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Species Concepts and Speciation in General Biology

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  • Species concept used by early taxonomists

    The morphological species concept was likely used, classifying species based on physical appearance of preserved specimens.
  • Species concept incorporating reproductive compatibility

    The biological species concept defines species by their ability to interbreed and produce fertile offspring.
  • Species concept using molecular and cladistic data

    The phylogenetic species concept uses genetic data to identify the smallest group sharing a common ancestor.
  • Historical species concept applied to Galapagos tortoises

    Subspecies were recognized based on potential interbreeding, reflecting the biological species concept.
  • Current species concept applied to Galapagos tortoises

    Molecular data supports recognizing each tortoise population as a separate species under the phylogenetic species concept.
  • Mode of speciation for Galapagos tortoises

    Allopatric speciation due to geographic isolation on different islands or volcanic craters.
  • Mechanisms causing population change after isolation

    Mechanisms include mutation, natural selection, genetic drift, and gene flow, leading to genetic divergence.
  • Prezygotic reproductive barriers

    Barriers preventing fertilization, such as temporal, habitat, behavioral, mechanical, and gametic isolation.
  • Postzygotic reproductive barriers

    Barriers after fertilization, including reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown.
  • Temporal isolation example

    Species reproduce at different times, preventing mating.
  • Behavioral isolation example

    Differences in mating behaviors prevent interbreeding.
  • Hybrid zone allele frequency expectation

    Allele frequencies gradually change across the hybrid zone, showing a cline from one species to the other.
  • Outcome of hybrid zone with no hybrids after 40 years

    Likely reinforcement, where natural selection strengthens reproductive barriers to prevent hybridization.
  • Reinforcement in hybrid zones

    Selection against hybrids increases reproductive isolation between species.
  • Fusion in hybrid zones

    Two species merge into one due to extensive gene flow and lack of reproductive barriers.
  • Stability in hybrid zones

    Hybrids continue to be produced and coexist with parent species over time.
  • Fundamental niche

    The full range of environmental conditions where a species can survive and reproduce without competition.
  • Realized niche

    The actual conditions and areas a species occupies due to competition and other biotic factors.
  • Competitive exclusion principle

    Two species competing for the same resources cannot coexist indefinitely; one will outcompete the other.
  • Character displacement

    Evolutionary change in species traits that reduces competition when species coexist.
  • Effect of removing A. distichus on A. insolitus niche

    A. insolitus expanded its realized niche to open areas and showed morphological changes due to reduced competition.