BIO 345 Exam 2

what is the two-fold cost of sex?

**An asexually reproducing population will grow at twice the rate as a sexually reproducing population** -the cost of producing males -males cannot contribute DIRECTLY to producing offspring **Sexually reproducing populations must produce both sexes, but effectively only half of them can give birth to offspring of their own** -in contrast, in an asexual population, all offspring of an asexually reproducing individual can potentially give birth

How is population size REGULATED?

**only INVERSE density-dependent factors can regulate population size -regulate = population size is brought closer to carrying capacity (K) *increase r and ƛ when N is low *decrease r and ƛ when N is high ***Population decline above K is faster than population growth below K***

Metapopulation

*recall that populations are often patchily distributed across a species geographic range Key concept: spatially isolated populations can be linked by dispersal to form "meta-populations" Meta-population: -series of local populations existing in discrete patches LINKED BY DISPERSAL -not all patches are colonized (local extinction) -vacant patches can be colonized by immigrants from connected patches -repeated extinction and colonization events occur

Effects of selection on different types of alleles

*selection can only act on expressed traits Additive: -will spread through the population and become fixed the fastest due to having double the phenotypic effect Dominant: AA or Aa -will spread through the population faster than the recessive allele because there are two options for selection to pick from (AA or Aa) -show their effect even if only one allele is present, so a dominant allele is likely to be MORE VISIBLE to selection than a recessive allele Recessive: aa -will take awhile to be seen by selection, and so their frequency remains low until they are eventually selected for -take awhile to be seen by selection because both alleles must be present in order for the phenotype to be produced -likelihood of aa being picked is low and so it takes awhile to occur

what is extinction? what are the different kinds?

-Extinction results from demographic processes at the POPULATION LEVEL Local Extinction: -no longer found in a given area -extinction of a single population Ecological Extinction: -there are so few individuals that the species can no longer play its ecological role -decreased population size Biological extinction: -no longer found on earth -extinction of ALL populations of a species

Results of genetic drift

-a loss of genetic variation results WITHIN populations -genetic divergence results BETWEEN populations -evolution results: allele frequencies change -genetic drift happens faster in small populations

Bottleneck

-a population bottleneck is a sharp reduction in the size of a population due to environmental events or human activities -a bottleneck causes genetic drift and a reduction in genetic variation -higher sampling error will occur after a genetic bottleneck because the population size is reduced *rare alleles are likely to be lost during a bottleneck Example: -entire herds northern elephant seals were killed for their blubber and population size dramatically decreased in size

Classic model of meta-populations

-all patches are equally likely to be colonized or go extinct -patch occupancy changes over time (not realistic)

what is an apex predator?

-an alpha predator or top predator -a predator at the top of the food chain, with no natural predators -occupy the highest trophic level Ex. killer whales are an apex predator

why doesn't a lethal allele go to 0 after a number of generations?

-because the allele is hidden in the heterozygous genotype, and so it can be continued to be selected for since selection cannot see the deleterious allele in the homozygous phenotype -eventually, genetic drift will get rid of the recessive allele as it becomes really rare

what processes influence population size in a closed population?

-birth rate -death rate N= B-D dN/dt= B-D *NOT immigration and emigration

what processes influence population size in an open population?

-birth rate -death rate -immigration -emigration N= B-D + I-E dN/dt= B-D + I-E

Population subdivision

-causes genetic structure -enhances the effects of genetic drift (divergence in allele frequencies) and populations have more genetic diversity between them No subdivision -one large population of individuals with little genetic diversity Extreme subdivision -no migrants -no gene flow -populations that are segregated and have a lot of genetic diversity between them Some subdivision: -some migrants -gene flow

what is the sixth extinction?

-due to the human species -increase in the rate of extinction since the industrial revolution -the rate of extinction is not even across the globe

what is a trophic level?

-each of several hierarchal levels in an ecosystem, comprising organisms that share the same function in the food chain and the same nutritional relationship to the primary sources of energy -species that obtain energy in similar ways (the number of feeding steps removed from primary producers)

mutation-selection balance

-equilibrium frequency reached through "tug of war" between negative selection and new mutations -occurs when the rate at which deleterious alleles created by mutation equals the rate at which deleterious alleles are eliminated by selection (negative) -explains the persistence of rare, deleterious mutations in population -negative selection is when selection acts against harmful mutations to get them to exit the population

Where does genetic variation come from?

