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Great Ideas in Science: Lecture 14 – Ecosystems Professor Robert Hazen UNIV 301 All living systems live in ecosystems of many interacting organisms. Three Definitions of Evolution 1. 2. 3. Evolution as Change: Life on Earth has changed over time Common descent: All living things on Earth descended from a common ancestor. Natural selection: The process by which life evolved is Darwinian natural selection First Definition of Evolution: Change Over Time Observational evidence overwhelmingly supports the theory that life originated on Earth billions of years ago as a single cell, and has been changing ever since. Fossils Molecular Biology Cellular biology Genetics Comparative anatomy Observations of nature and of breeding Extinct Animals TRILOBITES If you accept observational evidence, then the unambiguous conclusion is that life has changed over time. Three Related Terms 1. 2. Creationism Young Earth Creationism 3. Scientific Creationism 1. Creationism Creationists believe that God created the universe and life. Many creationists accept the Bible’s creation story as a metaphor; they rely on empirical evidence (Psalm 19). Many scientists are also creationists in this sense. 2. Young Earth Creationism Young-Earth creationists believe in a literal reading of Genesis. • • • • Earth is about 10,000 years old. Geology features caused by Noah’s Flood. All species created in modern form. Minor evolutionary changes only. For many young-Earth creationists, the findings of science are irrelevant at best, and possibly dangerous and subversive. 3. Scientific Creationism Scientific creationists search for empirical evidence that supports the tenets of young-Earth creationism. SC is not science, because its basic tenets are not subject to change based on empirical evidence. Even if its tenets conformed to observational evidence, “scientific” creationism would not be science. Should creationism be taught in the science classroom? Second Definition of Evolution: Common Descent Common descent means that all living things descended from the first living cell. Tree diagrams reveal ancestral relationships. Second Definition of Evolution: Common Descent Common descent means that all living things descended from the first living cell. Tree diagrams reveal ancestral relationships. The search for fossil intermediates supports common descent. Fossils Fossils prove that life on Earth has changed over time; most extinct. Fossils demonstrate that these changes are gradual and progressive (simple to complex) All known fossils fit into a pattern of continuous evolution. Geological Time Fossils Strata Younger = higher Gradual Evolution Objections to Common Descent “Darwinists rarely mention the whale because it presents them with one of their most insoluble problems. They believe that somehow a whale must have evolved from an ordinary landdwelling animal, which took to the sea and lost its legs. … A land mammal that was in the process of becoming a whale would fall between two stools – it would not be fitted for life on land or sea, and would have no hope of survival.” Alan Haywood, 1985 Whale Evolution Ambulocetus Whale Evolution Ambulocetus Whale Evolution Rodhocetus Whale Evolution Basilosaurus Whale Evolution The power of the theory of evolution by natural selection is its predictive power. If we see a gap in the fossil record, then we can predict what kind of rock and what age of rock to search, and we can make a good guess as to what kind of fossil we’re likely to find. From DNA to Protein 1. 2. 3. 4. Transcription: Use DNA to make mRNA Attach mRNA to ribosome Translation: RNA to amino acids Fold amino acids into protein The Genetic Code The Cell Theory, 1839 All living things are composed of cells The cell is the fundamental unit of life All cells arise from previous cells CONCLUSIONS: Observational evidence overwhelmingly supports the hypothesis of common descent for all known life forms, living and fossil, on Earth. Third Definition of Evolution: Natural Selection (Darwin) • Populations exhibit variation. • More individuals are born than will survive. • The most fit individuals are more likely to reproduce. Charles Darwin (1809-1882) Charles Darwin: The Beagle at Galapagos Microevolution Phacops trilobites: Almost unchanged from 440 to 370 million years! Microevolution Unanswered Questions about Evolution How does macroevolution occur? Why are some species static? What is the rate of evolution? What is the rate of extinction? What causes mass extinctions? Macroevolution How did such an amazing diversity of trilobites arise? Eye Evolution “To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree …” Charles Darwin, On the Origin of Species Eye Evolution D. Nilsson & S. Pelger, “A pessimistic estimate for the time required for an eye to evolve.” Proc. R. Soc. Lond. B 256, 53-58 (1994). Selection rules for model eye evolution: 1. Vary curvature, aperture, and central refractive index randomly by 1%. 