ENV 200 Chapter 4, Fall 2013

The Origin of Biodiversity • Biological evolution: the process by which life on Earth changes over time through changes in the genes of populations The Origin of Biodiversity • Natural selection: a credible explanation for how biological evolution happens • Proposed in 1858 independently by: – Charles Darwin (1809 – 1882) – Alfred Russel Wallace (1823 – 1913) Charles Darwin (1809 – 1882) • Meticulously gathered evidence for the Theory of Evolution by Natural Selection Charles Darwin (1809 – 1882) Alfred Russel Wallace Charles Darwin (1809 – 1882) • 1859: First edition of “The Origin of Species by Means of Natural Selection” published • Sold out in one day!! Charles Darwin (1809 – 1882) • The book generated controversy!! Genetic Variability • First step in biological evolution • Occurs through mutations • Random changes in DNA molecules in a cell; can be inherited by offspring • Occur due to random changes in coded genetic instructions when DNA molecules are copied each time a cell divides OR due to exposure to mutagens ( X-rays, radioactivity…) Mutations • Mutations may occur in any cell; only mutations in reproductive cells are passed to offspring. • Mutations may result in a new genetic trait that gives an individual and its offspring better chances for survival and reproduction under existing environmental conditions or later on when the conditions change. Natural Selection • Second step in biological evolution • Occurs when some individuals of a population have genetically based traits that enhance their ability to survive and reproduce; Natural selection therefore acts on individuals in a population. Adaptation • Adaptation – Adaptive trait: Any heritable trait that enables an individual organism to survive and reproduce more than other individuals under prevailing environmental conditions – The adaptive trait has to be heritable and must lead to differential reproduction. A group of bacteria, including genetically resistant ones, are exposed to an antibiotic Most of the normal bacteria die The genetically resistant bacteria start multiplying Eventually the resistant strain replaces the strain affected by the antibiotic Normal bacterium Resistant bacterium Genetic Resistance: the ability of one or more organisms in a population to tolerate a chemical designed to kill it! Biological Evolution • Populations (NOT INDIVIDUALS) evolve by becoming genetically different • Biological evolution by natural selection: – Genes mutate. – Individuals are selected. – Populations evolve that are better adapted to survive and reproduce under existing environmental conditions. • When environmental conditions change, populations – adapt. – migrate. – become extinct. Adaptation through Natural Selection Has Limits • Will we adapt to changes in the environment in the near future? – Only if genetic change precedes change in the environmental conditions (Favorable genetic trait already in gene pool or results from mutation) – Reproductive capacity – Weeds, bacteria, mosquitoes, rats, cockroaches will most probably adapt to changes in environmental conditions quickly. Common Myths about Evolution by Natural Selection • “Survival of the fittest” is not “survival of the strongest” • Organisms do not develop traits out of need or want • No grand plan of nature for perfect adaptation “Stool Pigeon”?? Passenger Pigeons • Good to eat • Feathers for making pillows • Bones used as fertilizer Passenger Pigeons • 1813: A single huge flock took three days to fly past Audubon, famous bird expert!! • 1858: Passenger pigeon hunting a big business • 1878: One trapper killed 3 million birds at their nesting grounds in Michigan!! • March 24, 1900: Last wild passenger pigeon shot by a young boy in Ohio!! Passenger Pigeon • Extinct!! • Uncontrolled commercial hunting • Habitat loss: Forests cleared to make room for farms and cities Extinction • Complete disappearance of a species from earth • Occurs when a species cannot adapt and successfully reproduce under new environmental conditions • Natural but sometimes increase sharply Extinction • All species on earth are destined to become extinct!! • Background extinction: continuous low level extinction of species, occurring throughout the history of life on earth Extinction • Mass extinction: extinction of many species in a relatively short period of geologic time • Fossil record shows five mass extinctions!! • Due to each mass extinction, 50 to 95% of all species on earth became extinct!! • Biodiversity returned to higher levels after each mass extinction!! Dinosaurs went extinct!! Extinction • Causes of past mass extinctions poorly understood • Major climate change • Large scale catastrophes (The earth being hit by a comet or a large asteroid) Extinction Rate • Percentage (or number of species) that go extinct within a certain time period • Estimated background extinction rate: 1 per million species per year or 0.0001% • Current annual rate of species extinction: one hundred to one thousand times the background rate!! Extinction Rate Extinction Rate Extinction • Extinction decreases biodiversity. • Current rate may constitute mass extinction!! The “Big 5” Millions of years to recover Anthropogenic Extinction • We are destroying and degrading biodiversity!! • We have disturbed at least half the earth’s land surface!! • We are also degrading aquatic biodiversity. Anthropogenic Extinction Anthropogenic Extinction Animal species prematurely extinct due to human activities, mainly habitat destruction and overhunting!! Percentage of Various Species Threatened with Premature Extinction Sixth Mass Extinction!! Anthropogenic Extinction Anthropogenic Extinction Anthropogenic extinction is driven by HIPPO: Habitat Loss & Degradation Introduced, Invasive Species Population Growth Pollution Overexploitation HIPPO and HIPPCO • Habitat destruction, degradation, and fragmentation • Invasive (nonnative) species • Population and resource use growth • Pollution • Climate change • Overexploitation Habitat Loss Habitat is lost due to human use!! • Urbanization • Agriculture, grazing • Desertification • Global Climate Change Habitat Destruction, Degradation, and Fragmentation Invasive (Nonnative) Species Invasive species are introduced by humans!! 50,000 species in U.S. alone!! Cost over $130 billion annually!! Invasive (Nonnative) Species • Why are species introduced? – Food – Shelter – Medicine – Aesthetic enjoyment Invasive (Nonnative) Species • Why do they become invasive? Nonnative species may have no natural predators, competitors, parasites and pathogens. Invasive (Nonnative) Species Invasive (Nonnative) Species Invasive (Nonnative) Species Invasive (Nonnative) Species • Colerpa taxifolia, a tropical green alga, introduced to the Mediterranean in 1984 • Crowds out most plants • Inedible to most animals • Tangles boat propellers What is Happening to the Honeybees? • Honeybees responsible for 80% of insect- pollinated plants • Dying due to – Pesticides – Parasites • Bee colony collapse syndrome Pollution takes many forms!! Pollution Acid Mine Drainage (coal mines) Trash Light Nutrients Overexploitation means using resources unsustainably (spending capital)!! Overexploitation Forests Overexploitation Plant & Animal Populations Overexploitation means using resources unsustainably (spending capital)!! What Else? • Illegal killing, capturing, and selling of wild species threatens biodiversity. • Poaching and smuggling of animals and plants – Animal parts – Pets – Plants for landscaping and enjoyment A Rhino, Poached!! Elephants and Ivory Protest Against Poaching – Kenya Endangered Species • So few individual survivors the species could soon become extinct over all or most of its natural range Threatened Species • Vulnerable species • Still abundant in its natural range • Likely to become endangered in the near future because of declining numbers Some Endangered and Threatened Species!! Why are they threatened or endangered?? Confiscated Products Made of Endangered Species