● Ecology = the study of how living things interact with each other and their environment.
● Abiotic = nonliving / biotic = living
● Abiotic factors = precipitation, temperature, soil, and solar radiation.
● Biotic factors = mutualisms, pollination, and predatorprey relationships.
● Individualpopulation (group interacting conspecifics)community (interacting populations of heterospecifics)ecosystem (communities + abiotic environment)biomebiosphere.
● We study ecology to understand and analyze the services provided by nature such as water filtration, disease spread, crop damage, wildfires, and how pollination affects crop yields.
● Increase in rainfall = increase in acorns = increase in mice & deer = increase in ticks = increase in lyme disease = increase in selfies = western fence lizard?
If you want to learn more check out What is meant by measure of central tendency?
● Humans are different than other species since we modify our environment (technology), have different life expectancies, unique language and speech, agriculture, tool usage, more intelligent, love/empathy, consciousness, culture transmission.
● Cholera leads to death due to dehydration.
● It spreads when people ingest contaminated food or water and defecate into areas where there is human traffic. ○ Treated with salt solution (IV fluids), and antibiotics.
○ Bacteria rapidly multiply in the large intestine which then penetrates cells of the intestinal wall and prevents it from absorbing water and digesting food.
● Rapid and productive replication in the human host during outbreaks increases.
● In natural aquatic habitats, a reservoir for example hosts V. cholerae and the human becomes the next host and biomass amplification system.
○ Infected people defecate in the reservoir and cause a cycle (amplify).
● Endemic cholera in South Asia.
● Premonsoon = some cholera casesmonsoon (warm, wet water) (abiotic factor)postmonsoon = lots of cholera cases. ● Postmonsoon = algal blooms (photosynthetic organisms).
○ Part of algae include nitrogen fixing heterocysts. Don't forget about the age old question of Is sahelanthropus a hominin?
We also discuss several other topics like Which medical conditions can mimic anxiety?
○ On the heterocysts is E. coli and bacteria associate with the heterocyst to take advantage of the nitrogen (parasitic infection).
● Copepod blooms follow algal blooms.
○ Copepodia harbor the bacteria.
● Copepod is a subclass of crustacean zooplankton.
○ They are the most numerous animal on Earth.
○ Chitincontaining exoskeleton.
○ These copepods eat the algae!
● Cholera attach themselves to the chitin surface of the copepod.
● Cholera bacteria digests the copepods (predation).
● Chitin utilization involves 3 steps: sense and move, attach, and degrade.
○ The cholera bacteria obtains a nutrient function (carbon, nitrogen, energy) as well as a genomic function (acquisition of new genes).
○ Metabolic pathway also allows the cholera bacteria to infect humans (metabolic pathway for environmental niche and new pathogenic trait to adapt to the host niche).
● We know very little of the factors that cause algal and copepod blooms.
● Regional and global climate change lead to monsoon rains along with deforestation is acquired in runoff = human, animal waste and chemical fertilizers is added into the runoff = algal bloom = copepod bloom = transmission to human host = infection and disease.
● Knowledge (public health policy) = intervention = disease control.
● India population is increasing which means an increase in the use of fertilizer. Don't forget about the age old question of How do you find the integrating factor by inspection?
○ Increasing nitrogen use = higher crop yields = greater human health???
● Deforestation in the Himalaya Foothills + monsoon rains causes soil erosion, flooding and runoff in the Gangetic Flood Plain in India and Bangladesh.
● Deforestation = expansion of agriculture and terracing (hillside steps).
● Soil erosion and runoff ends up in the rivers.
● All sediment runoff comes through the rivers and into the ocean.
● Cannot really change the abiotic pieces of the puzzle.
● Therefore, stop making people utilize the rivers to achieve cholera prevention.
○ Tubewells were drilled, but created arsenic contamination to millions of persons.
○ Largest masspoisoning in history (hyperpigmentation, keratosis, skin cancer, and internal cancers. ○ Origin of the arsenic was from the Himalaya mountains (bedrock).
