Ecology Exam 2

What are other revolutionary forces that cause change in allele frequency?

-Mutation
-Genetic drift
-Gene flow
-Natural Selection

Define mutation

Any change in genomic sequence of an organism, could be a gene mutation or chromosome mutation

Beneficial mutations

increase the fitness of the individual that possesses it

Neutral mutations

neither increase nor decrease fitness of an individual

Detrimental mutations

reduce the fitness of the individual

What is genetic drift?

-Random change in allele frequencies over time

-Happens by chance, NOT because traits are better

-Strongest in small populations: leads to loss of variation, fixation (only 1 allele left)

Give one example of genetic drift

-Mexican tetra (cavefish)

-live in dark caves, lack pigmentation (genetic drift) and lost eyes

What is the difference between natural selection and genetic drift

-Genetic drift is random, not due to chance, more noticeable in small populations
-Natural selection is not random, based on fitness, works in larger populations

Bottleneck effect

-A sudden reduction in population size (due to disaster, disease, etc.)

-Survivors are a random subset → not genetically representative of original population

Ex: cheetahs had multiple bottlenecks and now have very low genetic diversity, 90% genetic similarity (leads to poor sperm quality, more disease, higher extinction risk)

What is the founder effect

-A small group leaves and starts a new population
-Founders of the new population are a random sample (diff. allele frequencies, less genetic diversity)

What is the relationship between the founder effect and bottleneck?

Founder effect and bottleneck are both examples of genetic drift
-Ex: Pitcairn island, 27 founded the island, diff. genetic makeup than original British population
-New population not equal to full genetic diversity of original population

Define nonrandom mating

-Individuals don’t mate randomly

-allele frequencies=do not change
-Genotype frequencies=do change
-Types: inbreeding, positive assortative mating, negative assortative mating

What is inbreeding

Mating with relatives

Brings out recessive harmful alleles
-Effect: increases homozygous, decreases heterozygous

Inbreeding depression

-Reduced fitness due to inbreeding

-Harmful recessive allele become expressed
Ex: Spanish royal family (high inbreeding→ low survivorship)

Inbreeding coefficient (F)

probability two alleles are identical by descent
-0= no inbreeding

-1= complete inbreeding

-What affects F: number of generations of inbreeding

-Increased F→ increased homozygous

What is positive assortative mating

-Similar individuals mate

-Effect: increases homozygous, decreases heterozygous

Ex: tall people marrying tall people, inbreeding

What is negative assortative mating

Opposites mate
-Effect: increases heterozygous

Gene flow

Movement of alleles from one population to another
-Prevent populations from becoming genetically diff. from one another
-Increases genetic variation within a population

Define asexual reproduction

-One parent
-Offspring= genetically identical (clones)
-Ex: bacteria, whiptail lizards

Define sexual reproduction

-Two parents
-Combines genes→ genetic variation

What are the costs of sexual reproduction

-finding a mate
-Energy/time for mating
-”two-fold cost of sex” (only female produce offspring)

What are the benefits of sexual reproduction

-Genetic variation
-Better ability to: adapt, survive disease, survive environmental changes

What is the red queen hypothesis

-Species must constantly evolve just to survive
-Why sexual reproduction helps: creates genetic variation, helps organisms keep up with parasites, diseases, predators
-without variation→ species gets wiped out

What is anisogamy?

form of sexual reproduction involving the fusion of two gametes that differ in size and form
-Eggs= big + energy expensive
-Sperm= tiny + cheap

What are the consequences of cheap sperm vs costly eggs?

Females invest a lot: eggs, pregnancy, care

-Solution: be selective

Males: invest little

-Solution: mate as much as possible

Explain the certainty of maternity vs paternity

-Females: always sure offspring is theirs, more parental care
-Males: not always sure, less investment

-Leads to sexual selection behaviors

What is sexual selection

Differences in reproductive success due to mating competition
-Intrasexual selection + intersexual selection

What is intrasexual selection (competition)

-same sex competing (usually males), ex: fighting
-Ex: deer antlers, bigger body size, aggressive behavior

What is intersexual selection (mate choice)

-One sex chooses (usually females), attraction

What is operational sex ratio (OSR)

Ratio of males to females ready to mate
-If more males: strong male competition, more intrasexual selection

-If more females: females compete or become choosy

What are sneaker males?

-Males that don’t fight but sneak mating opportunities
Ex: cuttlefish pretend to be female to avoid detection then mate secretly

Define sperm competition

-Competition between sperm from different males
-How? females mate with multiples mates, sperm compete inside reproductive tract

What is the strategy of sperm competition

-Remove other sperm

-Produce more sperm

-Faster sperm

-Females can even choose sperm

Direct benefits of female choice

-Immediate benefits to female such as food, protection, territory

Indirect benefits of female choice

-Genetic benefits

Good genes→ healthier offspring

Explain “bad” traits that evolve

-Surviving with a disadvantage= that gene must be good
Ex: peacock tail: heavy + visible but signals strong genetics because it survived this far

What is life history?

