Ecology Exam 2 (Ch. 8-12)

Sexual monomorphism

From human’s eyes, can’t tell males & females in species apart → look identical

Sexual dimorphism

From human’s eyes, can tell difference between both sexes in species

Sexual selection vs. Natural selection

• Sexual selection: nonrandom mating b/c of intrasexual competition & intersexual mate choice

• Natural selection: process where organisms that are better adapted to their environment tend to survive & produce more offspring

• They can both conflict sometimes (better survival vs. more attractive males) → i.e. peacocks

Similarities between sexual selection and natural selection

Both have opposing evolutionary forces occurring simultaneously

Sexual selection violates which assumption of HWE?

Random mating: Every individual has an equal chance of mating w/ any other individual of opposite sex, regardless of their genotype or physical traits

• Nonrandom mating or preferential mating can change genotype frequencies

• Sexual selection = another means for evolution to occur

Intrasexual selection

• Individuals of one sex competes among themselves for mates

• Selection is result of contests within one sex

Intersexual selection

• Members of one sex consistently choose mates from among members of the opposite sex on the basis of some particular trait

• Favors elaboration of trait

Why do females choose males that practice resource partitioning?

Females gain direct benefits that improve their survival or reproductive success

Why might there sometimes be conflict between sexual selection and natural selection?

• Elaborative traits make animal more vulnerable to predation/visual predators

• Trait elaboration will ultimately be balanced by natural selection

  • Sexual selection favors traits that increase reproductive success

  • Eventually, traits become so elaborate that they decrease reproductive success

Sociality

Cooperative breeding, feeding, defense, maintenance, but restricted mating opportunities

• More social living → individuals are grouped together → mating may be limited to certain members of the group → restricted mating opportunities

We would expect more extreme versions of sociality when …

There’s high relatedness among helpers and low cost to helpers

What are reasons why sociality may have evolved in different animal systems?

• Need for group defensive of high-quality territories

• Defense of mates and young

What benefits might sociality provide to current-day societies/helpers?

• Inclusive fitness

• Safety or increased resources

• Experience

• Potential to inherit territory

• Potential to recruit helpers

Inclusive fitness

The survival and reproduction of an individual, plus the survival and reproduction of genetic relatives of the individuals

• = kin selection

• Genes are shared, to greater/lesser extent, among related individuals (kin)

• Helpers increase their own fitness (proliferation of their genes into subsequent generations) by increasing fitness of their kin

• Inclusive fitness > cost = cooporation evolves

Eusociality + 3 Main Components to Define a Eusocial Group/Species

• Extreme case of sociality

  • 1) Individuals of more than one generation living together

  • 2) 100% cooperative care of young

  • 3) Division of individuals into non reproductive and reproductive castes

    • Caste: a group of individuals that are physically distinctive & engage in specialized behavior within a social unit

    • Diff size variation for diff roles

    • Queen = reproducing individual

What is Hamilton’s Rule and Its Relation to Inclusive Fitness or Eusociality?

• Cooperation can evolve when the overall genetic payoff of helping is greater than the reproductive cost of helping

• Relation to Inclusive Fitness: Hamilton’s rule explains when helping relatives is favored

• Relation to Eusociality: Hamilton’s rule explains genetic payoff from that help

How have humans caused apparent conflict between sexual selection and artificial selection in some mammal species?

• Human predation

  • Antlers/horns for intrasexual competition → hunters look for bigger ornaments as trophies (but big ornaments = good for intrasexual selection)

  • Horn/antler size decrease in time

  • Humans = artificial selection

What factors contribute to a species’ geographic distribution?

