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Chapter 4 Evolution and Biodiversity Chapter Overview Questions How do scientists account for the development of life on earth? What is biological evolution by natural selection, and how can it account for the current diversity of organisms on the earth? How can geologic processes, climate change and catastrophes affect biological evolution? What is an ecological niche, and how does it help a population adapt to changing the environmental conditions? Chapter Overview Questions (cont’d) How do extinction of species and formation of new species affect biodiversity? What is the future of evolution, and what role should humans play in this future? How did we become such a powerful species in a short time? LIFE!!! 1 billion years of chemical change to form the first cells, followed by about 3.7 billion years of biological change. Biological evolution – a “life-changing” experience! Darwin and Wallace – natural selection Figure 4-2 Modern humans (Homo sapiens sapiens) appear about 2 seconds before midnight Age of mammals Age of reptiles Insects and amphibians invade the land Recorded human history begins about 1/4 second before midnight Origin of life (3.6-3.8 billion years ago) First fossil record of animals Plants begin invading land Evolution and expansion of life Fig. 4-3, p. 84 Past life Our knowledge about past life comes from fossils, chemical analysis, cores drilled out of buried ice, and DNA analysis. Fossil record – what species lived when? Very incomplete Figure 4-4 Mutations! Biological evolution by natural selection involves the change in a population’s genetic makeup through successive generations. genetic variability – happens through… Mutations: random changes in the structure or number of DNA molecules in a cell that can be inherited by offspring. Happen through mutagens or random mistakes Populations evolve by becoming genetically different, not individuals Natural Selection and Adaptation Three conditions are necessary for biological evolution: Genetic variability, traits must be heritable, trait must lead to differential reproduction. An adaptive trait is any heritable trait that enables an organism to survive through natural selection and reproduce better under prevailing environmental conditions. When things get bad, an organism can: Adapt Migrate Go extinct Simplified process: mutations natural selection populations evolve Coevolution: A Biological Arms Race Interacting species can engage in a back and forth genetic contest in which each gains a temporary genetic advantage over the other. This often happens between predators and prey species. http://www.youtube.com/watch?v=CCYvPUChnIo Hybridization and Gene Swapping New species can arise through hybridization. Occurs when individuals to two distinct species crossbreed to produce a fertile offspring. Killer bees! (Africanized bees = European honeybee + African honeybee) Some species (mostly microorganisms) can exchange genes without sexual reproduction. Horizontal gene transfer Can happen with infection, interaction, or consumption Limits on Adaptation through Natural Selection A population’s ability to adapt to new environmental conditions through natural selection is limited by its gene pool and how fast it can reproduce. Humans have a relatively slow generation time (decades) and output (# of young) versus some other species. We also do not have unique beneficial mutations arise often. Viruses (though not “living”) adapt quickly because of their quick and numerous “reproduction” and quick mutation rate (in some viruses) Evolution through natural selection is about the most descendants. Organisms do not develop certain traits because they need/want them. There is no such thing as genetic perfection. Fittest ≠ Strongest Plate tectonics The movement of solid (tectonic) plates making up the earth’s surface, volcanic eruptions, and earthquakes can wipe out existing species and help form new ones. The locations of continents and oceanic basins influence climate. The movement of continents have allowed species to move. Volcanic eruptions and earthquakes disrupt environment 225 million years ago 65 million years ago 135 million years ago Present Fig. 4-5, p. 88 Climate Change Changes in climate throughout the earth’s history have shifted where plants and animals can live. Figure 4-6 ASTEROIDS! Asteroids and meteorites hitting the earth and upheavals of the earth from geologic processes have wiped out large numbers of species and created evolutionary opportunities by natural selection of new species. The four basic principles of sustainability have helped earth to adapt! Niches Each species in an ecosystem has a specific role or way of life. Fundamental niche: the full potential range of physical, chemical, and biological conditions and resources a species could theoretically use. Realized niche: to survive and avoid competition, a species usually occupies only part of its fundamental niche. Generalist and Specialist Species: Broad and Narrow Niches Generalist species tolerate a wide range of conditions. Specialist species can only tolerate a narrow range of conditions. Specialists have less competition, but generalists survive better under rapidly changing environmental conditions. Natural selection can lead to an increase in specialized species. Number of individuals Specialist species with a narrow niche Niche separation Generalist species with a broad niche Niche breadth Region of niche overlap Resource use Fig. 4-7, p. 91 Evolutionary Divergence Each species has a beak specialized to take advantage of certain types of food resource. Figure 4-9 Resource partitioning reduces competition and allows sharing of limited resources. Avocet sweeps bill through mud and surface water in search of small crustaceans, insects, and seeds Ruddy turnstone Herring gull is a searches tireless scavenger under shells and pebbles Dowitcher