Ecology and Evolution Final Exam
Unit 1
Introduction to Evolution
● Evolution - the change in the allele frequencies of a population across generations
● What processes cause evolution?
○ Natural selection
○ Genetic drift
○ Migration
○ Mutation
● Microevolution - evolutionary change witnessed over a short time scale (as short as one
generation to the next)
● Macroevolution - evolutionary change seen over paleontological time (1000s, 100,000s,
millions of years)
Mechanisms of Evolution
4 methods of evolution
1. Natural selection
2. Genetic drift
3. Migration
4. Mutation
Natural selection - higher reproduction of individuals with favorable traits for a certain
environment, leading to an increased frequency of favorable alleles in the next generation
○ Survival of the fittest; non random and differential reproduction depending on
traits
● Four postulates (requirements) of natural selection
○ Variation must exist among organisms in a population
○ Some of that variation must be heritable (passed to offspring)
○ Survival and reproductive success is variable
■ Struggle for survival due to limited resources
■ More offspring are born than can survive
○ Individuals that are best able to survive and reproduce are not random
■ Individuals with certain traits are more likely to survive and reproduce
● Polygenic trait - a trait controlled by multiple genes
● Adaptations - heritable traits or behaviors that increase an organism/s ability to survive
and reproduce
, ○ Since environments change, the trait is that adaptive may also change
● Heredity - transmission of genetic material from parents to offspring
● Heritability - the fraction of variation that can be attributed to genetics
● Gregor Mendel (1822 - 1884)
○ Each parent passes a combination of discrete “factors” (alleles/genes)
○ Each gamete contains only one “factor”
○ There are dominant and recessive “factors”
○ Mendel’s work was unknown to Darwin and Wallace
● Evolutionary fitness - an individual’s ability to survive and reproduce
● Relative fitness - an individual’s ability to survive and reproduce relative to the rest of
their population
● Selection pressure - an environmental factor that puts pressure on a population causing
one phenotype to be better than another
○ Can be an abiotic or biotic factor
● Microevolution - evolution occurring on a short time scale across a few generations
○ Ex: bacteria antibiotic resistance and the evolution of “superbugs”
● Macroevolution - evolution occurring over paleontological time (over thousands or
millions of years)
● Stabilizing selection - selection that favors the average phenotype (mean stays the same,
but diversity decreases as more individuals are near the mean)
● Directional selection - selection that favors phenotypes at one end of the spectrum (mean
moves towards the end with higher fitness, reducing genetic variation)
● Diversifying selection - selection that favors at least two distinct traits / phenotypes
(could allow the mean to stay the same and genetic variation is increased by this)
● Frequency-dependent selection - selection that depends on the trait’s frequency in a
population
○ Positive FDS = the more common trait increases fitness
○ Negative FDS = the more rare trait increases fitness
○ Positive FDS leads to stabilizing selection and negative FDS leads to diversifying
selection in a population
● Sexual dimorphism - phenotypic differences between males and females
○ Males are typically larger, more colorful, and/or more ornamented than females
● Sexual selection - selection that favors phenotypes that increase an individual’s ability to
find and reproduce with good mates
○ Mating is more costly for females (invest more resources to their offspring)
○ Female fitness is limited due to resources, while male fitness is limited by their
access to good mates
○ Females are choosy with mates and males compete with each other
○ Some species exhibit gender role reversal (ex: seahorses)
● Honest signals - a trait that gives a truthful impression of an individual’s fitness
, ● Handicap principle - the idea that traits that are costly handicaps can only be possessed
by individuals with the highest fitness who can thereby afford the cost
● Good genes hypothesis - the idea that impressive ornaments show off an individual’s
efficient metabolism and/or their ability to fight off disease
● Artificial selection - the deliberate manipulation of fitness by humans through selective
breeding (ex; the domestication of plants and animals for human consumption)
Genetic drift - the effect of chance on a population’s gene pool; changes in allele frequencies
that are random
○ Individuals are diploid (2n) and gametes are haploid (n)
○ Gametes contain a random sampling of an individual's alleles, so each gamete has
a 50/50 chance of containing each allele
○ Sampling error leads to genetic drift
○ Allele frequencies drift across generations, and the magnitude of this drift is
inversely proportional to the size of the population (big population, small drift,
and vice versa)
○ Genetic drift can lead to a loss of or a fixation of alleles (0% or 100% frequency
of an allele) which causes a loss of genetic diversity
● Bottleneck effect - the magnification of genetic drift as a result of natural events or
catastrophes
○ Sudden random reduction of population size and the new smaller population does
not have the same allele frequencies as the original population
● Founder effect - an event that initiates an allele frequency change in part of the
population, which is not typical of the original population
○ The colonization of an island by a small population that doesn’t have the same
amount of diversity or allele frequencies as the original population
○ Dispersal of a population across a barrier (river, mountain, etc.)