• Abiotic conditions (temp, precipitation, pH, salinity)

• Biotic conditions (competition, predation, disease)

• Ability to disperse

• Historical/geological factors

Niche

The environmental factors that influence the growth, survival, & reproduction of a species (the place where organisms can survive)

• All factors necessary for species existence:

  • When, where, how the species survives

  • Both biotic and abiotic factors involved

Ecologists Defining Niche: Joseph Grinnell

• Early ideas of niche focused on physical environment

  • Rainfall, humidity, soil moisture, barometric pressure, temperature, light intensity, cloudiness

  • 1877-1939

Ecologists Defining Niche: Charles Elton

• Incorporated ideas of biological interactions

  • Mostly considered niche to be product of interactions w/ other organisms & food resources

• 1900-1991

Ecologists Defining Niche: G. Evelyn Hutchinson

• n-dimensional hypervolume

  • n = # of environmental factors important to the survival & reproduction of a species

• Fundamental niche

• Realized niche

Fundamental niche

• The physical conditions under which a species might live in the absence of interactions w/ other species

• Just abiotic conditions

• n-dimensional hypervolume

Realized niche

• The actual niche of a species whose distribution is limited by biotic interactions such as competition, predation, disease, parasitism

• Is usually smaller than fundamental niche b/c of biotic factor limits

BAM Diagram: “A”

• Abiotic Interactions aka fundamental niche

  • Environmental areas where population can survive

• Factors: climate may indirectly affect food production, water supply, habitat

• Shifted by evolution of species itself, physiological tolerance

  • i.e. evolution of a species’ frost tolerance

BAM Diagram: “M”

• Mobility aka historical accessibility/ability to get to a place

• Shifted by external forces (NOT change in abiotic or biotic factors)

  • Natural disaster, species being kidnapped by a human & put on another continent, climate change, continental change

  • Shift in “M” = shift in realized niche

Potential realized niche

• Areas where a population could survive (includes biotic & abiotic interactions)

• Only way to shift this: any factors that change fundamental niche (abiotic conditions) or factors that change biotic conditions

Actual realized niche

• Areas of potential realized niche that organism has had access to

  • was able to move or migrate throughout history to get there

A change in physiological tolerance could change what following aspects of the BAM diagram?

• Fundamental niche

• Potential realized niche

• Realized niche

Small-scale distribution patterns

• No general trends

• Patterns: Random, Regular, Clumped

Random Distribution

• Caused by neutral interactions …

  • Among individuals

  • Between individuals and environment

• Individuals are scattered unpredictably b/c individuals don’t strongly attract or repel each other, and resources are fairly uniform

Regular Distribution

• Caused by:

  • Antagonistic interactions among individuals

  • Local depletion of resources

• Individuals are evenly spaced b/c individuals compete or repel each other, so they maintain distance

Clumped Distribution

• Caused by attraction among individuals OR to a common source

• Individuals occur in groups/patches b/c resources are patchy, or individuals benefit from being together

Large-scale distribution patterns

• Have a trend → clumped

  • don’t have all of random, regular patterns

How does organism size relate to population density?

Increase in size = decreased density in an area b/c they need more resources

How has mammal body size changed through the past thousands of years? What factors have caused these shifts?

a) Dinosaurs go extinct ~65 million years ago → mammals became bigger to a general size limit

• Extinction events got rid of super large mammals that were occupying large-body-size niches on land = ecological opportunities opened

b) Recently, mammal size declining

• Climate change + human hunting

What factors directly cause a population to increase or decrease in size?

• Factors that lead to increase

  • Number of births

  • Number of immigrants

• Factors that lead to decrease

  • Number of deaths

  • Number of emigrants

Dispersal

• When an individual is born in one place and then moves from another

• Individual leaves from where they were born

Passive vs. Active Dispersal

• Passive: organism doesn’t choose where it’s going/dispersing

  • i.e. seeds being dispersed by wind

• Active: organism makes choice to where it’s going/dispersing (could be a bad or good choice)

Dispersal Kernal

How far individuals in a population are likely to move from their starting location

• The probability distribution of dispersal distance

Functional response

When more food is available, an individual eats more

Numerical response

• When more food is available, the environment can support more individuals → populations get bigger

• Downstream effects

  • a species may increase in number, which can indirectly affect other species that reproduce more slowly through increased competition for resources

Population

A group of individuals of a single species inhabiting a specific area

• One group

Subpopulation

A portion of a larger population that lives in one particular patch and is connected to the rest of the larger population it’s part of through immigration and emigration