probes deeply for small into mud in search of invertebrates snails, marine worms, and small crustaceans Brown pelican dives for fish, which it locates from the air Black skimmer seizes small fish at water surface Louisiana heron wades into water to seize small fish Flamingo feeds on minute organisms in mud Scaup and other diving ducks feed on mollusks, crustaceans,and aquatic vegetation (Birds not drawn to scale) Oystercatcher feeds on clams, mussels, and other shellfish into which it pries its narrow beak Piping plover feeds on insects and tiny crustaceans on sandy beaches Knot (a sandpiper) picks up worms and small crustaceans left by receding tide Fig. 4-8, pp. 90-91 SPOTLIGHT Cockroaches: Nature’s Ultimate Survivors 350 million years old 3,500 different species Ultimate generalist Can eat almost anything. Can live and breed almost anywhere. Can withstand massive radiation. Figure 4-A Speciation Speciation: A new species can arise when member of a population become isolated for a long period of time. Genetic makeup changes, preventing them from producing fertile offspring with the original population if reunited. Geographic isolation: different groups of same population of species becoming geographically isolated for a long time. Reproductive isolation: mutation and change by natural selection occurs independently in each isolated population. Can take different amounts of time depending on the species Adapted to cold through heavier fur,short ears, short legs,short nose. White fur matches snow for camouflage. Arctic Fox Northern population Early fox Population Spreads northward and southward and separates Southern Population Different environmental conditions lead to different selective pressures and evolution into two different species. Adapted to heat through lightweight fur and long Gray Fox ears, legs, and nose, which give off more heat. Fig. 4-10, p. 92 Extinction Extinction occurs when the population cannot adapt to changing environmental conditions. Endemic species: only lives in one area The golden toad of Costa Rica’s Monteverde cloud forest has become extinct because of changes in climate. Figure 4-11 Cenozoic Era Period Millions of years ago Quaternary Today Tertiary 65 Mesozoic Cretaceous Jurassic 180 Triassic Species and families experiencing mass extinction Extinction Current extinction crisis caused by human activities. Many species are expected to become extinct Extinction within the next 50–100 years. Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including many foraminiferans and mollusks. Extinction Triassic: 35% of animal families, including many reptiles and marine mollusks. Bar width represents relative number of living species 250 Extinction 345 Extinction Permian Paleozoic Carboniferous Devonian Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites. Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites. Silurian Ordovician Cambrian 500 Extinction Ordovician: 50% of animal families, including many trilobites. Fig. 4-12, p. 93 More extinction! Background extinction: a certain number of species disappear at a low rate as local environmental conditions change. Scientists estimate average background extinction is 1-5 species per million species. Mass extinction: significant rise in extinction rates above background level. Usually catastrophic and widespread, with 25-70% of existing species wiped out in up to 5 million years. We have had 5 mass extinctions Mass depletion: somewhere in between. Effects of Humans on Biodiversity The scientific consensus is that human activities are decreasing the earth’s biodiversity. Figure 4-13 GENETIC ENGINEERING AND THE FUTURE OF EVOLUTION We have used artificial selection to change the genetic characteristics of populations with similar genes through selective breeding. We have used genetic engineering to transfer genes from one species to another. Figure 4-15 Genetic Engineering: Genetically Modified Organisms (GMO) AKA Transgenic Organisms GMOs use recombinant DNA genes or portions of genes from different organisms. Figure 4-14 Phase 1 Make Modified Gene E. coli Cell Extract DNA Gene of interest DNA Identify and Identify and remove portion extract gene of DNA with with desired trait desired trait Extract Plasmid Genetically modified plasmid Insert modified plasmid into E. coli Plasmid Remove Insert extracted plasmid (step 2) into plasmid from DNA of (step 3) E. coli Grow in tissue culture to make copies Fig. 4-14, p. 95 Phase 2 Make Transgenic Cell E. Coli A. tumefaciens (agrobacterium) Foreign DNA Plant cell Host DNA Nucleus Transfer plasmid copies to a carrier agrobacterium Transfer plasmid to surface of microscopic metal particle Agrobacterium inserts foreign DNA into plant cell to yield transgenic cell Use gene gun to inject DNA into plant cell Fig. 4-14, p. 95 Phase 3 Grow Genetically Engineered Plant Transgenic cell from Phase 2 Cell division of transgenic cells Culture cells to form plantlets Transfer to soil Transgenic plants with new traits Fig. 4-14, p. 95 THE FUTURE OF EVOLUTION Biologists are learning to rebuild organisms from their cell components and to clone organisms. Cloning has lead to high miscarriage rates, rapid aging, organ defects. Genetic engineering can help improve human condition, but results are not always predictable. Do not know where the new gene will be located in the DNA molecule’s structure and how that will affect the organism. Controversy Over Genetic Engineering There are a number of privacy, ethical, legal and environmental issues. Should genetic engineering and development be regulated? What are the long-term environmental consequences? Case Study: How Did We Become Such a Powerful Species so Quickly? We lack: strength, speed, agility. weapons (claws, fangs), protection (shell). poor hearing and vision. We have thrived as a species because of our: opposable thumbs, ability to walk upright, complex brains (problem solving).