B6 - How Species Form PDF

B6 - How Species Form I can… Describe modern evolutionary theories (punctuated equilibrium versus gradualism) How Species Form Biological species consist of populations that can breed and produce a group of viable offspring that can also reproduce in nature Reproductive iso...

B6 - How Species Form I can… Describe modern evolutionary theories (punctuated equilibrium versus gradualism) How Species Form Biological species consist of populations that can breed and produce a group of viable offspring that can also reproduce in nature Reproductive isolation: ○ Dissimilar species can’t mate (Ex. Elephants and frogs can’t mate) ○ Populations that breed at different time periods (Ex. Breed in fall vs. spring) Forming New Species Speciation: Two general pathways that can lead to the creation of a new species 1. Transformation: Accumulated change in a population, original species gets replaced 2. Divergence: One or more species arise from a parent species - increases biological diversity because it increases number of species Isolation of Populations Geographical barriers: Keep populations physically separated ○ Physical barriers only need to be present long enough for speciation to occur ○ Leads to reproductive isolation ○ Ex. Bodies of water, islands separating Biological barrier: Occur between species that share same ranges ○ Ex. Different niches, different fertile time As time passed, different lineages of finches abegan to become geographically and reproductively isolated from each other. Speciation in Reproductively Isolated Populations When populations become reproductively isolated, speciation has occurred Animals can become reproductively isolated within geographical range of parent population if they begin to use resources that aren’t used by their parents Adaptive Radiation Adaptive radiation: Diversification of common ancestral species into a variety of differently adapted species Ex. Darwin’s finches Adaptive Radiation Why does it occur? ○ As offspring of original ancestor disperse, they encounter new environments with slightly different selective pressures ○ Selective pressure: Environmental condition or conditions that select for certain characteristics of individuals, and select against others ○ Selective pressure resulted in different feeding and mating habits as well as physical differences Modern Evolutionary Theory Two models that scientists have proposed: 1. Gradualism: Describes evolution as gradual change, occurs steadily in a linear fashion According to model, big changes, such as evolution of new species, occur as result of many small changes 2. Punctuated equilibrium Long periods with very little change punctuated by rapid periods of change and speciation (comes and goes in bursts) Theory proposed that when species first diverges from parent species, major morphological changes occur New selective pressures will select for different adaptations, resulting in next generation being quite different from parent generation Modern Evolutionary Theory