Population Dynamics Overview

Study Notes

Population: a group of individuals of the same species living in a defined area at a specific time.
Key characteristics of a population:
- Size: number of individuals.
- Natality: birth rate.
- Mortality: death rate.
- Sex ratio: proportion of males to females.
- Age structure: distribution of individuals across different age groups.
Recruitment: the number of new individuals reaching breeding age plus immigration.
Immigration: the influx of new individuals into a population.
Emigration (Dispersal): individuals leaving a population.
Exponential Growth Curve: a population's rate of growth accelerates over time.
Exponential growth is rare in nature because limiting factors, such as starvation, predation, and disease, restrict growth.

Sigmoid Growth Curve: a population's growth rate initially increases rapidly, then slows down as it approaches carrying capacity.
Inflection point (IP): the point on the curve where the population is still growing but at a slower rate.
Carrying capacity (K): the maximum number of individuals that an environment or habitat can sustain.
Variation in environmental factors can influence carrying capacity over time.
If carrying capacity is exceeded, the population growth rate drops.

Density-dependent mortality factor: a factor that increases mortality as a population becomes denser (e.g., predation, disease, starvation).
Density-independent mortality factor: a factor that increases mortality regardless of population density (e.g., hurricanes, floods, fires, catastrophic events).

Sex ratio: the relative abundance of each sex within a population.
Primary sex ratio: the sex ratio at fertilization.
Secondary sex ratio: the sex ratio at birth.
Tertiary sex ratio: the sex ratio of juveniles.
Quaternary sex ratio: the sex ratio of adults.
The sex ratio can be influenced by various factors, such as mortality rates and management practices (e.g., "Don't Take a Jake Rule" for turkeys).

K-selected species: large, long-lived organisms that produce few offspring and invest heavily in parental care (e.g., elephants, whales).
r-selected species: small, short-lived organisms that produce many offspring with high mortality and little parental care (e.g., rodents, fish, insects, amphibians).

Population growth can be calculated using equations that account for births, deaths, immigration, and emigration.
r = (b - d) + (i - e)
- r = actual increase or decrease of the population.
- b = natality (birth rate).
- d = mortality (death rate).
- i = immigration.
- e = emigration.
Additive mortality: assumes that mortality factors act independently and their effects are additive (e.g., 40 rabbits die from predation and 40 from starvation for a total of 80 deaths). This is often unrealistic in nature, as factors can interact and influence each other.