• Separate local groups

  • Frogs in each pond

Metapopulations

A group of separate subpopulations/populations of the same species that live in different habitat patches but are connected by dispersal (individuals moving between patches)

• Each patch has their own local population, but individuals can move between them

• Individuals can sometimes disperse between them

• All the connected local groups together

  • All the frog subpopulations together

Source-sink dynamics

• Habitat quality varies among patches

• Sources: High-quality habitats that produce more individuals

  • Some individuals disperse to other patches

• Sinks: Poor quality habitat

  • Only maintained by immigration/immigrants coming from source populations (w/out it, population would eventually disappear/go extinct)

Cohort Life Table

• Record all births, observe until they die

• For animals of short generation times/use for individuals that are short-lived

Static Life Table

• A snapshot in time

• Record age of death and then depending on frequency of age groups, estimate life span by looking at differences in proportion of individuals in successive age classes

• Use for individuals that live very long

Survivorship Curve: Type 1

• High survival when young → most die when old

• Most individuals survive through early and middle life

• Death rate increases as get old

• Examples: humans, elephants, many large mammals

Survivorship Curve: Type 2

• Die at equal rates regardless of age

• Examples: many birds, squirrels, some rodents

Survivorship Curve: Type 3

• Most individuals don’t make it past birth

• Those who make it past birth will live for a very long time

• i.e. Pecan tree, many plants, fish, insects, oysters

Net reproductive rate (R₀)

The average number of offspring produced by an individual

• l_xm_x = reproductive rate at age x

l_x

Proportion surviving to age x

• Survival

m_x

Average number of offspring produced by an individual at age x

• Reproductive output

• Fecundity/reproduction at age x

x

Age

If R₀ < 1 …

Population is declining

If R₀ = 1 …

Population is stable

If R₀ > 1 …

Population is increasing

Geometric rate of increase (λ)

The change in population size in organisms w/ pulsed reproduction

• N_t + 1 = population size in future

• N_t = previous population size

Pulsed reproduction

All individuals of one generation die before next generation reproduces

• i..e annual plants, annual insects

When to use geometric rate of increase?

Use when generations do not overlap

Generation time (T)

The average age of reproduction in a population w/ overlapping generations

Per capita rate of increase (r )

Difference between per capita birth rate and death rate

When to use per capita growth rate / rate of increase?

Use for population that’s growing continuously w/ overlapping generations

If r < 0 …

Population is declining

If r = 0 …

Population is stable

If r > 0 …

Population is increasing

Realized r

Actual growth rate under real environmental conditions

R_max

Maximum potential population growth under ideal conditions

The value of realized r is generally …

Lower than the intrinsic rate of increase (r_max) due to environmental limitations

Fecundity schedule

Age-related variation in fecundity

• Fecundity: how many offspring an individual produces

  • affected by number of females produced

Life table

Age-related variation in morality

Fecundity schedule + life table = …

Population growth rate

What are the three types of population growth discussed in class?

Geometric growth, exponential growth, logistic growth

When would it be appropriate to use geometric growth to model a population?

Use when reproduction happens in separate pulses and generations do not overlap

• One generation reproduces

• That generation dies before the next generation reproduces

• Population growth therefore occurs in distinct steps rather than continuously

• Graph is J-shaped

Geometric Growth Equation

• N_t = population at time, t

• N₀ = starting population

• λ = geometric rate of increase

• t = number of time intervals/generations

When would it be appropriate to use exponential growth to model a population?

• Use when generations overlap and population growth is continuous

• Parents can still be alive and reproducing while their offspring are also reproducing

• The model assumes:

  • an unlimited environment

  • a constant per-capita rate of increase ( r)

  • abundant resources

• As population gets bigger, more individuals are reproducing, so population adds more individuals per unit of time

• Graph is J-shaped

Exponential Growth Equation

When would it be appropriate to use logistical growth to model a population?

