Chapter 24- Origin of Species PDF

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This chapter in AP bio focuses on how did species development. It goes into detail about how all organisms evolved from prokaryotes. ...

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Chapter 24- The Origin of Species Macroevolution - the origin of new taxonomy Microevolution- the changes in time of allele frequencies within a population (micro leads to macro) Speciation: origin of new species 2 processes Anagenesis (phyletic evolution)- accumulation of heritable changes associated with transformation of one species into another Cladogenesis (branching evolution)- budding of new species from a parent species that continues to exist (basis of biological diversity because of increases the number of species) Reproductive Isolation (isolation of gene pools) (species isolated by barriers that prevent fertilization) Prezygotic barriers- impede mating between species or hinder the fertilization of the ova if members of 2 different species attempt to reproduce Ex) Habitat (snakes: some live in water and other live on land) Ex) Behavioral (fireflies: have different mating signals) Ex) Temporal (salmon: seasonal mating) Ex) Mechanical (flower; pollination anatomy) Ex) Genetic (frog's: egg coat receptors prevent sperm from other species to fertilize the egg) Reduced hybrid viability (zygote fail to develop or reach sexual maturity) Reduced hybrid fertility (mule: horse x donkey from a sterile mule) Hybrid breakdown (2nd generation hybrids are sterile) One definition of species is a group of populations whose individuals have the potential to interbreed and produce fertile offsprings. However this definition has limitations. Asexual reproducers interbreeding is meaningless Exceptions: coyotes breed with dogs and wolves and produce viable hybrid offsprings, but all 3 reamian different species Complex situations: 4 different subspecies of deer mouse with some interbreeding where ranges overlap Alternative definitions Morphological species concept- species should be separated by physical

characteristics taxonomically; includes fossils. The key aspect of this definition is that individuals of a species are morphologically similar to one another, yet morphologically distinct from individuals from another species. Ecological species concept- species should be defined by their unique rolls in environments; where species live and what they do, not by what they look like. Modes of Speciation Allopatric Speciation Geographical barriers form Magnitude of barriers depends on organisms abilities to disperse themselves: either mobility of spores, pollen, or seeds. Example pupfish of Death Valley Springs. 50000 years ago the area had a rainy climate. 4000 years ago and became dry and desert-like. all that is left of the original lakes/rivers is small Springs all varying in temperature and salinity. Each each spring has its own species of pupfish. Sympatric Speciation New species arise within the range of a parent population. No Geographic barrier. Sympatric speciation occurs when populations of a species that share the same habitat become reproductively isolated from each other. Usually caused by a genetic change. An example is a genetic mutation- polyploidy (extra set of chromosomes which caused a reproductive barrier from parent species). Sympatric Speciation Animals Genetic factors cause a group to become fixed on resources not used by parent population. an example is soapberry beatles. Hybrid Zone Two populations diverge after geographic isolation then make 2 degree contact and interbreed at overlap range (hybrid zone). Small but stable. Still two distinct populations outside hybrid zone. Punctuated Equilibrium and Gradualism Punctuated equilibrium is rapid change followed by periods of no evolution. On the other hand, gradualism states that evolution is always happening and that change is slow and steady....