Population Growth & Demographic Transition: Key Concepts and Factors

What can age structure diagrams indicate about population growth rates?

The shape of the structure can be interpreted to reveal population growth rates.

What factors are associated with infant mortality rates?

Access to good healthcare and nutrition for mothers.

What are density-independent factors that can affect population growth?

Major storms, fires, heat waves, or droughts.

What are density-dependent factors that can affect population growth?

Access to clean water and air, food availability, disease transmission, or territory size.

What does the rule of 70 state regarding population growth?

Dividing the number 70 by the percentage population growth rate approximates the population's doubling time.

What is the demographic transition?

The transition from high to lower birth and death rates as a country develops from a preindustrial to an industrialized economic system.

How is the demographic transition model (DTM) typically represented?

Through a four-stage model demonstrating changes in birth and death rates.

What are characteristics of developing countries in terms of demographics?

Higher infant mortality rates and more children in the workforce compared to developed countries.

What is a characteristic of a rapidly growing population in terms of age structure?

It will have a higher proportion of younger people compared to stable or declining populations.

What factors affect the total fertility rate (TFR) in human populations?

The age at which females have their first child, educational opportunities for females, access to family planning, and government policies.

What does it mean if a population's fertility rate is at replacement levels?

The population is considered relatively stable.

What factors influence whether a human population is growing or declining?

Birth rates, infant mortality rates, overall death rates, access to family planning, nutrition, education, and postponement of marriage.

What limits global human population growth according to Malthusian theory?

The Earth's carrying capacity and basic limiting factors.

Generalist species

Species that tend to be advantaged in habitats that are changing.

Specialist species

Species that tend to be advantaged in habitats that remain constant.

K-selected species

Species that 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/life expectancy, and reproduce more than once in their lifetime.

r-selected species

Species that 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.

Biotic potential

The maximum reproductive rate of a population in ideal conditions.

Invasive species

Species that typically have a minimal adverse effect on r-selected species but can adversely affect K-selected species.

Survivorship curve

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.

Type I survivorship curve

A survivorship curve typically followed by K-selected species.

Type II survivorship curve

A survivorship curve that can be followed by K-selected species.

Type III survivorship curve

A survivorship curve typically followed by r-selected species.

Carrying capacity (K)

The maximum population size that an environment can sustain.

Overshoot

Occurs when a population exceeds its carrying capacity.

Dieback

A major ecological effect of population overshoot, often severe to catastrophic, due to lack of available resources leading to famine, disease, and/or conflict.

Resource availability

The extent to which resources are available to a population for growth.

Population growth

The increase in the number of individuals in a population, which is limited by environmental factors, especially by the available resources and space.

Total resource base

The overall amount of resources available, which is limited and finite over all scales of time.

Accelerated population growth

Occurs when the resources needed by a population for growth are abundant.

Resource distribution

The allocation of resources within a population, which can become unequal when the resource base shrinks.

Mortality

The rate of death within a population, which can increase due to resource scarcity.

Fecundity

The reproductive capacity of an individual or population, which can decrease due to resource scarcity.

Population decline

Occurs when population growth declines to, or below, carrying capacity due to resource limitations.

Biodiversity

Biodiversity in an ecosystem includes genetic, species, and habitat diversity.

Genetic Diversity

The more genetically diverse a population is, the better it can respond to environmental stressors. Additionally, a population bottleneck can lead to a loss of genetic diversity.

Species Recovery

Ecosystems that have a larger number of species are more likely to recover from disruptions.

Habitat Loss

Loss of habitat leads to a loss of specialist species, followed by a loss of generalist species. It also leads to reduced numbers of species that have large territorial requirements.

Species Richness

Species richness refers to the number of different species found in an ecosystem.

Island Biogeography

Island biogeography is the study of the ecological relationships and distribution of organisms on islands, and of these organisms' community structures.

Colonization of Islands

Islands have been colonized in the past by new species arriving from elsewhere.

Specialist Species

Many island species have evolved to be specialists versus generalists because of the limited resources, such as food and territory, on most islands.

Ecological Tolerance

Ecological tolerance refers to the range of conditions, such as temperature, salinity, flow rate, and sunlight that an organism can endure before injury or death results.

Application of Ecological Tolerance

Ecological tolerance can apply to individuals and to species.

Natural Disruptions

Natural disruptions to ecosystems have environmental consequences that may, for a given occurrence, be as great as, or greater than, many human-made disruptions.

Earth System Processes

Earth system processes operate on a range of scales in terms of time. Processes can be periodic, episodic, or random.

Climate Change

Earth's climate has changed over geological time for many reasons.

Sea Level Variation

Sea level has varied significantly as a result of changes in the amount of glacial ice on Earth over geological time.

Habitat Changes

Major environmental change or upheaval commonly results in large swathes of habitat changes.

Wildlife Migration

Wildlife engages in both short- and long-term migration for a variety of reasons, including natural disruptions.

Organism Adaptation

Organisms adapt to their environment over time, both in short- and long-term scales, via incremental changes at the genetic level.

Environmental Changes

Environmental changes, either sudden or gradual, may threaten a species' survival, requiring individuals to alter behaviors, move, or perish.

Ecological Succession

There are two main types of ecological succession: primary and secondary succession.

Keystone Species

A keystone species in an ecosystem is a species whose activities have a particularly significant role in determining community structure.

Indicator Species

An indicator species is a plant or animal that, by its presence, abundance, scarcity, or chemical composition, demonstrates that some distinctive aspect of the character or quality of an ecosystem is present.

Pioneer Species

Pioneer members of an early successional species commonly move into unoccupied habitat and over time adapt to its particular conditions, which may result in the origin of new species.

Effects of Succession

Succession in a disturbed ecosystem will affect the total biomass, species richness, and net productivity over time.

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