Unit 2: Evolution and Adaptations Flashcards
Thomas Malthus provided Darwin with a mechanism for understanding
natural selection
carry capacity
- limiting factors in nature such as food resources stay constant in nature or grow arithmetically
- when the carrying capacity is reached limiting factors in populations begin to take place
- a population cannot exceed the carrying capacity without ramifications
Populations tend to grow [–] if uncontrolled
exponentionally
Competition for resources ensures
that not all individuals recieve everything required to reproduce at high capacity
Reproductive Success
- the measure of ability to contribute DNA to future generations
- # of generations that are raised to reproductive age
Fitness
strategies and adaptations that produce more offspring are likely to remain and thrive in the population and become the norm
What are the three prerequisites or “ingredients” for evolution by natural selection
- variation among the individuals in a population for a particular trait
- variation must be heritable - it must have a genetic basis
- variation in the trait must have consequences for the fitness of individuals, resulting in differences in survival + reproductiive success
The gene pool is
shared by all the individuals within the population
each individual has their own subset
what is a gene pool
all traits that could potentially get passed on
population
all the individuals of the same species that can interbreed
consequences
some versions are more successful and some are not successful
Bottleneck Effects can lead to
decrease in diversity and eventual population decline
could be due to disease or natural disaster
Bottleneck Effect
sharp reduction in size of population due to environmental events
Founder Effect
- When a small group of individuals form the gene pool for a new population
- move and don’t replicate original diversity
- not representative of original population
think of colonization
Selection can change the frequency of traits in 3 ways
- stabilizing
- directional
- disruptive
stabilizing selection
- outliers are unsuccessful
- becomes more uniform w/ less variation
- leads to a lack of phenotypic diversity over time
Directional selection
- moves populations toward a current environmental goal
- shift towards one trait
- variations of traits that allow organisms to survive shift graph
- as food availability changes, increased beak size is advantageous
Disruptive selection
- when more than one phenotype is adaptive within the environment
- intermediate traits don’t survive the best
- extremes survive
- two successful traits
What happened during the 1970 drought
- resulted in large birds
- large strong, beaks
Why did average beak depth in Darwin’s finches changes
- changes in seed size and hardness due to environmental changes
- strong selection pressure
What happened during the 1980
- resulted in small birds
- small beaks
- soft seeds
- due to El Nino influence
The direction of selection may not be the same as that of
overal evolution
What are the driving forces for changes
selection osciallations
Random mutation can lead to
evolution
Hardy-Weinberg Equilibrium in Allele Frequency Equation
p + q = 1
conditions for hardy-weinberg equilibrium
- random mating
- no emigration
- no immigration
- no mutation
mutation rates in humans have been esitmated to be in the order of [–] to [–] per [–] per [–]
mutation rates in humans have been esitmated to be in the order of 10^-4 to 10^-6 per gene per generation
the rate of nucleotide substitutions is estimated be 1 in 108 generation, implying that
30 nucleotide mutations would be expected in each human gamete
Selective pressure by predators can
drive selection
* example: predators prefer larger amphipod offspring, so small offspring are more likely to survive and reproduce
Peppered moths demonstrate allelic frequency shift due to
- a change in environmental conditions (SO2)
- industrial melanism
what is industrial melanism
increase in pollution darkens roosting areas
Rattites are more closely related to [–] than each other, indicating [–]
Rattites are more closely related to flighted-birds than each other, indicating **a more complex phylogeny **
In allopatric speciation, genetic drift can
generate separate species
independent evolution due to differing environmenal forces results in
inability to interbreed
allopatric speciation
- 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.
Sympatric speciation
- occurs when there are no physical barriers preventing any members of a species from mating with another, and all members are in close proximity to one another
- A new species, perhaps based on a different food source or characteristic, seems to develop spontaneously
some populations can adapt to [–], which allows rapid [–]
- polyploidy
- sympatric speciation
polyploidy
- the acquistion of extra chromosomes
- many species can’t tolerate it, but those who can demonstrate rapid speciation due to inability to interbreed with original cospecies
The human genome demonstrates adaptation to a variety of
environmental conditions