-evolution requires genetic variation Genetic variation comes from... -mutations -recombination -gene flow

Hardy-Weinberg equation principles

-gamete/allele frequencies are given by p and q -genotype frequencies are given by p^2, 2pq, and q^2 -p+q=1 -p^2+2pq+q^2=1

random sampling/chance events

-genetic drift (change in allele frequency) results from random sampling -random sampling is a subset of individuals chosen from a larger set. Each individual is chosen randomly and entirely by chance *Sampling error is higher in smaller populations (alleles are lost more rapidly in smaller populations): Ex. choosing from a pool of 50% red marbles and 50% white marbles -if you are selecting a sample of only 2 marbles, you are more likely to pick a sample of only red marbles rather than if you were picking a sample of 100 marbles, you would get a more even distribution of red and white marbles

Change in allele frequency over time

-genetic drift causes a change in allele frequency -allele frequency performs a random walk (there is much more variation and randomness in the walk of a small population) *alleles are lost more rapidly in small populations* -the direction of change in allele frequency cannot be predicted -one allele will eventually be fixed, and the other will be lost (has to do with fitness) -the probability of an allele eventually being fixed or eliminated is proportional to initial frequency **higher initial frequency, higher chance of becoming fixed **smaller population, allele becomes fixed or lost more rapidly

Genetic drift

-genetic drift is the change in the frequency of an existing gene variant in a population due to random sampling of organisms (within small populations, there is always the possibility of unequal sampling, just due to CHANCE) *Genetic drift causes evolution: a change in allele frequency -one allele will eventually be fixed (has to do with fitness), the other eliminated: genetic drift tends to REMOVE GENETIC VARIATION within a population

how is the human population changing?

-human populations are changing the earth, but human populations are changing as well -history of humans: populations were growing very slowly, but the rate increased with the agricultural revolution, and skyrocketed with the industrial evolution -annual growth rate of 2%==> leads to an unsustainable population in the future if we take into account our ecological footprint

What are the Hardy-Weinberg assumptions?

-if a population IS in Hardy-Weinberg equilibrium, then evolution IS NOT occurring -if a population is NOT in Hardy-Weinberg equilibrium, then evolution IS occurring Hardy-Weinberg equilibrium means that no evolution is occurring due to five assumptions: 1) There is no selection -all individuals have equal probabilities of survival and reproduction 2) There is no mutation -genes do not change from one allelic state to another 3) There is no migration -genes are not added from outside the population 4) There are no chance events -the population is infinitely large 5) There is random mating -there are no mating restrictions (genetic or behavioral) -all recombination is possible -all individuals are potential partners

Kelp forests

-kelp forests are one of the most productive ecosystems (on par with productivity of tropical rainforests) -kelp forests are located along the coast of every continent -kelp forests do not exist in tropical environments -colder ocean waters have higher nutrient availability in upwelling zones for kelp forests to survive **kelp forests are high diversity regions that exist in temperate regions, not tropical regions -kelp forests are incredibly diverse: urchins, algae, fish, seals, lobsters

area-based counts

-method that is used because it is often impossible to count every single individual in a population -can count the number of individuals in a number of different locations within an area 1) total the number of individuals counted 2) find the average density -(# of individuals)/(area surveyed) 3) find the estimated population size -(average density)X(total habitat area)

Source-sink model of meta-populations

-most patches are incapable of supporting persistent populations -in these "sink" patches, populations are maintained by immigration from healthy "source" populations -patch size, distance, habitat suitability, and dispersal ability matter *source populations can "rescue" failing populations or colonize new patches

how to define instantaneous rates of births and deaths

-multiply population size by per capita (individual) rates B (instantaneous births) =bN D (instantaneous deaths) = dN -now populations change as a result of per capita birth and death rates dN/dt= (b-d)N **NOTE: b-d is equal to the intrinsic rate of increase (r)

Types of mutations

-mutation is the ultimate source of genetic variation (although sexual reproduction results in the MOST genetic variability, there would be no variability at all without mutations) -different mutations can affect a different number of bases 1) Point mutations -base substitutions, insertions, deletions -changes in the nucleotide sequence can alter the amino acid sequence or introduce stop codons -when bases are inserted or deleted, it can cause a change in how the whole DNA strand is read (a frame shift mutation) and produce a non-functional protein 2) Gene duplications -changes in the order of genes on chromosomes can affect recombination during meiosis, which may affect their fate (whether they are broken up by recombination) 3) Changes in chromosome structure -inversions, translocations 4) Changes in chromosome number -polyploidy -changes in the number of genes can provide raw material for evolution, can also affect dosage of a particular gene

Can any population truly increase in size forever?