The schedule of an organism’s life:

-Growth

-Development

-Reproduction

-Survival

-Answers: “when should I reproduce?” “how many offspring should I have?”

Define evolutionary fitness

How successful an organism is at passing on its genes
-Fitness doesn’t equal strongest or hottest

-Fitness= number of surviving offspring

Define a fast life history

r-selected: Insects, dandelions

-Many offspring

-Small body size

-Early reproduction

-Short lifespan

-Little parental care

Define a slow life history

k-selected: elephants, humans
-Few offspring

-Large body size

-Late reproduction

-Long lifespan

-High parental care

What is the principle of allocation

-Energy is limited

-If you spend energy on one thing you have less for another

-Energy used for reproduction=less for growth

What are ecological trade-offs

Improving one trait→ reduces another
-Ex: large eggs, higher survival but fewer eggs

-No perfect strategy, just compromises in nature

What is the relationship between offspring size vs number?

-Inverse relationship (organisms balance survival vs quantity)

Bigger offspring=fewer
Smaller offspring=more

What is Lack’s principle

-Animals produce the maximum number of offspring they can successfully raise

-They do not produce the max number possible!

Why is clutch size smaller? (Why don’t animals have as many babies as they physically could?)

1) Trade-off with survival

2) Too many offspring lowers fitness
3) Parent vary in ability

Ex: birds lay fewer eggs than they physically could because they can’t feed them all

What are the characteristics of early reproduction vs delayed reproduction?

Early: smaller size, shorter lifespan

Delayed: larger size, longer lifespan

-large organisms can produce more/better offspring

What is the guppy experiment?

-Wanted to see if predation changes life history strategies

-Studied guppies with two environments: low elevation=high predation, high elevation (low predation)

Results:

-High predation guppies reproduced earlier, had more offspring, offspring are smaller, mature faster (fast life history)

-Low predation guppies reproduced later, had fewer offspring, offspring are larger, grow more before reproducing (slow life history)

What is the big takeaway from the guppy experiment?

Life history traits are evolutionary responses to the environment

What is semelparity?

-Reproduce once then die

-Ex: salmon, cicadas

-This evolves in low survival, unpredictable environment

What is iteroparity?

Reproduce multiple times
-Ex: birds, humans

-This evolves in stable environments, higher survival

What is the grandmother hypothesis

-Older females stop reproducing to help offspring/grandchildren survive

-Helping relatives=increases fitness→ passing on shared genes

Ex: humans, killer whales

What are the key terms in population growth graph?

-Growth rate: births-deaths

-Intrinsic rate (r ): max growth under ideal conditions

-Carrying capacity (k): max population environment can support

What is logistic growth?

model of population growth where a population grows rapidly at first (exponentially) but slows down and levels off at max carrying capacity

What are the types of survivorship curves and what do they mean?

-Type I: late death (humans)

-Type II: constant death rate

-Type III: high early death (plants, fish)

What is senescence?

-Aging

-Decline in function with age
-Seen in long-lived organisms, iteroparous species (reproduce several times)

What is population growth?

-Change in population size over time

-Population growth when births > deaths

-Population shrinks when deaths > births

Change in pop. = Births + Immigration - deaths- emigration

What is the exponential growth model?

-Describes how a population growth when: nothing is limiting it
-Assumes unlimited food, no predators, no disease

-the bigger a population gets, the faster it grows

r=intrinsic rate of growth (max possible growth rate)

J-shaped curve

What is the geometric growth model

-Used in species with discrete reproduction (seasonal breeders)

-λ (lambda) = growth per time step

λ > 1 → population increasing

λ = 1 → stable

λ < 1 → population decreasing

What is the difference between exponential vs geometric?

Exponential: continuous growth, uses r, smooth curve

Geometric: discrete intervals, uses λ , step-like

What are limiting factors?

-Cause populations to not grow forever

-Density dependent vs independent

What are density-independent factors?

-Affect population regardless of size

Ex: weather, natural disasters

What is Density-dependent factors?

-Effect depends on population size

Ex: competition for food, disease, predation

What is negative density dependence?

-As population increases → growth decreases
-Why? more competition, more disease spread

What is positive density dependence (Allee effect)?

-Small populations grow slower
-Why? hard to find mates, less cooperation

What is carrying capacity (k)?

maximum population size environment can support

-At k: births=deaths, population is stable

What is a logistic growth model?

