M2 Flashcards
r vs k
r = growth rate: how quickly a pop increases early on
k = carrying capacity: how many indiv a pop can hold
Nₜ = N₀ert
predicting population size under exponential growth
methods of predicting population growth
- mark & recapture
- N = MC/R
- proportion of indiv marked in 2nd sampling should = proportion of full pop
- N = total pop size
- M = # of 1st sampling
- C = # of 2nd sampling
- R = # marked indiv recaptured in 2nd sampling
- photographic mark & recapture ➞ uses unique animal markings
- ex: giraffs
- avoids methodological problems like:
- placing tags
- tagging negatively affecting animals
- # of indiv/migration routes
- life tables
- formula
- what does the mark & recapture method assume about the population and our marked individuals?
- Reasons you might not catch any marked indiv in the second sampling
- steady pop size
- stationary pop/no migration
- no births/deaths
2.
- potential migration patterns
- timing
- wrong tags/tags fall off
- large/infinite pop ➞ not large enough sample to give accurate estimate
proportion of indiv marked in 2nd sampling should = proportion of full pop
N = total pop size
M = # of 1st sampling
C = # of 2nd sampling
R = # marked indiv recaptured in 2nd sampling
controls on pop size
density independent: factors do not depend on pop density
- factors affect in same way at same magnitude
- usually abiotic:
- strong enough to survive…
- windstorm
- hurricane
- floods
- fire
density dependent: factors do depend on pop density
- stronger impact on pop with more indiv
- usually biotic:
- predation
- disease
- resources
- waste
- fuel for fire
pop density
org living in that pop (same area)
logistic growth pattern
when a pop is large (close to k): growth slows
- K ≈ 0
- r ≈ 0 ➞ growth is slow
when a pop is small: slow growth that follows mostly exponential pattern
- K ≈ 1
- growth is exponential
predicting pop size under logistic growth
life tables
sets of data give an idea of how the pop is changing through time based on patterns of survival & reproduction
age demographics and r
r correlates to the proportion of indiv in their reproductive ages
- ↑ proportion of indiv in reproductive age = higher growth rate
- ↓ proportion of indiv in reproductive age (majority of pop post-reproductive age) = slower growth rate
human demographic transition
predictable pattern that human societies & pop tend to follow
humans are unusual compared to other species
- live long past reproductive ages
- produces complicated social dynamics in human systems
- financial/societal impacts of a top-heavy pop (↑ proportion of elderly)
- fewer paying into SS than taking out
birth rate is below death rate
Aristotle
species are static & deviations of ‘ideal’ are mistakes
- rigid ladder
- scala naturae did not incorporate any mechanism for change in species through time
Zhuang Zhou
species change over time, even into other species
- mutability in species
- cycle
development of understanding evolution
contrast in thought between static & changing species
Al-Jahiz
species can change based on envir
- acclimation
- microevolution
Al-Biruni
limited resources limit # of indiv in a given envir
Ibn Khaldun
descent w/ modification
- still hierarchical
- man came from monkey
- man’s relationship to the world & their place in it
Linneas
life is static
- laid foundation for scientific racism
- gave credence to distinct classes w/ scientific classification
Alexander Von Humbolt
- father of biogeography: study of where org live & why
- connected ranges of org to envir
- abiotic envir shapes who can live there
- outspoke against treatment of indigenous
catastrophism
earth/life shaped by major sudden events
- why we see physical form of earth the way we do
- org in diff layers = unrelated ➞ came from diff major events
- ex: volanoes & layers in earth
- George Cuvier
- Freidrich Tiedermann
gradualism
earth/life structured by long, slow processes
- erosion & sedimentation
- ex: grand canyon
- influenced Darwin
- Charles Lyell
- Mary Anning
George Cuvier
- catastrophist
- disappearance of some lineages driven by sudden major events
- appearance of new lineages from migration of new species
- shown in the layers of earth
- craniometry: measurements of human skull to support IQ variation in species
Freidrich Tiedermann
- catastrophist
- Cuvier’s student
- called him racist & his work shotty science
Charles Lyell
- gradualist about ecology
- species = static & immutable
Mary Anning
- gradualist
- avid fossile collector
- not accepted into british fossil society
- responsible for many discoveries from fossils
evidence for catastrophism
volcanoes & layers
