Speciation

• Species - a group of similar organisms that can reproduce and produce fertile offspring
• Speciation - the development of a new species

Geographical Isolation (Allopatric Speciation)

• A physical barrier divides the population
• Two different environments
• Natural selection and genetic drift changes the genotype and phenotype
• Two populations evolve separately
• They become reproductively isolated therefore becoming two distinct species

Reproductive Isolation (Sympatric Speciation)

• A reproductive isolation occurs because changes in the alleles and phenotype of the two populations prevent them from successfully breeding together - Genetic drift can cause further divergence between isolated gene pools

• Seasonal Changes:- individuals develop different mating or flowering seasons or become sexually active at different times of the year
• Mechanical Changes:- changes in genetalia prevent successful mating
• Behavioural Changes:- a group develops a different courtship ritual that is not attractive to the rest of the population

Premating

• Habitat Isolation - populations inhabit different local habitants within one environment
• Temporal Isolation - same environment but are reproductively active at different times
• Behavioural Isolation - two populations have different courtship patterns
• Geographical Separation - populations inhabit different continents or islands etc

Postmating

• Gametes Mortality - sperm cannot reach or fertlise the egg
• Zygote Mortality - fertilisation occurs, but the zygote fails to develop
• Hybrid Sterility - hydrid survives (viable) but is sterile and cannot reproduce (no meiosis)
• Hybrid Inviability - F1 hybrid has reduced viability -> incomplete development