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AP Environmental 1.4: Evolution 9/6/2016 Natural Selection Notes: • Natural selection: individuals with certain traits are more likely to survive and reproduce under a certain set of environmental conditions – Survival of the Fittest Focus on Key Vocabulary! • Natural selection: individuals with certain traits are more likely to survive and reproduce under a certain set of environmental conditions – Survival of the Fittest • Biological evolution: how earth’s life changes over time through changes in the genetic characteristics of populations – Darwin: Origin of Species 8 9 Factors that affect Natural Selection • Genetic variations – Occurs through mutations (changes in DNA) in reproductive cells – Genetic drift unequal numbers of a given genome, could lead to decreased variation FACT: Natural selection does not happen unless there is variation in a population. 12 1. Environmental Change 14 2. Competition Example: A population of giraffes feeds on leaves of small bushes on the ground and short trees. Suddenly, their environment changes! After a drought, all of the bushes on the ground die. The giraffes are left with only taller trees to eat from. Though some giraffes have necks that can reach those leaves, others do not. Example: A population of birds uses their beaks to dig into the soil and find worms to eat. The birds have a variety of beak sizes, but since there was always an abundant supply of worms all of the birds were able to feed. One spring the worm population decreased dramatically due to a disease and the birds had to compete over the worms. The birds with the longest beaks were able to dig deepest into the soil and find enough worms to survive. How did variation aid in survival? How did variation aid in survival? 15 16 1 AP Environmental 1.4: Evolution 9/6/2016 Bottleneck effect- population is reduced which reduces gene pool How Do New Species Evolve? • Speciation: one species splits into two or more species • Geographic isolation: happens first; physical isolation of populations for a long period • Reproductive isolation: mutations and natural selection in geographically isolated populations lead to inability to produce viable offspring when members of two different populations mate • Example: Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted. 19 Founders effect- when a new colony is started by a few members of the original population. This small population size means that the colony may have: – reduced genetic variation from the original population. – a non-random sample of the genes in the original population. • For example, the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events. 21 Extinction is Forever • Extinction – Biological extinction – Local extinction • Endemic species Golden Toad of Costa Rica, Extinct – Found only in one area – Particularly vulnerable • Background extinction: typical low rate of extinction • Mass extinction: 3-5 over 500 million years 24 22 Geologic Processes Affect Natural Selection Climate Change and Catastrophes Affect Natural Selection • Tectonic plate movement affected evolution and the location of life on earth • Ice ages followed by warming temperatures • Earthquakes • Collisions between the earth and large asteroids – New species & Extinctions • Volcanic eruptions 25 27 2