Speciation Flashcards
BIOLOGICAL SPECIES CONCEPT (BSC)
Species = a group of actually/potentially interbreeding organisms that is reproductively isolated from other groups
REPRODUCTIVE ISOLATION
Cannot mate successfully outside group
No hybridization (genetic exchange between distinct populations)
- Or hybrids die or are sterile
Creates a barrier to gene flow between species/exchange of genetic information
ISOLATING MECHANISMS
- geographic separation
- differences in behavior
- physical appearance
- # chromosomes
- reproductive physiology
GENE FLOW
The movement of genetic material within or between populations
Maintains similarities among members of the population(s)
NO GENE FLOW
- Migration not possible
- Local adaptations favored
- Phenotypes become distinct
- Species reproductively isolated
WITH GENE FLOW
- Migration possible between habitants
- Gene flow swaps local adaptation
- Phenotype intermediate
SPECIATION
The forming of new species due to evolution and natural selection
ANAGENESIS
- Time based speciation
- Slow gradual change that accumulates
CLADOGENESIS
- Involves splitting
- Population that splits into two
ALLOPATRIC SPECIATION
- Geographic separation, no-overlapping ranges
- Two or more population of a single species become geographically isolated and then diverge to form new species
COMPLETE REPRODUCTIVE ISOLATIONS MEANS
We have two new species
INCOMPLETE REPRODUCTIVE ISOLATIONS MEANS
Hybridization can occur
CHARACTER DISPLACEMENT
- Competition for resources creates a separation of the population within the same geographical location
- There are no physical barriers between the two populations, they are separate due to competition)
REINFORCEMENT
A situation where hybrids are selected against because their mosaic of traits are not beneficial to either environment
- Creates a separation of populations because hybridization between the two is not viable
CHARACTER DISPLACEMENT VS REINFORMCEMENT
Both cases, these mechanisms increase reproductive isolation
Character displacement: Via competition and niche partitioning
Reinforcement: Via selection against hybrids
PARAPATRIC SPECIATION
- Limited overlap in ranges (no true barrier)
- Groups in different parts of the range experience different environments
- At boundaries hybrids will be selected against
- Reproductive isolation not complete, but natural selection keeps populations separate
SYMPATRIC SPECIATION
- Overlapping ranges
- Differences between sub-groups develop without geographic separation
- Selection against intermediate types will lead
to two new species (disruptive selection) - Different adaptations to SAME environment
ECOLOGICAL NICHE
How a species exploits/uses its habitat
ADAPTIVE RADIATION
When a species colonizes a new habitat with many open niches
PHYLELTIC GRADIULAISM
- Tiny changes accumulated gradually via microevolution
- gradual transformation of one species into another
- Rates of evolution are constant and slow
- Anagenesis
PUNCTUATED EQUILBIRUIM
- Gould & Eldredge (1972)
- Short periods of rapid change after long periods of little or no change (Stasis)
- New species arise through splitting (isolation)
- Can be fast
- Cladogenesis
MOST ACCEPTED EXPLANATION FOR SPECIATION:
Different species occur due to different selection pressures or genetic drift