evidence for gradualism
gradual differences in traits over time in fossils
both homozygotes are overrepresented
- inbreeding
- natural selection- diversifying
one homozygote is overrepresented
long-term drift
heterozygotes are overrepresented
- outbreeding
2 natural selection - stabilizing
evolutionary thought by 1800s
accepted
unanswered Qs
accepted:
- gradual change is important
- earth is old
- extinction occurs
unanswered Qs:
- origins of new species
- species resemblance & underlying features
- reasons for poorly adapted vs well adapted
- mechanism for evolution
Jean-Baptiste Lemarck
- first use of “evolution”
- org passed down traits acquired from use/disuse w/in a lifetime
- actually describing acclimation, traits not passed on - hierarchical view of nature
- hierarchy = complexing force
- could move w/in levels but levels are not related
John Edminstone
- Darwin’s mentor
- learned nat hx & taxidermy on plantation
- freed in England & opened taxidermy shop ➞ taught darwin
- Darwin inspired by his nat hx stories
- very good at taxidermy ➞ still have specimens to this day
Darwin
observations
- org had similarities & differences across the Galapagos
- pigeon breeding selected desired traits ➞ maybe nature followed similar selection
focus:
- variety across groups
- how change occurs
- what mechanisms drive change throughout time
on the origin of species
- species change over time ➞ diverged gradually
- species share common ancestor ➞ descent w/ modification
- change due to increased survival/reproduction based on beneficial traits (fitness) ➞ natural selection
Alfred Russel Wallace
- similar observations to Darwin
- had to sell objects to fund trips
- corresponded with Darwin ➞ potentially swapped info
- diff evidence surfacing in support of nat selection
descent w/ modification
species descent from common ancestor ➞ see in common traits
ex: limb bones: same in all tetrapods, but adapted for diff fx
- walking (horses)
- flying (bats)
- hopping (frogs)
- swimming (porpoise)
homologous traits vs analogous traits
homologous: descended from common ancestor
- ex: spiked leaves/stems
- limb bones of humans & cats
analogous: convergent evolution ➞ similar in diff org b/c similar selective pressures
- analogous if ancestors did not have trait
- ex: streamlined body shape of dolphins (mammal) & sharks (fish)
- ex: wings of birds & insects
Natural Selection inferences
- there is a struggle for existence ➞ why is there not exponential growth?
- indiv vary in traits ➞ some = better competitors in the struggle for existence
- traits that enhance survival/reproduction (fitness) ↑ freq in pop in comparison over time ➞ adaptation
evolution
genetic change over time
- random change of freq in pop is independent of traits
- all pop evolve at all times
adaptation
type of evolution occurring through natural selection
- traits that keep org alive = ones that are inherited
microevolution
w/in species
- changes in freq of genetic variations across generations
- small-scale changes
- short time-frame (human time scale)
- population level
macroevolution
speciation
- accumulation of microevolutionary changes
- new genetic groups arise
- long time-frame (geologic scale)
- large-scale changes
conditions for natural selection
- reproduction
- variation in traits
- inheritance
- differential success aka fitness: indiv w/ diff traits differ in survival/reproductive success
- trait value does not cause diff success in reproductive if expressed at diff points in lifetime
patterns of selection
- stabilizing
- directional
- disruptive/diversifying
- balancing
- frequency-dependent
- spatial variation
- temporal variation - sexual selection
stabilizing selection
phenotypes nearest the mean have highest fitness
- mean stays same
- ↓ variation
- ↑ in medium & ↓ in extreme
- distribution narrows
- newborn birthweight
directional selection
phenotypes at 1 extreme have highest fitness
- mean trends towards extreme
- ex: bent grass & copper mine tolerance
disruptive/diversifying selection
phenotypes at both extremes have higher fitness than mean
- ↑ variation
- maintains diversity
- bimodal pattern
- ex: coho salmon
balancing selection
selection maintains variation in a pop
frequency-dependent selection
type of balancing selection where the rarer phenotype has the highest fitness
- phenotype frequency oscillates over time
- dominant ≠ beneficial
- ex: cichlid fish
spatial & temporal variation
forms of balancing selection
- spatial variation: diff traits for same species in adjacent bushes
- ex: stick bugs in adjacent bushes
- variation in time:
- ex: seasonally fluctuating selection
