Download Evolution in Populations

Macroevolution: Evolution of New Species
Species: a group of organisms that can interbreed & produce fertile offspring
Speciation: the evolution of new species (by genetic change or change in form)
- occurs when members of similar populations no longer interbreed
Methods of Speciation:
 Reproductive Isolation: occurs when formerly interbreeding organisms can no longer mate &
produce fertile offspring
o
Genetic Isolation – genetic differences are too great to breed successfully
o
Geographic Isolation - occurs when physical barriers divide a population & prevent
interbreeding
Beetles in Grassland Become Green
Beetles in Woody Habitat
Become Brown
o
Behavioral Isolation – mating behaviors or mating seasons don’t allow for mating
o
Polyploidy – any species with extra sets of chromosomes (common in plants)
 Polyploids can interbreed or self-fertilize, forming separate species
o
Hybridization – When two closely related species attempt to mate
 Typically results in sterile offspring, but can sometimes lead to new successful
species
Speed of Speciation (Macroevolution):
 Gradualism: the idea that species originate through a slow, gradual change of adaptations over
long periods of time
 Punctuated Equilibrium: the idea that species
can remain stable for long periods until
environmental changes cause many new species
to appear.
o Environmental changes lead to rapid
changes in a populations gene pool
o Speciation occurs in 10,000 years or less
Patterns of Macroevolution
 Divergent Evolution (Adaptive Radiation): species
diverge, or become increasingly distinct from an
ancestral species
o Often occurs when populations adapt to use
different niches
o Example: Darwin’s Finches / Hawaiian
Honeycreepers
 Convergent Evolution: The process by which unrelated species become similar as they adapt to
similar environments.
o Example: Emu (Australia), Ostrich (Africa), Rhea (South America)
 Coevolution: Organisms that live in close
association develop adaptations to one another’s
existence.
o Example: moth and orchid (mutualism)
 Extinction: When all members of a species die off or fail to reproduce
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Scientists estimate that 99% of all species that ever lived on Earth have become extinct
Many cases of extinction are the result of environmental change
When the environment changes, species that were well adapted can become poorly
adapted
If the environment changes faster than a species can adapt, extinction can result