-no -in the real world, exponential growth cannot continue indefinitely (due to things such as limited resources) Ex. Calvatia giganteen (giant puffball) -if all spores reached maturity, the offspring of 2 individuals would weigh more than the entire planet in just two generations

what is the relationship between kelp, sea urchins, and sea otters?

-otters eat sea urchins, and therefore sea otters control the abundance and distribution of sea urchins -when many sea otters are present, the levels of sea urchins will decline==> therefore kelp can become more abundant

what are the effects of physical disturbance of trophic cascade?

-physical disturbance matters and can change the effects of trophic cascade Ex. a storm hits and removes the amount of canopy in Southern California, leading to a lower productivity and lower presence of kelp even in the absence of sea urchins

what are the assumptions of the mark-recapture estimating abundance method?

-population size does not change during sampling period (no births, deaths, immigration, emigration) -equal chance of being caught -marking does not harm the individual -marks are not lost over time

key concepts about populations

-populations are dynamic entities that vary in size over space and time -populations are often patchily distributed across a species geographic range -populations are influenced by habitat suitability, historical factors, dispersal, and biotic interactions

How does variation in lambda (finite growth rate) affect population size?

-populations in which lambda varies over time grow more SLOWLY than predicted -EX. cyclic growth and fluctuating growth patterns *populations with a lower growth rate have a higher extinction risk

what is a trophic cascade?

-powerful indirect interactions that can control entire ecosystems, occurring when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation -a change in the rate of consumption at one trophic level that results in a series of changes in species abundance or composition at lower trophic levels Ex. killer whales are an apex predator, they can change to eat sea otters when they have no other prey available to them ===> will cause a change in lower trophic levels

Key concepts to know about recessive alleles

-rare alleles are almost always carried in a heterozygous state -recessive alleles are invisible to selection when they are carried in the heterozygous state -selection cannot drive a dominant allele to fixation (without genetic drift) because the recessive allele is hidden in the heterozygote and therefore continues to persist since selection cannot eliminate it *as a result, most diseases are due to recessive mutations

recombination and independent assortment

-recombination and independent assortment during meiosis generates variation (Ex. in humans with 23 chromosomes, there are 8 million possible gamete combinations) -independent assortment ensures novel combinations of alleles *most genetic variability in a population results from sexual reproduction; in any given generation, input from mutation is very small*

what is the relationship between kelp density and sea urchins?

-sea urchins limit the abundance and distribution of kelp -urchins are voracious herbivores, so they eat all of the blades of kelp (preventing them from photosynthesizing) and destroy the kelp -when there are a lot of urchins present, there will not be a lot of kelp present

Why is natural selection more powerful in large populations?

-selection is stronger in larger populations because the effects of genetic drift are weaker in large populations -small advantages in fitness can lead to large changes over the long term (whereas in a small population, these small advantages may be lost rapidly simply due to chance, and so selection never has the chance to act upon them) -larger populations are more genetically diverse and have more allelic diversity: and so natural selection has more to work with

Key concepts to know about selection

-selection occurs when genotypes differ in fitness -the outcome of selection depends on the frequency of the allele and effects on fitness -population size influences the power of drift and selection -drift is more powerful in small populations, and so selection is less efficient in small populations -drift is weaker in large populations, and so selection is more efficient in large populations

Key concept: Extinction risk increases greatly in small populations

-small populations have a higher risk of extinction due to chance -demographic and environmental stochasticity matter more in small populations -small populations are more likely to experience problems associated with genetic drift and inbreeding depression Ex. Tanzania lions: disease outbreak almost drove lion population to extinction. Current population descended from the few survivors ==> reduced fertility due to sperm abnormalities *Introducing individuals from more genetically diverse populations can reduce small populations suffering from genetic drift and inbreeding depression Ex. prairie chicken: locally extinct through much of their original range due to habitat loss and fragmentation. Isolated populations exhibited reduced reproductive fitness. Translocation of birds from larger, more diverse populations increased per capita birth rates and population size

founder effect

-the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population -founder effect causes genetic drift and a reduction in genetic variation within the population Example: -after entire herds of elephants seals were overhunted and experienced a population bottleneck, the Mexican government attempted to protect them on the Isla Guadalupe -this small, isolated founder population grew and eventually recolonized the mainland, however, because all the current elephant seals are descendants of the same 20-100 seals, the whole population is very genetically similar (lack of genetic variation makes them very vulnerable to new diseases or negative environmental changes) -lack of genetic variation in small populations can also cause inbreeding depression