2. If visual acuity (spatial resolution) increases, then retain that variation. Eye Evolution This evolutionary sequence is continuously driven by selection. What is the Rate of Evolution? Punctuated Equilibria (a) versus Gradualism (b) Mass Extinctions Mass Extinctions and the Rate of Evolution Rate of extinction Mass extinctions Mechanisms • 10%-20% extinct in 5-6 million years • 30%-90% extinct • At least 5 episodes • Asteroids • volcanoes Mass Extinctions Evidence from the Fossil Record Mass Extinctions Evidence from Iridium Mass Extinctions Evidence from Foraminifera What Causes Mass Extinctions? Human Activities What Causes Mass Extinctions? Human Activities Ecology and Ecosystems Ecology: The study of natural living systems Ecosystems: Consist of biotic and abiotic components Community: All organisms in an ecosystem • Producers • Consumers • Decomposers Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms 1. Ecosystems consist of both living and nonliving parts 2. Energy flows through 3. Matter is recycled 4. Every organism occupies an ecological niche (two species cannot occupy same niche) 5. Stable ecosystems achieve balance among populations 6. Ecosystems can be disrupted Every Ecosystem Consists of Both Living and Nonliving Parts Abiotic: The chemical and physical environment Biotic: All living organisms that form the ecological community Energy Flows Through Ecosystems Food Web • Interactions of organisms Trophic Levels • • • • Photosynthetic plants Herbivores Carnivores Decomposers Most energy is lost as heat • 10% is transferred from one level to the next. Matter is Recycled by Ecosystems Carbon: Atoms continuously cycle Stable Ecosystems Achieve a Balance Among Their Populations Homeostasis is a balance among populations. Resources are always limited. While we observe some variation in populations, overall they are relatively constant. Law of Unintended Consequences Changing one part of a complex system may cause unintended changes in other parts of the system Nile perch Peter’s mountain mallow Three Environmental Problems Acid Rain 2. Ozone Hole Greenhouse Effect 1. 3. These are very different problems, though all arise from human activities that change composition of the atmosphere. 1. Acid Rain and Urban Air Pollution 1. Acid Rain and Urban Air Pollution Burning introduces chemicals • Nitrogen oxides • Sulfur compounds • Hydrocarbons Consequences • Air pollution • Acid rain Reduce emissions • Power plants • Vehicles 2. The Ozone Problem Ozone • Molecule of 3 oxygen atoms • Absorbs ultraviolet radiation The Ozone Layer • Concentration in stratosphere • Detected with aircraft 2. The Ozone Problem The concentration of ozone is reduced yearly over Antarctica This problem has been linked to release of chlorofluorocarbons (CFCs) One solution is to reduce emissions of CFCs 3. The Greenhouse Effect Atmosphere traps heat like a greenhouse One consequence is global warming, or climate change Three main points CO2 is a greenhouse gas Burning fossil fuels increases CO2 Average global temperature has significantly increased: 1990s was the warmest decade until the 2000s, which was even warmer. 3. Greenhouse Effect Debates About Global Climate Change Are increased CO2 levels responsible for these temperature increase? To what extent do the world’s oceans exchange CO2 with the atmosphere? To what extent does solar energy output vary over time? Changing Ocean Currents? Gulf stream & N Atlantic current Debates About Global Climate Change What impact might global warming have? Melting ice caps Rising ocean levels Warming of Northern Hemisphere Debates About Global Climate Change What impact might global warming have? Melting ice caps Rising ocean levels Warming of Northern Hemisphere Ecological impacts Debates About Global Climate Change What impact might global warming have? Melting ice caps Rising ocean levels Warming of Northern Hemisphere Ecological impacts Meteorological impacts Debates About Global Climate Change What impact might global warming have? Melting ice caps Rising ocean levels Warming of Northern Hemisphere Ecological impacts Meteorological impacts Possible international solutions? A final thought… Most environmental problems are tied to some extent to the growth of human population. • Today ~ 6 billion • 2050 ~ 9 billion • 2100 ??? How many people can Earth sustain? Estimates vary widely from 3 to 30 billion people It depends on your definition of “sustain.” All experts agree that a population of greater than 30 billion is a unsustainable.