Demography and Population Structure

These flashcards cover the core concepts of demography, population structure, population genetics (Hardy-Weinberg Equilibrium), and S-I-R disease modeling based on the Class 6 lecture notes.

Population Structure

The static demographic makeup or composition of a population at a moment in time, including age, sex, geographic distribution, and allele frequencies.

Population Dynamics

The underlying processes explaining how and why populations change in their distribution, abundance, and structure over time.

Net Reproductive Rate ($R_0$)

The average number of female offspring produced by an individual female in her lifetime; it is calculated by summing the survival-adjusted fecundity column ($l_x b_x$) in a life table.

Cohort

A group of individuals born during the same time period, such as larvae spawned in the same year.

Cohort Life Table

A demographic tool containing data collected by tracking a specific cohort through time from birth to death.

Static Life Table

A short-term snapshot recording the birth and death rates by age across an entire population at one time.

Age Distribution

The current distribution of individuals categorized by age within a population.

Proportion Surviving ($l_x$)

The fraction of a cohort surviving to a specific age $x$, calculated as $l_x = \frac{N_x}{N_0}$.

Age-specific Mortality ($q_x$)

The proportion of individuals at age $x$ that die before reaching the next age class, calculated as $q_x = \frac{d_x}{N_x}$.

Age-specific Fecundity ($b_x$)

The average number of offspring produced by an individual of a specific age $x$. (Note: Referred to as $m_x$ in some textbooks).

Type I Survivorship Curve

A pattern where individuals have high survival rates until old age, at which point mortality increases rapidly; characteristic of species like Humans and Elephants.

Type II Survivorship Curve

A pattern where individuals have a constant probability of dying at any age; characteristic of species like Robins and Starlings.

Type III Survivorship Curve

A pattern characterized by extremely high mortality in the juvenile stage, with stable survival rates for those reaching adulthood; characteristic of species like Barnacles and White Oak.

Nodes

In life cycle graphs, these represent specific categories or classes of individuals, such as juveniles or mature adults.

Transitions

The connections or arrows in a life cycle graph that show the probability of moving between life stages, such as maturation or survival.

Population Genetics

The study of how genetic variation is distributed within a population and how that variation changes over time.

Allele

Different versions of DNA that code for the same heritable trait.

Genotype

The specific combination of alleles an individual inherited (e.g., homozygous $BB$ or heterozygous $Bb$).

Phenotype

The physical expression of an individual's genotype.

Hardy-Weinberg Equilibrium (HWE)

A null hypothesis stating that genotype frequencies will remain constant and proportional to allele frequencies ($p^2$, $2pq$, and $q^2$) in the absence of evolution.

HWE Assumptions

The five conditions required for a population to remain in Hardy-Weinberg Equilibrium: random mating, no mutations, large population size, no gene flow, and no natural selection.

S-I-R Model

A structured population model used to track disease spread through three classes: Susceptible ($S$), Infected ($I$), and Recovered ($R$).

Beta ($\beta$)

The parameter representing the infection rate in disease modeling.

Gamma ($\gamma$)

The parameter representing the recovery rate in disease modeling.

Disease Reproduction Number ($R_0$)

The number of new infections produced by one sick individual, calculated as $R_0 = \frac{\text{rate of infections}}{\text{rate of recovery}}$. If $R_0 > 1$, the disease will spread.

Herd Immunity

Indirect protection from an infectious disease that occurs when a sufficiently large percentage of a population becomes immune, making transmission unlikely.

Vaccination Threshold ($p$)

The proportion of a population that must be vaccinated to achieve herd immunity ($R_0 < 1$), calculated using the relationship $R_0 \times (1 - p) < 1$.

Harmonia axyridis

The scientific name for the Asian lady beetle, used as an example to demonstrate heritable color patterns and testing for Hardy-Weinberg Equilibrium.

North Atlantic Right Whale

A species used as an example for life cycle graphs, categorized by stages: Calf, Immature Female, Mature Female, and Mature Female with Calf.

Cohort Life Table

A demographic tool containing data collected by tracking a specific cohort through time from birth to death.

Static Life Table

A short-term snapshot recording the birth and death rates by age across an entire population at one time.

Life Cycle Graphs

Visual representations of the life stages and transitions of organisms, indicating the probabilities of moving between different life stages.

S-I-R Model

A structured population model used to track disease spread through three classes: Susceptible ($S$), Infected ($I$), and Recovered ($R$). The rates of change for each group are represented by differential equations: $\frac{dS}{dt} = -\beta SI$, $\frac{dI}{dt} = \beta SI - \gamma I$, $\frac{dR}{dt} = \gamma I$.

Rate of Change for Susceptible ($\frac{dS}{dt}$)

Represents the rate at which susceptible individuals become infected, calculated as $\frac{dS}{dt} = -\beta S\frac{I}{N}$, where $\beta$ is the infection rate and $I$ is the number of infected individuals. Change in S = Loss from class due to getting sick.

Rate of Change for Infected ($\frac{dI}{dt}$)

Represents the rate at which infected individuals change status, calculated as $\frac{dI}{dt} = \beta SI - \gamma I$, where $\gamma$ is the recovery rate. Change in I = Gain from class due to getting sick - Loss from class due to recovery.

Rate of Change for Recovered ($\frac{dR}{dt}$)

Represents the rate at which infected individuals recover, calculated as $\frac{dR}{dt} = \gamma I$, where $\gamma$ is the recovery rate. Change in R = Gain from recovery.