Unit 3: Populations

Population

a group of organisms of one species living in the same place at the same time that interbreed

What are some examples of resources that populations compete within each other for?

food, mates, shelter, etc.

Numbers of the population will:

continually go up and down

Population Increase

caused by births and immigration

Population Decrease

caused by deaths and emmigration

Population Equation

birth + immigration - death + emigration

Population Ecology

study of how and why the population sizes change over time and space

Ecologists try and determine ____________ ____ in a given area.

population size

If the population size has increased or decreased, ecologists try to understand the ________ that caused this change

factors

Keystone Species

a species that has a disproportionately large effect on the communities

Ecosystem Species

any species that creates, significantly modifies, maintains or destroys a habitat

Indicator Species

a type of organism that signal the health, or lack of health, of environmental conditions

Methods to Measure Populations

• count every individual (ex. census not very feasible in most situations)

• quadrant (count fraction and estimate/extrapolate population size)

• mark-recapture (very common)

Population Dispersion

• clumped (species living in large groups (most common: near required))

• uniform (individuals are evenly spaced (usually antagonistic interactions))

• random (no pattern to the location where species is (not common in nature))

Generalist

• broad niche

• wide range of tolerance

• raccoons, rats, crows

• invasive species

• adapt to changes more easily

Specialist

• small niche

• narrow range of tolerance

• corals, frogs, pandas

• indicator species

• more susceptible to extinction

Life History Strategies

Type I

Type II

Type III

Type I

• few offspring

• high parental care

• late-loss

Type II

• 3-6 offspring

• average parental care

• constant loss

Type III

• many offspring

• low parental care

• early loss

Reproductive Strategies

K-selected

r-selected

K-selected

• energy into survival > reproduction

• fewer, larger offspring

• lower population growth

• kangaroo, killer whale

• thrive best in ecosystems with fairly constant environmental conditions

• populations remain close to carrying capacity (K)

• populations have a slower growth and are more stable

r-selected

• energy into reproduction > survival

• many small offspring

• high population growth

• rats, bunnies, cockroaches

• opportunists; take advantage of favorable conditions.

• when favorable conditions are gone, the population may crash

• populations go through irregular or unstable cycles

• populations grow rapidly in a boom-and-bust cycle

Specialist = ___________ = _____________

K-selected

Type I

Generalist = ___________ = _____________

r-selceted

Type III

Two types of population growth curves

• exponential growth (J)

• logistic growth (S)

Exponential Growth Curve (J-Curve)

• putting some individuals in an area for the first time where they have no competition, plentiful resources and no predators

• causes population to grow rapidly at an ever increasing rate

• ex- invasive species

  • a plant/animal that is not native and can reproduce exponentially, believed to cause damage to the environment, human economy, and/or human health

Biotic Potential

• maximum reproduction rate of a population in ideal conditions

• more theoretical

Limiting Factors

limit the population size from reaching its biotic potential

• 2 parts: density-dependent and density-independent

Density-Dependent

have an increasing effect as the population increases

Examples of Density-Dependent Factors

food, diseases, predators, space

Density-Independent

factors can affect population regardless of their density

Examples of Density-Independent Factors

temperature, storms, floods, droughts

Logistic Growth Curve (S-Curve)

• starts off as “J” curve but then limiting factors begin reducing rate of population growth (point of inflection on graph)

• eventually population will reach carrying capacity (K)

Carrying Capacity (K)

maximum population size that an environment can support (this line levels out over time)

• can go over

• if overshoot = rapid die-off

Predator-Prey Relationships

keep each other’s populations in check leading to a “boom and bust” type of population cycling

Population Bottleneck

• a drastic reduction in population size

• greatly reduces genetic diversity, making this population more susceptible to disease and extinction

Types of Population Fluctuations

• irregular

• stable

• cyclic

• irruptive

Irregular Population Fluctuation

• no recurring pattern

• chaos in the system, or just not yet understood?

Stable Population Fluctuation

• fluctuates slightly around carrying capacity

• ex; tropical rainforest: temps/rainfall are steady

Cyclic Population Fluctuation

• rise and fall in predictable fashion

• ex. predator - prey relationship

Irruptive Population Fluctuation

• usually stable, but sometimes explodes and crashes

• ex. algae bloom and insects: due to seasonal changes and nutrient availability

Advances in …(4 things) helped to increase the human population

• medicine

• sanitation

• agriculture

• technology

• # b in 1650

• # b around the 1800s

• # b around 1925ish

• # b around 1960ish

• #, #, and # b between 1960ish and 2000

• # and # b after 2000

• 0.5

• 1

• 2

• 3

• 4, 5, and 6

• 7 and 8

1676

invention of the microscope; helped understanding of disease and advanced medicine and hygiene

1775

invention of smallpox vaccine; first mass use of a vaccine

1760-1840

industrial revolution brought the use of fossil fuels are an emergence of technology and machinery to run industries

1864

Louis Pasteur invented pasteurization- using heat to kill bacteria

1907

blood types discovered, allowing for safe blood transfusions

1908

using chlorine to sanitize water invented

1913

invention of nitrogen fertilizers helped feed the world

1928

invention of anti-bacterial penicillin by Alexander Fleming has saved millions

1950’s-60’s

green revolution helped industrialize and mass-produce food

Panic About Overpopulation is equal to ….

