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Speciation Notes Speciation • Speciation - the evolutionary formation of new biological species, usually by the division of a single species into two or more genetically distinct ones. • Species - members of the population that interbreed to produce fertile offspring Three Causes of Speciation a. Geographic isolation b. Reproductive isolation • • Organisms may look different and yet be the same species. These two ants are sisters—two ants of the species Pheidole barbata, fulfilling different roles in the same colony. Organisms may appear to be alike and be different species. These meadowlarks look almost identical, yet do not interbreed with each other—thus, they are separate species. c. Change in chromosome number • Polyploid species result from nondisjunction (chromosomes fail to separate properly) during meiosis or mitosis. So, how long does it take for a new species to evolve? Rates in Speciation a. Polyploid speciation only takes one generation b. Gradualism- the idea that species evolve at a slow, steady rate, with small, adaptive changes gradually accumulating over time. c. Punctuated Equilibrium - argues that speciation occurs quickly, in rapid bursts, with long periods of genetic equilibrium in between. • • Caused by changes in the environment, which rapidly change a population’s gene pool i.e. Raise in temperatures, introduction of competitive species, reproductive isolation Do patterns of evolution always look the same? Why might they be different? What causes the evolution of new species? Patterns of Evolution a. Divergent Evolutionwhen species that were once similar diverge (become more and more different) b. Adaptive RadiationWhen one species evolves into an array of different species to fit environmental habitats c. Convergent Evolution when species that were unrelated evolve similar characteristics • Occurs when unrelated species occupy similar environmental habitats in different areas of the world. Similar environmental pressures and similar natural selection pressures allows different species to look alike.