- daily fluctuating selection for org with short life-spans
sexual selection
driven by:
- competition for mates
- ex: elephant seals - ex: elks w/ their antlers - ex: nudibranch hermaphrodites
- mate choice: runaway selection ➞ ornaments to attract males drive mate choice (the bigger the better)
- ex: peacock's feathers - ex: baboons blue testicles - ex: bird's plumes
altruism
behavior that ↓ indiv fitness but ↑ other’s fitness
hamilton’s rule
defines how benefits to close relatives (↑ reprod output) can outweigh costs to the altruist (own lost reprod output from altruistic event)
- when is kin selection supported by natural selection
r B > C
r = coefficient of relatedness: fraction of genes shared
B = benefit to relative: ↑ in offspring for relative
C = cost to altruist: loss of offspring for altruist
- ↑ benefits or relatedness incurs a higher cost
inclusive fitness
sum of an indiv own fitness & its contribution to success/survival of relatives
kin selection
favors behaviors that ↑ reproductive success of relatives, even at cost to indiv
- ex: belding ground squirrel
- ex: prairie dogs
- ex: worker bees
exceptions to hamilton’s rule:
- reciprocal altruism: altruist has reasonable expectation that sacrifices will be reciprocated in the future
- repeated interactions
- non-related indiv
- ex: vampire bats
- sexual selection: displays of altruism ↑ mating options
constraints on natural selection
- physical
- evolutionary hx
- tradeoffs
- lack of variation
constraints on natural selection: law of physics
physical limits on what an org/pop/species can do
a. gravity ➞ biggest mammals in ocean
b. circulatory systems:
- ex: insects’
- body membranes absorb O2
- only delivered locally
- most body has to be close to parts touching air
- high surface area
- larger insects have ↑ atm O2
constraints on natural selection: evolutionary hx
what resources were available at that time
- what kind of org did it evolve from/look like
ex: rays vs flounder: flat fish that swim along the ocean floor
- sharks: streamlined body shape, eyes on top of head ➞ evolution makes sense
- flounder: deep-bodied fish, had to turn on side & make eyes go on top of head to swim along floor ➞ cannot swim well
constraints on natural selection: tradeoffs
trying to ↑ one trait simultaneously ↓ another
- ex: corals: ↑ heat tolerance = slower growth
constraints on natural selection: lack of variation
variation is requirement for NS ➞ no variation ➞ NS cannot act upon species
- ex: california condor & cheetah: negligible genetic variation due to extremely ↓ pop size at 1 point
traits of domestication
- drooping ears
- piebald coloration: black & white spots
- short, rolled tails
- forehead marks
- wavy hair
- altered reproductive cycles
byproducts of intended breeding traits
fox farm experiment, hypothesis, & prediction
to study domestication in an experimental setting
hypothesis: ‘tameness’ & aggression are at least partially genetic
- inheritable & selected upon
prediction: selective breeding should ↑ tameness in foxes
domestication
selecting for tameness
- ex: pets to be tame ➞ compensable & personality
results of fox farm experiment
domestication in general is ↑ frequency of traits despite not being specifically selected for
- directional selection
sexual cannibalism in redneck spiders background & Q
- sexual dimorphism: females much larger than males
- females eat males during mating
- Q: how might NS promote this behavior over time
sexual cannibalism in redneck spiders: hypothesis for female benefit:
a. mistaken identity: males were mistaken for prey on web
- expectation: females eat every male on web at all times
- results: every instance occurred in sex position ➞ rejected
b. mate rejection: only eat unsuitable ones
- expectation: diff between males cannibalized & not
- results: no sig diff in male quality ➞ rejected
c. feeding opportunity: supplement diet/nutrition
- expectation: happens when females in poor condition
- results: majority of cannibalism in poorer condition ➞ supported
sexual cannibalism in redneck spiders: hypothesis for male benefit
a. resource investment: indirectly by providing resources to offspring ➞ ↑ quantity/quality of eggs in sac
- expectation: eggs in cannibal matings = higher quality or more
- results: no sig diff ➞ rejected
b. reproductive output: ↑ chance of successful fertilization by own sperm (not others)
- expectation: ↑ copulation time = ↑ proportion fathered
- results: cannibal mating = father more offspring from 1 mating ➞ supported
unanswered Q: results in only 1 mating, wouldn’t multiple future matings make up for the diff?
