AP Bio Unit 7

Darwin’s hypothesis

Organisms that left south America to go to Galapagos Islands allowed them to diversify and gave rise to new species.

Descent with modification

Evolution

Change in genetic make up of a population over time; descent with modification

Natural Selection

A process in which individuals who have certain traits tend to survive and reproduce at higher rates than other individuals because of those traits

Phenotypic variations in the population

Favorable phenotypes are measured by fitness through reproductive success

1. Traits are heritable

2. More offspring are produced that can survive

Selective pressures

External environmental factors that influence which organisms can survive+reproduce

Adaptations

Inherited characteristics of organisms that enhance their survival and reproduction

Differential survival

Unequal ability of individuals within a population to survive and reproduce due to variations in their inherited traits → competition is the cause

Artificial selection

Selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits

Ethology

The study of how evolutionary processes shape inherited behaviors and the ways that animals respond to specific stimuli

Proximate Cause

How a behavior occurs or how it is modified

• What’s the stimulus? More emphasis on nurture than nature

Ultimate Cause

Why a behavior occurs?

• nature heavy rather than nurture

Innate behaviors

Developmentally fixed, inherited, born with

Learned behaviors

Depend on environmental influence, experiences affect, high variation in a population

Fixed action patterns (FAPs)

Sequence of unlearned acts directly linked to a stimulus. Innate, stereotypical behavioral sequences, involuntary

• actions are unchangeable

• carried out to completion

• triggered by a sign stimulus (external)

Migration

Innate behavior, a regular long-distance change in location

triggered by environmental cues - sun position, earth’s magnetic field, body clock

Pheromones

Chemicals emitted by members of a species that can affect other membranes of the same species

Stimulus response chains

what a response to a stimulus serves as the next stimulus for a behavior

Waggle Dance

Honey bees communicate through body movements

Directed movements

Movements towards or away from a stimulus

Kinesis

A change in the rate of movement or the frequency of turning movements in response to a stimulus, non-directional

Taxis

Directional movement towards (positive) or away from (negative) a stimulus

Phototaxis

Movement in response to light

Chemotaxis

Movement in response to chemical signals

Geotaxis

Movement in response to gravity

Learning

Modification of behavior based on specific experiences

Imprinting

Long-lasting behavioral response to an individual

• during sensitive period of development (early in life)

• Occurs on the first individual they encounter (ducks follow their mothers)

A learned behavior!

Spatial learning

establishing memories based upon the spatial structure of the animal’s surroundings

• cognitive maps are formed, using landmarks and environmental cues

• ex: bird going back to its hidden nest

Associative learning

Ability to associate one environmental feature with another

ex: associating monarch butterflies with a foul taste

Social learning

Learning through observations and limitations of the observed behaviors

ex: chimps breaking open oil palm nuts

Mating bahviors

Animals can be monogamous or polygamous (one partner or multiple)

Altruism

Selfless behavior

• reduces fitness of individual but increases fitness of the population

Phototropism

A directional response that allows plants to grow towards (or away from sometimes) a source of light

Photoperiodism

Allows plants to develop in response to day length ; plants flower only at certain times of the year

Gene Pool

A population’s genetic makeup

• all copies of every type of allele

  • if theres only one allele present for a particular locus in the population, its is fixed

Microevolution

Small-scale genetic changes in a population

• driven by random occurrence (genetic drift, mutations, gene flow/migration, natural selection)

Genetic drift

Chance events that cause a change in allele frequency from one generation to the next

• can lead to loss of genetic variation

• can cause harmful alleles to become fixed

• two types:

  • bottleneck effect

  • founder effect

Bottleneck effect

When a large population is reduced by a non-selective disaster (floods, famine, fire, hurricane, hunting)

Some alleles in the surving population become overrepresented, underrepresented, or absent

Founder effect

When few individuals become isolated from a large population and establish a new small population with a gene pool that differs from the large population

• loss of genetic diversity

Gene Flow

The transfer of alleles into or out of a population due to fertile individuals or gametes

ex: pollen being blown to a new location

Directional Selection

Selection towards one extreme phenotype

Stabilizing selection

Selection towards the mean and against the extreme phenotypes

Disruptive selection

Selection against the mean, both phenotypic extremes have the highest fitness

Sexual selection

A type of natural selection that explains why many species have unique/showy traits

