Exam 2 Flashcards
Ecological Species Concept
defines a species by its ecological niche; applies to sexual and asexual species and emphasizes the role of disruptive selection
Macroevolution
-broad patterns of evolutionary change above the species level
-cumulative effect of many speciation and extinction events
Speciation
the process by which one species splits into 2 species
What does speciation contribute to biology?
-produced tremendous diversity of life
-helps to explain the unity of life
-forms a conceptual bridge between micro- and macroevolution
Temporal Isolation
species that breed at different times of day, in different seasons, or different years –can’t mix their gametes
Microevolution
changes in allele frequencies in a population over time
Behavioral Isolation
-prezygotic barrier
-courtship rituals and other behaviors unique to a species are effective barriers to mating
Biological Species Concept
-have the potential to interbreed in nature
-produce viable, fertile offspring
-don’t produce viable, fertile offspring with members of other such groups
Reproductive Isolation
-when biological barriers impede members of 2 species from interbreeding and producing viable, fertile offspring
-limits the formation of hybrids
Habitat Isolation
-prezygotic barrier
-two species that occupy different habitats within same area may encounter each other rarely, if at all
What was early life on Earth like?
-inhospitable
-little to no oxygen in atmosphere
-meteorite impacts and volcanic eruptions common
-seas full of mineral salts
Gametic Isolation
-prezygotic barrier
-sperm of one species may not be able to fertilize eggs of another species
Prezygotic Barriers
-block fertilization from occurring by impeding different species from attempting to mate
-preventing the successful completion of mating
-hindering fertilization if mating is successful
Mechanical Isolation
-prezygotic barrier
-mating attempted, but morphological differences prevent its successful completion
Postzygotic Barriers
-prevent hybrid zygotes from developing into viable, fertile adults
Reduced Hybrid Variability
-genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment
Reduced Hybrid Fertility
Meiosis may fail to produce normal gametes, resulting in sterility if the parent species have chromosomes of different number or structure (i.e. mules)
Hybrid Breakdown
First generation of hybrids are viable and fertile, but offspring in the next generation are feeble or sterile
What are the limitations of the Biological Species Concept?
-cannot be applied to fossils or asexual organisms (including all prokaryotes) because mating can’t be observed
-emphasizes absence of gene flow, but gene flow occurs between many morphologically and ecologically distinct species (i.e. grizzly bears + polar bears = grolar bears)
Morphological Species Concept
-distinguishes a species by its structural features
-applies to sexual and asexual species, doesn’t require info on the extent of gene flow
-Disadvantage: relies on subjective criteria
Allopatric Speciation
-gene flow restricted between populations by geographic isolation
-intrinsic barriers to reproduction due to genetic change driven by processes including divergent selection and genetic drift
-reproductive barriers prevent interbreeding even if contact restored
Sympatric Speciation
-reproductive barrier isolates subset of populations without geographic separation
-result from polyploidy, sexual selection, or natural selection resulting from switch in food or habitat
What are the two types of polyploidy?
Allopolyploids and Autopolyploids
Autopolyploidy
-have more than 2 sets of chromosomes from a single species
-in plants, mitotic errors can result in production of tetraploid cell from diploid cell
-fertile offspring produced through self-fertilization or mating with other tetraploids
-mating between tetraploids and diploids produces triploid offspring with reduced fertility