beak size in Galapagos finches observations
variations: 2 birds of same size, sex, & age living on the same island but 1 has 25% bigger beak
beak size in Galapagos finches explanation
- main food = seeds from tree
- drought wiped out trees ➞ ↓ resources ➞ huge ↓ in seed abundance
- fewer seeds = fewer birds
- difference in seed condition:
- larger, harder seeds take longer to open
- smaller beaks cannot crack seeds ➞ ∴ ↑ in mortality/ ↓ in pop size
bigger beaks = ↑ fitness
beak size in Galapagos finches & conditions for NS: differential success
1) adult build size (traits):
- birds w/ larger beaks = more likely to survive drought
- avg beak size post drought = ↑ than prior pop
- ↑ in freq of bigger-size beaks b/c pop size ↓
2) inheritance of beak size:
- beak size = inherited trait
- larger beak birds produce more offspring
directional selection (could be balancing if rainfall ↑)
alleles
different versions of a gene
chromosome
a long strand of DNA with hundreds to thousands of genes
gene
a section of DNA that codes for a particular trait
genome
all the genetic material in an indiv
nucleotide base pairs
thymine/uracil ⸻ adenine
- 2 H bonds
guanine ⸻ cytosine
- 3 H bonds
DNA structure
double helix of base pairs wound around histones then condensed into chromosomes inside the nucleus
centra dogma
glow of genetic material from DNA ➞ proteins
DNA (1) ➔ mRNA (2) ➔ proteins
1) transcription
2) translation
DNA sense (coding) strand
DNA anti-sense (non-coding) strand
transcription ⬇︎
mRNA (= sense (coding) strand of DNA w/ U replacing T)
translation ⬇︎
tRNA carries AA corresponding to the mRNA codon
transcription
DNA ➔ mRNA
nucleus
antisense strand: 3’ ➔ 5’
- mRNA transcript = copy of DNA sense strand w/ U instead of T
sense strand: 5’ ➔ 3’
translation
RNA ➔ protein
cytoplasm with tRNA
1) ribosome moves along mRNA reading codons (3 bases)
2) tRNA matches codon with anti-codon carrying AA
open reading frame
from start codon to stop codon
part of mRNA that IS used for protein synthesis
introns
part of mRNA that IS NOT used for protein synthesis
exons
protein structures
primary: linear sequence of AA through peptide bonds
secondary: H bonding between peptide backbone
a. alpha helix
b. beta pleated sheets
tertiary: interactions btwn R-grop side chains of secondary structures that twist & fold into 3-D
quaternary: multiple tertiary subunits
phenotype production & variation
- different alleles produce diff phenotypes of the same trait
- allele ➔ genotype ➔ phenotype - diff amounts of mRNA transcribed
- red canaries have more expression of certain genes - diff AA sequence
- changes in protein folding pattern changes AA sequence
- folding pattern is crucial for protein function - mutations:
- DNA not repaired or repaired incorrectly
types of mutations
DNA mutations:
a. substitution: nucleotide is exchanged
b. insertion: nucleotide is added
c. deletion: nucleotide is removed
- b & c = frameshift mutations
chromosomal mutations
a. numerical instability
- lose 1 chromosome
- gain 1 chromosome
- gain whole set of chromosomes
b. structural instability
- deletions: part of chromosome is lost
- amplifications: part of chromosome is lenghtened
- inversions: part of chromosome is flipped
- translocations: part of chromosome is swapped with another/ an adjacent chromosome
severity of mutations
most severe: non-synonymous substitutions: new codon changes AA ➞ could result in an early stop-codon
- frameshift mutations (insertions & deletions)
- substitutions
least severe: synonymous substitutions: new codon codes for same AA
genetic pedigree: dominance vs recessive
dominant: every affected indiv has an affected parent
recessive: indiv that is infected may have parents who are not
- may skip generations
complete dominance
single dominant allele produces dominant phenotype
- homo dominant & hetero show same phenotype
codominance
heterozygote shows both homozygous phenotypes