Males often have useless structures simply because females chose that trait

Can produce traits that are harmful to survival

• ex: colorful features in male peacocks make then easier to spot by predators

***Makes certain inherited traits more successful when trying to mate and reproduce***

Hardy Weinberg Principle

The frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work

Hardy Weinberg Equilibrium

1. no mutations

2. random mating

3. no natural selection

4. extremely large population size

5. no gene flow

p + q = 1

p = frequency of the dominant allele in a population

q = frequency of the recessive allele in a population

p²+2pq+q²=1

p²=percentage of the homozygous dominant individuals

pq=percentage of the heterozygous individuals

q²=percentage of the homozygous recessive individuals

Change in population

dN/dt = B - D

B = birth rate

D = death rate

dN/dt = change in population size

Exponential Growth

J shaped curve

dN/dt = r(max)*N

r(max) = max per capita growth rate of the population

N = population size

Logistic Growth

Per capita rate of increase approaches zero as the population size its carrying capacity

dN/dt = r(max)*N*((K-N)/K)

r(max) = maximum per capita growth rate of the population

N = population size

K = carrying capacity

K-selection (density-dependent)

Selection for life history traits that are sensitive to population density

• high-density populations that are close to carrying capacity (K)

R-selection (density independent)

Selection for life history traits that maximize reproductive success

• seen in low density populations with little competition

Life History

the traits that affect an organism’s schedule of reproduction and survival

• when reproduction begins

• how often the organism can reproduce

• the number of offspring produce per reproductive episode

Density-dependent regulation

factors that can slow or stop growth by decreasing birth rate or increasing death rate in population

• competition, predation, toxic wastes, territoriality, disease

Density-independent regulation

factors that exert their influence on population size, but the birth/death rate doesn’t change

• weather, climate, natural disasters

Allopatric Speciation

Physical barrier divides population

or Small population is separated from main population

• prevents gene flow

Sympatric Speciation

New species evolved while still inhabiting the same geographic region as the ancestral species

→Usually due to exploitation of a new niche

Speciation

Formation of new species due to reproductive isolation:

pre/postzygotic barriers

Prezygotic barriers

Prevent mating or hinder fertilization:

• habitat

• temporal

• behavioral

• mechanical

• gametic

Habitat isolation

Species live in diff areas or the occupy different habitats within the same area

Temporal Isolation

Species breed at different times of the day, year, or season

Behavioral isolation

Unique behavioral rituals separate species

Mechanical isolation

Reproductive anatomy of one species doesn’t fit that of the other species

Gametic isolation

Proteins on the surface of gametes do not allow for the egg and sperm to fuse

Postzygotic Barriers

Prevent a hybrid zygote from developing into a viable, fertile adult

• reduced hybrid viability

• reduced hybrid fertility

• hybrid breakdown

Reduced Hybrid Viability

The genes of different parent species may interact in ways that impair the hybrid’s (child) development or survival

ex: domestic sheep + domestic goat = hybrid embryo dies early on

Reduced hybrid fertility

A hybrid can develop into a healthy adult, but it is sterile, not reproductive

Usually due to differences in number of chromosomes between parents

Hybrid breakdown

The hybrid of the first gen may be fertile but when they mate with a parent species or one another, their offspring will be sterile

Microevolution

Change in allele frequencies within a single species or population (natural/sexual selection, genetic drift, gene flow)

Macroevolution

Large evolutionary patterns (adaptive radiation, mass extinction)

Punctuated equilibrium

When evolution occurs rapidly after a long period of stasis. Stop-Start-Stop

Gradualism

When evolution occurs slowly over 100s, 1000s, 1000000s of years

Divergent evolution

Groups with the same common ancestor evolve and accumulate differences resulting in the formation of a new species

Adaptive radiation

If a new habitat or niche becomes available, species can diversify rapidly

think of the diff versions of Darwin’s finches

Convergent evolution

Two different species develop similar traits despite having different ancestors due to environmental pressures

• analogous traits

Fundamental niche

The niche (role) potentially occupied by the species if there were no limiting factors (predators, competitors, etc)

Realized niche

The portion of the fundamental niche the species actually occupies

Interspecific interactions

Interactions of individuals from one species with individuals of another

competition, predation, herbivory, symbiosis, facilitation

Competitive exclusion principle

Two species competing for the same resource cannot coexist permanently

Niche partitioning

Natural selection drives competing species into different patterns or resource use, or different niches

Cryptic coloration

Camouflage

Batesian mimircy

Harmless species mimics a harmful one

Mullerian mimicry

Two or more bad-tasing species resemble each other

Parasitism

(+/-) when one organism (parasite) derives nourishment from another (host)

Mutualism

(+/+) when both organisms benefit from the relationship

Commensalism

(+/0) when one organism benefits and the other is neither harmed or unharmed, neutral

Facilitation

(+/+) or (+/0) when one species has a positive effect on the survival and reproduction of another without an intimate association of symbiosis

• common in plants

Species Richness

number of diff species

Relative abundance

The proportion each species represents of all the individuals in the community

Simpson’s diversity index

Used to calculate diversity based on species richness + rel. abundance

Diversity Index = 1 - sum of(n/N)²

n= total number of organisms of a particular species

N= total number of organisms of all species

High Div. index = high biodiversity