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Chapter 4 Evolution and Biodiversity ORIGINS OF LIFE • 1 billion years of chemical change to form the first cells, followed by about 3.7 billion years of biological change. Figure 4-2 Biological Evolution • By natural selection involves the change in a population’s genetic makeup; Leads to biodiversity. Figure 4-2 How Do We Know Which Organisms Lived in the Past? • • • • Fossils Radiometric Dating Ice Cores DNA analysis. Figure 4-4 EVOLUTION, NATURAL SELECTION, AND ADAPTATION • Macroevolution • Microevolution - brought about by mutation, natural selection, gene flow, & genetic drift • Gene pool • Differential reproduction • Directional Selection • Disruptional Selection • Stabilizing Selection EVOLUTION, NATURAL SELECTION & ADAPTATION • BIOLOGICAL EVOLUTION BY NATURAL SELECTION INVOLVES THE CHANGES IN A POPULATION’S GENETIC MAKEUP • NOTE: POPULATIONS- NOT INDIVIDUALS – EVOLVE BY BECOMING GENETICALLY DIFFERENT. NATURAL SELECTION ACTS ON INDIVIDUALS. STEPS OF BIOLOGICAL EVOLUTION • 1. DEVELOPMENT OF GENETIC VARIABILITY IN A POPULATION OCCURRING THROUGH MUATIONS. BENEFICIAL MUTATIONS RESULT IN NEW GENETIC TRAITS THAT GIVE AN INDIVIDUAL AND ITS OFFSPRING BETTER CHANCES FOR SURVIVAL AND REPRODUCTION IN THE ENVIRONMENT. STEP 2 • NATURAL SELECTION – OCCURS WHEN SOME INDIVIDUALS OF A POPULATION HAVE GENETICALLY BASED TRAITS THAT INCREASE THEIR CHANCES OF SURVIVAL AND ABILITY TO REPRODUCE OFFSPRING WITH THOSE TRAITS; STEP 2 • NATURAL SELECTION EXPLAINS HOW POPULATIONS ADAPT TO CHANGES IN THE ENVIRONMENT. Natural Selection and Adaptation: • Three conditions necessary for biological evolution of a population by natural selection: – 1) Genetic variability – 2) Heritable traits – 3) Trait must lead to Differential reproduction – enables individuals with trait to leave more offspring than other members of a population SUMMARY: BIOLOGICAL EVOLUTION BY NATURAL SELECTION • GENES MUTATE – INDIVIDUALS ARE SELECTED – POPULATIONS EVOLVE THAT ARE BETTER ADAPTED TO SURVIVE AND REPRODUCE UNDER EXISTING ENVIRONMENTAL CONDITIONS. 3 TYPES OF NATURAL SELECTION • Stabilizing Selection-- The extremes are selected against. Example: height; most beings tend to the average height- not too many really short ones or really tall ones. • Directional selection-- One extreme value is selected for. Example: speed; faster is always better so a population will tend to get faster over time. NATURAL SELECTION • Disruptive selection-- The extremes are both selected for. This type of selection is not as common as the first two. Example: Prey-type animal with distinctive markings which the predators know will over time move away from the norm in both directions. DISRUPTIVE SELECTION Extreme phenotypes selected for STABILIZING SELECTION Increase in individuals with intermediate phenotype DIRECTIONAL SELECTION Eliminates one extreme variation from an array of possible phenotypes. Results in a shift towards the other extreme. Coevolution: A Biological Arms Race • Predator and prey species • Batesian Mimicry (1 bad, 1 not) • Mullerian Mimicry (many poisonous animals are brightly colored) Plate Tectonics – Also Responsible for Changes in Species’ Distribution & Evolution 225 million years ago 65 million years ago 135 million years ago Present Fig. 4-5, p. 88 Climate Change and Natural Selection • Changes in climate – affects biodistribution & evolution Figure 4-6 ECOLOGICAL NICHES AND ADAPTATION – 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 tolerate a wide range of conditions. • Specialist can only tolerate a narrow range of conditions. Figure 4-7 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 Specialized Feeding Niches • Resource partitioning- reduces competition and allows sharing of limited resources – “you take yours & I’ll take Figure 4-8 mine” Evolutionary Divergence • Adaptive radiation – through beak shapes Figure 4-9 SPECIATION AND BIODIVERSITY • Speciation: Allopatric & Sympatric • Allopatric – Involves a geographical barrier • Sympatric –Does not involve a geographical barrier Allopatric Speciation • Involves a geographic barrier that physically isolates populations of a species and blocks gene flow; • Once isolated, allopatric populations living in different places accumulate genetic differences due to natural selection, genetic drift and new mutations Sympatric Speciation (common in plants, rare in animals) • Results from chromosomal changes and nonrandom mating • Sympatric populations become genetically isolated even though their ranges overlap • Mechanisms include,(Gametes are 2n, not n) – – – – Polyploidy Allopolyploidy Autopolyploidy Nonrandom mating SPECIATION, EXTINCTION, AND BIODIVERSITY • Speciation: new species arise when members of a population become isolated for a long period of time. – 3 Types of Reproductive isolation: – 1) Temporal isolation – 2) Behavioral isolation – 3) Geographic isolation Temporal Isolation • Occurs because species mate at different times • Examples: – Different species of plants flower at different times – Closely related species of fireflies mate at different times of night Behavioral Isolation • Differences in: – courtship behavior, – chemical signals or vocalizations – Color or morphology that allow individuals to recognize their own species Fireflies respond only to the light pattern emitted by their own species Geographic Isolation • Leads to reproductive isolation, divergence of gene pools and speciation. Figure 4-10 Extinction: Lights Out The golden toad of Costa Rica’s Monteverde cloud forest has become extinct because of changes in climate. • Background extinction • Mass Extinction • Adaptive radiation • Gradualism • Punctuated Equilibrium • Fitness 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 SHAPING GENE FREQUENCIES • 2 Types of Artificial selection: 1. Selective Breeding – get desired traits 2. Hybridization – get variety Genetic engineering – used to create transgenic organisms Figure 4-15 Genetic Engineering: Genetically Modified Organisms (GMO) Figure 4-14