Lecture 8, Natural Selection 1_NOTES

Lecture 8, Natural Selection 1_NOTES - So how do we get to...

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Unformatted text preview: So how do we get to estimate things like “r”? Demography: a study of the vital statistics (birth, death) of a population and how they vary with age Life table: vital statistics of a cohort (group of individuals born about the same time) Remember Darwin’s attempt to examine elephant populations took this approach Survivorship (lx) = proportion of individuals surviving to age or stage x r el ati ve to age cl ass 0 All ind. that are born complete survival Survivorship Curves Type I: most individuals survive to old age (large mammals) Type II: constant probability of dying (some birds; unusual) Type III: most newly born individuals die, but survival of adults is high (most commonly observed: marine invertebrates, insects, Age-specific fecundity (mx) - average number of offspring produced by an individual of age or stage x In this pop, newborns don’t reproduce Net Reproductive Rate (R0) = a ver age number of offspr ing p r oduced by an individual dur ing its entir e lifetime the product of survival and fecundity, summed over all age classes Σ lxmx What does it mean to have R0 > 1 ? R0 < 1? R0 = 1? r can be estimated using R0 as: ln (R0 / Generation Time) (but we aren’t going to do 1(0) + (0.8)(0.2) + (0.6)(0.3) + (0.4)(1) + (0.4)(0.6) + (0.2)(0.2) + (0)(0) = 1. an also use life table approach to look at the “value” of each age class Not all individuals are equal in their effect on future population growth: The “value” of an individual to pop. growth varies by age: -young individuals have a lifetime left, but some probability of not surviving to reproduce at all -older individuals have less life left, but are assured of reproducing if they have made it that far. “reproductive value” - the expected reproduction of an individual from their current age onward What you need to know to determine reproductive value: (1) Age-specific survivorship If Type III survivorship: young individuals worth little (most die) If Type I survivorship: young individuals worth much, as they have high prob of survival and a lifetime of reproduction. (1) Age-specific fecundity Age of first reproduction: (determines how long an individual must survive before having any reproductive value) How does fecundity change with age? WHO CARES? Reproductive value tells you which age classes most influence future population growth.- which to target to save, or to eliminate in a population Application of reproductive value: Which is a more effective conservation strategy? 1. Help hatchlings survive the first year of life (“Headstarting”) QuickTime ™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 2. Protect adults by requiring fishing net to have “escapes” for adult turtles (TED) Blue Planet Video What demographic information do you need to know to Model predictions of the effect of “headstarting” vs. Turtle Excluder Devices (TEDS) Crowder et al. 1994 Heppell et al. 1996 Changing age structure over time in the United States tells us something about “spurts” of population growth QuickTime™ and a QuickTime™ and a TIFF (Uncompressed) decompressor TIFF (Uncompressed) decompressor are needed to see this picture. are needed to see this picture. C. Haub http://www.prb.org/Articles/2008/globalaging.aspx Predicted age distribution of Japan in 2055 In 2055, 19 percent of Japan's population will be ‘old old’, including 634,000 centenarians. At the same time, the country's population size will have shrunk from 128 million today to 90 million. The consequences for the country's pension and health care systems are without precedent. Using age structure to predict human population growth [Humans have type 1 survivorship… generally] Which populations are increasing? Decreasing? Conclusions • Demographic data let us estimate r • They allow us to identify critical life stages for targeting in either conservation or in removal (if these are pest species) • They allow us to predict future needs of populations and future growth rates. Lecture 8: Natural Selection & A Brief History of Evolutionary Thought History I. Facts that we now take for granted A. The Earth is old: __4.5 billion years (BY) old_ A. B. The planet has changed since it was formed C. Life has been around for a long time: _3.5 billion (BY) D. The biological world has changed since life originated E. All life on Earth has descended from _a single ancestor All _a F. The degree of resemblance among organisms corresponds to The their relatedness their G. Resemblance among relatives is due to inheritance of genes: 1. 