○ Weathering and transport oxidizes arsenicbearing sulfide minerals which ends up in the water.
○ This happens during monsoons where land gets covered by water, water leads to rust, and arsenic ends up in the water. ● Solution = treat the water with sari cloth which removes algae and copepods that are carrying the bacteria. ● Sari cloth = lower levels of infection.
● Other solutions = reforestation, control of population, growth/migration, change agricultural practices, restrict fertilizer use, provision of safe water, vaccination.
● Increased rainfall leads to more oaks that produce acorns which are eaten by deer (predators), so their pop. goes up. Mice also eat the acorns which increases ticks (parasites on mice and deer) = lyme disease, so pop. of selfies will increase. ● Western fence lizard = when ticks bite them, it clears the lyme disease from their system. We also discuss several other topics like What is the difference between intersexual and intrasexual selection?
● Characteristics of a population = size, dispersion, age structure and density (individuals/area).
● Ways to measure density = count (standard census methods), count sample and extrapolate, proxy, mark recapture. ● Example: counting ducks in a pond would require counting a sample and extrapolating to estimate their density. ● Proxy such as scant (feces) and genotyping it to determine the density. Also nests, feeding damage, tracks etc. ● Markrecapture = fish tag, wing tag, bird bands, number insects, paint insects.
● N = n1n2/m
○ N = population size
○ n1 = # captured and marked
○ n2 = # captured in second sample.
○ m = # recaptured
● Factors that influence the spacing of individuals in a population =
○ Ecological needs (biotic and/or abiotic)
○ How resources are distributed (biotic and/or abiotic)
○ Interactions among organisms or individuals
■ Repulsive = competition for certain resources so individuals would not be found close to each other. ■ Attractive = when organisms are mating or traveling in herds.
● Random dispersion
○ Giant sneeze, random dots.
○ Every individual has an equal and independent probability of being in a certain space. We also discuss several other topics like What was happening in the 1940s in france?
○ Examples include dandelions = random seed dispersal.
○ Pretty common in plants, not animals.
● Clumped dispersion
○ Individuals are more likely to be found near other individuals.
○ Examples of this occur with clumped resources such as starfish eating clams are clumped together predating the clams. ○ Animals that travel in family groups or herds.
● Uniform dispersion
○ Individuals are evenly distributed.
○ Penguins (territorial), defend a perimeter around their nests.
○ Joshua trees since there is limited rainfall and take up all the resources (distribution) around them to grow. ● Populations are dynamic.
● Life tables = agespecific summary of the vital statistics of a population.
● Data from life tables gives us survivorship curves.
○ Humans have a TYPE 1 survivorship curve.
● Reproductive table = an agespecific summary of the reproductive rates in a population.
● Agespecific fecundity = average number of offspring produced by an individual of age x.
● Net reproductive rate (R) = average number of offspring produced by an individual during its entire lifetime. ● Life history = schedule of an organism’s life
○ Life span
○ age/size at reproductive maturity
○ Number of reproductive events
○ Allocation of energy to reproduction
○ Number and size of offspring
● Semelparity = one reproductive event followed by death
● Iteroparity = many reproductive events
● Principle of allocation = given finite resources, an organism must partition between different life history functions ● SIR model
○ S = susceptible
○ I = infected
○ R = recovered
○ N = population
○ Beta = infection rate
○ Gamma = recovery rate
● dS/dt = beta x S x I
● dI/dt = beta x S x I gamma x I
● dR/dt = gamma x I
● In diagram:
○ S = everything had disease and eventually recovered
○ I = starts at 1, people get infected and enter recovered population
○ R = starts at 0 and eventually increases thru time
● Rknot = newly infected / initial infection
● Vaccinations automatically move the susceptible population to the recovered population
● Unregulated / exponential population growth model
● N(t) = N(0) x e^rt
● New populations grow exponentially due to
○ New habitat
○ After a catastrophe
● However, increasing population size gives rise to:
○ Shortages in food and other limiting resources
○ Greater intraspecific aggression
○ Increased attention from predators
○ Greater risk of disease outbreaks
● These factors can lower birth rates and elevate death rates
● Carrying capacity (K) = max population a habitat can support
● Populations exhibiting logistic growth are directly or indirectly regulated by their own density.
