Population Growth and Human Influences on the Environment

What controls population growth?• Three important characteristics in nature:

– 1. Geographic Distribution• Range that describes the area inhabited by a population.• Example: bacteria on a plate or whales in the Atlantic Ocean.

– 2. Density • Number of individuals per unit area. • Example: Low density, cacti in the desert.

– 3. Growth Rate• Availability of food, survivorship and type of reproduction• Example: Rabbits with lots of food, no predators and a high

reproductive rate will grow exponentially.

Population Growth• Three factors affect population size…

– 1. Number of births.• Populations grow if more individuals are born than die.

– 2. Number of deaths.• Populations grow if fewer individuals die. Then there are more

adults to survive and reproduce.

– 3. Number of individuals entering and leaving the population.

• Immigration – movement of individuals into an area (growth) • Emigration – movement of individuals out of an area (shrink)• Many reasons can cause individuals to move, like food

availability, mate choices, finding new territories, etc.

Types of Population growth: Exponential

• If a population has unlimited space and food and no predators and disease, the population will increase exponentially.

• Occurs when individuals reproduce at a constant rate.

• As more individuals are added to the population, they also reproduce.

Types of Population Growth:Logistic

• Logistic growth occurs when a population’s growth slows or stops after exponential growth.

• Typically happens after resources become less available.

• Could be affected by decrease in births, increased death rates or emigration.

The line at the top is called the Carrying Capacity. This is simply the largest number of individuals that a given environment can support.

Limits to growthDensity Dependent

• Limiting factor – factor that causes population growth to decrease.

• 1. Density dependent limiting factor – based upon population size– Example: Competition, predation, parasitism or disease.

Limits to GrowthDensity Independent

• 2. Density independent limiting factor – affects the entire population regardless of size.– Example: Extreme weather, seasonal cycles and human

activities

Human Population Growth• Until 500 years ago with the advent of increased

agriculture, industry and medicine, human population has increased dramatically.

• The only significant dip was the Bubonic Plague in the 1300s C.E.

World Population growth Rates.

It is projected that our doubling time (the amount of time required for a population to double in size) is 61 years.

12 Billion by 2050!

As the world grows in people, there are increased needs for food, housing and services.

Demography• Demography – study of human population.• Birthrates, death rates, and age structures of

countries predict their population rates.• Shown through graphs called age-sex pyramids.

To the left, a country with little growth (Denmark)

To the right, a country with massive growth (Rwanda)

Demographic Transition Model

The demographic transition consists of four stages, which move from high birth and death rates, to declines first in birth rates then in death rates, and finally to a stage of low birth and death rates. Population growth is most rapid in the second stage.

Future Human Population Growth• Will human population reach it’s

carrying capacity?• If population does not slow it will

dramatically hurt the environment and the global economy.

• Ways to affect population growth– Raising the status of girls & women– Family Planning (Birth Control)– Control of Disease (HIV, Ebola, etc)– Education of Children (Literacy)– Technology (agriculture, sustainable

living practices)– Government policy (China)

Human Impacts on Resources and Local Ecosystems

• Humans major affects on the biosphere: – Hunting and Gathering (extinction of species,

introduction of non-native species, domestication)– Agriculture (creates populations that do not move, use

up resources in an area, pesticides use, clear land for crops)

– Industry (Pollution, Acid Rain, Greenhouse gases, Global Warming, Biomagnification)

– Urbanization/Cities (Deforestation, Pollution, loss of biodiversity of plants and animals, need for wildlife products and loss of major Rainforests)

Biomagnification• Biomagnification - is the bioaccumulation of a

substance up the food chain by transfer of residues of the substance in smaller organisms that are food for larger organisms in the chain.

• It generally refers to the sequence of processes that results in higher concentrations in organisms at higher levels in the food chain (at higher trophic levels).

• These processes result in an organism having higher concentrations of a substance than is present in the organism’s food.• Examples: PCBs, DDT, Mercury, other heavy metals.

Rachel Carson• Rachel Carson conservationist and the

worked to create environmental policy to prevent environmental problems caused by synthetic pesticides.

• The result was Silent Spring (1962), which brought environmental concerns to the public.

• Silent Spring spurred a reversal in national pesticide policy—leading to a nationwide ban on DDT and other pesticides—and the grassroots environmental movement it inspired the creation of the Environmental Protection Agency (EPA).

The Future of Humankind: Sustainability

• Use of alternative, renewable energy sources – Examples: wind, solar, biofuels, reducing fossil fuel dependence

• Genetic engineering of agriculture and natural pest control• Pollution controls • Water conservation and purification• Creation of Protected Wildlife Areas • Forestry controls (replanting trees, protecting Rainforests)• Regulation of Climate

– Example: reduction of Greenhouse gases and Ozone depleting chemicals

• Sustainable housing (Energy, Water & materials)• Reduce, Reuse and Recycle!