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Define the following: • • • • • Micro Macro Gradual Barrier Reproductive Isolation Diversity and Speciation What is a species? • A population or group of populations whose members: – have the ability to breed with one another IN NATURE – Produce fertile offspring Macroevolution • Dramatic biological changes including: – Origin of new species (speciation) – Extinction – Evolution of major new features Reproductive Isolation • Reproductive barriers keep two very similar species from interbreeding. Reproductive Barriers Between Species • Timing – Different breeding seasons. – Breed at different times of the day. Reproductive Barriers Between Species • Behavior Reproductive Barriers Between Species • Habitat – Wolves and domestic dogs Reproductive Barriers Between Species • Reproductive structures are incompatible. Reproductive Barriers Between Species • Hybrid offspring may be infertile. Geographic Isolation • Separation of populations as a result of geographic change or dispersal to isolated places. Geographic Isolation • Small “splinter” populations can break off from a larger population and evolve into a new species. • Speciation only occurs if one population can no longer breed with the other population. Adaptive Radiation • Evolution from a common ancestor of many species adapted to diverse environments. Rates of Speciation Do Now Identify three homologous structures that all of these organisms share. Do you think these structures arose independently of one another or did they arise from a common structure? Evolution: A remodeling Process Section 15.2 Refining Existing Adaptations • In some cases complex structures evolve from simpler structures. • Example: Eyes of different mollusks Limpet • The cells can only detect light or dark. It can’t detect the direction of the light. Slit Shell Mollusk • Detects light and the direction of light, allowing the animal to move towards or away from the light. • Can not form an image. • Pinehole Eye: – Dim image – little light enters the eye • Eye is fragile as it is exposed to the outside environment. Marine Snail • Allows more light in than the pinehole does. • Image is brighter but still fuzzy. • Cornea protects the eye. Squid • Camera type eye which makes a sharp image. • The shape of the lens changes to sharpen the image. Simple vs. Complex • Simple eyes are enough to meet the needs of certain organisms. • Complex eyes probably evolved from small steps of adaptation. Adapting Existing Structures to New Functions • How has the shell of a lobster adapted? • Think about the environments where these animals live. Adapting Existing Structures to New Functions • How has the penguin adapted? The fossil record How fossils form • Hard parts such as shells, bones, or teeth, are long-lasting and may become preserved as fossils. • Under the right conditions, minerals dissolved in groundwater seep into the tissues of a dead organism and replace its organic material. The remains become petrified—they turn to stone. What we can learn Some fossils consist of footprints, animal burrows, or other impressions left in sediments. These tracks provide clues about whether the animal walked or ran and about its size and speed. Dating fossils: Relative Ages Because younger sediments are usually layered over older ones, you can tell which layers formed before others. The relative ages of fossils reflect the order in which groups of species existed compared to one another. Dating fossils: Absolute Ages • Radiometric dating - method most often used to determine the absolute ages of rocks and fossils. • Based on the measurement of certain radioactive isotopes in objects. How is radiometric dating done? • Every radioactive isotope has a fixed rate of decay. • half-life - the number of years it takes for 50 percent of the original sample to decay. How is radiometric dating done? Uranium-238 has a half-life of 4.5 billion years. Uranium-238 is not present in living organisms. It occurs in molten lava and volcanic rock that forms as lava cools. After volcanic rock forms, no more uranium-238 is incorporated. As the isotope decays it becomes lead-206. By measuring the ratio of uranium-238 to lead206, researchers can find the absolute age of volcanic rocks. Direct determination • Fossils contain isotopes of elements that accumulated in the organisms when they were alive—i.e. carbon-12 and radioactive carbon-14. • When an organism dies radioactive decay continues. Changes in the ratio of carbon-14 to carbon-12 can be measured to calculate how long the organism has been dead. • What was the mass before nuclear decay if two half lives occurred and the mass after nuclear decay was 8g? • The uranium-238 to lead-206 ratio in a rock is found to be equal. How old is the fossil if the half life of uranium is 4.5 billion years? • 32 • 4.5 billion years old. Taxonomy What is Taxonomy?? • The identification, naming, and classification of species. • Why bother with taxonomy? Linnaean System • 2 part Latin name – 1st part was the genus name – 2nd part was the species name • Example: Panthera pardus (lepard) Phylogenetic Tree • A diagram that reflects a how evolutionary relationships are thought to develop. • Homologous structures are used to determine how closely related organisms are. PROBLEMS! • Not all similar structures are inherited from a common ancestor! • Unrelated species who share a similar environment may have developed similar adaptations (analogous structures) for that environment. This process is known as convergent evolution. Cladograms • Phylogenetic tree constructed from a series of two-way branch points. • The cladogram to the right shows that lepards and cats are more closely related than wolves and cats. Cladograms • Each evolutionary branch is called a clade. • A clade consists of an ancestral species and all its decedents. • How many do you see here? Make this cladogram