● K is determined by:
○ Availability of food
○ Nest sites
● Regulated population growth dN/dt = rN(1 N/K)
○ If N is close to K = slow growth
○ If N<<K then the population is growing exponentially.
● Populations grow fastest at half the carrying capacity
● Unregulatedthe per capita growth rate doesn’t change as the population becomes larger. ● Regulatedthe per capita growth rate gets smaller as the population approaches K.
● Populations of Kselected species tend to exist close to their carrying capacity (hence the term Kselected) where intraspecific competition is high
rselected species have a large number of small offspring (hence their r designation)
WHERE HAVE WE TALKED ABOUT THESE TYPES OF STRATEGIES
rselected = semelparity (lots of offspring reproducing at once)
Kselected= iteroparity, long longevity, and long times to reproduction.
NOT ALL FACTORS WILL CAUSE POPULATIONS TO LEVEL OFF @ K—BUT THOSE THAT DO ARE CALLED densitydependent factors.
Effects increase in intensity with crowding
– Prevent populations from growing larger in process called REGULATION
– e.g., food supply and places to live
– Sometimes also: effects of predators, parasites, and diseases
Here, Predatorprey cycles is a densitydependent factor.
Predators increase with more prey, but predators by eating prey will regulate the population size of prey. When prey decline (due to predation), fewer predators can be sustained (and supported) so predator population will decrease.
Thus prey population size will regulate the predator population size.
DENSITYINDEPENDENT FACTORS (limiting factors): may remove individuals from populations, thereby depressing numbers, but cannot regulate them
– Effects do not intensify with crowding; cannot reduce growth rates
– e.g., temperature, precipitation, catastrophic events
Negative density dependence = as population increases, you are growing slower and slower. Positive density dependence = as population increases, growth rate also increases.
Community = an assemblage of species living in close enough proximity for potential interaction.
Species role determined by its traits.
classical example is Darwin’s finches.
Species traits (phenotypic, morphological, and behavioral traits) determine the niche and niche feeds back to the traits (adaptations to specific environments).
Species interactions =
Interspecific and intraspecific competition
Interference is direct competition for resources and territory and space.
Competitive exclusion principle: For 2 competing spp to coexist in a stable environment, they must occupy different ecological niches; without differentiation, one species will eliminate or exclude the other through competition.
Resource partitioning = coexistence
Logistic equation showing negative density dependence from competition.
it is one of the factors that weigh down the carrying capacity.
Intraspecific competition will be the most limiting to population growth
certain variation for natural selection
operating in a smaller niche space to avoid overlap.
Ecological character displacement = a process of evolutionary divergence of coexisting species.
Sympatric populations = ranges overlap (cooccur)
Allopatric populations = ranges that do not overlap
When finches occur in sympatry, their traits are more different than when they are by themselves (allopatry). Strong force in driving species divergence = competition avoidance.
predator species kills and consumes the prey species.
– herbivores eat parts of a plant or alga.
parasite hurts the host and gains something with the interaction of the host.
Predatorprey interactions can influence:
The population dynamics of both prey and predator
The characteristics of both
Produce expensive broadbased antiherbivore defenses (tannins and tough leaves, sharp prickles, spines, thorns, or trichomes hairs on the leaf often with barbs, sometimes containing irritants or poisons. )
Produce inexpensive qualitative (toxic) defenses to discourage generalist herbivores: effective ecological barrier Toxins: poisonous or bitter tasting. Cyanogenic glycosides (poisonous): Sorghum grain expresses HCN in its roots, and thus is resistant to pests such as rootworms that plague its cousin, corn.
Fluoroacetic acid: disrupts metabolism by inhibiting the aconitase step of the citric acid cycle (the cycle which produces energy as well as key amino acids!)