● Genetic drift affects the whole genome and is random with respect to fitness. It usually
leads to a reduction of the average fitness of a population due to a decrease in diversity
Terrestrial biomes
● Terrestrial biome - ecological community of plants, animals, and other organisms that is
adapted to a characteristic set of environmental conditions
● Variables that shape climate include temperature, precipitation, sunlight, and wind
○ Temperature and precipitation are very good at defining biomes because of their
influence on the net primary productivity (measurement of energy accumulation
within an ecosystem)
○ NPP = (carbon fixed, biomass generated) - (carbon released, cellular respiration)
○ Places with high amounts of sunlight and rainfall have a high NPP (these are the
components necessary for photosynthesis)
, ○ NPP is in decline in terrestrial biomes due to climate change (more droughts and
flooding) and in oceans its decreasing as well
● Robert Whittaker - recognized trends of temperature and precipitation as a means of
defining different biomes
○ There are 3 zones based on temperature (hot, temperate, and cold)
○ There are 2 zones based on precipitation (high precipitation and low precipitation)
● Tropical wet forests:
○ Temperature = warm/hot and stable
○ Precipitation = high
○ Dominant vegetation = broad-leafed, evergreen plants
○ High biodiversity, lack of seasonality
○ High net primary productivity
○ Low nutrients in soil, but slash and burn agriculture releases nutrients into soil
● Savanna (tropical grasslands):
○ Temperature = warm/hot and stable
○ Precipitation = low (extensive dry season)
○ Dominant vegetation = grasses
○ These are tropical regions that experience a very little amount of rainfall
● Subtropical deserts:
○ Temperature = warm/hot (can experience some temperature variation throughout
the year)
○ Precipitation = very low
○ Dominant vegetation = plants that are well adapted to low amounts of water, have
deep roots, and have seeds that can remain dormant for long periods of time
○ Typically located 15-30 degrees North or South of the equator
● Rain shadow deserts - deserts located on a mountainside and experience little rainfall in
comparison to the other side of the mountain
● Chaparral:
○ Temperature = warm
○ Precipitation = low (mostly only rains in the winter)
○ Dominant vegetation = shrubs that are adapted to experience periodic fires and
some species even need the fire
● Temperate grasslands:
○ Temperature = seasonal, warm/cool
○ Precipitation = low, seasonal
○ Dominant vegetation = grasses
○ Typically found at mid latitudes
○ Soils are rich in organic matter, but the cold winter temperatures and frozen
waters create defined growing seasons
Unit 1
Introduction to Evolution
● Evolution - the change in the allele frequencies of a population across generations
● What processes cause evolution?
○ Natural selection
○ Genetic drift
○ Migration
○ Mutation
● Microevolution - evolutionary change witnessed over a short time scale (as short as one
generation to the next)
● Macroevolution - evolutionary change seen over paleontological time (1000s, 100,000s,
millions of years)
Mechanisms of Evolution
4 methods of evolution
1. Natural selection
2. Genetic drift
3. Migration
4. Mutation
Natural selection - higher reproduction of individuals with favorable traits for a certain
environment, leading to an increased frequency of favorable alleles in the next generation
○ Survival of the fittest; non random and differential reproduction depending on
traits
● Four postulates (requirements) of natural selection
○ Variation must exist among organisms in a population
○ Some of that variation must be heritable (passed to offspring)
○ Survival and reproductive success is variable
■ Struggle for survival due to limited resources
■ More offspring are born than can survive
○ Individuals that are best able to survive and reproduce are not random
■ Individuals with certain traits are more likely to survive and reproduce
● Polygenic trait - a trait controlled by multiple genes
● Adaptations - heritable traits or behaviors that increase an organism/s ability to survive
and reproduce
, ○ Since environments change, the trait is that adaptive may also change
● Heredity - transmission of genetic material from parents to offspring
● Heritability - the fraction of variation that can be attributed to genetics
● Gregor Mendel (1822 - 1884)
○ Each parent passes a combination of discrete “factors” (alleles/genes)
○ Each gamete contains only one “factor”
○ There are dominant and recessive “factors”
○ Mendel’s work was unknown to Darwin and Wallace
● Evolutionary fitness - an individual’s ability to survive and reproduce
● Relative fitness - an individual’s ability to survive and reproduce relative to the rest of
their population
● Selection pressure - an environmental factor that puts pressure on a population causing
one phenotype to be better than another
○ Can be an abiotic or biotic factor
● Microevolution - evolution occurring on a short time scale across a few generations
○ Ex: bacteria antibiotic resistance and the evolution of “superbugs”
● Macroevolution - evolution occurring over paleontological time (over thousands or
millions of years)
● Stabilizing selection - selection that favors the average phenotype (mean stays the same,
but diversity decreases as more individuals are near the mean)
● Directional selection - selection that favors phenotypes at one end of the spectrum (mean
moves towards the end with higher fitness, reducing genetic variation)
● Diversifying selection - selection that favors at least two distinct traits / phenotypes