incomplete dominance
intermediate heterozygote phenotype
incomplete dominance
intermediate heterozygote phenotype
law of segregation
2 copies of each gene ➞ gametes receives one gene copy from mother & one copy from father
law of independent assortment
alleles of different genes are inherited independently during meiosis
- genes far apart on the same chrom can assort indep (crossing over)
- linked genes generally do not
- expect nearly equal proportion of the 4 diff types of gametes ➞ genes not on same chrom
- contributes to genetic diversity
mitosis
produces 2 identical sister chromosomes of same gene
meiosis
produces 4 unique haploid gametes
human genome
humans = diploid (2n) ➞ 2 copies of each chrom
- 23 copies of chrom ➞ 46 total
Mendel’s test crosses
dominant phenotype x recessive phenotype
unknown dominant genotype (PP or Pp) x known recessive genotype (pp)
predictions:
a. if purple-flowered parent is PP ➞ all purple offspring
b. if purple-flowered parent is Pp ➞ 1/2 white & 1/2 purple offspring
homologous recombination
crossing over: genes at different loci swap with homologous pair during prophase I of meiosis
linkage
genes close to each other on the same chrom will be inherited together
- disproportionate ratios btwn gametes
- if AB are on same chrom & BC are on the same chrom, then A & C are on the same chrom
recombination freq
genes on diff chrom: expect nearly equal proportion of the 4 diff types of gametes
genes on same chrom: proportions of gametes are not equal
- majority = non-recombinant (linked)
- minority = recombinant
sex-linked chrom
present on X chrom
- males = hemizygous for x-linked genes ➞ if inherited will 100% show phenotype/trait
- women who are hetero for X-linked genes = carriers
- sons = 50% chance of being infected
- men cannot be carriers
pleiotropy
one gene affects multiple diff traits/phenotypes
polygenic inhertence
one trait is additively controlled by many genes
- phenotype controlled by combination of many different genes
- every gene is allowed to act
- continuous distribution
- range/variation of phenotypes
- ex: height, color
epistasis
multiple genes interact to determine phenotype
- one gene can mask another
heritability
degree of phenotypic variation that is due to genetics
- envir can influence phenotype
- 0 = not at all genetic (envir factors only)
- scatter plot all over the place - 0.5: scatter plot somewhat concentrated trending upwards
- 1 = completely genetic (no envir effect)
- scatter plot concentrated in an upward trend
natural selection acts on _________
- an indiv ➞ who survives & reproduces
- phenotype
microevolution
changes in allele freq & mean variance of traits
- across a population
allele freq
proportion of an allele across all indiv or their gametes
- B, b
- f(homo dominant) + 1/2 f(hetero)
p = dominant
q = recessive
p + q = 1 ← always adds to 1
genotype freq
proportion of indiv in a pop with a genotype
- always add up to 1
- p2 = homo dominant
- 2pq = hetero
- q2 = homo recessive
- p2 + 2pq + q2 = 1
- freq of homo genotype is always freq(allele)2
- freq of hetero genotype = freq(allele 1) x freq(allele 2)
HWE assumptions
in a non-evolving pop, genotype & allele freq reach equilibrium after 1 gen & remain constant given:
- no mutation
- no gene flow
- random mating
- no genetic drift: chance events have no affect on very large (infinite) pop size
- no NS: all alleles have equal fitness ➞ equal chance of surviving & reproducing
- serves as null hypothesis: if any condition fails ➞ pop is evolving
- no pop actually follows all HW assumptions
to determine if a pop is in HWE:
- determine observed gene freq
- use observed gene freq to to est allele freq in a pop
- calculate expected gene freq under HW assumptions (p2 = __, q2 = ___)
- if observed & expected are same: pop IS in HWE
- if observed & expected are diff: NOT in HWE ➞ pop is evolving
which assumptions might have been violated?
