Population Dynamics 3: Human Populations

Trends in Human Population Growth Demography: the study of statistics related to human populations, such as population size, distribution, movement, births, and deaths. Human population was relatively stable until recent times. Around the 1700s, the population began to grow exponentially.

Factors Affecting Growth Humans can increase their food supply by improved agricultural techniques and domesticate animals. Breakthroughs in medicine Storage of food Better shelter All these helped to increase the carrying capacity of our environment.

Exponential Growth Growth rate has dramatically increased over the last 300 years. The birth rate has actually stayed the same, but the death rate has decreased significantly so that the population growth was about 2% per year. Recently, this has slowed to about 1.2% per year. Doubling time: the amount of time it takes for a population to double in size. At a growth rate of 1.2%, our 7 billion people is expected to double in the next 58 years. Imagine having to double the number of homes, food and jobs to accommodate this! Developed countries (Canada, USA, Western Europe) are growing more slowly than developing countries (Mexico, Honduras, etc)

Population Age Structure Age structure varies from country to country as well as population growth. Population pyramids can shoot the age distribution in a population. A triangular shape shows that there will be an explosive growth. A rectangular shape shows a stable population An inverted triangle shows a population decrease.

Population Age Structure

Earth’s Carrying Capacity So far humans have been able to alter the carrying capacity, but for how much longer? Ecological Footprint: the amount of productive land that is required for each person in a defined area for food, water, transportation, housing, waste management, etc. The average per person globally is 2 hectares of land.

Available Biocapacity Earth’s carrying capacity for the human population is called the available biocapacity Includes cropland, grazing land, fishing grounds, forest land, carbon absorption land, and building area. Estimated that 1/4 of the Earth’s surface constitutes the biocapacity. Right now, our ecological demand exceeds our ecological supply by 23%

Practice Page 556 # 2 - 6, 10, 11, 13.

Population Dynamics: Managing Growth and Resources

Energy Requirements One cost of a growing population is a demand for more energy. Globally, energy generation is predicted to increase an average of 2.3% each year! Coal burning continues to be the main source of electricity production. Coal burning produces CO2 (global warming), sulfur dioxide and nitrogen oxides (acid rain), mercury emissions.

Biomagnification Biomagnification is the increase in concentration of a substance that occurs in a food chain and is not broken down by environmental processes.

Pollution-Free Energy Renewable forms of energy such as wind, solar, geothermal, hydroelectric energies are less harmful

Food Requirements Another consequence of increasing human population size is the greater need for food. A lot of the rainforest land is being cleared and used for farmland (deforestation), but the soil in rainforests is quite poor and heavy rainfalls cause soil erosion. Sustainable harvesting of resources should be done so we don’t exhaust the supplies or cause ecological damage. We have also overharvested fisheries mainly due to our fishing techniques that also pick up “bycatch” and disrupt other fish and sea creatures in that area.

Waste Disposal Oceans have served as waste disposal sites. Sources of marine garbage include cargo and passenger ships, oil platforms, runoffs from rivers. Plastics are the worst for marine life, as well as fishing lines and nets. Plastics often have chemicals that mimic estrogen and many organisms are developing female characteristics Landfills are filling up as well. Solution: increase awareness, change behaviours, recycle and technology changes.

Preserving Biodiversity Another problem with human population growth is a decline in biodiversity. Biodiversity stabilizes ecosystems Monoculture is a problem… might increase crop yield, but the resilience of the ecosystem is limited. Overexploitation: the excessive harvesting or killing of a species until it no longer exists or is significantly reduced. EG buffalo herds. Can cause extinction or reduce the population to below the minimum viable population size which causes inbreeding and low genetic diversity Invasive Species: non-native species that take over EG zebra mussels

Practice: Page 569 # 1, 3, 5, 7, 10, 11, 12, 15.