TOPIC 6: EVOLUTION Flashcards
What is evolution?
is a change in the genetic composition of a population of a species over time
the match of individuals to their environment is a product of the successes and
failures of their ancestors
* the present form and function of individuals are specializations to their
environment
What does this mean “the match of individuals to their environment is a product of the successes and
failures of their ancestors”?
indiv. is a way it is b/c of successful and unsuccessful strategies of its ancestors
- unsuccessful cause them to die before reproducing
- successful will then reproduce and those strategies will be present in the next generation
Adaptation
is the change in a genetically determined trait in response to environmental
conditions that enhances the ability to cope with the environment; becoming specialized for your environments, some traits are better to survive and become an adaptation
evolutionary process that takes place in a population over many generations
through natural selection
- TYPE OF EVOLUTION
Fitness
is the proportionate contribution of an individual to future generations
Involves:
* Number of offspring produced
* Number of offspring surviving to reproductive age
- how much of its own genes show up in future generations
- relative term need to have more offspring than other indiv. in pop; may mean you have to sacrifice your own life if it means passing on genes which means traits will show up in next generation (puts emphasis on repro than survival)
Natural Selection
operates on the individual
In any given environment
* Traits which enable individuals to grow, survive and reproduce are passed on to
future generations and selected for
- Individuals without those traits are selected against
Selection pressures
- Environmental conditions = abiotic factors
- Species interactions (predators, competitors) = biotic factors
establish differences in fitness among individuals with
different genotypes and phenotypes
Explain the broad idea of natural selection
- Individual variation has a genetic basis → traits are inherited
- Individuals with favourable traits are more likely to reproduce
- these individuals leave more descendants than others
- Favourable traits are passed on to future generations at a higher frequency
- Genetic composition of the population changes over generations or
evolves
List and explain the assumptions of natural selection
- Individuals of a species are not identical – genetic variation
- the indiv. can’t be identical b/c then there are not traits to select for or against and they will all pass on the same traits - Some of this variation is heritable; traits that are best need to be passed on
- ## Individuals leave different numbers of descendants – varying fitness
- Fitness depends on the interaction between an individual’s traits and its abiotic & biotic
environment
stabilizing selection
a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value
- selects against the extremes (large and small body size) favours the middle size
- medium sized have higher fitness
Directional selection:
occurs when a single phenotype is favored, causing the allele frequency to continuously shift in one direction.
- due to climatic event or predator removal
Diversifying (or disruptive) selection:
occurs when extreme values for a trait are favored over the intermediate values.This type of selection often drives speciation.
Biological Species Concept
– distinguish species based on their potential to interbreed
and produce fertile offspring
- implies that reproductive isolation (or genetic isolation) defines a species
because reproduction is the means of transferring genetic information (DNA)
Allopatric Speciation
individuals are geographically isolated by a physical barrier (e.g. river,
mountain, unsuitable habitat)
- Local environmental conditions will cause different selective pressures
leading to divergence over time
occurs when a species separates into two separate groups which are isolated from one another. A physical barrier, such as a mountain range or a waterway, makes it impossible for them to breed with one another. Each species develops differently based on the demands of their unique habitat or the genetic characteristics of the group that are passed on to offspring.
Sympatric Speciation
subpopulations are isolated without geographical isolation (e.g. timing of
breeding, behavioural differences, etc.)
groups of organisms in a population stop interbreeding when they still live in the same place
Speciation
- Premating – prevent mating
* Separation of mating events in space and time
* Behaviour – e.g. mating songs of male birds (attract females)
* Mechanical or structural incompatibility - Postmating – reduced survival or reproductive success of offspring