, but the evolution of detoxification mechanisms results in specialist herbivore species.
Grazing animals that tend to eat hard, silicarich grasses, have highcrowned teeth, which are capable of grinding tough plant tissues and do not wear down as quickly as lowcrowned teeth.
Birds: The purpose of the crop is to store food until it is passed to the stomach. Then food is passed to the stomach, where digestive enzymes mix with and break down the food. Next is the gizzard, where food is crushed and ground up by small stones that the bird has swallowed.
Bunnies have 2 poops to breakdown physical compounds in plants.
Tobacco hornworms: prefer Solanaceae (nightshade family);
Herbivores generate enzymes that counter and reduce the effectiveness of numerous toxins. One such enzyme group, mixed function oxidases (MFOs), detoxify harmful plant compounds by catalyzing oxidative reactions. The induction/expression of these enzymes after nicotine ingestion allows the larval tobacco hornworms to increase feeding on the toxic plant tissues.
Parasites are very common and abundant: It is likely that at least one third of species are parasitic.
Parasites reduce host biological fitness by general or specialized pathology, such as parasitic castration and impairment of secondary sex characteristics, to the modification of host behavior. Parasites increase their fitness by exploiting hosts for resources necessary for their survival, e.g. food, water, heat, habitat, and transmission.
One species provides a service, while the other receives nutrition
400,000 angiosperm species are flowering plants.
species grew due to animal pollination.
plants are providing the resource.
bees are providing the service (pollination).
Both species are (+) affected.
Fruit! The other innovation of angiosperms. Fruit attract animals so animals will eat their fruit and deposit them away from the parent plant to avoid competition between parent plant and offspring.
Seed dispersal by animals = service.
Animal pollination = service
Almost exclusively FACULTATIVE
egrets foraging in fields among cattle or other livestock. As livestock graze, they stir up various insects which the egrets catch and eat. The egrets benefit because the livestock have helped them find their meals, while the livestock are typically unaffected.
One species is benefiting and the other species can care less (it doesn’t hurt it or help it).
Caterpillar chewing on plant (herbivory), plant produces chemical volatiles which attracts parasitic wasps (resourceservice mutualism) and they lay eggs in the caterpillars (parasitism) and the volatiles prevent moths from laying eggs.
Wasp gets food for offspring.
Plant getting defense.
Needed for life:
• Precipitation (H2O).
• Oxygen (atmosphere)
• Nitrogen (fixed by bacteria in soil)
• Phosphorus (obtained from rock)
1st law of thermodynamics
= energy is neither created nor destroyed.
base of all abiotic life.
On top of NPP are the food webs.
Primary producers doing NPP (plants and phytoplankton)
Decomposers recycle nitrogen and phosphorus that goes back to primary producers.
The total energy is lost mostly as heat.
Every time you move up, there is less and less individuals since there is less energy.
Decomposers take a piece of each trophic level and recycle it back.
Topdown: The consumers are keeping the food web in check.
Bottomup: phytoplankton for example control populations.
Dominant species = high biomass and influence in the ecosystem that they occur.
California chestnut was the most abundant and dominant.
Keystone species has a large influence NOT because of abundance/biomass.
Climate: huge influence on the distribution of organisms. Why?
Major physical components of climate
The sun and earth’s orientation determines seasonality and latitudinal variation in climate.
More direct sunlight at equator, so hotter there than poles
At higher latitudes (poles), a beam of sunlight spreads over a greater area àless heat to any one spot, so will be cooler.
The earth’s titled axis and annual passage around the sun cause strong seasonal cycles at mid and high latitudes. The belts of wet and dry air move northward and southward with the seasons.
Daylength, precipitation and temperature vary seasonally.
Pronounced winter and summer at high latitudes. Pronounced wet and dry seasons at mid latitudes (especially around 20 degrees). On June 21 (summer) the sun is directly above 23.5 north latitude (Tropic of Cancer); one December 21 (winter) it is directly above 23.5 south latitude (Tropic of Capricorn)..
