Populations are groups of the same species. Populations make up communities and have many factors that can influence their population size, population density, and population distribution. A population’s rate of growth reflects how healthy the group of organisms is. The equation r=(b+i)-(d+e) displays the factors that impact r (the growth rate).
Population: Refers to a group of organisms of the same species that lives in the same area.
Population Size: The number of of individuals in a population.
Population Density: The individuals that make up the population size per unit area or volume.
Population Distribution: How the individuals in a population are distributed throughout their habitat.
Age-Sex Structure: The number of individuals of each sex and age in the population.
Population Pyramid: A bar graph that represents age-sex structure.
Survivorship Curve: A line graph that represents the number of individuals alive at each age.
Population Growth Rate (r): How fast a population changes in size over time.
Immigration: When part of a population joins another population elsewhere.
Emigration: When part of a population leaves to go elsewhere.
Dispersal: When offspring move away from their parents.
Migration: The regular movement of individuals or populations every year during certain seasons.
Exponential Growth: Pattern of population growth in which a population starts out growing slowly but grows faster as population size increases.
Logistic Growth: Pattern of population growth in which growth slows and population size levels off as the population approaches the carrying capacity.
Carrying Capacity: Represented by the variable (K), carrying capacity is the largest population size a niche can support without being harmed.
K-Selected Species: Species that live in a stable environment, in which their population growth is controlled by density-dependent factors.
r-Selected Species: Species that live in an unstable environment, in which their population is uncontrolled and rapid.
Populations make up communities and act as a unit of natural selection and evolution. Its health can be measured by how large it is and how fast it is growing.
The population growth rate (r) gives us an idea on how fast a population changes over time. The rate can be calculated with this equation:
r = population growth rate
b = birth rate
i = immigration rate
d = death rate
e = emigration rate
Think of immigration as coming in, emigration as exiting.
There are other factors that can affect population size and growth:
Population growth reflects the changes in the size of the population over time.
Survivorship curves show how deaths affect populations. You may see one of these three types of curves:
Types of population growth pattern: