BSC2011L - Quiz 9 Notes

Population Ecology

Population

A group of individuals of the same species living in the same geographic area; can be described by size, density, and distribution.

Population Growth Factors

The four components that determine changes in population size:

• Births (B): Increase population size

• Deaths (D): Decrease population size

• Immigration (I): Individuals entering a population

• Emigration (E): Individuals leaving a population

Population Growth Equation

Change in population size = (Births + Immigration) – (Deaths + Emigration).

Exponential Growth

Population growth under unlimited resources where the per-individual growth rate (r-max) stays constant; produces a J-shaped curve.

r-max (Intrinsic Rate of Increase)

The maximum per-individual rate of increase under ideal, unlimited conditions.

Logistic Growth

Population growth that slows as resources become limited and levels off at the carrying capacity; produces an S-shaped curve.

Carrying Capacity (K)

The maximum population size that an environment can sustainably support with available resources.

Lag Phase

Early stage of logistic growth when population size (N) is much smaller than carrying capacity (K), resulting in slow growth.

Exponential Growth Phase

Middle stage of logistic growth when resources are still abundant and growth is rapid.

Equilibrium Phase

Final stage of logistic growth when N = K and births equal deaths; the population stabilizes.

Density-Dependent Factors

Biotic factors whose effects on population growth increase when population density increases; they regulate population size around carrying capacity.
Examples: Intraspecific competition, predation, disease.

Density-Independent Factors

Abiotic factors that affect population growth regardless of population density.
Examples: Harsh winter, drought, natural disasters.

Population Crash

A sudden, dramatic decline in population size due to limiting factors; often caused by density-independent events (e.g., harsh winter in the reindeer example).

Demography

The statistical study of human populations, including size, birth rates, death rates, and age structure.

Age Structure

The distribution of individuals across different age groups within a population; used to predict population growth trends.

Expansive Age Structure

Pyramid-shaped structure with a large young population; indicates rapid population growth (e.g., Gambia).

Stationary Age Structure

Rectangular age structure with similar numbers of young, middle, and older individuals; indicates a stable population (e.g., USA).

Constrictive Age Structure

Narrow base with fewer young individuals; indicates a declining population (e.g., Germany).

Interpreting Age Structure Histograms

• Wide base → growing population

• Straight/rectangular sides → stable population

• Narrow base → declining population

Identifying r-max on Exponential Curves

On graphs with two exponential curves:

• The steeper curve = higher r-max

• The flatter curve = lower r-max

Intraspecific Competition

Competition among individuals of the same species for limited resources; a density-dependent factor.

Binary Fission

A form of asexual reproduction in bacteria leading to exponential growth when resources are unlimited (example with E. coli).

Most basic mathematical model in population ecology:

dN/dT = rN

• N is the current population size

• T is time

• r is the number of births an inidividual produces (per capita rate of increase)