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Major Trends in Evolution Microevolution • Small changes over time in the allele frequencies within a species which could eventually lead to speciation • Micro = Small Macroevolution • Large scale evolutionary changes that separate genera, families, orders, classes and even phyla of organisms • Macro = Large Patterns of Descent • Evolution over time can follow several different patterns. • Factors such as environment and predation pressures can have different effects on the ways in which species exposed to them evolve. 1. Gradual Change • Direction selection towards a particular phenotype or genotype • occurs very slowly 2. Divergent Evolution • Speciation which results in 2 different species • 2 populations diverge after being isolated • Can occur via allopatric, parapatric or sympatric mechanisms 3. Adaptive Radiation • Multiple divergence (speciation) which occurs more-or-less simultaneously. Many similar species arise from one common ancestor 4. Convergent Evolution • Unrelated organisms (no common ancestor) evolve similar features due to environmental selective pressures • Organisms have a common lifestyle or habitat • Torpedo-shaped bodies for swimming in dolphins and sharks • Wings for flight in insects, birds, mammals 5. Co-evolution • 2 or more species affect one another’s evolution • Plants and their insect pollinators • Dodo birds and their food source • Parasites and their hosts • Predators and their prey 6. Parallel Evolution • 2 similar organisms (with a common ancestor) evolve along similar lines due to living in similar environments with similar selective pressures. • The 2 groups are isolated • Sabre tooted cats, marsupial and placental mammals, Name the Pattern of Descent Gradual Change Convergent Evolution Adaptive Radiation Co-evolution Divergent Evolution Parallel Evolution Convergent Evolution Trends in Microevolution Phyletic Gradualism vs. Punctuated Equilibrium Phyletic Gradualism • • • • Darwin Gradual change over time Speciation occurs very slowly Gaps in the fossil record – many missing links or lack of transitional forms Punctuated Equilibrium • Eldridge and Gould • Long periods of no change, punctuated by fairly large changes in a short time period • Speciation occurs rapidly • Explains why transitional fossils may not exist It’s Story Time!! • Read the information pages on Phyletic Gradualism and Punctuated Equilibrium • Pick a number. Write a story for your assigned organism that parallels the story you read Background for Evolution Stories • Stripes and spots are for camouflage. • Zebras are related to horses, they travel in herds and their predators are lions. They live in grasslands. • Cheetahs are predators that have to chase their prey to catch it. They evolved from cougars who have plain coats. • Snakes likely evolved from lizards who have legs. Snakes like to burrow beneath the ground. • Leopards are predators that have to chase their prey to catch it. They live in forests and are related to tigers. • Pandas climb trees and use their hands to obtain their food (bamboo). Their thumbs are like human thumbs and allow for grasping. (See p.19 of your text book) • Elephants trunks are modified noses. Aside from smelling, trunks can suck up water, rip leaves off branches and transfer these to the mouth. • Rose thorns serve as protection against predators (herbivores that like to eat roses). Thorns are short sharp modified branches.