U3: Population

Terms

● Population Density: The measurement of the amount of individuals in a population in one area.

● Population dispersion: How individuals of a population in a particular area are spaced.

○ Three types: Uniform, random, and clumped.

● Random dispersion: The position of any member is not determined or influenced by another member of that species.

● Clumping dispersion: Species members group or pack together.

○ This is the most common dispersion.

● Uniform: Members of a species spread out evenly across a region.

● Biotic potential: How much the population would grow with unlimited resources

● Carrying capacity (K): The maximum growth a population can reach based on available resources.

● Population growth is shown by two different graphs. The J-Curve represents exponential growth. The S-Curve represents logistic growth, a growth where resources are limited.

● To predict long term population growth the rule of 70 is applied. The rule of 70 states that you can find the time it’ll take for a population to grow by dividing 70 by the current growth rate (percentage). 

○ Equation: 70/GR%

○ Population size is heavily dependent on the species.

■ There are two types of species R-selected and K-selected.

● Survivorship curve: Number of organisms that are born in a population and survive over time. Different species have different kinds.

○ Type 1 (K-Selected): Most species reach adulthood with a mortality increase as higher ages are reached

○ Type 2: Constant mortality and survival rate

○ Type 3 (R-Selected): Most offspring die young but survivors live relatively long lives.

● Boom and bust cycle: Common amongst r-selected species, this is when populations have a high birth number and lose a significant amount of survivors.

Human Populations

● There are an estimated 7 to 8 billion people on planet Earth.

○ The top three countries with the biggest populations are China, India, and the U.S. 

● A country’s population change overtime = (birth rate + immigration rate) – (death rate + emigration rate) / 10

● Key factors in human population change/birth rate:

o Availability of birth control

o Demand for children in the labor force

o Women's education

o Retirement systems

● Immigration: People move into a population.

● Emigration: People move out of population.

● Total fertility rate: Measurement of how many children, on average, a woman bears in her lifetime.

● Replacement birth rate: Amount of children a couple must bear to replace themselves.

● Infant mortality rate: Number of deaths under one for every 1000 of lives.

● Age structure pyramids are used to show populations.

o They’re split into age, gender, and pre-reproductive (0-14), reproductive (15-44) and post-reproductive (45 and older).

● Population momentum: Significant population increases overtime.

● Age Structure Pyramid

● Demographic transition model: used to predict population trends based on birth and death rates of a population.

○ Zero population growth is achieved when both the birth rate and death rate are evenly matched.

○ This chart has four states and as the population moves from one state to the next, it’s called a demographic transition.

1. Pre-Industrial state: The growth rate is slow while the death rate is high. Usually due to a harsh environment resistance.

2. Transitional state: Birth rates are high and death rates are low. This can contribute to stability in the environment and leads to population boom.

3. Industrial state: Population growth is still high but birth rate drops.

4. Postindustrial state: population comes close to a zero birth rate or below.

● 4 major factors that have contributed to human population growth: improved nutrition, medical care, systems for better waste disposal, and the availability of clean water. 

○ Increased food production also plays a large role.

■ Nearly half of the land on Earth is used for food production.

○ However, unreliable irrigation use and the widespread use of pesticides and fertilizers have harmed the Earth’s ecosystems.

● Genetically modified organisms (GMOs): Adding DNA strands to crops to build up pest resistance. This leads to loss in biodiversity.

● Malnutrition: Poor nutrition due to an imbalanced or unhealthy diet.

● Undernourished: People who have not sustained a proper amount of nutrients to grow and be healthy.

● Food Desert: When areas, typically low-income, lack access to fresh, healthy food, they turn to and start relying on processed foods.

● Urban Sprawl: People emigrate out of the city and to the suburbs. Most of the population on earth live in urban areas.

● Ecological Footprint: Environmental impact of a society or individual person.

● I = P×A×T: Used to determine humans' impact on the environment.

○ I: Total Impact P: Population size A: Affluence T: Level of technology

● International Union for Conservation of Nature: Evaluates conservation statues of species. Created the Red List of Threatened Species.

○ Critically endangered: Very high risk of extinction.

○ Endangered: Species is likely to go extinct.

○ Vulnerable: Species are likely to become endangered without action.

○ Background extinction: Natural extinction that happens outside of large events.

○ Scientists believe the extinction rate is going 50 to 500 times faster than average due to human impacts. 

● HIPPCO: Human factors that lead to species extinction.

○ H: Habitat destruction or degradation

○ I: Invasive species

○ P: Population growth

○ P: Pollution

○ C: Climate change

○ O: Overharvesting and overexploitation

● Marine Animal Protection Act of 1972: Protects marine animals from falling below sustainable population levels.

● Endangered Species Act Program for the protection of threatened plants and animals and their habitats of 1973: Prohibits commerce of endangered or threatened species.

● Convention on International Trade in Endangered Species of Flora and Fauna, 1973: International treaty that bans the selling, trading, or capturing of any endangered species.