current populations vs HWE
on avg across all genes, pop match HW expectations pretty closely
- on avg across all pop: many pop match HW expectations pretty closely
- but indiv genes are affected by HW assumptions differently
- some ➞ hetero
- others ➞ 1/both homo
HWE: mutations
- only source of genetic variation
- every mutation starts out in 1 indiv ➞ very low freq
- substitutions, insertions/deletions, chromosomal rearrangements
- replication mistakes & repairs: DNA is not repaired or repaired incorrectly ➞ new allele
HWE: mutations examples
- sickle- cell anemia: single base-pair mutation changes the shape of red blood cells
- cystic fibrosis: triple-base (codon) deletion changes protein ➞ ion channels cannot move chloride ions & fluid outside cell ➞ build up of mucous
- lizards white mutation: each species has diff nucleotide substitution mutation ➞ changes 1 AA to white
- allows diff species to live in both white sand dunes & forests
- disruptive selection
gene flow
migration: movement of alleles through indiv or their gametes
- new allele introduced to pop ➞ changes allele/gene freq ➞ starts out low but allele becomes more common
- w/in pop: ↑ gene variation
- homogenize distant gene pools/pop
- org can migrate without moving
- ex: pollen, marine animals
genetic drift
chance events in small pop cause unpredictable changes in allele freq
- random
- rare alleles are lost entirely after a single generation in small pop
- random event effects are stronger in smaller pop
- graph w/ many squiggles
- reduces gene diversity
- ↑ homozygosity ↓ in heterozygosity
- can be stronger than NS
when given observed & expected w/in pop size, cannot predict which direction drift will shift in freq
consequences of genetic drift:
- loss of overall diversity through loss/fixation of alleles
- no gen diversity ➞ cannot adapt
- ↑ in homozygosity
- ↑ in deleterious recessive conditions
- can ↑ freq of “low fitness” alleles
- ↑ susceptibility to future stressors
extreme cases of genetic drift
- genetic bottleneck: pop size severely ↓ from envir impacts
- new pop has very diff gene/allele distribution than original pop
- lost allele will never come back
- more serious neg impact b/c only small pop remains & that is only sources of gen diversity
- ex: northern elephant seals
- founder effect: new pop created w/ few indiv from original pop
- small pop size ➞ alleles have disproportionately higher freq than original pop
- larger original pop remains and can maintain gen diversity (& possibly migrate to founder pop)
- ex: European starling
random mating
only occurs when every indiv has an equally likely chance of mating with another
HWE: non-random mating influences
- sexual selection
- mate preference
- proximity
inbreeding
mating between relatives
- familial relatives
- ex: cousins, 2nd cousins etc
↓ level of heterozygosity & ↑ homozygosity compared to expected
assortative mating
mating between indiv w/ same/similar genotype
- traits & genes
- ex: butterflies w/ red wings only mate w/ other red wings
HWE: non-random mating consequences
- inbreeding ↓ heterozygosity & ↑ homozygosity
- predictable effects on geno freq
- allele frequencies don’t change, gene freq do
- homozygotes are overrepresented in pop compared to HWE: more observed than expected based on HW assumptions
- inbreeding ↑ freq of deleterious recessive alleles
- relatives are more likely to carry same one ➞ increases likelihood of inheriting recessive alleles from both parents
- heterozygotes don’t suffer fitness consequences, offspring do
ex: Florida panthers & Charles II of Spain
HWE: NS consequences
- fit alleles are overrepresented in future gen
- ↓ freq of unfavorable traits
- favors particular alleles over others
- directed selection
rare dominant allele vs rare recessive allele
rare dominant:
- rises in frequency faster
- heterozygote is still a carrier
- has beneficial phenotype
rare recessive:
- takes a long time to rise to fixation
- slow rise
- no beneficial phenotype ➞ selected against
- all beneficial phenotypes are masked by dominant
recessive deleterious allele examples
- huntington: progressive breakdown of neural cells
- disease = complete dominance