NOT WHAT EXACTLY HAPPENS.
sunlight @equator is warming up the ocean and land causing air to rise = low pressure area (rain). air sinks at the poles = high pressure.
Rotation of earth: west to east
The Earth’s rotation deflects surface flow of Hadley cells.
Coriolis deflection of a body moving toward the north or south results from the fact that the earth's surface is rotating eastward at greater speed near the equator than near the poles.
IT DEFLECTS EARTH’S WIND PATTERNS
Rotation of earth: west to east
Coriolis deflection of a body moving toward the north or
south results from the fact that the earth's surface is
rotating eastward at greater speed near the equator than
near the poles.
Causes the deflection of highlow pressure systems around the globe.
As you look from the North Pole toward the equator, is the balloon spinning clockwise or counterclockwise? The balloon appears to be spinning counterclockwise.
As you look from the South Pole toward the equator, is the balloon spinning clockwise or counterclockwise? The balloon appears to be spinning clockwise.
What happened when you tried to draw a straight line from the North Pole to the equator?
The line was not straight but instead veered west or right of the intended path.
What happened when you tried to draw a straight line from the South Pole to the equator?
The line was not straight but instead veered west or left of the intended path.
WIND PUSHES water
Ocean currents move warm and cold water around the ocean basins, with major effects on regional climates. **heat or cool the overlying air masses
Pinwheels of ocean currents caused by Earth’s winds.
Drought deciduous shrub community
Interior sage scrub!
When there isn’t any water, leaves are lost from the shrubs. = drought deciduous
Evergreen chaparral (what we live in).
scleritized leaves (hard leaves)
humans are creating more fires and are transitioning to grassland communities.
Rain shadow effect.
Air is pushed up a mountain where air rising drops its precipitation. And the other side, there is no water.
30 N&S are the hot deserts.
Rockies, Andes, and Himalayas creates a desert at 30 degrees.
Temperatures have been on an increasing trend for a while. But what has been concerning is the rapidity and cause of warming. There was no asteroid or major devastating eruption, etc. Instead, human effects have accelerated warming.
The greenhouse effect : CO2, water vapor, and other greenhouse gases reflect infrared radiation back toward Earth; this warms the climate and is important for keeping Earth's surface at a habitable temperature.
CO2 cycles because of seasons, since there are less plants in the winter and more plants in the summer (reduces CO2 in the atmosphere).
CO2 emissions have jumped astronomically with human activity.
We know this because of fossil fuels and as C14 goes to C12.
As carbon ages it drops neutrons and gets lighter.
Life on Earth is protected from damaging effects UV radiation by a protective layer of ozone of molecules (O3) in the atmosphere
Destruction of atmospheric ozone (O3) is caused mainly by chlorine from chlorofluorocarbons (CFCs) and other other chlorinecontaining industrial compounds
(breaks down under sunlight).
The breakdown of this ozone shield leads to increased UV light entering the atmosphere and can cause damage to plants and animals
Net Primary Production at 0 degrees (equator) > 60 N/S (temperate rainforests) > 30 N/S (hot deserts) > 90 N/S (cold deserts).
Biogeography = study of the distribution of organisms.
# of species increases with area
Slope z is how quickly we accumulate species.
What determines how we accumulate species?
Tropics would have a steeper slope of species area curve vs. temperate environment since tropics has more species to accumulate.
Accumulate more species of birds since they move around more.
The more complex the environment, the more species accumulate.
Isolation = less species accumulation in Hawaii than on the mainland.
More isolated islands have less species.
And less species richness
Abundance of species is not static, always changing during time = turnover with time and space. Communities are dynamic, not static.
•Population sizes of all species should decrease with decreasing land area and therefore the probability of extinction increases (think small populations and genetic drift and inbreeding)
•Consequently the extinction rate from a small island should be substantially greater than the extinction rate of a large island
•A small island will have a lower equilibrium number of species than a larger one and a higher equilibrium turnover (TSN vs TLN)
•Distance of an island from the source pool will affect immigration rate
•No matter the mechanism of dispersal, if a barrier exerts a filtering effect, then the probability of an organism crossing the barrier decreases as the width of the barrier increases
•The immigration curve for a near island will be higher than the curve from an isolated island •Near island should have higher equilibrium number of species and turn over rates than distant islands
•Get new species through immigration and lose species through extinction.
