sixth mass extinction event – Resource depletion – Population growth – Development Biodiversity losses and species extinction • Extinction = occurs when the last member of a species dies and the species ceases to exist • Extirpation (local extinction) = the disappearance of a particular population from a given area, but not the entire species globally – Can lead to extinction • Mass depletion =occurs when the rate of extinction is greater than usual background rate • Commercial extinction =too few to make it worth catching and sell Extinction is a natural process • Paleontologists estimate 99% of all species that ever lived are now extinct • Background rate of extinction = natural extinctions for a variety of reasons – 1 extinction per 1 to 10 million species for mammals and marine species – 1 species out of 1,000 mammal and marine species would go extinct every 1,000 to 10,000 years Earth has experienced five mass extinctions • In the past 440 million years, mass extinctions have eliminated at least 50% of all species • After every mass extinction the biodiversity returned to or exceeded its original state The current mass extinction is human caused • During this Quaternary period, we may lose more than half of all species – Hundreds of human-induced species extinctions, and multitudes of others, teeter on the brink of extinction • The current global extinction rate is 100 to 1,000 times greater than the background rate – This rate will increase tenfold in future decades due to human population growth and resource consumption People have hunted species to extinction for millennia Extinctions followed human arrival on islands and continents Current extinction rates are higher than normal • The Red List = an updated list of species facing high risks of extinctions – 23% of mammal species – 12% of bird species – 31 - 86% of all other species • Since 1970, 58 fish species, 9 bird species, and 1 mammal species has gone extinct – In the U.S., in the last 500 years, 236 animal and 17 plant species are confirmed extinct – Actual numbers are undoubtedly higher Ecology is studied at several levels • Ecology and evolution are tightly intertwined • Biosphere = the total living things on Earth and the areas they inhabit • Ecosystem = communities and the nonliving material and forces they interact with • Community = interacting species that live in the same area Levels of ecological organization • Population ecology = investigates the quantitative dynamics of how individuals within a species interact • Community ecology = focuses on interactions among species • Ecosystem ecology = studies living and nonliving components of systems to reveal patterns – Nutrient and energy flows Organismal ecology: habitat • Habitat = the environment in which an organism lives – Includes living and nonliving elements – Scale-dependent: from square meters to miles • Habitat use = each organism thrives in certain habitats, but not in others • Habitat selection = the process by which organisms actively select habitats in which to live – Availability and quality of habitat are crucial to an organism’s well-being – Human developments conflict with this process Organismal ecology: niche • Niche = an organism’s use of resources and its functional role in a community – Habitat use, food selection, role in energy and nutrient flow – Interactions with other individuals • Specialists = species with narrow niches and very specific requirements – Extremely good at what they do, but vulnerable to change • Generalists = species with broad niches that can use a wide array of habitats and resources – Able to live in many different places Population characteristics • All populations show characteristics that help scientists predict their future dynamics • Population size = the number of individual organisms present at a given time – Numbers can increase, decrease, cycle or remain the same Population characteristics • Population density = the number of individuals within a population per unit area – High densities make it easier to find mates, but increase competition, and vulnerability to predation – Low densities make it harder to find mates, but individuals enjoy plentiful resources and space Population characteristics • Population distribution (dispersion) = spatial arrangement of organisms within an area – Random – haphazardly located individuals, with no pattern – Uniform – individuals are evenly spaced due to territoriality – Clumped – arranged according to availability of resources • Most common in nature Birth and death rates • Crude birth/death rates = rates per 1000 individuals • Survivorship curves = the likelihood of death varies with age – Type I: More deaths at older ages – Type II: Equal number of deaths at all ages – Type III: More deaths at young ages Four factors of population change • Natality = births within the population • Mortality = deaths within the population • Immigration = arrival of individuals from outside the population • Emigration = departure of individuals from the population • Growth rate formula = – (Crude birth rate + immigration rate) - (Crude death rate + emigration rate) = Growth rate Exponential population growth • Steady growth rates cause exponential population growth – Something increases by a fixed percent – Graphed as a J-shaped curve • Exponential growth cannot be sustained indefinitely – It occurs in nature with a small population and ideal conditions Limiting factors restrain growth • Limiting factors = physical, chemical and biological characteristics that restrain population growth – Water, space, food, predators, and disease • Environmental resistance = All limiting factors taken together Carrying capacity • Carrying capacity = the maximum population size of a species that its environment can sustain – An S-shaped logistic growth curve – Limiting factors slow