BIOL 286: Lecture #5 Review (Population Growth & Demography)

Population growth can be impacted by . . .

demography

demography

The quantitative description of a population and its characteristics

Demographic characteristics of a population: (3)

(1) age structure; (2) proportion of sex; (3) variation in individual reproduction and survival (e.g. time to reproduction

population boundaries

The geographic

Population boundaries mark the point at which individuals are unlikely to . . .

. . .

Why do we care about population boundaries?

Because the demography of populations may vary

population connectivity

The degree to which populations are connected by dispersal or movement of organisms

The more connected populations are

the more . . . they and their demographics are. Correspondingly

ecological population

A group of individuals of a species that occupy a defined area

evolutionary population

A local group of individuals that mate at random (a deme)

Distinguish between ecological and evolutionary populations.

Principally

age structure

A demographic characteristic of a population outlining the relative number of individuals of each age present in said population

Age structure diagrams can provide insight into . . . of a population

the ecology and history

Describe the morphological features of an age structure depicting a stable population.

An age structure depicting a stable population shows a smoothly tapering form in which each successive age class is slightly smaller than the one before it. The base is moderately broad

Describe the morphological features of an age structure depicting a decreasing population.

An age structure depicting a decreasing population has a distinctly constricted base

Describe the morphological features of an age structure depicting an increasing population.

An age structure depicting an increasing population has a distinctly constricted peak

life table

An age-specific summary of the survival pattern of a population

Types of life tables: (2)

(1) cohort life table; (2) static life stable

cohort life table

A life table that follows a single group of individuals born at the same time throughout their lives until the last individual dies

static life table

A life table based on a sample population and ages of those individuals at a single time point

age-specific survivorship

The proportion of a cohort surviving from birth to a given age x

Age-specific survivorship formula: . . .

lx = Nx/N0

age-specific mortality

The proportion of individuals alive at the beginning of an age interval but who ultimately died during that interval

Age-specific mortality formula: . . .

Dx = Nx - N(x + 1)

survivorship curve

A graphical representation of the pattern of age-specific survivorship (lx) of a population

Types of survivorship curves: (3)

(1) Type I; (2) Type II; (3) Type III

Types of survivorship curves: Type I

A survivorship curve characterized by relatively high survival until old age

Types of survivorship curves: Type II

A survivorship curve where survivorship is relatively constant across age cohorts

Types of survivorship curves: Type III

A survivorship curve characterized by high early mortality that decreases among older age cohorts

Habitat . . . may affect survivorship curves; this means these curves may . . .

habitat; differ among populations within a species

Survivorship curves can differ among . . .

sexes

Provide an example of how survivorship curves may differ among sexes.

In polygynous mammals

life expectancy (ex)

Represents the mean amount of time an individual of a given age x is expected to life; distinct from life span

Life expectancy (ex) may increase if an individual . . .

survives an age class with high mortality

life span

The maximum number of years an individual can potentially live

Demonstrate how to compute life expectancy for a given age class x from a life table: (3)

(1) Calculate the average number of individuals alive between age class x and x + 1: Lx = (nx + n(x + 1))/2; (2) Calculate the age classes remaining for an individual in age class x: Tx = inf(sigma)k = x (Lk); (3) Divide the number of remaining age classes for an individual of age class x Tx by the number of individuals belonging to age class x: ex = Tx/nx

Life expectancy formula: . . .

ex = Tx / nx

net reproductive rate (R0)

The number of offspring produced by an individual over their life span

Net reproductive rate formula: . . .

R0 = n(sigma)x = 0 (lx*bx)

age-specific birth rate (bx)

The number of births to women in a certain age cohort divided by the number of women in that cohort

The product of age-specific survivorship (lx) and age-specific birth rate (bx) (i.e. lx*bx) represents . . .

The realized reproductive output of an individual which includes the probability that an individual survives to that age

Net reproductive rate (R0) is typically calculated from . . . life tables

female-only

Interpret the meaning of the net reproductive rate R0 for a given population: R0 = 1

The population is stable

Interpret the meaning of the net reproductive rate R0 for a given population: R0 > 1

The population is increasing

Interpret the meaning of the net reproductive rate R0 for a given population: R0 < 1

The population is decreasing

discrete generations

Generations that have no overlap in reproduction

Discrete generations are observed where . . .

meaning . . .

overlapping generations

Population structure in which parents may still reproduce while their offspring are of a reproductive age

In overlapping generations

. . .

