Population Ecology Lecture 4 Flashcards

A collection of vocabulary terms and key concepts from the Introduction to Population Ecology lecture, covering distribution, density, niche types, and growth models.

Population

A group of individuals of the same species that live in the same location and interact more closely with one another due to physical proximity.

Population Dynamics

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

Metapopulation

A group of connected subpopulations that exchange individuals through dispersal.

Distribution

The size, shape, and location of the area a population occupies, typically dictated by abiotic and biotic factors.

Density

The number of individuals per unit area, such as the $0.5$ crows per square mile in California versus $16$ in New York.

Abundance

The total number of individuals in a population, which may also be measured in biomass; for example, the American crow population is approximately $31$ million.

Subpopulation

A part of a larger population that has limited exchange with other parts through immigration and emigration.

Immigration

The dispersal process involving the arrival of individuals into a new location.

Emigration

The dispersal process involving individuals exiting their native locations.

Fundamental Niche

The range of physical conditions a species could live in, shaped by abiotic factors such as water availability, nutrient availability, and temperature.

Realized Niche

The actual space a species lives in, shaped by biotic interactions such as competition, predation, disease, and parasitism.

Population Modeling

The mathematical analysis of population characteristics within its environmental context to describe and predict population dynamics.

State Variable

The information that describes the current state a system is in, usually the variable of interest that changes over time, such as population size ($N$).

Parameter

A number or measurable quantity, often constant, on which dynamics depend, such as birth rate ($b$) or per capita growth rate ($r$).

Geometric Growth Model

A discrete time model used for populations with pulses of reproduction and non-overlapping generations, such as annual plants.

Discrete Time

Specific intervals or distinct time steps used in difference equations, represented as $N_{t+1}$.

Lambda ($\lambda$)

The geometric growth rate, representing the average number of offspring left by an individual during one time interval, defined as $\lambda = 1 + b - d$.

Exponential Growth Model

A continuous time model used for populations with overlapping generations where reproduction occurs continuously, such as humans or fish.

Continuous Time

Infinitely small time intervals or instantaneous change used in differential equations, represented as $\frac{dN}{dt}$.

Per Capita Growth Rate ($r$)

The intrinsic rate of increase, calculated as the birth rate minus the death rate ($r = b - d$).

Difference Equation

An equation used to predict how state variables change over a discrete time step, such as $N_{t+1} = \lambda N_t$.

Differential Equation

An equation describing change in a system over continuous time, such as $\frac{dN}{dt} = rN$.

Geometric Growth Fate ($\lambda = 1$)

The condition where births equal deaths ($b = d$), resulting in a flat trend where the population size remains constant.

Exponential Growth Fate ($r > 0$)

The condition where the per capita growth rate is positive, leading to an increasing population size over time.

Geometric Growth Eqn (Time $t$)

The formula to find the population at any time $t$ in a discrete model: $N_t = N_0 \lambda^t$.

Exponential Growth Eqn (Time $t$)

The formula to find the population at any time $t$ in a continuous model: $N(t) = N_0 e^{rt}$.

Factors Driving Population Dynamics

The key factors influencing population dynamics include:

• Abundance of resources
• Mortality rates
• Birth rates
• Immigration and emigration rates
• Environmental changes
• Species interactions (predation, competition, etc.)

Assumptions of Population Growth Models

Population growth models often assume:

• Constant environmental conditions
• Homogeneous population (no genetic diversity)
• No immigration or emigration impacts
• Resources are either unlimited (exponential growth) or limited (logistic growth)
• Individuals are identical in reproductive capacity

Different Values of Lambda ($\lambda$)

Values of $\lambda$ (geometric growth rate) indicate:

• \lambda < 1: Population is decreasing
• $\lambda = 1$: Population is stable
• \lambda > 1: Population is increasing

Different Values of Per Capita Growth Rate ($r$)

Values of $r$ (per capita growth rate) indicate:

• r < 0: Population is declining
• $r = 0$: Population is stable
• r > 0: Population is growing