•The immigration rate (define as the rate of arrival of propagules of species not already present on the island) declines from some maximum value when the island is empty to zero where the island contains all the species in the pool and there are no more new species to arrive
•As the number of species grows there remain fewer new species on the mainland to colonize the island •Extinction rate (defined as the rate of loss of existing insular species) should increase from zero when there are no species on the island to become extinct to some maximum vlaue when all the species in the mainland pool are inhabiting the island.
•As the island fills, the number of species that can suffer extinctions increases and therefore extinction rates should increase accordingly
• where the extinction and immigration curves cross, the rate of extinction=the rate of immigration resulting in an equilibrium number of species (S hat) and an equilibrium rate of species turnover (T hat)
•This point represents a stable equilibrium because if the number of species is perturbed from this value, it should theoretically return to it.
•For example suppose that a natural disaster causes the extinction of insular species, temporarily reducing the number of species from Shat to Sprime. Then the immigration rate will exceed the extinction rate and the island will accumulate species unit it returns to Shat
Large, far island = less extinction and immigration, so less turnover.
Small, near island = more extinction and immigration, so more turnover.
The more isolated = less extinction and more area = higher the speciation.
Higher adaptive radiation on these hotspots.
Richness effects = more productive and stable, better able to resist and better able to recover, more resistant to invasion, more stability of ecosystem services.
Complementarity effect – Species differ in the way they utilize resources (resource partitioning). Hence, as species diversity increases, utilization of all resources increases.
Conserving biodiversity of species, individuals (abundance), genetic
protect and restore habitat as well as ecosystem processes
Restoration biology = restore biodiversity and habitat interactions
Channel islands food web:
Pigs and sheep were introduced to islands = exponential growth and disturbed the island dynamic. Bald eagles excluded the golden eagles.
Bald eagles were the keystone species.
DDT was becoming concentrated in higher trophic levels = bald eagles were lost.
What is (biological/organic) evolution
A change in the genetic composition of a population.
• What is adaptive evolution?
A change in the genetic composition of a population due to natural selection.
• What is an adaptation?
An inherited characteristic of an organism that enhances its survival and/or reproductive success in a specific environment.
• What is population genetics?
The scientific study of the genetics of the evolutionary process.
• Lamarck (in 1809) hypothesized that species evolve adaptations through use and disuse of body parts, followed by the inheritance of these acquired characteristics.
Conclusion: His belief in adaptive evolution was correct, but his proposed mechanism was wrong.
Evidence used by Darwin
malthus exponential growth
Natural Selection: the differential survival and reproduction in nature of organisms having different heritable characteristics, resulting in the perpetuation of those characteristics that best adapt the organisms to a specific environment
While dominance/recessive relationships are common, many alleles act more or less additively to create the ‐ ‐ phenotype of an individual
Sex linked inheritance
Mendel’s 2nd law applies when genes are on different chromosomes or far apart on the same chromosome
Single base nucleotides = sequence variation in the human genome
Long term association of closely linked genetic loci can be used to map and identify genes that influence human diseases = GWAS!
Goal of GWAS: to find genes that, when mutated, predispose us to some genetic disorder.
Single cross involving 3 loci can create a distribution similar to a continuous normal distribution.
equal reproductive fitness
equal survival fitness
Importance of HW ratios
gene frequencies stay constant regardless of dominance
they provide an important link between gene and genotype frequencies = null hypothesis
basis for population genetic theory
Genetic fingerprinting uses microsatellite loci
As a null hypothesis:
No differential selection
Large population size
Heterozygote advantage occurs when the heterozygote has a higher fitness than both homozygotes
Given heterozygote advantage, natural selection acts to maintain a stable polymorphism at that locus.