Inbreeding

-the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically -relatedness among mates -inbreeding occurs more often in small populations -one generation eliminates inbreeding (even if child receives a bad recessive allele from inbred parent, it is unlikely that an unrelated mate will also have that mutation, so they will receive a good copy from the other parent and be a heterozygote) *inbreeding increases the percentage of loci that are homozygous for alleles identical by descent (family members are more likely to have the same recessive mutations, and so if each parent passes on the same recessive mutation, then the child will be homozygous for the recessive mutation) *recessive alleles are more likely to be exposed to selection

how do niche models estimate the current or future distribution?

-they assess environmental conditions at locations where the species is known to occur (niche characteristics) -generate habitat rules that describe conditions in which the species is most likely to occur -project "likely" distribution using these rules

what kinds of populations are likely to grow rapidly?

-those with a high number of individuals surviving at reproductive age -usually have a lower survival rate of elderly individuals

density-dependent vital rates

-vital rates: how fast vital statistics change in a population -vital rates depend on density (N) -with birth rates are balanced by death rates, the population reaches a stable equilibrium Carrying capacity (K): -the maximum population size that can be supported in a given area (stable equilibrium) -growth rate should equal 0 at K -birth rates equal death rates at K

How do mutations occur?

-when DNA is synthesized, an enzyme called DNA polymerase reads one strand of a DNA molecule and constructs a complementary strand -if DNA polymerase makes a mistake and it is not repaired, a mutation has occurred

Two ways in which you need to be able to calculate Hardy-Weinberg equilibrium

1) Given phenotype frequencies and information about dominance/recessive. Asked to calculate genotype frequencies if the population is in Hardy-Weinberg equilibrium (i.e. if no evolution were occurring) Steps: -calculate p and q -use the H-W equation p^2+2pq+q^2 to calculate genotype frequencies 2) Given numbers of individuals with each genotype and asked whether the population is in H-W equilibrium Steps: -write out observed genotype frequencies -use number of individuals to calculate allele frequencies (p and q) -now use the H-W equation to calculate genotype frequencies IF the population is not evolving -compare the observed to expected frequencies. If they are the same then they are not evolving, if different then they are evolving

Given the genetic and ecological costs of sexual reproduction, why does sexual reproduction still persist?

1) Sex creates new advantageous genotypes (faster evolution) -in asexual species, advantageous mutations must occur in the same lineage -in sexual populations, advantageous mutations can be combined across lineages (shuffles alleles into new combinations) 2) Sex breaks up and can remove deleterious mutations "Mueller's ratchet" -Mueller's ratchet is the accumulation of harmful mutations -when deleterious mutations occur in asexual populations, the least mutated class gets smaller and smaller, while the mutated class continues to grow -this is because asexual populations can only evolve towards ever greater loads of deleterious mutations (the ratchet has "clicked forward" and cannot be moved back)

what are the three costs of sex?

1) The cost of producing males -the "two-fold" cost of sex 2) The cost of finding mates -exacerbated by low population density 3) The costs of mating -mating is risky and time-consuming

Methods of determining abundance

1) area-based counts -allows you to estimate abundance 2) mark-recapture -allows you to estimate abundance -population size -survival rate -movement

what are the assumptions of the logistic growth model?

1) births and deaths are continuous 2) it takes time for populations to reach K 3) environmental conditions are unchanging (K is constant) 4) changes in dN/dt perfectly track changes in N (no time lags)

mark-recapture method for determining abundance

1) capture a subset of individuals 2) mark each individual with a unique tag 3) release marked individuals 4) rinse and repeat... Formula: (# marked in first capture M1)/(total population size N) = (# marked in second capture R)/ (total second capture M2) (M1)/(N)=(R)/(M2) -solve for N N= M1xM2/R Example: 1st capture = 23 sea otters 2nd capture = 15 sea otters, 4 marked N= (23x15)/4 =86 sea otters

what are the different types of population patterns?

1) exponential growth -population grows continuously, overlapping generations (humans, perennial plants) -curved, increasing, continuous line 2) Geometric growth -population grows at regular time intervals (cicadas, annual plants) -curved, increasing, discontinuous line 3) logistic growth -an adjusted model that shows how a population reacts to K (carrying capacity) -logistic growth equations show how a population may stabilize at carrying capacity -increasing line that eventually plateaus at an equilibrium point 4) fluctuations -a lot of variation in growth, but no clear pattern -usually due to random changes in the environment 5) regular cycles/cyclic growth -populations go back and forth between high and low density -ex. low population==> abundance of resources ==> population increases drastically ==> low abundance of resources due to large population ==> size of population decreases dramatically -also has to do with predation ex. cyclic growth in lemmings

characteristics of mutations

1) mutation is an unstoppable phenomenon -despite cellular mechanisms to correct errors during DNA replication, mutation still occurs 2) mutation is not directed by the organism or the environment -it is random with respect to effects on fitness (but the ones that persist are not random) -i.e. mutation does not occur because it will be beneficial, but whether or not the mutation persists and is passed to offspring is not random (it might be selected for) 3) rates depend on the type of mutation -also varies among genes -different organisms have different rates of mutation -mutation rates are low, but genomes are large -point mutations are the most common, but affect the least number of bases. Conversely, gain or loss of whole chromosomes is the most rare, but affects more bases

what are the assumptions of the exponential growth model?

1) time is continuous rather than discrete 2) births and deaths occur instantly and simultaneously 3) birth and death rates are constant (no density or environmental effects) -no random events, no natural disasters, no infant mortality, no biotic interactions 4) individuals are identical (no genetic variation, no age or size differences) -the likelihood of survival at each stage is the same -the likelihood of mortality from one stage to the next is the same -the likelihood that any one of these individuals will contribute to the next generation by reproduction is the same **Exponential growth occurs when conditions are favorable

Given the effect of different types of alleles, do you think most diseases are caused by: A: recessive mutations B: dominant mutations C: additive mutations D: all types of mutation

A: recessive mutations why?

what is sex?

Broad sense: -genetic material from different ancestors brought together in a single descent Stictest sense: -eukaryotic haploid-diploid cycle -meiosis and syngamy (fusion of gametes)

what type of beneficial allele will spread through a population and become fixed the fastest? A) dominant alelle B) recessive allele C) additive allele

C) additive allele -a beneficial additive allele will spread through a population and become fixed the fastest because the allele yields twice the phenotypic effect, making it MORE VISIBLE to selection -selection will pick this allele more frequently and so it will become more common in the population

Sea otters are an example of... A: ecosystem engineer B: foundation species C: keystone species D: apex predator

C: keystone species -a species that has a large effect on energy flow and community structure despite its small size or abundance *sea otters are not an example of an apex predator even though they limit the abundance and distribution of sea urchins because they are not at the top of the food chain, they still have predators that can LIMIT THEIR abundance and distribution

which growth rate indicates a population that is not changing in size? A: ƛ=1, r=1 B: ƛ=0, r=0 C: ƛ=1, r=0 D: ƛ=0, r=1

C: ƛ=1, r=0 *lambda (finite growth rate) must be greater than or less than one in order to be increasing or decreasing because it is a PROPORTION *r (intrinsic rate of increase) must be greater than or less than zero in order to be increasing or decreasing because it is not a proportion

To be considered part of a single population, individual organisms must.... A: be the same species B: live in the same geographic area C: interact with one another D: all of the above

D: all of the above

Most mutations are... A: beneficial B: mildly good C: lethal D: mildly bad

D: mildly bad -most mutations are not lethal because the ones that are lethal are lost before you are even born -lethal mutations are "hidden" because they never make it out alive *individuals are born with about 40 unique mutations that are mostly due to point mutations

Demographic vs Environmental stochastiscity

Demographic stochasticity: -variation (or sampling error) in birth, death, and migration rates -produced by CHANCE EVENTS that affect INDIVIDUALS in a population -causes random variation in population growth rates even in a constant environment Environmental stochasticity: -good years and bad years -produced by CHANCE EVENTS that affect the ENTIRE POPULATION -causes random variation in average vital rates and population growth rate -random variation in population growth at a larger scale *DS and ES cause fluctuations in population growth rate ==> population size **ES has a larger impact than DS

Dominant and additive alleles

Dominant allele: -a dominant allele masks the presence of the recessive allele in a heterozygote -for example, if a is recessive lethal at birth, survival to reproduction for all genotypes is... 100% for AA 100% for Aa 0% for aa Additive allele: -an additive allele yields twice the phenotypic effects when two copies of it are present -for example survival to reproduction is... 100% for AA (two copies of additive allele yields twice the survival to reproduction rate) 50% for Aa 0% for aa *an additive allele makes the phenotype more obvious to selection, and so it spreads through a population and becomes fixed the fastest* Example of an additive allele AA= red flower Aa= pink flower aa= white flower

what is an ecological footprint? Ecological surplus/deficit?