and stop exponential growth • Carrying capacity changes Humans have raised their carrying capacity by decreasing the carrying capacity for other species Perfect logistic curves aren’t often found Population density affects limiting factors • Density-dependent factors = limiting factors whose influence is affected by population density – Increased risk of predation and competition for mates occurs with increased density • Density-independent factors = limiting factors whose influence is not affected by population density – Events such as floods, fires, and landslides Biotic potential and reproductive strategies vary • Biotic potential = the ability of an organism to produce offspring • K-selected species = animals with long gestation periods and few offspring – Have a low biotic potential – Stabilize at or near carrying capacity – Good competitors • r-selected species = animals which reproduce quickly – Have a high biotic potential K-selected vs. r-selected species Population changes affect communities • As population in one species declines, other species may appear • Human development now displaces other species and threatens biodiversity – As Monteverde dried out, species from lower, drier habitats appeared – But, species from the cloud-forest habitats disappeared Challenges to protecting biodiversity • Social and economic factors affect species and communities – Nature is viewed as an obstacle to development – Nature is viewed as only a source of resources – Human population growth pressures biodiversity Preserving biodiversity • Natural parks and protected areas help preserve biodiversity – Often, they are underfunded – Ecotourism brings jobs and money to developing areas Biodiversity encompasses several levels • Humans are reducing Earth’s diversity of life • Biodiversity – sum total of all organisms in an area – Split into three specific levels: • Species diversity • Genetic diversity • Ecosystem diversity Species diversity • Species Diversity = the number or variety of species in the world or in a particular region – Richness = the number of species – Evenness or relative abundance = extent to which numbers of individuals of different species are equal or skewed – Speciation generates new species and adds to species richness – Extinction reduces species richness The taxonomy of species • Taxonomists = scientists who classify species – Physical appearance and genetics determines a species – Genera = related species are grouped together – Families = groups of genera • Every species has a twopart scientific name: genus and species Subspecies: the level below a species • Subspecies = populations of species that occur in different areas and differ slightly from each other – Divergence stops short of separating the species – Subspecies are denoted with a third part of the scientific name Bengal tiger = Panthera tigris tigris Siberian tiger = Panthera tigris altaica Genetic diversity • Encompasses the differences in DNA among individuals within species and populations • The raw material for adaptation to local conditions • Populations with higher genetic diversity can survive – They can cope with environmental change • Populations with low genetic diversity are vulnerable – To environmental change – Disease – Inbreeding depression = genetically similar parents mate and produce inferior offspring Ecosystem diversity • Ecosystem diversity = the number and variety of ecosystems • Also encompasses differing communities and habitats • Rapid vegetation change and varying landscapes within an ecosystem promote higher levels of biodiversity Some groups contain more species than others • Species are not evenly distributed among taxonomic groups – Insects predominate over all other life-forms – 40% of all insects are beetles • Groups accumulate species by – Adaptive radiation – Allopatric speciation – Low rates of extinction Insects outnumber all other species Measuring biodiversity is not easy • Out of the estimated 3 - 100 million species on Earth, only 1.7 - 2 million species have been successfully catalogued • Very difficult to identify species – Many remote spots on Earth remain unexplored – Small organisms are easily overlooked – Many species look identical until thoroughly examined • Entomologist Terry Erwin found 163 beetle species specialized on one tree species Biodiversity is unevenly distributed • Living things are distributed unevenly across Earth • Latitudinal gradient = species richness increases towards the equator Canada has 30 - 100 species of breeding birds, while Costa Rica has more than 600 species Latitudinal gradient has many causes • Climate stability, high plant productivity, and no glaciation • Tropical biomes support more species and show more species evenness – Diverse habitats increase species diversity • Human disturbance can increase habitat diversity – But only at the local level • Biodiversity loss is more than extinction Decreasing numbers are accompanied by smaller species’ geographic ranges • Genetic, ecosystem, and species diversity are being lost. • The Living Planet Index summarizes trends in populations – Between 1970 and 2003, the Index fell by 30% Biodiversity loss has many causes • Reasons for biodiversity losses are multifaceted, complex, and hard to determine – Factors may interact synergistically • Four primary causes of population decline are: – Habitat alteration – Invasive species – Pollution – Overharvesting • Global climate change now is the fifth cause Habitat alteration causes biodiversity loss • The greatest cause of biodiversity loss – Farming simplifies communities – Grazing modifies the grassland structure and species composition – Clearing forests removes resources organisms need – Hydroelectric dams turn rivers into reservoirs upstream – Urbanization and suburban sprawl reduce natural communities – A few species (i.e., pigeons, rats) benefit from changing habitats Habitat alteration has occurred in every biome Particularly in tropical rainforests, savannas, and tropical dry forests Invasive species cause biodiversity loss • Introduction of non-native species to new environments – Accidental: zebra mussels – Deliberate: food crops • Island species are especially vulnerable • Invaders have no natural predators, competitors, or parasites • Cost billions of dollars in economic damage Pollution causes biodiversity loss • Harms organisms in many ways – Air pollution degrades forest ecosystems – Water pollution adversely affects fish and amphibians – Agricultural runoff harms terrestrial and aquatic species – The effects of oil and chemical spills on wildlife are dramatic and well known • The damage to wildlife and ecosystems caused by pollution can be severe – But it tends to be less than the damage caused by habitat alteration or invasive species Overharvesting causes biodiversity loss • Vulnerable species are large, few in number, long-lived, and have few young (K-selected species) – The Siberian tiger is hunted without rules and regulations – The early 1990s saw increased poaching because of powerful economic incentives – Many other species affected: Atlantic gray whale, sharks, gorillas Today the oceans contain only 10% of the large animals they once did Climate change causes biodiversity loss • Emissions of greenhouse gases warms temperatures – Modifies global weather patterns and increases the frequency of extreme weather events – Increases stress on populations and forces organisms to shift their geographic ranges • Most animals and plants will not be able to cope Warming has been the greatest in the Arctic The polar bear is being considered for the endangered species list It isn’t currently on list and may not make the list because part of the ESA, endangered species act, is habitat protection. For polar bears this would mean protecting sea ice from melting-or reduction in global warming. Biodiversity loss has a variety of causes Biodiversity provides free ecosystem services • Provides food, shelter, fuel • Purifies air and water, and detoxifies wastes • Stabilizes climate, moderates floods, droughts, wind, temperature • Generates and renews soil fertility and cycles nutrients • Pollinates plants and controls pests and disease • Maintains genetic resources • Provides cultural and aesthetic benefits • Allows us to adapt to change The annual value of just 17 ecosystem services = $16 - 54 trillion per year Biodiversity helps maintain ecosystem function • Biodiversity increases the stability and resilience of communities and ecosystems – Decreased biodiversity reduces a natural system’s ability to function and provide services to our society • The loss of a species affects ecosystems differently – If the species can be functionally replaced by others, it may make little difference – Extinction of a keystone species may cause other species to decline or disappear • “To keep every cog and wheel is the first precaution of intelligent tinkering” (Aldo Leopold) Biodiversity enhances food security • Genetic diversity within crops is enormously valuable – Turkey’s wheat crops received $50 billion worth of disease resistance from wild wheat • Wild strains provide disease resistance and have the ability to grow back year after year without being replanted • New potential food crops are waiting to be used – Serendipity berry produces a sweetener 3,000 times sweeter than sugar Some potential new food sources Organisms provide drugs and medicines • Each year pharmaceutical products owing their origin to wild species generate up to $150 billion in sales – The rosy periwinkle produces compounds that treat Hodgkin's disease and leukemia Biodiversity generates economic benefits • People like to experience protected natural areas, creating economic opportunities for residents, particularly in developing countries – Costa Rica: rainforests – Australia: Great Barrier Reef – Belize: reefs, caves, and rainforests • A powerful incentive to preserve natural areas and reduce impacts on the landscape and on native species • But, too many visitors to natural areas can degrade the outdoor experience and disturb wildlife People value and seek out nature • Biophilia = connections that humans subconsciously seek with life – Our affinity for parks and wildlife – Keeping of pets – High value of real estate with views of natural lands • Nature deficit disorder = alienation from the natural environment – May be behind the emotional and physical problems of the young Do we have ethical obligations to other species? • Humans are part of nature and need resources to survive • But, we also have conscious reasoning ability and can control our actions – Our ethics have developed from our intelligence and our ability to make choices • Many people feel that other organisms have intrinsic value and an inherent right to exist Conservation biology responds to biodiversity loss • Conservation biology = devoted to understanding the factors that influence the loss, protection, and restoration of biodiversity – Arose as scientists became alarmed at the degradation of Conservation scientists work at multiple levels • Conservation biologists integrate evolution and extinction with ecology and environmental systems – Design, test, and implement ways to mitigate human impacts • Conservation geneticists = study genetic attributes of organisms to infer the status of their population • Minimum viable population = how small a population can become before it runs into problems • Metapopulations = a network of subpopulations – Small populations are most vulnerable to extinction and need special attention Island biogeography • Equilibrium theory of island biogeography = explains how species come to be distributed among oceanic islands – Also applies to “habitat islands” – patches of one habitat type isolated within a “sea” of others – Explains how the number of species on an island results from an equilibrium between immigration and extirpation – Predicts an island’s species richness based on the island’s size and distance from the mainland Species richness results from island size and distance • Fewer species colonize an island far from the mainland • Large islands have higher immigration rates • Large islands have lower extinction rates The species-area curve • Large islands contain more species than small islands – They are easier to find and have lower extinction rates Small “islands” of forest rapidly lose species • Forests are fragmented by roads and logging • Small forest fragments lose diversity fastest – Starting with large species • Fragmentation is one of the prime threats to biodiversity Should conservation focus on endangered species? • Endangered Species Act (1973) (ESA) = forbids the government and private citizens from taking actions that destroy endangered species or their habitats – To prevent extinction – Stabilize declining populations – Enable populations to recover • As of 2007, the U.S. had 1,312 species listed as endangered or threatened Despite opposition, the ESA has had successes • Peregrine falcons, brown pelicans, bald eagles, and others have recovered and are no longer listed • Intensive management has stabilized other species – The red-cockaded woodpecker – 40% of declining populations are now stable • These successes occur despite underfunding of the U.S. Fish and The ESA is controversial • Many Americans support protection of endangered species • Opponents feel that the ESA values endangered organisms more than the livelihood of people – Private land use will be restricted if an endangered species is present – “Shoot, shovel, and shut up” = landowners conceal the presence of endangered species on their land • But, the ESA has stopped few development projects – Habitat conservation plans and safe harbor agreements = landowners can harm species if they improve habitat for the species in other places Other countries have their own version of the ESA • Species at Risk Act (2002) = Canada’s endangered species law – Stresses cooperation between landowners and provincial governments – Criticized as being too weak • Other nations’ laws are not enforced – The Wildlife Conservation Society has to help pay for Russians to enforce their own anti-poaching laws Protecting biodiversity • Captive breeding – individuals are bred and raised with the intent of reintroducing them into the wild – Zoos and botanical gardens • Some reintroductions are controversial – Ranchers opposed the reintroduction of wolves to Yellowstone National Park – Some habitat is so fragmented, a species cannot survive Protecting biodiversity • Cloning – a technique to create more individuals and save species from extinction – Most biologists agree that these efforts are not adequate to recreate the lost biodiversity • Ample habitat and protection in the wild are needed to save species Umbrella species • Conservation biologists use particular species as tools to conserve communities and ecosystems – Protecting the habitat of these umbrella species helps protect less-charismatic animals that would not have generated public interest • Flagship species – large and charismatic species used as spearheads for biodiversity conservation – The World Wildlife Fund’s panda bear • Some organizations are moving beyond the single species approach to focus on whole landscapes International conservation efforts • UN Convention on International Trade in Endangered Species of Wild Fauna and Flora (1973) (CITES) – protects endangered species by banning international transport of their body parts • Convention on Biological Diversity (1992) – – Seeks to conserve biodiversity – Use biodiversity in a sustainable manner – Ensure the fair distribution of biodiversity’s benefits – By 2007, 188 nations had signed on – Iraq, Somalia, the Vatican, and the U.S. did not join Biodiversity hotspots • Biodiversity hotspots – prioritizes regions most important globally for biodiversity – Support a great number of endemic species = species found nowhere else in the world – The area must have at least 1.500 endemic plant species (0.5% of the world total) – It must have lost 70% of its habitat due to human impact There are 34 global biodiversity hotspots 2.3% of the planet’s land surface contains 50% of the world’s plant species and 42% of all terrestrial vertebrate species Community- based conservation • Protecting habitats makes good sense, but this affects people living in and near these areas • Community-based conservation = conservation biologists actively engage local people in protecting land and wildlife – Protecting land deprives people access to resources – But, it can guarantee that these resources will not be used up or sold to foreign corporations and can instead be sustainably managed • Many projects have succeeded – But, others have not, due mainly to funding problems Innovative economic strategies • Debt-for-nature swap = a conservation organization pays off a portion of a developing country’s international debt – In exchange for a promise by the country to set aside reserves – Fund environmental education, and – Better manage protected areas • Conservation concession = conservation organizations pay nations to conserve, and not sell, resources Conclusion • Loss of biodiversity will result in a mass extinction • Primary causes of biodiversity loss are: – Habitat alteration, invasive species, pollution, overharvesting of biotic resources, and climate change • Human society cannot function without biodiversity’s benefits • Science can help save species, preserve habitats, restore populations, and keep natural ecosystems intact