Transcript Speciation
Speciation The evolution of species Speciation Occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment Geographic Isolation Occurs whenever a physical barrier divides a population The divided groups progress differently in response to their environments Ex. Finches on different Galapagos islands Reproductive Isolation Occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring Ex. One population of tree frog mates in the spring and the other in the summer Chromosomes Chromosome numbers play a role in speciation Any species with a multiple of the normal set of chromosomes is known as a polyploid Can be caused by mistakes in meiosis or mitosis If their offspring survive, they are usually unable to reproduce, but some can with other polyploids Ex. Wheat, cotton, apples, and bananas Timeline Speciation can occur quickly or slowly Gradualism – the idea that species originate through a gradual change of adaptations Punctuated equilibrium – argues that speciation occurs relativley quickly, in rapid burst followed by long periods of genetic equilibrium Both theories are supported by different fossil evidence Patterns of Evolution Support the idea that natural selection is an important agent of evolution Three main patterns ◦ Adaptive radiation ◦ Divergent evolution ◦ Convergent evolution Adaptive Radiation An ancestral species divides into many species to fit a number of diverse habitats Ex. Honeycreepers on the Hawaiian Islands Divergent Evolution Species that were once similar to each other become increasingly distinct Caused by different populations adapting to different environmental conditions, and they become more different as they adapt, eventually becoming separate species Convergent Evolution Occurs when unrelated species occupy similar environments in different parts of the world, but because they share a similar environment, these two different species adapt to be very similar to each other