• When environment limits population growth

• A population may initially grow almost exponentially when it is small and resources are abundant

• As pop size increases, environmental limitations become stronger, causing growth to slow as pop approaches its carrying capacity (K)

• This produces characteristic S-shaped (sigmoidal) curve/graph

What factors might limit geometric or exponential growth?

• Geometric and exponential growth assume abundant resources, including:

  • food

  • space

  • nutrients

  • water

• Natural populations cannot maintain unlimited growth for many generations because resources and energy are limited

• So these types of growth can eventually be limited by things such as food, space, disease, parasitism, predation, or environmental disturbances

When is logistic growth likely?

When environment limits population growth

• Pop may start with rapid/exponential growth when (N) is small, but as pop becomes larger, environmental limitations increase and growth slows

• Eventually pop approaches carrying capacity (K)

What is carrying capacity and why does it matter w/ logistic growth?

• Carrying capacity (K): the theoretical maximum population of a species that a particular ecosystem can sustain

• It matters b/c it determines where population growth begins to level off

  • As N → K, population growth slows

  • When N = K, population growth is 0 in logistic model

What happens if the carrying capacity is overshot by a population?

• If N > K, the pop has a negative growth rate, meaning pop size decreases

• Sometimes, pop can crash after dramatically overshooting carrying capacity

• Too many individuals for environment → pop declines back toward/below K

Instantaneous population growth rate eqn in logistic growth model

• 1 - N/K = effect of environmental limitation

• r_max = intrinsic rate of increase/maximum per capita rate of increase under ideal environmental conditions

• K = carrying capacity

• N = current pop size

• dN/dt = instantaneous rate of pop change

Population has a positive growth rate if …

N < K

• population increases

Population has a negative growth rate if …

N > K

• population decreases

Population has a stable growth rate if …

N = K

• Growth rate is 0

When is population growth (dN/dt) at its maximum in logistic growth?

When N = K/2

• aka when its at half of its carrying capacity, K

When is the maximum per capita growth rate, r_max?

At the beginning of the graph, when N is near 0

What are stressors or factors limiting growth in a population?

Abiotic and Biotic factors can alter birth & death rates, which changes pop growth and pop size

• Abiotic (nonliving factors): flood/drought, extreme temps, fire, volcanic eruption, landslide

• Biotic (living factors): disease, predation, food availability

Density dependent factors

• Stressors that become stronger as population density increases

• i.e. West Nile virus

Density independent factors

• Stressors that affect populations regardless of how dense the pop is

• i.e. a blizzard

Are there general trends in whether abiotic vs. biotic factors are density dependent or independent?

• Yes

  • Abiotic factors usually → density independent

  • Biotic factors usually → density dependent

• But there are exceptions:

  • Abiotic factor can become density dependent if a storm occurs but there are only a limited number of sheltered roosts

  • Biotic factor can act density independently if a particularly severe disease kills individuals regardless of population density

How does population age distribution reflect potential future growth, maintenance, or decline?

A population's age distribution reflects its history of survival and reproduction and can indicate its potential for future growth

Pyramid-shaped age distribution

• Rapidly growing population

  • Many young individuals

  • Fewer old individuals

  • Large # of young individuals will eventually enter reproductive ages

• High potential for future population growth

Constant age distribution

• Stable/slow-growing population

• Similar proportions across many age classes

• Indicates slow growth or population maintenance

Few young individuals

• Declining population

• Relatively fewer young individuals than old individuals

• Less replacement potential

• Negative future growth/decline

Why is the relationship between number of seeds and size of seeds negative?

• Plants have a limited amount of energy/resources available for reproduction

  • More seeds → smaller seeds

    • Many seeds means that less energy can be invested, so result in smaller seeds

  • Larger seeds → fewer seeds

    • It takes more investment of energy to make large seeds, so can’t make too many of them

Reproductive effort

The amount/proportion of an organism's available resources or energy that it allocates toward reproduction

Trade-offs to reproductive effort

• 1) More energy invested in reproduction means less energy available for maintaining the parent's body

• 2) Reproduce early → potentially affect survival/growth; Reproduce later → risk dying before reproducing