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lecture 2

by: Jordyn

lecture 2 ISB 202

GPA 3.6
Appl Envir & Organismal Bio
Pamela Rasmussen

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Appl Envir & Organismal Bio
Pamela Rasmussen
Class Notes
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This 3 page Class Notes was uploaded by Jordyn on Friday February 27, 2015. The Class Notes belongs to ISB 202 at Michigan State University taught by Pamela Rasmussen in Winter2015. Since its upload, it has received 31 views.


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Date Created: 02/27/15
How Biodiversity Arose Speciation 0 When two species gradually arise form one Species are groups of organisms reproductively isolated from other such groups 0 Can happen if sufficient genetic variability exists to start process 0 Further selection andor random changes can cause additional mutations to stabilize between populations Why is speciation important 0 Because all biodiversity is the result of speciation Small heritable differences accumulate and over a long time lead to big differences Eventually to major lineages Phases of speciation 0 Geographic isolation phase 1 Most common mechanism of speciation Two populations of the same species become physically isolated for long periods Allopatric Speciation model 1 Initiated by a physical barrier 2 Genetic differences accumulate 3 Reproductive isolation occurs separate species Reproductive isolation phases 23 0 Develop different characteristics due to random mutations andor selection operating on isolated populations in different ways 0 Eventually populations diverge so much in genetic makeup they cant interbreed successfully Mechanisms of reproductive isolation 0 Premating isolating mechanisms Prevent individuals from mating 0 Temporal o Populations isolated by breeding at different times 0 Habitat 0 Different habitats Behavioral o Speciesspeci c courtship rituals Gametic Barrier o Incompatibility of eggs and sperm 0 Mechanical o Incompatibility od male and female gentaHa 0 Postmating isolating mechanism Offspring form mating s don t survive or don t reproduce Hybrid inviability Offspring die as embryos Hybrid sterility Offspring sterile o EX mules o Donkeys have 62 chromosomes horses 64 o Mules usually sterile 0 Can just be reduced to be selected against Tigers and lions can produce offspring called ligers and tions but ligers and tions cannot produce offspring what mechanism causes this hybrid sterility Usual type of evolution 0 Divergent evolution Where organisms normally evolve more and more differences Related species become less and less similar with time and continued evolution Butter y becoming two different species De nitions 0 Adaptions traits that organism possesses that allow it to survive and reproduce better in its environment or particular niches o Niche lifestyle organism Adaptive radiation 0 Rapid evolution of a single or a few species into many to ll many adaptive niches Often occurs when inhabited areas by competitors are colonized ex empty niches found 0 Especially noticeable on isolated islands When species is separated geographically and one or both isolates evolve in different direction lf then reunited geographically 3 possibilities lnterbreed eventually losing differences and merging 0 Adaptive radiation Compete for same resources one becoming extinct Avoid competition of one or both speciation 0 Adaptive radiation Darwin s finches Galapagos 0 Now species 310 species per island 0 All share common nch ancestor from S America or Cadbbean o Evolved in Galapagos in absence of most other bird species 0 Evolved in Galapagos in absence of most other bird species 0 Different species crush big or small seeds catch insects take nectar or buds even drink blood Driving force for evolution was availability of different food sources Adaptive radiation TenrecsMadagascar o All share common insectivore ancestor Probably arrived near end of age of the dinosaurs 6070 mya Filled vacant niches of many small mammals Some like hedgehogs otters mice shrews moles gerbils ect Hawaiian Honey creepers o All share a single nchlike ancestor 0 Very few other birds ever reached Hawaii 0 Nectar feeding woodpeckers insect eating seedcracking What do terraces honeycreepers and Darwin s nches have in common all show adaptive radiation all evolved in high Convergent evolution 0 When organisms that aren t closely related evolve similar traits ln adaptation to similar environments andor adaptation to similar environments andor adaptation to similar niches o Analogy o Restated when unrelated species evolve common solutions to the same problems 0 Doesn t make them more closely related genetically o All above examples of adaptive radiation also include examples of convergent evolution Adaptive radiationconvergent evolution Australian marsupials quotHorned beetlesquot 0 Many different solutions to problem of overpoweringdislodging rivals Horns arise form different body parts Take different shapes Occur in several groups


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