Patterns of Descent with Modification

• Species


  Groups of interbreeding natural populations that are reproductive isolated from other such groups
• Geographic/Ecological/ Habitat Isolation 


  refers to separation of members of a population by a physical barrier, such as a mountain or body of water, which disrupts the gene flow between them and begins the process of speciation
• Temporal/ Seasonal Isolation 


  differences in the timing of critical reproductive events prevent members of closely related species, which could otherwise breed with one another, from mating and producing hybrid offspring.
• Behavioral Isolation 


  reproductive isolation based on the behavior of species in the context of mating rituals and signals
• Mechanical Isolation 


  two species are said to be mechanically isolated when differences in their reproductive organs prevent interbreeding and thus, prevent tye birth of sterile hybrid.
• Gametic Isolation 


  inhibits mating between two distinct species, by ensuring that their gametes don't interact with each other. This incompatibility of gametes prevents the formation of inter-species hybrids, and maintains the integrity
• Hybrid Inviability 


  Sperm and egg from the two species may combine, but the gametic information is insufficient to carry the organism through normal development. The embryo dies after a few cleavages or sometime before birth.
• Hybrid Sterility 


  Different species breed and produce offspring, which does survive to become an adult. However, the adult suffes from very low fertility, therby incapable of giving birth to offspring.
• Hybrid Breakdown 


  Two related species can hybrizide, and their F1 offspring are fertile. But successive generations (F2 and beyond) suffer lower viability of fecundity. Thus they cannot become an established population.
• Allopatric Speciation 


  Involves the physical separation of a species into two groups.
• Allopatric Speciation 


  May occur due to climatic changes, movement of tectonic plates leading to fragmentation of a mass of land eruption of a landmass, formation of waterways, or the presence pf an impassable mountain range.
• Allo means....

  Other
• Parapatric Speciation 


  Occurs due to partial spatial isolation of populations, and is characterized by a small overlap in their ranges as well as significant gene flow amongst the population.
• Allopatric Speciation 


  Gene flow reduces due to changes in local conditions, and the two population become reproductively isolated.
• Para in Parapatric means....

  beside
• Peripatric Speciation 


  A small group of members inhabiting a peripheral range region undergoes reproductive isolation to form a new species