Biology 1114 chapter 24/25 notes
Biology 1114 chapter 24/25 notes bio1114
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This 5 page Class Notes was uploaded by hannah warren on Monday February 2, 2015. The Class Notes belongs to bio1114 at a university taught by professor nelson in Fall. Since its upload, it has received 129 views.
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Date Created: 02/02/15
Chapter 2425 How New Species Arise Professor Nelson Biology 1114 no definition of species is completely satisfactory two concepts most useful morphologica species concept MSC bioogica species concept BSC MSC species distinguished by morphology anything you can see or measure shape color behavior biochemistry goal is to define separate groups ideally with no intermediates most commonly used three main problems gradations obvious boundaries between groups absent polymorphism same species has different appearances cryptic species two species very similar in appearance mullerian mimicry quotcopy cat species sweat bee and honey bee popuations whose members have the potential to interbreed with one another to produce viable fertile offspring but who cannot produce such offspring with members of other populations used in modern synthesis for a population to be a species under the BSC the question is whether gene flow occurs with other populations gene flow occurs between organisms within a species but NOT between different species species are genetically isolated from each other criteria may be hard to verify need potential for interbreeding in nature no hybrids or nonviable hybrids not all species reproduce sexually hard to apply to prokaryotes and asexual eukaryotes fossi species speciation creation of new species anagenesis speciation over time cladogenesis splitting of species into two increasing total organic diversity using BSC cladogenesis question becomes how does gene flow become low or nonexistent between two populations allopatric speciation two populations differentiate in geographically separate locations Common in animals less so in plants 1 separation of two parental populations 2 genetic divergence of parental populations 3 reproductive isolation of parental populations sometimes final reproductive isolation is achieved only after two populations reestablish contact sources of separation geographic barrier arises peripheral population cutoff founders colonize new territories many cases the founding population is small populations likely to genetically diverge a fusion of two species would occur in a hybrid zone when the hybrids have the same fitness as either parent can be substantial gene flow parent species can fuse into a single species gene flow can occur but hybrids aren t as fit as either parental type creates strong selective pressure to minimize interbreeding between two parental types Prezygotic Barriers habitat isolation tempora isolation breeding season behaviora isolation nocturnal or not etc mechanica isolation genitalia don t match up gametic isolation egg rejects sperm other chemical cues Postzygotic Barriers reduced hybrid viability reduced hybrid fertility hybrid breakdown reinforcement of barriers occurs when hybrids are less fit that the parent species over time hybridization decreases where reinforcement occurs reproductive barriers should be stronger in sympatric speciation sympatric females choose own species alopatric females don t have distinct preference sympathy reinforces reproductive isolation sympatric speciation two populations differentiate in a single geographic location common in plants origin of at least half of plant species by mechanism of polyploidy ess common in animals polyploidy cell division error gametes produce tetraploid tetraploid produces offspringnew species sometimes happens by switch in behavior Macroevolution microevolution evolution below species level subspecies populations macroevolution origin of new genera higher taxa generaly arise by accumulation of micro changes big picture of evolution reconstruction of ancestry of speciesorganisms geologica recordbiogeography mass extinctions adaptive radiations fossi records geological record four eras cenozoic contains mammals birds insects started 65 million years ago mesozoic reptiles gymnosperms 250 million years ago paleozoic colonization of land by sea plantsanimals 540 million years ago precambrian prior to 540 million years ago hard bodied animals Continental Drift earth s surface composed of moving crustal plates that are responsible for mountains volcanoes sea floor valleys etc continents aggregate about once every 12 billion years ast aggregated at the end of the Paleozoic era 250 million years ago Pangea split into Laurasia and Gondwana now continents almost maximally dispersed heps contain current distribution of organisms Mass Extinctions severa evident in fossil record two biggest End Permian ended Paleozoic 96 marine species lost End Cretaceous ended Mesozoic reptiles dinosaurs extinct end permian may be due to volcanoes increase in C02 sea level changes mass extinction currently in progress due to human impact on the environment add element of chance making future evolution impossible to predict historica contingencies accidents of fate vital to story of evolution being successful at current time no guarantee of survival surviving taxa radiate into niches left vacant by extinction takes millions of years to diversify again Adaptive Radiation evolution of many species from one ancestral species occurs rapidly common when new adaptive zone is occupied new area is colonized or after a mass extinction common feature unoccupied niches are available for exploitation first species to exploit has huge advantage niche how an organism makes its living new adaptive zonenew major niche adaptive radiation occurs most readily when conditions are good for allopatric speciation large land mass island clusters etc speciation facilitated if islands aren t too far apart or too few in number between mass extinctions successful species persistsuppress new types
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