Malthusian Catastrophe

Malthus (1798)

human population is growing exponentially while food supply grows linearly

Panic about overpopulation can lead to …

war, famine, disease

• ex. irish potato famine

Effects of Overpopulation

• hunger

• poverty

• rapid spread of diseases

• depletion of resources like water, energy, minerals

• habitat destruction → loss of biodiversity

• pollution

• climate change

Ecological Footprint

the quantity of nature it takes to support people or an economy

• a measure of sustainability

• more developed/affluent a country, larger this is

World Popultion

7.9 billion

United States Population

334 million

Most Populated Countries

china

india

united states

China Population

1.44 billion

India Population

1.40 billion

Factors Affecting A Countries Population

• fertility and birth rates

• life expectancy and death rates

• migration

Replacement - Level Fertility

number of children a couple would have to have to replace themselves

• developed countries: 2.1

• developing: 2.5 or higher

  • higher infant mortality

Total Fertility Rate (Fecundity)

average number of children a woman will have during her childbearing years

(decreasing as a country becomes more developed)

If fertility rate is at replacement levels, a population is considered relatively _______

stable

World Average Fertility Rate

2.4

Highest Average Fertility Rate

Niger: 2.4

Lowest Average Fertility Rate

Taiwan and South Korea

United States Average Fertility Rate

1.7

How is it that the U.S. population is still growing if the average women is having less than 2 children?

immigration and some women are having more than just 1 or 2

Birth Rate

the rate at which the births take place in a population during a particular time or period

How to decrease fertility and birth rates?

• education: higher education for women is the greatest factor to lower birth rates in a country

• access to contraception/family planning: also directly correlated with lowering fertility rates

• anti-naturalist policies:

  • ex, Singapore raised the legal marrying age to shorten fertility window

  • China one-child policy

Life Expectancy and Death Rates

people live longer as countries become more developed (better living conditions and increased access to healthcare)

women live longer than men (gender specific diseases, hazardous lifestyle choices, wars, more dangerous jobs, genetics)

Death Rates

the rate at which the deaths take place in a population during a particular time or period

Migration

immigration is moving in a country and emigration is moving out of a country

(due to political, demographic, economic, social, and environmental factors)

• when human needs are not being met

• during economic, social, and/or political unrest

• another country offers better opportunities

!!immigration and emigration must be factored into a countries growth rate!!

Developed Countries

growth domestic product: high

industrialization: high

infant mortality: low

life expectancy: 75-90

literacy rate: high

education: most finish high school

healthcare system: good

Developing Countries

growth domestic product: low

industrialization: low

infant mortality: high

life expectancy: 45-60

literacy rate: low

education: many do not finish 8th grade

healthcare system: not good

Crude Birth Rate (CBR)

the annual number of births per 1,000 people in a population

Population Density

how many individuals (per capita) in a given area

Population Density Equation

number of individuals/unit area

Crude Birth Rate Equation

(number of births/total population)*1000

Crude Death Rate (CDR)

the annual number of deaths per 1,000 people in a population

Crude Death Rate Equation

(number of deaths per year/total population)*1000

National Growth Rate

how a country’s population has changed over time, expressed as a percent

!!if it says global = do not include immigration/emigration number!!

National Growth Rate Equation

(CBR -CDR/10) = r%

OR

(births-deaths/total population) x 100 = r%

Doubling Time (Rule of 70)

predicts when a population will double based on growth rate (expressed as a percent)

Doubling Time (Rule of 70) Equation

double time(in years) = 70/growth rate %

Finding Future Growth

using the growth rate to predict this

!!a growth rate at 3% would be expressed as 1.03 in an equation. A growth rate of 0.25% would be expressed a 1.025 in the equation!!

Finding Future Growth Equation

(initial population) x (growth rate)^years = final population

Total Fertility Rate will likely drop below ____ (replacement levels) by 2064

2.0

Population Momentum

global population will continue for decades even when Total Fertility Rate drops below 2.0 due to age structures

Many experts believe global population will reach carrying capacity around ___ billion by ____

• 11

• 2100

______ will continue to have rapid growth for the century (__________ current population)

• Africa

• tripling

Population Pyramids / Age Structure Diagrams

snapshot of the population of a country at a given time

• shows the proportion of individuals at various ages

• shape indicated if a population is growing, stalled, or decreasing (growth rate)

Pre - Industrial (Stage 1)

• CBR (high) = CDR (high), low population growth

• short life expectancy, high infant mortality

• disease, poor health care, poor sanitation

• US/Europe: before late 18th century

• almost no countries now in Stage 1 (tribal communities)

Transitioning (Stage 2)

• death rates decline

• improved health care, access to water and food, vaccines

• fertility rates remain high

• leads to rapid population growth

Industrial (Stage 3)

• economy and education improves

• family income up

• access to contraception

• population growth rate slows

Post - Industrial (Stage 4)

• CBR < CDR

• high affluence / economic development

• more elderly

• government may encourage immigration of money incentives to have more children