Ecological Footprint: -total area of productive ecosystems required to support a population (the opposite of carrying capacity) -the impact of a person//community on the environment, expressed as the amount of land required to sustain their use of natural resources Ecological surplus/deficit: -the difference between the capacity of productive ecosystems to support a population and the ecological footprint of that population

Exponential growth (dN)/(dt)=rN

Exponential Growth: population grows continuously, overlapping generations, density independent growth **(dN)/(dt)=rN dN/dt= change in population size (Nt-N0) at EACH INSTANT IN TIME r=intrinsic rate of increase N=current population size **So, the intrinsic rate of increase multiplied by the current population size equals the change in population size at each instant in time

Exponential growth Nt=N0e^rt

Exponential Growth: population grows continuously, overlapping generations, density independent growth **Nt=N0e^rt Nt= population size at time t (in the future) N0= number of individuals at time 0 (now) e= constant (2.71828) r=intrinsic rate of increase t= time (pay attention to units)

Extinction vortex and Minimum Viable population (MVP)

Extinction Vortex: -small population drops below a certain size -becomes even more vulnerable to problems that threaten small populations (genetic drift, inbreeding, loss of genetic variability) -decreases population size even more -spiraling toward extinction Minimum Viable Population (MVP): -the smallest population size that can persist in nature -theoretical threshold for the extinction vortex **Extinction risk increases greatly in small populations

Organisms must interbreed (share genetic material) to be considered a population: A: true B: false

False -organisms do not need to interbreed in order to be part of the same population -Ex. asexual reproduction in plants

***Growth Rate rules of thumb

Finite growth rate: ƛ= (Nt+1)/(Nt) ƛ < 1 : population size is decreasing (Nt+1 < Nt) ƛ = 1 : population size is constant (Nt+1 = Nt) ƛ > 1 : population size is increasing (Nt+1 > Nt) Intrinsic rate of increase: (dN)/(dt)=rN r < 0 : population size is decreasing (Nt < N0) r = 0 : population size is constant (Nt = N0) r > 0 : population size is increasing (Nt > N0)

Fitness

Fitness: -the reproductive success of an individual with a particular phenotype -Fitness (W) = (probability of survival) X (number of offspring produced) Components of fitness: -survival to reproductive age -mating success -fecundity (the ability to produce an abundance of offspring) Relative Fitness: -fitness of a genotype standardized by comparison to other genotypes **Natural selection occurs when genotypes differ in average fitness

Geometric growth Nt=(ƛ^t)(N0)

Geometric growth: population grows at regular time intervals Nt=(ƛ^t)(N0) Nt= number of individuals at time t (Ex. 2028) N0= number of individuals at time 0 (now) (Ex. 2018) ƛ= finite growth rate t = number of time intervals How to use this equation: 1) First calculate finite growth rate (ƛ) using the equation ƛ= (Nt+1)/(Nt) 2) Use the finite growth rate calculated in step one to determine the number of individuals at a given time in the future using this equation Nt=(ƛ^t)(N0) (N2028)=(ƛ^10)(N2018) *there is ten years between 2028 and 2018, so the number of time intervals is 10

Geometric growth ƛ= (Nt+1)/(Nt)

Geometric growth: population grows at regular time intervals ƛ= (Nt+1)/(Nt) ƛ= finite growth rate Nt= number of individuals at time t (ex. 2017) Nt+1= number of individuals at time t+1 (ex. 2018) t= time interval (annual) How to use this equation: 1) use ƛ= (Nt+1)/(Nt) to predict the finite growth rate from year to year 2) then use number calculated for ƛ to predict population size at some time point in the future using the equation Nt=(ƛ^t)(N0) **Finite growth rate is the rate of increase per individual per unit of time **Finite growth rate is the rate of increase for a population that is growing at a finite rate of 50% per year

inbreeding depression

Inbreeding depression: -the reduced survival and fertility of offspring of related individuals -inbreeding depression results in reduced fitness -rare deleterious alleles are more likely to combine in homozygotes Ex. the inbreeding coefficient expected for the offspring of a brother and a sister is very high compared to less related individuals

