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Patterns of Evolution. SBI3U0. Patterns of Evolution. We have learned: Evolution occurs in slow steps Mutations Genetic Drift and Natural Selection Changing allele frequencies Accumulation of mutations and natural selection often leads to speciation
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Patterns of Evolution SBI3U0
Patterns of Evolution • We have learned: • Evolution occurs in slow steps • Mutations • Genetic Drift and Natural Selection • Changing allele frequencies • Accumulation of mutations and natural selection often leads to speciation • What patterns do we see in this speciation? • Do species always evolve to be drastically different from one another?
Adaptive Radiation • Adaptive radiation occurs when one species evolves into several different species • This usually happens relatively quickly • The new species usually fill empty ecological niches • What forces these new species to form? • Usually the introduction of new resources that aren’t being used by other species • A prime example is the many species of finches Darwin observed in the Galapagos islands • Aptly named Darwin’s finches as a group
Darwin’s Finches • On mainland South America the finch species feed mainly on seeds • Other food sources (insects, fruits, plants, etc...) are mainly consumed by other species • The finch population is strictly limited by stabilizing selection • Smaller finches must compete with other species for smaller seeds • Larger finches must compete with other species for larger/harder seeds
Darwin’s Finches • When the ancestor of the current finch species traveled over to the Galapagos islands there was little competition for food • This allowed the finches who were naturally larger or smaller to exploit different food sources from the bulk of the finch population • Thus there was a niche for those birds • As they passed down their genes, the populations of birds exploiting alternative food sources grew • This lead to the eventual sympatric speciation of these birds
Divergent Evolution • Every ecosystem has a wide range of niches and roles • Eg: every ecosystem has producers, consumers, decomposers, and scavengers • Among these groups are several different specialized species • One species can eventually evolve into several different species that fill different niches and roles • This is called divergent evolution
Divergent Evolution - Rodents Squirrel, Deer mouse, flying squirrel, porcupine, beaver
Divergent Evolution - Marsupials Kangaroo, Koala, Wallaby,Wombat, Possum
Divergent Evolution - Marsupials Tasmanian Devil, Diprotodon, Bandicoot, Thylacine
Convergent Evolution • Convergent Evolution • When two species evolve to occupy the similar niches • This is most obvious when you compare species from different ecosystems • If two separate species are placed under similar selective pressures they tend to evolve similar structures
Convergent Evolution Cacti – Americas Euphorbia – Africa
Convergent Evolution Sharks – Mostly Deep Sea Dolphins – Shallow water (continental shelves)
Coevolution • In many instances organisms evolve traits alongside one another • This is called coevolution • Two organisms can place selective pressures on each other • This forces them to evolve together • They often become more and more dependant on one another • Referred to as an “evolutionary arms race” • Most common in species with symbiotic relationships
Coevolution Hawk Moth Madagascar Long-spurred Orchid 30 cm tongue 30 cm spur (with nectar)
Patterns of Evolution Brazil nut Agouti
Homework • Pg 345 #1-7