Describe the growth of populations with discrete generations.

A graph of population size over time features periods of increase and decrease as parents reproduce and die

Describe the growth of populations with overlapping generations.

A graph of population size over time is continuous

Types of population growth: (2)

(1) exponential growth; (2) logistic growth

Types of population growth: Exponential growth

A pattern of population growth in which a population's per capita growth rate stays the same regardless of population size

When do populations undergo exponential growth? (3)

(1) colonizing new areas; (2) abundant resources; (3) lack of predation

To represent exponentially growing populations with discrete generations

we use . . .

Population size equation for exponentially growing populations with discrete generations at time t: . . .

Nt = R0^t * N0

To represent exponentially growing populations with overlapping generations

we use . . .

intrinsic rate of increase (r)

T rate at which a population could grow if it had unlimited resources.

Intrinsic rate of increase formula: . . .

r = b - d

Interpret the meaning of the intrinsic rate of increase r for a given population: r < 0

The population declines

Interpret the meaning of the intrinsic rate of increase r for a given population: r = 0

The population is stable

Interpret the meaning of the intrinsic rate of increase r for a given population: r > 0

The population grows

The derivative of population size over time (dN/dt) is equal to . . .

The intrinsic rate of increase r multiplied by N (i.e. dN/dt = r*N

Population size equation for exponentially growing populations with overlapping generations at time t: . . .

Nt = N0 * e^rt

Describe how population regulation ties back to Darwin and Wallace's ideas of natural selection: (5)

(1) Individuals have high reproductive potential. In the absence of other forces

Examples of biotic factors regulating population growth: (5)

(1) predators; (2) food supply (prey

Examples of abiotic factors regulating population growth: (5)

(1) storms; (2) fires; (3) droughts; (4) nutrient availability; (5) light availability

Biotic factors regulating population growth can act in . . . or . . . fashion

(1) top-down; (2) bottom-up

Directionality of population growth regulation by biotic factors refers to . . .

the direction of regulation through the food chain

top-down population regulation

Regulation by which higher trophic levels alter population sizes

bottom-up population regulation

Regulation by which lower trophic levels alter population sizes via energy and biomass availability

Outline bottom-up population regulation with respect to Galapagos penguin population due to El Nino.

During an El Nino

Top-down population is usually driven by . . . and . . .

predators; parasites

density-dependent effects

A regulatory effect whereby

At higher population densities

there can be: (6)

Allee effect

A density-dependent effect whereby population growth rates increase with population size

Provide examples contexts in which Allee effects might be observed: (2)

(1) sparse populations make it difficult to find mates; (2) larger groups deter predators

density-independent effects

A type of regulatory effect that is independent of population density

Examples of density-independent effects: (4)

(1) climate; (2) weather events; (3) fire; (4) pollution

Density independence means that . . .

mortality and reproduction do not change with population density

logistic population growth

A type of population growth in which a population's per capita growth rate grows progressively smaller as population size approaches a maximum imposed by limited resources in the environment

carrying capacity

The maximum number of individuals of a population can be supported by local resources

Logistic population growth curve equation: . . .

dN/dt = r * N[(K - N)/K]

Interpret the meaning of the population rate of change dN/dt for a given population with respect to N (number of individuals) and K (carrying capacity): dN/dt is negative

The population declines; N > K

Interpret the meaning of the population rate of change dN/dt for a given population with respect to N (number of individuals) and K (carrying capacity): dN/dt is positive

The population grows; N < K

Interpret the meaning of the population rate of change dN/dt for a given population with respect to N (number of individuals) and K (carrying capacity): dN/dt = 0

The population is stable; N = K

Stable populations . . . and are achieved by . . .

fluctuate within relatively narrow limits; the sum of both density-dependent and density-independent regulatory factors

A population must not be . . . to be stable

at equilibrium

Population regulation can be related to . . .

such as . . . or . . .