- length = incomplete dominance
- late onset
- only affects after reproduction ➞ recessive allele still passed down
- no fitness difference bwtn those infected & those not ➞ mechanism for maintaining deleterious alleles
- sickle cell anemia: red blood cells sickle-shaped ➞ build up & clog vessels ➞ cannot carry O₂
- heterozygous = codominant ➞ no ⊝ side effects
heterozygous advantage
heterozygotes with deleterious alleles are more resistant to other dis
- don’t suffer the ⊖ side effects of one dis but get benefit resistance to another
- ex: sickle-cell anemia carriers (heterozygotes) don’t suffer ⊖ side effects but have ↑ resistance to malaria
- malaria has selection that contrasts that of sickle cell
underrepresented vs overrepresented
underrepresented: observed freq is lower than expected
- selected against
overrepresented: observed freq is higher than expected
- selected for
Nᵪoff
of offspring of indiv at age x
lᵪ
survivorship: where is mortality primarily occurring
- lᵪ = Nᵪ ÷ N₀
mᵪ
fecundity: avg # of offspring each indiv has at that age
- mᵪ = Nᵪoff ÷ Nᵪ
lᵪmᵪ
what age group has the most offspring
G
generation time: avg age of reproduction
- should be close to age where most reproduction occurs (lᵪmᵪ)
- G = ∑ xlᵪmᵪ ÷ ∑ lᵪmᵪ
R₀
net reproductive rate: avg # of offspring each indiv has throughout their lifetime
- R₀ = ∑ lᵪmᵪ
- R₀ = 1 ➞ pop size is not changing
- cannot be negative
r
rate of increase in a pop
r ≈ (lnR₀) ÷ G
- works best when pop is not changing ➞ r = 0
- larger reproductive output by indiv should have a larger increase in pop size
- correlates to prop of indiv in their reproductive age
selelction
the ways that species adapt to envir pressures that determines relative fitness (reproductive success & survival)
relationship between R₀ and r
when R₀ = 1, r =1 ➞ every indiv is replacing themself in future gen
when R₀ > 1, r > 0
when r < 0, R₀ < 1 (but greater than 0)
r and K graphically
highest carrying capacity = tallest line
fastest growth rate = shortest time to reach its K
Natural Selection
mechanism of evolution: process through which org survive, reproduce, adapt, & change
- influenced by envir pressures & species interactions
geological influences on Darwin’s theory of evolution
gradualism: accumulated impact of changes that occur very slowly over very long periods of time ➞ Darwin applied to genetic & morphological changes
artificial selection vs natural selection
both are the process of genetic change
differ in the mechanisms that determines which traits are beneficial
- NS: environment in which the organism exists (abiotic factors & biotic interactions)
- AS: human preference
when is altruism supported by NS
Any time it increases your fitness
a. Inclusive fitness: partial contribution of an individual’s close relatives to that individual’s fitness
- Hamilton’s Rule defines how benefits to close relatives (in terms of higher reproductive output) can outweigh costs to the altruist (in terms of their own lost reproductive output due to the altruistic event)
- Kin selection: increasing family members’ reproductive success increases the probability that your genetic makeup is inherited
b. Reciprocal altruism: behaviors that increase other’s fitness knowing that they will do the same for you in future
c. Sexual selection: displaying altruism increases mating options
what contributes to genetic diversity?
- sexual reproduction mixes whole genomes from 2 diff pop
- independent assortment mixes sets of chrom & allows org to make genetically unique gametes
- recombination mixes alleles on a chrom ➞ creates new chrom combinations diff than inherited
- mutations
importance of genetic diversity
important for maintaining a healthy pop & responding to new selective pressures
non-adaptive vs adaptive evolution
non-adaptive: genetic change that does not (necessarily) benefit the species’ ability to survive and/or reproduce
- mutations, genetic drift, random mating & gene flow, are partially/completely random & may negatively impact the pop
adaptive ➞ only NS selects pheno/geno that are beneficial to envir
expectation for heterozygote frequency in 50, 100, n generations
starting frequency to the power of the generation
