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* Chapter 3 *Central Case Study: Striking Gold in a Costa Rican Cloud Forest * Golden toads were discovered in Monteverde, Costa Rica in 1964 * 200 males in a 16-ft. area * The mountainous cloud forest was ideal for amphibians * The toads vanished from Earth within 25 years * Climate change caused the dry out * A fungus also killed them forest to *Evolution is the wellspring of biodiversity * Species: a population or group of populations … * Whose members share characteristics and …. * Can breed with each other to produce fertile offspring * Population: a group of individuals of a species that live in the same area * Evolution: means change over time * Biological evolution: genetic change in populations over time * Genetic changes lead to changes in appearance, functioning, or behavior over generations *Natural selection * Evolution may be random * Or directed by natural selection * Natural selection: The process whereby inherited characteristics that enhance survival and reproduction … * Are passed on more frequently to future generations than those that do not * • It is one of the best-supported and most illuminating concepts in science – It is the foundation of modern biology • It is vital for a full appreciation of environmental science – Knowing ecology and learning the history of life • Evolutionary processes influence agriculture, pesticide resistance, medicine, health, etc. • In 1858, both Darwin and Wallace proposed natural selection as the mechanism of evolution *Natural selection shapes * * * organisms Natural selection explains nature’s patterns Premises of natural selection: * * * Organisms struggle to survive and reproduce * Some individuals are better suited to their environment and reproduce more effectively They produce more offspring than can survive Individuals of a species vary in their characteristics because of genes and the environment Natural selection acts on genetic variation *Species adapt to the environment * A parent that produces more offspring passes on more genes to future generations * Over time, characteristics (traits) that lead to better reproductive success become more prevalent * Adaptive trait (adaptation): a trait that promotes reproductive success * Sexual reproduction also leads to genetic variation * Producing new combinations of genes * Environmental conditions determine the pressures of natural selection * Organisms need time to adapt to changing conditions * * Natural selection weeds out unfit individuals * It also helps elaborate and diversify traits * Which leads to the formation of new species *Evidence of natural selection is everywhere * It is evident in every adaptation of every organism * Artificial selection: the process of selection conducted under human direction * Producing the great diversity of dog breeds and crops * * Biological diversity (biodiversity): the variety of life across all levels of biological organization * Species * Genes * Populations * Communities * Scientists have described 1.8 million species * Up to 100 million species may exist * Tropical rainforests are rich in biodiversity *Speciation produces new types of organisms * The process of generating new species from a single species * Allopatric speciation: species form as a result of physical separation of populations * The main mode of speciation * Populations can be separated by glaciers, rivers, mountains * Each population, with its own set of mutations, diverges *Speciation results in diverse life forms * How do major groups diverge over time? * Phylogenetic trees: branching diagrams show relationships among species, groups, genes, etc. * Represent life’s history * * Fossil: an imprint in stone of a dead organism * Fossil record: the cumulative body of fossils worldwide * Phylogenetic trees and the fossil record show: * Life has existed on Earth for 3.5 billion years * Life evolved complex structures from simple ones * Life evolved large sizes from small ones * But natural selection can also favor simplicity and small size *Extinction * Most species that once lived are now gone * Extinction: the disappearance of a species from Earth * Species last 1–10 million years * Biological diversity is now being lost at an astounding rate * This loss of species is irreversible Number of species = speciation – extinction *Some species are vulnerable to extinction * Extinction occurs when the environment changes rapidly * Natural selection can’t keep up, so species can’t adapt * Many factors cause extinction: * Climate change, changing sea levels, severe weather * Arrival of new species, small populations * Specialized species * Endemic species: exists only in a certain, specialized area * Very susceptible to extinction * These species usually have small populations * Earth has had several mass extinctions * Background extinction rate: extinction usually occurs slowly, one species at a time • Mass extinction events: killed off massive numbers of species at once * * • Occurred five times in Earth’s history 50–95% of all species went extinct at one time Cretaceous-Tertiary (K-T) event: 65 million years ago * A gigantic asteroid caused dinosaur extinction * End-Permian event: 250 million years ago * 75–95% of species went extinct from unknown causes * * Humans are causing the sixth mass extinction event * Population growth, development, resource depletion * Destruction of natural habitats * Hunting and harvesting of species * Introduction of non-native species * This loss affects humans * We need organisms for food, fiber, medicine, services * Amphibians are disappearing faster than any other group * 170 species have already vanished