-Shows realistic population growth

S-shaped curve

-Stages:

1) Fast growth

2) slowing down

3) plateau at K (growth rate = 0)

What is age structure?

Distribution of individuals across age groups

-Predicts future growth
-Population shapes:

Triangle=growing population

Rectangle=stable
Inverted=declining

What is demography

-Study of birth rates, death rates, migration W

What are life tables?

Tracks survival & reproduction by age (shows which life stages are most vulnerable)

-Ix: probability of surviving to age x
-px: probability of surviving to next age

-qx: probability of dying

Define Net reproductive rate (Ro)

-Average number of offspring per individual

Ro >1 population is increase

Ro = 1 stable

Ro<1 population is decreasing

What are survivorship curves?

proportion of individuals surviving at each age for a given species or group
-Type I: late death (humans)

-Type II: constant death

-Type III: high early death (plants, fish)

-diff species survive differently

What is an ecological niche?

-An organisms’ role in its environment

It includes: what it eats, what eats it, when it’s active, environmental conditions it can tolerate

-Includes biotic + abiotic factors

What is the diff. between niche, habitat and geographic range?

-Habitat: physical place organism lives

-Niche: role + interactions + conditions (determines habitat!)

-Geographic range: where species is fond on Earth

Define niche as “hypervolume”

-Niche= multi-dimensional space of conditions
-Ex: species depends on temperature, food type, water, predators

Define competition and niche?

-Species often compete for same resources, to lessen competition they develop different niches

What is fundamental vs. realized niche?

-Fundamental: where a species could live (no competition or predators)

-Realized: where it actually lives, includes competition + predation (smaller than fundamental!)

Ex: barnacles→ one species gets pushed into a smaller zone due to competition

What is Gause’s competitive exclusion principle?

Two species cannot occupy the exact same niche long-term
-Ex: paramecium experiment, when grown together one species die
-Why? they compete for the same limited resource

What is niche partitioning?

-Species divide resources to reduce competition

-Overlap of resources exists but usage differs

-Ex: warblers → each species uses different parts of the tree

What some other forms of niche partitioning?

-Temporal: active at diff. times (nocturnal, diurnal)

-Resource: eat diff. food sizes
-Spatial: use diff. areas

What is character displacement?

-Species evolve differences to reduce competition

-Happens with high competition→ natural selection favors differences

-Competition drives evolution of differences!

Ex: birds develop diff. beak sizes to eat diff. foods

What is niche breath?

-Breadth: range of resources used?

Wide=generalist

Narrow=specialist

What is niche separation?

How species differ in resource use

What is the real-world importance of niche?

-Predict species distribution

-Understand invasive species

-Predict climate change effects

What is biodiversity?

The variety of species in a community

-Two parts: species richness, species evenness

What is species richness?

-Number of different species in a community

-Does not tell you how many individuals of each (two communities can have same richness and look very diff.)

Ex: 10 species = richness of 10

what is species evenness?

How evenly individuals are distributed among species

-Ex: high evenness: all species are roughly equal numbers

-Low evenness: one species dominates

What is the diff. between absolute and relative abundance?

Absolute: number of individuals

Relative: proportion of each species

What are rank-abundance curves?

graph used to visualize species richness and evenness

x-axis: species rank

y-axis: abundance

-longer curve: more species (high richness)

-flatter curve: more even (similar abundances)

-steep curve: low evenness (dominant species)

Define Shannon diversity index

-measures both richness and evenness

H value:

0 → only 1 species

High → many species + even (more diversity)

What increases/decreases diveristy?

Habitat size: bigger area→more species

Define island equilibrium model?

Diversity is a balance between immigration and extinction

-at equilibrium: immigration=extinction

What affects diversity?

1) Distance: closer → more immigration

2) Size: larger → lower extinction

Define environmental compexity

More complex habitat=more niches
-Ex: more vegetation layers= more bird species

What is the relationship between nutrients and diversity?

-More nutrients doesn’t always equal more diversity

-Why? too many nutrients → one species dominates (competitive exclusion)

Why are the tropics so biodiverse?

More sunlight and precipitation = more energy, more life

-more time for species to evolve, less extinction (?)

What are biodiversity hotspots?

Areas with: high species richness, many endemic species ( restricted to a specific, unique geographic location)

-Found in: tropics, islands, Mediterranean climates

What is the intermediate disturbance hypothesis?

-disturbance: events like fire, storms

-Moderate disturbance → highest diversity

Why? too little disturbance = dominant species take over, too much disturbance = only a few survive

How can consumers affect diversity?

-Herbivores can: increase or decrease diversity depending on what they eat and which species they remove

Ex: snails eating algae → more species coexist