Predicting change in allele frequency from one generation to the next

Information needed for prediction: 1) initial allele frequency 2) fitness of the genotypes at the locus of interest Example: Given: -the initial allele frequency is 0.5 for A and 0.5 for a -a is recessive lethal at birth Predict the change in allele frequency in the next generation 1) Write out fitness of each genotype AA= 1 Aa= 1 aa= 0 2) Determine the number of individuals that survive with each genotype (assuming a population of 1000 individuals) -p^2 (AA)= (0.5)X(0.5) ==> .25 X 1000 individuals = 250 AA survivors -2pq (Aa) = 2(0.5)(0.5)==> .50 X 1000 individuals = 500 Aa survivors -q^2(aa) = (0.5)X(0.5) ==> .25 X 0 individuals = 0 aa survivors (now population only consists of 750 individuals) 3) Determine the new genotype frequencies -250/750 = 0.333 AA -500/750 = 0.667 Aa -0/750 = 0.0 aa 4) Determine the new allele frequencies - (250x2+500)/1500 = 0.667 A - (0x2+500)/1500 = 0.333 a What if selection continued over many generations? -A would continue to increase over a -it would take awhile for the lethal allele to go to zero because it is hidden in the heterozygous form and so it is continued to be selected for

what is the difference between density-dependence and density-independence?

Key Concept: population size and growth can be influenced by density-dependent and density-independent factors Density-Independence: -population growth rate (r) does not change with the density of individuals in the population Density-Dependence: -population growth rate (r) does change with the density of individuals in the population

what is the difference between lambda (ƛ) and r

Lambda (ƛ)= finite growth rate -used in geometric growth: a population that grows at regular time INTERVALS (usually annually) and can only grow a certain amount at each unit of time -rate of increase per individual per unit of time R=intrinsic rate of increase -used in exponential growth: a population that grows CONTINUOUSLY, overlapping generations -the rate at which a population increases in size if there are no density-dependent forces regulating the population -the maximum theoretical rate of increase of a population per individual

Migration and gene flow

Migration: -the movement of individuals from one population to another Gene flow: -the movement of genes from one population to another -gene flow COUNTERACTS SUBDIVISION by homogenizing allele frequencies -makes Allele frequencies more similar among populations

does Mueller's ratchet occur in sexually reproducing populations?

NO -sex breaks the ratchet by reconstituting the least mutated classes (by recombination, assuming the deleterious mutations are different amongst lineages) -because one parent has the mutation, and one doesn't, so there is less chance for mutation to be passed on because shuffling and recombination occurs -sex is recombination!!!

What is population biology?

Nt= N0 + B -D + I -E SO, the number of individuals at a time in the future is equal to the number of individuals now (time zero) plus the number of births, minus the number of deaths, plus the number of immigrants, minus the number of emigrants -population biology involves coming up with mathematical functions to describe these parameters Ex. does birth rate depend on resource availability does death rate depend on population size?

How to determine the likelihood that a meta-population will persist

Pm= 1-e^x e= local extinction rate x= number of local populations Pm=(1-e^x)^n n=number of years *use this formula if you want to know persistence over multiple years Example: -assume that all three populations have a 50% chance of going extinct Probability that all three populations will go extinct: p= (e1 x e2 x e3) = (0.50 x 0.50 x 0.50) =0.125 Probability of regional persistence for a year: Pm= 1-e^x =1 - 0.50^3 =0.875

Example of a H-W problem where you are given phenotype frequencies and asked to calculate genotype frequencies if the pop. were in H-W equilibrium

Question: -In a population of 100 mice, 81 mice have light fur (dd), and the remaining 19 mice have dark fur (DD or Dd) -Find p and q for this population and calculate the frequency of heterozygous genotypes in the population Answer: 1) Using provided info, find q q^2 (dd) = 81/100 ==> 0.81 q (d) = square root of 0.81 ==> .90 2) Find p using number calculated for q p+q=1 p+.90=1 p=.10 3) Find p^2 (DD) .10^2=.01 3) Find 2pq 2pq(Dd)=2(.10)(.90)==> .18 Frequency of genotypes in population under H-W assumption: DD: .01 Dd: .18 dd: .81