This is the case for the sickle cell anemia polymorphism in West & Central Africa, natural ‐ selection has resulted in a less than ideal adaptive solution. It increases the average survival of individuals in the population to malaria (due to the resistance of heterozygotes to malaria), but it also increases the frequency of a very serious genetic disease.
Frequency dependent selection – fitness of phenotypes depends on the abundance of the ‐ phenotype. Results in a stable polymorphism if phenotypes are fittest when rare.
Experimental work on the peppered moth by Kettlewell in the 1950s – he placed moths on both sooty and lichen covered tree trunks. He also carried out mark release recapture experiments in polluted woods ‐ ‐ (Birmingham) and non polluted woods (Dorset). ‐
Showed (a) birds did eat the moths, and (b) the expected patterns of relative survival of the two morphs.
Kettlewell’s experiments (like almost all experiments) could be criticized (e.g. he put moths on tree trunks, & used high densities of moths). BUT the methods were unbiased and the results supported the hypothesis
In higher latitude (temperate) zones seasonality is changing – winter conditions are starting later and ending sooner.
We can expect:
(a) breeding seasons to start earlier in Spring, and
(b) winter dormancy to start later in Fall.
Get directional selection when the distribution of seed size changes
(e.g. during drought).
Get stabilizing selection when the seed distribution remains fairly constant, when selection favors a fixed optimal beak depth.
Get directional selection when the distribution of seed size
changes (e.g. during drought).
Get stabilizing selection when the seed distribution remains fairly constant, when selection favors a fixed optimal beak depth.
Directional natural selection is where one end of a genetically based phenotypic distribution is favored over the other, or, in its simplest form, it can be when one allele is favored over another e.g. peppered moth. It can be divided into:
positive selection – results in spread of new advantageous alleles in a population, e.g. industrial melanism in the 1800s.
negative (or purifying) selection – results in removal
of rare deleterious alleles. Such selection acts to prevent accumulation of mutations that result in genetic disorders that lower fitness.
The equilibrium between new copies of deleterious (disadvantageous) alleles entering a population by mutation and the removal by natural selection.
Applies to human genetic diseases.
Recessive disadvantageous alleles: As noted earlier,
negative selection cannot eliminate copies in heterozygotes. As a result, disadvantageous alleles accumulate due to the input of new mutations until this is balanced by their loss due to selection against mutant homozygotes e.g. PKU mentioned earlier (q
• Founder Effect & Population Bottlenecks
• Random Genetic Drift
• Non random mating: Inbreeding (e.g. selfing) ‐
• Inbreeding Depression
• Positive assortative mating
Mimicry – Mullerian & Batesian
•Maintaining multigenic sets of alleles under disruptive selection (e.g. mimicry inbutterflies) •Sexual selection: intrasexual vs. intersexual
•Runaway selection for extremetraits
•Experiments: female preference; good genes
•Plant sex: Pollinators & pollinationstrategies
• Local adaptation & Geneflow
• Species concepts.
• Ring species & hybridization
• Allopatric & sympatricspeciation
• Prezygotic & postzygoticisolation
• Speciation on islands ‐ adaptiveradiation
• Ecological speciation (early stages = host races)
• Chromosomal sympatric speciation
• Auto‐ vs. allo‐polyploidy
• Vicariance allopatric speciation
• Continental drift & platetectonics
• Biogeography & continentaldrift
• Stratigraphy & biostratigraphy
• Geological Record: Eons (3), Eras, &Periods.
• Radiometric Dating
• Timescale of life on earth
• Origin of Life
• Major transitions: Prokaryotes, O2,eukaryotes, Cambrian explosion.
• Mass extinction &adaptive radiation.
• Origin of birds,mammals
• Taxonomy, Linnaeus & hierarchicalclassification
• Phylogenetic trees (branches &nodes)
• Taxa, clades, and the outgroup
• Cladistics – shared derived characters.
• Phylogenetic trees ‐ Methods
• Tree of Life – tracing back to a single origin
• Hominins – recent human ancestors
• Modern Humans