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my own bio study guide test 3

my own bio study guide test 3 - Morphological species...

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Morphological species concepts Species means “kind” or “appearance” (good working definition) problems = males and females look very different, children and adults look very different, species may vary in morphology over their range, may vary due to functional roles The Biological Species Concept “A species is one or more populations of individuals that share a gene pool under natural conditions, and produce fertile offspring that are reproductively isolated from other species. ---the main focus is on GENETIC DIFFERENTIATION Genetic Divergence --gradual accumulation of differences in the gene pools of populations ---Natural selection, genetic drift, and mutation can contribute to divergence ---gene flow counters divergence Reproductive Isolation = the cornerstone of the biological species concept --- speciation is the attainment of reproductive isolation --- reproductive isolation results as a bi-product of genetic change Problems with Biological Species Concept --the biggest difficulty with the BSC is that we cant assess gene flow and reproductive isolation without detailed study. Biologists think about species in terms of BSC ---However, most of what we know about species diversity assumes morphospecies How Species form and achieve reproductive isolation ----They use Reproductive isolating mechanisms: --prevent pollination or mating --block fertilization or embryonic development --cause offspring to be weak or sterile These are divided into different categories: -- prezygotic— before mating and fertilization -- post-zygotic— after fertilization Prezygotic Isolation consists of many parts Mechanical Isolation ---Wasp and Zebra Orchid --orchid scent causes many kinds of male wasps to try and mate with flower --however, only one species fits flower well enough to pollinate it
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Temporal Isolation --Two closely related cicada species emerge to mate on very different cycles (13 year vs. 17 yr) --although they overlap in habitat, sexual parents only overlap every 200 years Behavioral Isolation --Mating rituals such as songs or other courtship displays can prevent gene flow between similar species! Ecological Isolation --some insects live in sympatry but feed and lay their eggs on different plants. --reproducing adults never come into contact with eachother Post-zygotic mechanisms = early death, sterility, and low survival rates How Species form (part 2): Models for speciation Allopatric speciation =physical separation of populations leads to new species -Some sort of barrier arises and prevents gene flow in geographically isolated populations --effectiveness of barriers varies with species Sympatric speciation= ecological separation in same locality causes populations to diverge --species forms within the home range of parent species --feeding preferences localize species in different areas.
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Parapatric speciation= populations in contact along a common border evolve into distinct species --neighboring populations become distinct species while maintaining contact along a common border.
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