2. Individuals differ, even close relatives The magnitude of the difference between relatives The reflects time since they _shared a common ancestor_ _shared II. The Evolution of Evolutionary Thought A. Non-evolutionary perspectives Being Realm of Being God Angels Demons Man Realm of Becoming Woman Animals Minerals • Man Man • Monkeys Monkeys • Quadrapeds (mammals) Quadrapeds • Bats Bats • Ostrich Ostrich • Birds Birds • Aquatic birds Aquatic • Flying fish Flying Whales? Whales? • Fish Fish • Eels Seals? Eels Seals? • Sea serpents Sea • Reptiles Reptiles • Slugs Slugs • Shellfish Shellfish • Insects Insects • Worms Worms • Polyps (hydras) Polyps • Sensitive plants Sensitive • Trees Trees • Shrubs Shrubs • Herbs Herbs • Lichens Lichens • Mold Mold • Minerals Minerals • Earth Earth • Water Water • Air Air • Ethereal matter Ethereal _early attempts _early to organize life._ life._ Scala naturae from Charles Bonnet (circa 1760) (circa Non-Being II. The Evolution of Evolutionary Thought A. Non-evolutionary perspectives Georges Cuvier_(1769-1832): Paleontologist, anatomist & anti-evolutionist Paleontologist, • History of life in a particular place recorded in fossil beds / strata II. The Evolution of Evolutionary Thought A. Non-evolutionary perspectives How did Cuvier explain sequential changes of fossils in different rock layers? in Revolutions / Catastrophes (“Catastrophism”): • • • Species are _immutable_ All species created separately Boundaries between fossil strata caused by floods, Boundaries earthquakes, etc. etc • New species appeared in more recent layers by repopulating from elsewhere • Similarities between organisms (homology) reflect a Similarities divine plan divine II. The Evolution of Evolutionary Thought B. The Foundations of the theory _Sir Charles Lyell_ (1797-1875) _Sir geological uniformitarianism & gradualism (vs. catastrophism) 2 billion years 1500 1500 meters “The The present is the key to the past.” the The Colorado River cut through 2 billion years of rock in 7-15 million years II. The Evolution of Evolutionary Thought B. The Foundations of the theory By the end of the 18th century, By these facts were becoming accepted by scientists… 1. Organisms have changed to 1. Organisms some extent over time (evolved) (evolved) 2. Extinctions are commonplace 3. The earth is OLD (much older The than Biblical estimates of 5000than 9000 years) II. The Evolution of Evolutionary Thought II. B. The Foundations of the theory But some nagging questions persisted... 1. Why do organisms appear to be designed? 1. Why 1. Where do new species come from? 2. Why do organisms resemble each other, even in their Why underlying features? Shared ancestry and inheritance (_homology_)? 3. Why do organisms have vestigial structures? Evolutionary Why relicts (organisms are built on their ancestor’s body plans) OR an undiscovered function? OR 4. Why do organisms sometimes seem to be so badly designed? Why Evolutionary legacy OR a cruel / inept designer or creator? OR II. The Evolution of Evolutionary Thought C. Pre-Darwinian evolutionary thought Lamarck’s Proposal: Lamarck’s 1. __principle of use and dissuse. __principle ...Disuse leads to vestigial organs ...Disuse 1. Inheritance of acquired characteristics ...through use & disuse Jean-Baptiste de Lamarck (1744-1829) III. The Theory of Evolution by Natural Selection A. Charles Robert Darwin Charles Robert Darwin (12 Feb. 1809-19 April 1882) (12 Wanted to be a doctor but preanesthetic medicine made him anesthetic _nauseas__ _nauseas__ He left med school to become He an Anglican minister & beetle fancier fancier Gave this up to be the Gave naturalist on the HMS Beagle (1831-1836) (1831-1836) III. The Theory of Evolution by Natural Selection A. Charles Robert Darwin It was not an easy journey... It III. The Theory of Evolution by Natural Selection A. Charles Robert Darwin On the voyage, Darwin noted the amazing On diversity or life across the continents diversity Back home, the Galapagos finch and Back mockingbird specimens helped lead to the idea of _descent with modification (evolution as genealogical change) as A page from Darwin's Notebook B showing the first evolutionary tree diagram evolutionary III. The Theory of Evolution by Natural Selection A. Charles Robert Darwin Darwinian descent with modification: we now represent Darwinian this fact with a branching _phylogenietic tree diagram _phylogenietic But, what caused modification/adaptation? III. The Theory of Evolution by Natural Selection A. Charles Robert Darwin In 1838, Darwin read Malthus’ (1798) Essay on the Principle of