Final Exam Review BIOGEO.docx

Different forms of a gene at the same locus are

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Different forms of a gene at the same locus are responsible for differences between individuals and their inheritable traits - New alleles arise by mutation and changes in the frequencies of alleles in populations occur through genetic drift, gene flow and natural selection - Founder effect: when a small number of individuals are isolated from a larger population; they may have much less genetic variation that the original species and the characteristics that the isolated population has will be affected by chance Darwin’s finches – explain adaptive radiation - Repeated episodes of colonization and divergence, mostly among different islands produced six genera and fifteen species exhibiting different forms and lifestyles - Adaptive radiation: the development of many species from a single founding species Allopatric Speciation - Formation of new species by geographic isolation - Can occur with and without variance - Numerous causes of isolation o Change dispersal on distant island or continent
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o Splitting of continents Mode I: Vicariance - An extreme environmental change that creates a barrier to dispersal somewhere within the range of an ancestral species - Tend to isolate many co-distributed species at the same time Mode II: Peripheral isolates or founder events - Individuals may disperse across an existing barrier to colonize a previously uninhabited region - Tends not to happen to multiple species simultaneously - Genetic drift may be more prevalent than natural selection initially and populations may diverge more rapidly Sympatric Speciation - Formation of new species within the same geographic area - Challenge: individuals in the same geographic region have no physical barriers to cause reproductive isolation – new traits from mutations can be passed throughout the population - Difficult for genetically distinct, reproductively isolated new species to arise – but some evidence exists - Evolutionary ecologists are finding that the reproductive isolations required for sympatric speciation can occur between individuals of the same species within the same geographic region in a number of different ways Sympatric variability - Resulting from adaptive radiation - Driven by need t exploit different niches (resources) - Result from intense competition Mechanisms of isolation - Behavioural - Niche specialization - Temporal isolation (time of day for activity) Peripatric Speciation - Geographic pattern of speciation (small isolated) - Rapid speciation can occur at edges, small gene pool, limited genetic drift (founder principle) - Or limited genetic diversity causes bottleneck (not enough variability to fuel development of more new species). Determines whether new species forms or not – need variation - It looks sort of like allopatric speciation with dispersal or parapatric with some spatial separation - Drive towards speciation may not be a driver for dispersal here (allopatric) – small groups becomes isolated over time – scale - Recognition of peripatric speciation often related to low genetic variability in founder population and proximity to source population Sympatric and Parapatric Speciation
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Speciation can also occur within spatially overlapping populations. The degree of overlap is the
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