(could allow the mean to stay the same and genetic variation is increased by this)
● Frequency-dependent selection - selection that depends on the trait’s frequency in a
population
○ Positive FDS = the more common trait increases fitness
○ Negative FDS = the more rare trait increases fitness
○ Positive FDS leads to stabilizing selection and negative FDS leads to diversifying
selection in a population
● Sexual dimorphism - phenotypic differences between males and females
○ Males are typically larger, more colorful, and/or more ornamented than females
● Sexual selection - selection that favors phenotypes that increase an individual’s ability to
find and reproduce with good mates
○ Mating is more costly for females (invest more resources to their offspring)
○ Female fitness is limited due to resources, while male fitness is limited by their
access to good mates
○ Females are choosy with mates and males compete with each other
○ Some species exhibit gender role reversal (ex: seahorses)
● Honest signals - a trait that gives a truthful impression of an individual’s fitness
, ● Handicap principle - the idea that traits that are costly handicaps can only be possessed
by individuals with the highest fitness who can thereby afford the cost
● Good genes hypothesis - the idea that impressive ornaments show off an individual’s
efficient metabolism and/or their ability to fight off disease
● Artificial selection - the deliberate manipulation of fitness by humans through selective
breeding (ex; the domestication of plants and animals for human consumption)
Genetic drift - the effect of chance on a population’s gene pool; changes in allele frequencies
that are random
○ Individuals are diploid (2n) and gametes are haploid (n)
○ Gametes contain a random sampling of an individual's alleles, so each gamete has
a 50/50 chance of containing each allele
○ Sampling error leads to genetic drift
○ Allele frequencies drift across generations, and the magnitude of this drift is
inversely proportional to the size of the population (big population, small drift,
and vice versa)
○ Genetic drift can lead to a loss of or a fixation of alleles (0% or 100% frequency
of an allele) which causes a loss of genetic diversity
● Bottleneck effect - the magnification of genetic drift as a result of natural events or
catastrophes
○ Sudden random reduction of population size and the new smaller population does
not have the same allele frequencies as the original population
● Founder effect - an event that initiates an allele frequency change in part of the
population, which is not typical of the original population
○ The colonization of an island by a small population that doesn’t have the same
amount of diversity or allele frequencies as the original population
○ Dispersal of a population across a barrier (river, mountain, etc.)
● Genetic drift affects the whole genome and is random with respect to fitness. It usually
leads to a reduction of the average fitness of a population due to a decrease in diversity
Terrestrial biomes
● Terrestrial biome - ecological community of plants, animals, and other organisms that is
adapted to a characteristic set of environmental conditions
● Variables that shape climate include temperature, precipitation, sunlight, and wind
○ Temperature and precipitation are very good at defining biomes because of their
influence on the net primary productivity (measurement of energy accumulation
within an ecosystem)
○ NPP = (carbon fixed, biomass generated) - (carbon released, cellular respiration)
○ Places with high amounts of sunlight and rainfall have a high NPP (these are the
components necessary for photosynthesis)
, ○ NPP is in decline in terrestrial biomes due to climate change (more droughts and
flooding) and in oceans its decreasing as well
● Robert Whittaker - recognized trends of temperature and precipitation as a means of
defining different biomes
○ There are 3 zones based on temperature (hot, temperate, and cold)
○ There are 2 zones based on precipitation (high precipitation and low precipitation)
● Tropical wet forests:
○ Temperature = warm/hot and stable
○ Precipitation = high
○ Dominant vegetation = broad-leafed, evergreen plants
○ High biodiversity, lack of seasonality
○ High net primary productivity
○ Low nutrients in soil, but slash and burn agriculture releases nutrients into soil
● Savanna (tropical grasslands):
○ Temperature = warm/hot and stable
○ Precipitation = low (extensive dry season)
○ Dominant vegetation = grasses
○ These are tropical regions that experience a very little amount of rainfall
● Subtropical deserts:
○ Temperature = warm/hot (can experience some temperature variation throughout
the year)
○ Precipitation = very low
○ Dominant vegetation = plants that are well adapted to low amounts of water, have
deep roots, and have seeds that can remain dormant for long periods of time
○ Typically located 15-30 degrees North or South of the equator
● Rain shadow deserts - deserts located on a mountainside and experience little rainfall in
comparison to the other side of the mountain
● Chaparral:
○ Temperature = warm
○ Precipitation = low (mostly only rains in the winter)
○ Dominant vegetation = shrubs that are adapted to experience periodic fires and
some species even need the fire
● Temperate grasslands:
○ Temperature = seasonal, warm/cool
○ Precipitation = low, seasonal
○ Dominant vegetation = grasses
○ Typically found at mid latitudes
○ Soils are rich in organic matter, but the cold winter temperatures and frozen
waters create defined growing seasons