Population, which examines patterns of __human population Population, growth and competition._ growth He then understood the “struggle for existence”, which lead to his He discovery of Natural Selection discovery He thus began 20 years of work secretly collecting detailed He 20 examples to support his theory of evolution by natural selection selection Darwin aimed to show that: Darwin • “species had not been created separately” • “natural selection had been the chief agent of evolutionary natural change.” change.” III. The Theory of Evolution by Natural Selection B. _o shoot! Alfred Russel Wallace The crisis of 1857-58: A letter from Alfred Russel Wallace... The C. DARWIN to A.R. WALLACE Down, Bromley, Kent, May 1, 1857. My dear Sir,—I am much obliged for your letter of am Oct. 10th from Celebes, received a few days ago..., I can plainly see that we have ago..., thought much alike and to a certain extent have come to similar conclusions... ...I am now preparing my work for publication, but I find the subject so very large, that though I have written many chapters, I do not suppose I shall go to press for two years. suppose Alfred Russel Wallace (1823-1913); photo taken when (1823-1913); he was 25 he III. The Theory of Evolution by Natural Selection C. Observations leading to the theory Six observations led to three inferences: Six Observation 1: Populations should increase exponentially if all offspring survived to reproduce (from Malthus) (from Observation 2: Populations do NOT increase exponentially: they remain at a relatively constant size size Observation 3: Limited availability of resources, predation or disease control population size: Most offspring do NOT survive offspring INFERENCE 1: there is a “struggle” for existence INFERENCE due to excess fecundity due III. The Theory of Evolution by Natural Selection C. Observations leading to the theory Observation 4: The individual members Observation of a species always differ in phenotype of Observation 5: Offspring tend to resemble parents; some resemblance is due to inherited factors, and some is due to shared environments due INFERENCE 2: individuals with INFERENCE phenotypes that allow them to win in the struggle for existence will have more kids who will tend to inherit those winning traits. winning There are predictable and stable differences in the traits There possessed by those who do and those who do not survive in the struggle for existence = DIFFERENTIAL SURVIVAL the III. The Theory of Evolution by Natural Selection C. Observations leading to the theory Observation 6: New and stable “varieties” with desirable qualities can be created by artificial selection can Wild “cabbage” Wild III. The Theory of Evolution by Natural Selection III. C. Observations leading to the theory 14,000 years of evolution by artificial selection (gets you a Chihuahua from a wolf) III. The Theory of Evolution by Natural Selection III. C. Observations leading to the theory English English Carrier Carrier Saxon Fairy Swallow English Pouter Indian Faintail Jacobin III. The Theory of Evolution by Natural Selection C. Observations leading to the theory Observation 6: New and stable “varieties” with desirable qualities Observation New can be created by artificial selection can artificial INFERENCE 3: heritable traits that enhance survival and INFERENCE reproduction in nature will increase in frequency in the population through time. population This is Natural Selection: As defined in the textbook: “The differential contribution of As offspring to the next generation by various genetic types belonging to a population” belonging III. The Theory of Evolution by Natural Selection III. D. Formal statement of the theory of NS A formal statement of the conditions for natural selection: formal 1. Individuals must reproduce to form the next generation 1. Individuals 2. Individuals within a population must vary in phenotype 3. Individuals pass on at least some of their traits to their 3. offspring (_inheritance) offspring 4. Individuals with different traits have _differential survival 4. or reproductive success during the struggle for existence during Traits that are heritable and that enhance survival and/or Traits reproduction relative to other members of the population relative will increase in frequency from generation-to-generation, so long as a particular selective regime persists so ...
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This note was uploaded on 11/29/2010 for the course BIOLOGY 1211 taught by Professor Patricelli during the Spring '10 term at UC Davis.

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