Glossary
Age Structure Diagrams
Graphical representations showing the distribution of different age groups in a population, often separated by gender.
Example:
A country with a wide base in its age structure diagram indicates a large proportion of young people, suggesting future rapid population growth.
Biotic Potential
The maximum reproductive rate of a population under ideal conditions, with unlimited resources and no limiting factors.
Example:
If a single pair of rabbits were to reproduce without any predators, disease, or food limitations, they would demonstrate their biotic potential by rapidly increasing their numbers.
Carrying Capacity
The maximum population size of a particular species that a given environment can sustainably support indefinitely.
Example:
A small island can only support a certain number of deer before food resources become too scarce, illustrating its carrying capacity.
Crude Birth Rate
The number of live births per 1,000 people in a population per year.
Example:
If a town of 10,000 people has 150 births in a year, its crude birth rate is 15 per 1,000.
Crude Death Rate
The number of deaths per 1,000 people in a population per year.
Example:
A country with a high crude death rate might be experiencing a widespread epidemic or have a very old population.
Demographic Transition
A model describing the historical shift from high birth rates and high death rates to low birth rates and low death rates as a country develops economically.
Example:
Many developing nations are currently in the transitional stage of the demographic transition, experiencing declining death rates but still high birth rates.
Density-Dependent Factors
Limiting factors whose effects on a population intensify as the population density increases.
Example:
The spread of a disease is a density-dependent factor; it spreads more easily and rapidly in a crowded population.
Density-Independent Factors
Limiting factors whose effects on a population are not related to the population density.
Example:
A severe wildfire is a density-independent factor that can decimate a forest population regardless of how many trees were initially present.
Exponential Growth
Population growth that occurs at a constant rate, resulting in a J-shaped curve, typically seen when resources are unlimited.
Example:
A bacterial colony in a petri dish with abundant nutrients will initially show exponential growth as it rapidly doubles in number.
Family Planning
The practice of controlling the number of children in a family and the intervals between their births, often through contraception or education.
Example:
Access to education and family planning services can significantly lower a country's total fertility rate.
Generalist Species
A species that can thrive in a wide variety of environmental conditions and utilize diverse resources.
Example:
A raccoon is a classic example, able to live in forests, suburbs, and cities, eating almost anything.
Industrial Stage
The third stage of the demographic transition, where birth rates begin to decline due to urbanization, increased education for women, and access to family planning, while death rates remain low.
Example:
As a society moves into the industrial stage, families often choose to have fewer children due to changing economic and social factors.
K-Selected Species
Species characterized by a low reproductive rate, high investment in offspring, longer lifespans, and slow maturation.
Example:
Elephants are K-selected, having few calves but investing significant parental care over many years.
Logistic Growth
Population growth that slows as the population approaches its carrying capacity, resulting in an S-shaped curve, reflecting limited resources.
Example:
A population of rabbits introduced to a new habitat will initially grow fast, but eventually, their growth will slow and level off as they approach the environment's logistic growth limit.
Overshoot
The phenomenon where a population temporarily exceeds the carrying capacity of its environment.
Example:
If a deer population on an island grows too large and consumes all available vegetation, it has overshot its carrying capacity, leading to resource depletion.
Population Density
The number of individuals of a population per unit area or volume.
Example:
Monaco has a very high population density due to its small land area and large number of residents.
Post-industrial Stage
The fourth stage of the demographic transition, characterized by low birth rates and low death rates, leading to stable or even declining population growth.
Example:
Many developed countries are in the post-industrial stage, facing challenges like an aging population and potential labor shortages.
Pre-industrial Stage
The first stage of the demographic transition, characterized by high birth rates and high death rates, resulting in little to no population growth.
Example:
In the pre-industrial stage, harsh living conditions and lack of medical care meant that many children were born, but many also died young.
Replacement Level Fertility
The average number of children a couple must have to replace themselves in the population, typically around 2.1 children per woman.
Example:
For a population to remain stable without immigration, its replacement level fertility must be met, accounting for some child mortality.
Rule of 70
A simple formula used to estimate the doubling time of a population or any quantity growing at a constant annual percentage rate.
Example:
If a country's population is growing at 2% per year, the Rule of 70 suggests it will double in approximately 35 years (70/2).
Specialist Species
A species that requires specific, stable environmental conditions and has a narrow ecological niche.
Example:
The koala is a specialist, relying almost exclusively on eucalyptus leaves for its diet and habitat.
Total Fertility Rate (TFR)
The average number of children a woman is expected to have over her lifetime.
Example:
A country with a Total Fertility Rate of 1.5 means that, on average, women are having fewer than two children, which can lead to population decline.
Transitional Stage
The second stage of the demographic transition, marked by declining death rates due to improved sanitation and healthcare, while birth rates remain high, leading to rapid population growth.
Example:
During the transitional stage, a country might see a population boom as more children survive to adulthood.
Type I Survivorship Curve
A survivorship curve where most individuals survive to old age, with a high mortality rate late in life.
Example:
Humans typically exhibit a Type I curve due to good healthcare and low infant mortality.
Type II Survivorship Curve
A survivorship curve showing a constant mortality rate throughout an organism's life.
Example:
Birds often follow a Type II curve, facing a relatively consistent risk of death at any age.
Type III Survivorship Curve
A survivorship curve characterized by high mortality rates early in life, with few individuals surviving to old age.
Example:
Many fish species have a Type III curve, producing thousands of eggs, but only a small fraction survive to adulthood.
r-Selected Species
Species characterized by a high reproductive rate, low investment in offspring, short lifespans, and quick maturation.
Example:
A housefly is an r-selected species, producing many offspring quickly with minimal parental investment.