Human Ecology

Exponential Growth

• Bacteria placed in nutrient broth of optimal temperature

Exponential growth:

• when population growth at any point is 2N , N= # of generations

• will occur under ideal conditions with unlimited resources

• Ex. After 5hrs, 25 = 32

• J-shaped graph

• Exponential Growth CANNOT continue indefinitely due to limiting factors:

– Factors that stop or control population growth

– Examples: Food, light, water, space, parasitism and disease, predators, energy resources, oxygen, accumulation of waste products, competition, disasters – fire, floods, drought, etc.

Carrying Capacity and Logistic Growth

• Logistic Growth:– Exponential at first

then levels off as it reaches carrying capacity

– Growth rate = 0– S-shaped graph

• Carrying Capacity:– Maximum population

that environment can support

Population Growth of Humans

Factors affecting human population growth

• Agricultural revolution/food production• Increase in knowledge of diseases• Better health care and hygiene/sanitation• Advances in Medicine and technology• Resulting in a decrease in death rate, a

longer life span, and an increased birth rate in some areas

• NOTE: there has been a decrease in fertility rates in underdeveloped nations

Limiting Resources

• Renewable Resources– Can be replaced – Food supply, solar energy, wind/air, water,

soil, living things (trees), geothermal energy, nuclear energy

• Non-Renewable Resources

- cannot be replaced in one’s lifetime

- fossil fuels

Source: United Nations, World Population Prospects, The 1998 Revision; and estimates by the Population Reference Bureau.

•Human population is estimated to rise over 9 billion by the year 2150.

• Many think it will then level off or decline at this point.

•If growth continues, may result in population crash due to overcrowding and competition for food.

•May also result in famines, disease and wars.

Human Population Growth and the Environment

As the human population grows, we take up more space, consumer more resources, and produce more wastes!

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Disruption of Existing Ecosystems

• Urbanization – Shift from rural (farming) areas to cities– Increased Industrialization – Destruction of farmland and deforestation– Results in

• Decreased amount of space for other species• Loss of habitats• Decreased biodiversity• Disruption of ecosystem by introducing new

species into an area w/no known predator

Poor Farming Practices

• Over farming and over grazing– result in areas w/o a cover of vegetation– No plants…no roots to hold soil– Leads to soil erosion: removal of soil by

wind or water and desertification

Deforestation – can also lead to soil erosion, washing away of nutrients

Pollution

• Noise

• Water – ex. Sewage, animal wastes, toxic chemicals (DDT, fertilizers), thermal pollution

• Air – ex. burning of fossil fuels leads to increased levels of carbon dioxide, acid rain, smog

• Land – ex. solid wastes, garbage

RESTORING ENVIRONMENT

• PRESERVING RESOURCES: 3 R’s– Reduce: avoid using resource, ex. Walk, bike,

carpooling– Reuse: use product over again instead of

throwing it out, ex. Dishes instead of paper plates

– Recycle: using a product to make another product, ex. Paper, metal, plastic, glass

• Use biological pest control, not pesticides – ex. Using lady bugs to control aphids

– Use phermones – sex hormones to attract pests

• Compost heaps: natural recycling of nutrients, no need for chemical fertilizers, reduces amount of waste in landfill

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The Value of Biodiversity

• Species diversity – the # of different species in a biosphere

• Genetic diversity – the sum total of all genetic differences

• Provide us with foods, industrial products, medicines, etc.

Threats to Biodiversity

• Habitat alteration

• Demand for wildlife products

• Pollution – biological magnification (ex. bald eagle and DDT)

• Introduced species – invasive species