Unit 3 · Populations

Generalist vs. specialist species ● (core concept) — Specialist species tend to be advantaged in habitats that remain constant, while generalist species tend to be advantaged in habitats that are changing.

K-selected species ● (core concept) — K-selected species tend to be large, have few offspring per reproduction event, live in stable environments, expend significant energy for each offspring, mature after many years of extended youth and parental care, have long life spans, and reproduce more than once in their lifetime. Competition for resources in their habitats is usually relatively high.

r-selected species ● (core concept) — r-selected species tend to be small, have many offspring, expend or invest minimal energy for each offspring, mature early, have short life spans, and may reproduce only once in their lifetime. Competition for resources in their habitats is typically relatively low.

Biotic potential ● (core concept) — Biotic potential refers to the maximum reproductive rate of a population in ideal conditions.

Intermediate reproductive strategies ● (core concept) — Many species have reproductive strategies that are not uniquely r-selected or K-selected, or they change strategies in different conditions at different times.

r-selected invasive species ● (core concept) — K-selected species are typically more adversely affected by invasive species than r-selected species, which are minimally affected. Most invasive species are r-selected species.

Survivorship curve ● (core concept) — A survivorship curve is a line that displays the relative survival rates of a cohort (a group of individuals of the same age) in a population, from birth to the maximum age reached by any one cohort member. There are Type I, Type II, and Type III curves.

Survivorship curves by reproductive strategy ● (core concept) — Survivorship curves differ for K-selected and r-selected species: K-selected species typically follow a Type I or Type II curve, and r-selected species follow a Type III curve.

Carrying capacity and overshoot ● (core concept) — Carrying capacity (denoted K) is the maximum population size an environment can sustain. When a population exceeds its carrying capacity, overshoot occurs, with environmental impacts including resource depletion.

Dieback ● (core concept) — A major ecological effect of population overshoot is dieback of the population (often severe to catastrophic) because the lack of available resources leads to famine, disease, and/or conflict.

Limiting factors on population growth ● (core concept) — Population growth is limited by environmental factors, especially by the available resources and space.

Finite resource base ● (core concept) — Resource availability and the total resource base are limited and finite over all scales of time.

Resource abundance and growth ● (core concept) — When the resources needed by a population for growth are abundant, population growth usually accelerates.

Resource scarcity and population decline ● (core concept) — When the resource base of a population shrinks, the increased potential for unequal distribution of resources will ultimately result in increased mortality, decreased fecundity, or both, resulting in population growth declining to, or below, carrying capacity.

Age structure diagrams ● (core concept) — Age structure diagrams show the distribution of a population by age; population growth rates can be interpreted from the shape of the structure.

Age structure of growing populations ● (core concept) — A rapidly growing population will, as a rule, have a higher proportion of younger people compared to stable or declining populations.

Total fertility rate (TFR) ● (core concept) — Total fertility rate (TFR) is the average number of children a woman is expected to have in her lifetime. It is affected by the age at which females have their first child, educational opportunities for females, access to family planning, and government acts and policies.

Replacement-level fertility ● (core concept) — If fertility rate is at replacement levels, a population is considered relatively stable.

Infant mortality factors ● (core concept) — Factors associated with infant mortality rates include whether mothers have access to good healthcare and nutrition. Changes in these factors can lead to changes in infant mortality rates over time.

Components of human population change ● (core concept) — Human population growth and decline are determined by the rates of birth, death, immigration, and emigration. Birth rates and death rates are affected by factors such as access to education, family planning, healthcare, and nutrition.

Limits to human population growth ● (core concept) — Factors limiting global human population include the Earth's carrying capacity and the basic factors that limit human population growth as set forth by Malthusian theory.

Density-dependent vs. density-independent factors ● (core concept) — Density-independent factors, such as major storms, fires, heat waves, or droughts, affect populations regardless of size. Density-dependent factors, such as access to clean water and air, food availability, disease transmission, or territory size, become more limiting as population density increases.

Rate of natural increase (RNI) ● (core concept) — The rate of natural increase (RNI) is a demographic metric measuring population growth or decline, calculated by subtracting the crude death rate from the crude birth rate, typically expressed as a percentage.

Rule of 70 ● (core concept) — Doubling time of a population can be estimated by dividing 70 by the annual population growth rate expressed as a percentage (the rule of 70).

Demographic transition ● (core concept) — The demographic transition refers to the transition from high to lower birth and death rates in a country or region as development occurs and that country moves from a pre-industrial to an industrialized economic system. It is typically demonstrated through a four-stage demographic transition model (DTM).

Developing-country demographics ● (core concept) — Characteristics of developing countries include higher infant mortality rates and more children in the workforce than developed countries.