Chapter 5: Populations

Population

Population

The individuals that belong to the same species and live in a given area at a particular time.

Community

All of the populations of organisms within a given area.

Population ecology

The study of factors that cause populations to increase or decrease.

What are the 5 basic characteristics of any population?

Size, density, distribution, sex ratio, age structure

Population size (N)

The total number of individuals within a defined area at a given time.

Population density

The number of individuals per unit area at a given time.

Population distribution

A description of how individuals are distributed with respect to one another.

Sex ratio

the ratio of males to females in a population

age structure

a description of how many individuals fit into particular age categories

Population growth

the change in the size of a population over time

Can be positive or negative (still called growth)

Intrinsic growth rate

the maximum potential for growth of a population under ideal circumstances with unlimited resources.

r-selected species

A species that has a high intrinsic growth rate, which often leads to population overshoots and die-offs.

Quantity vs. quality of offspring.

Example: Frog

K-selected species

A species with a low intrinsic growth rate, the population increases slowly until it reaches carrying capacity.

Invest heavily into offspring to ensure survival.

Example: Elephant

Exponential growth

Growth whose rate becomes ever more rapid in proportion to the growing total number or size.

Exponential growth occurs when a population is provided unlimited resources and begins to grow at its intrinsic growth rate.

Limiting Resource

A resource that a population cannot live without AND that occurs in quantities lower than the population would require to increase in size.

Logistic growth

A growth model that describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment.

Carrying capacity

The limit of how many individuals in a population the environment can sustain.

What type of growth do K-selected species experience?

logistic growth

What type of growth do r-selected species experience?

they experience frequent boom and bust cycles due to their high intrinsic growth rates.

Density dependent factor

A factor that influences an individual's probability of survival and reproduction in a manner that depends on the size of the population. Ex. Predation or food availability.

Density independent factors

A factor that has the same effect on an individual's probability of survival and reproduction at any population size. Ex. Natural disasters.

uniform distribution

organisms spread out evenly. Territorial birds and some plants vying for resources tend to adopt this distribution.

Random distribution

displays no apparent pattern and is typical of many (but not all) plant communities especially forests.

Clumped distribution

this is typical of animals that live in groups such as meerkats or elephants

Survivorship

the probability that an individual organism will survive.

Survivorship curve

A graph that represents the distinct patterns of species survival as a function of age.

In a survivorship curve, organisms are divided into various cohorts which are plotted against survivorship.

Cohorts

groups of organisms who share a similar age.

Type I survivorship curve

A pattern of survival over time in which there is high survival throughout most of the lifespan, but then individuals start to die in large numbers as they approach old age.

Type II survivorship curve

A pattern of survival over time in which there is relatively constant decline in survivorship through most of the lifespan.

Type III survivorship curve

A pattern of survival over time in which there is low survivorship early in life with few individuals reaching adulthood.

Mathlusian theory

In 1798 Thomas Malthus predicted that human population would surpass the Earth's carrying capacity

Food production is linear

Population growth is exponential

Demography

The study of human populations and population trends.

cultural carrying capacity

Optimum level that would allow most people to live in reasonable comfort and freedom without impairing the ability of the planet to sustain future generations.

Immigration

The movement of people into a country or region, from another country or region.

Emigration

The movement of people out of a country or region.

Crude birth rate (CBR)

The number of births per 1,000 individuals per year.

Crude death rate (CDR)

The number of deaths per 1,000 individuals per year.

Population Growth Equation

(births + immigration) - (deaths + emigration)

The rule of 70

doubling time = 70/growth rate

Doubling time

The number of years it takes a population to double.

the percentage is what is needed in the denominator - DO NOT move the decimal when given a growth rate as a percentage!

true

Total fertility rate (TFR)

An estimate of the average number of children that each woman in a population will bear throughout her childbearing years.

Fecundity

the ability to produce an abundance of offspring or new growth; also known as Fertility.

Replacement-level fertility

The total fertility rate required to offset the average number of deaths in a population in order to maintain the current population size. Replacement level fertility tends to be higher in developing countries because mortality among young people tends to be higher.

Life expectancy

The average number of years that an infant born in a particular year in a particular country can be expected to live.

Infant mortality

The number of deaths of children before their first birthday per 1,000 live births.

Child mortality

The number of deaths of children under age 5 per 1,000 live births.

Net migration rate

The difference between immigration and emigration in a given year per 1,000 people in a country.

Theory of demographic transition

The theory that as a country moves from a subsistence economy to industrialization and increased affluence (wealth) it undergoes a predictable shift in population growth.

Pre-Industrial

Phase 1: Stable or Zero Population Growth (ZPG) because high birth rates and high death rates offset each other.

Transitional

Phase 2: The death rates drop rapidly, but birth rates do not change. Population growth is greatest at this point.. Rapid population growth because birth rates remain high but death rates decline because of better sanitation, clean drinking water, availability of food and health care.

Industrial

Phase 3 The birth rates decline and population growth slows. Slowing population growth as the economy and educational system improves and people have fewer children.

Demographic Trap

a point where birth rates remain high despite lowered death rates.

Post-Industrial

Phase 4. The population stops growing and sometimes begins to decline. Stabilizing population growth because the relatively high level of affluence & economic development encourage women to delay having children.

Family planning

The practice of regulating the number or spacing of children through the use of birth control.

IPAT equation

An equation used to estimate the impact of the human lifestyle on the environment:

Impact = Population × Affluence × Technology

Gross domestic product (GDP)

A measure of the value of all products and services produced in one year in one country. Used to measure the affluence of a nation.

Transects

a line that crosses an entire area when studying the distribution of a species

Quadrats

Square frame used for sessile organisms to determine species richness, population estimate

mark and recapture

Mark animal, return to environment and recapture it

Mark and recapture formula

Percent marked/100 x Number Marked / N (Population Estimate)

Removal sample

Take out species, which is not in their best interest, and don't return it

What does a rapid age structure diagram look like?

large at the bottom

What does a stable/zero growth age structure diagram look like?

What does a slow growth age structure diagram look like?

A triangular shape with a very large and wide base. Looks like rapid but it wider for much longer

What does a negative growth age structure diagram look like?

Larger at the top

Global population growth rate

(CBR-CDR)/10

Growth rate for a population or region

(CBR+Immigration)-(CDR+Emmigration) / 10