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SPECIATION
the process by which one species splits into 2 or more species |
-focal point of evolutionary theory because the appearance of new species is the source of biological diversity |
-it forms the bridge between microevolution and macroevolution |
PREZYGOTIC BARRIERS
impede mating or hinder fertilization if mating does occur |
- habitat isolation |
-temporal isolation |
-behavior isolation |
-mechanical isolation |
-gametic isolation |
HOW FAST DOES SPECIATION OCCUR?
-the time interval between speciation events varies considerable, from a few thousand years to tens of millions of years |
- punctuated equillibrium: isolated episodes of rapid speciation between long periods of little to no change |
gradualism: accumulation of gradual changes over time |
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WHAT IS A SPECIES
a group of populations whose members can interbreed in nature and produce viable, fertile offspring, but cannot produce viable, fertile offspring with other such groups |
POSTZYGOTIC BARRIERS
barriers that prevent the hybrid zygote from developing into a viable, fertile adult |
-reduced hybrid viability |
-reduced hybrid fertility |
-hybrid breakdown |
TYPES OF SPECIATION
Allopatric Speciation |
geographic barrier between the 2 populations |
Sympatric Speciation |
populations that live in the same geographic area |
-polyploidy |
-habitat differentiation |
-sexual selection |
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WHY DOES SPECIATION OCCUR
reproductive isolation |
the existence of biological barriers that impede members of 2 species from interbreeding and producing viable offspring |
HOW DOES SPECIATION OCCUR?
- speciation can occur in 2 main ways depending on how gene flow is interrupted between populations of the existing species |
- allopatric speciation-geographic isolation |
-sympatric speciation- no geographic isolation |
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