Population Concepts Population growth Human population Problems from a growing population

Population Growth How populations change in size Populations grow if… Additions – births and immigration Subtractions – deaths and emigrations Populations grow if… … additions are greater than subtractions Populations decline if… … subtractions are greater than additions

Patterns of Population Growth Unlimited population growth More than enough resources such as food, water, space, light, etc. Births exceed deaths Population growth is “exponential” – the larger the population, the faster it grows – indefinitely “J-curve” pattern to graph of population vs. time

Patterns of Population Growth Limited population growth One or more resources (food, etc.) are limited or other factors increase deaths (disease, predators) Births become roughly equal to deaths Population size stabilizes and fluctuates around the “carrying capacity” of the environment “S-curve” pattern to graph of population vs. time

Patterns of Population Growth Exponential growth Carrying capacity J curve S curve Population Time DISEASE SPACE PREDATORS FOOD

Human Population – a special case Slow life-history pattern (pre-1800 CE) 99% of human history – hunter gatherers – population only about 1 million 10,000 years ago – agricultural revolution Farming increased the carrying capacity for humans More food led to larger families who could grow even more food By 1800 CE, human population reached 1 billion

Human Population – a special case Exponential growth (post 1800 CE) Population Year Years to Add 1 billion 1800 All human history 2 billion 1930 130 3 billion 1960 30 4 billion 1975 15 5 billion 1987 12 6 billion 1999 7 billion 2011

Human Population – a special case Exponential growth (post 1800 CE) (+)

Human Population – a special case Demographic Transition Model

Human Population – a special case Humans use science and technology to change the natural limitations on our population – to change the carrying capacity of our environment Exponential growth since 1800 Increased food production, safer preservation Better sanitation, safer drinking water Improved health care, better disease management Broader range of habitable locations (energy!) More people educated, higher levels of knowledge Lifestyle and cultural changes, urbanization

Impacts of Population Growth Shortage of firewood A limiting resource in many developing countries Necessary for cooking (malnutrition/starvation) Necessary for sanitizing water Water that kills 10 million deaths per year from tainted water (e.g., dysentery, typhoid, cholera, parasites) Same source for drinking and sewage disposal

Impacts of Population Growth Urban crisis Population grows faster than infrastructure Contributes to disease and social unrest Social unrest Domestic unrest from unemployment, urban crisis Conflicts between ethnic groups within a country Disputes between countries over shared resources