Example of a H-W problem where you are given the observed number of individuals with each genotype and asked to determine if the population is in H-W equilibrium

Question: -there are 100 individuals in a population -20 GG, 70 Gg, 10gg -is this population in H-W equilibrium? Answer: 1) Write out the observed genotype frequencies GG: .20 Gg: .70 gg: .10 2) Use the number of individuals to calculate the allele frequencies (p and q) (2X10+70)/(200)= 0.45 g (2X20+70)/(200)= 0.55 G 3) Use the H-W equation to calculate genotype frequencies ASSUMING the population is not evolving p^2 (GG)= 0.55^2 = 0.3025 2pq (Gg)= 2(0.55)(0.45) = .495 q^2 (gg) = 0.45^2= .2025 This population is not in H-W equilibrium because the expected genotype frequency does not match the observed genotype frequency, meaning that evolution IS OCCURRING *note: in step 2, we multiply by 2 and divide by 200 because we are dealing with a diploid organism, and, in homozygous individuals, 2 of 2 chromosomes are being contributed, and so we must account for both of them

Organisms that live in "patchy" habitats can represent a single population A: true B: false

True Ex. marine mammals can be part of a single population, but live kilometers apart because they are highly migratory

Allee effect

Under logistic growth: -per capita growth rate is predicted to decrease with increasing population size -individuals are more likely to survive and reproduce in smaller populations -population size stabilizes around the carrying capacity (regulatory density-dependence) Allee effect: -per capita and population growth rates are greatly reduced or negative in small populations (rather than high in small populations as predicted) -population size may decrease even more (non-regulatory density-dependence) : non regulatory because it is not an inverse density dependent relationship, it is a direct one, a decrease in pop. size causes a decrease in growth rate Reasons for the Allee effect: -difficulty finding mates -cooperative defense or feeding -habitat alteration

what is a population?

a group of interacting individuals of the same species living in the same geographic area

keystone species

a species that has a large effect on energy flow and community structure despite its SMALL SIZE or abundance

foundation species

a species that has large, community-wide effects on other species by virtue of its size and/or abundance

ecosystem engineer

a species that influences its community by creating, modifying, or maintaining physical habitat for itself and other species EX. plants

why are kelp forests good monitors of overall ecosystem health?

because they are highly variable in productivity from year to year

giant kelp is an example of... A: ecosystem engineer B: foundation species C: keystone species D: apex predator

both A and B Ecosystem engineer: -a species that influences its community by creating, modifying, or maintaining physical habitat for itself and other species Foundation species: -a species that has large, community-wide effects on other species by virtue of its size and/or abundance

intraspecific competition

competition between members of the SAME species *weak/no competition ==> increase in pop. size (increased birth rates/decreased death rates) *high/intense competition ==> decrease in pop. size (decreased birth rates, increased death rates)

Logistic growth model dN/dt=rN(1-N/K)

dN/dt=rN(1-N/K) -the logistic growth model shows how a population may stabilize at the carrying capacity *the closer N is to the carrying capacity, the slower the growth rate will be* "Unused portion of K": -if N=0 (far from carrying capacity), growth is exponential -if N=K (population at carrying capacity), growth rate is zero *Growth is fastest when N= K/2 Example: -dN/dt=rN(1-0/K) -dN/dt=rN(1~0) -dN/dt=rN(1) growth rate is exponential -dN/dt=rN(1-K/K) -dN/dt=rN(1~1) -dN/dt=rN(0) growth rate is zero

how is lambda (ƛ: finite growth rate) related to r (intrinsic rate of increase)?

r=ln(ƛ) Doubling time: t(double)= ln(2)/r SO, if you are given lambda (ƛ), how would you find the populations doubling time? 1) Determine r from lambda -r=ln(ƛ) 2) Use r to calculate the doubling time -t(double) = ln(2)/r

distribution

the geographic area where individuals of a given species are found

abundance

the number of individuals of a species present in a given area -population size (N) -population density (N per unit area)

inbreeding coefficient

the probability that two alleles are identical by descent ex. Hapsburg dynasty

can one species fit into multiple categories (foundation species, ecosystem engineer, keystone species)

yes Ex. kelp forests are an example of an ecosystem engineer and a foundation species