Speciation Species o Diversity arises w in a species stays in the species o o Each is unique and distinct This is also true of individuals or pops Species are distinct in an evolutionary sense when pops become genetically reproductively isolated for lack of gene flow Speciation o o o o Can occur with or without natural selection The divergence is strengthened by If a single population is split into two populations that are unable to interbreed different mutations will appear by chance in the two populations Two separate populations will gradually become distinct as different mutations are introduced and propagated in each population At some point they will become incompatible o Partially Reproductively Isolated Hybrid offspring may have reduced fertility or viability o Allopatric Speciation May form Dispersal Vicariance Peripatric Speciation Mainland Population Island Population the central population of a species geographically remote from the initial mainland population s habitat o Classically small ad often in an environment that s slightly different from that of the mainland population o Adaptive Radiation o Genetic Drift is more pronounced in small populations Occurs when there are many ecological opportunities available for exploitation Co speciation Sympatric Speciation Difficult to find evidence of it Instantaneous Speciation Chromosome may change in hybridization Tetraploid from each parental species o Some organisms cannot sustain this hybrid inherits a of chromosomes 2 from each Polyploid o Reinforcement of Reproductive Isolation inherits chromosome sets selection in favor of enhanced prezygotic isolation to prevent the production of less fit hybrid offspring the process by which diverging populations undergo natural Mating Discrimination Biological Species Concept BSC Problems Species are groups of interbreeding populations that are reproductively isolated from other species Different species breed with each other You would need to test whether organisms can reproduce in order to categorize them as a species o o o o o Organisms of the same species might not reproduce o Doesn t apply to asexual or extinct organisms Morphological Concept o Members of the same species usually look Some species look alike Problems Males may look different than females Members of a single species may not look alike Ring Species Hybridization o Mainly in plants Ecological Niche o A complete description of the role the species plays in its environment o Nutritional needs water habitat etc o It is impossible for two species to coexist in the same location if their niches are because between them for resources will lead to the extinction of them Ecological Species Concept ESC Evolutionary Species Concept EvSC the idea that members of a species all share a common ancestry and a common fate there is a one to one correspondence between a species and its niche o Requires that all members of a species are descended from a Reproductive Isolation o Prezygotic Isolation Incompatibility between sperm and egg Physical features Lock and Key interaction Temporal Separation Ecological Separation both components physical or biochemical must for successful isolated in time isolated by space Behaviorally Isolated o Post zygotic Isolation Typically involve some kind of Zygote must fail to develop after fertilization May produce viable but offspring Species Concepts different ways to define a species o Phylogenic Species o Morphological Species o Biological Species Tree of Life Recognizes more species than other species concepts shows how every species is connected Can be applied more easily Can t define cryptic species that differ in non physical traits Can t interbreed no gene flow Difficult to test