Populations

Population density = the number of individuals per unit area. Examples: 33 oak trees per acre 5 goldfish per aquarium 2 bears per square kilometer

Population size is affected by Births Deaths Immigration Emigration

Types of growth Exponential growth occurs when individuals in a population reproduce at a constant rate J shaped curve

Exponential growth graph

Populations will grow exponentially when there are unlimited resources.

Logistic growth occurs when a population’s growth slows or stops following a period of exponential growth.

Resourses become less available S-shaped curve of graph

Logistic growth graph

Carrying capacity is the largest number of individuals an environment can support.

Limits to Growth A limiting factor is something that causes population growth to decrease.

Limiting factors that depend on population size are called density dependent. Examples: disease, predation, competition, parasitism, waste build-up,

Like competition

Populations are often kept in check by the predator-prey relationship

Lynx and hare populations

Density independent limiting factors affect all populations in similar ways. Examples are weather and climate extremes

Density independent example: weather

Or climate extremes

Effects of Pollution on Ecosystems Air resources – cities produce smog, a pollutant from the burning of fossil fuels that can cause health problems -acid rain – nitric and sulfuric acids with a high pH which can kill plants and animals

Formation of Acid Rain Emissions to Atmosphere Nitrogen oxides Sulfur dioxide Chemical Transformation Nitric acid Sulfuric acid Precipitation Acid rain, fog, snow, and mist Dry Fallout Condensation particulates, gases IndustryTransportationOre smeltingPower generation

Pollution – DDT, a pesticide, became more concentrated as it moved up the food web… biological magnification

Biological Magnification of DDT Fish-Eating Birds Magnification of DDT Concentration 10,000, ,000 10,000 1,000, Large Fish Small Fish Zooplankton Producers Water

Ozone is a gas made up of molecules that consist of 3 oxygen atoms Antarctica has a “hole” in the ozone layer that has grown larger over the past 20 years

Causes of ozone depletion include: Aerosol sprays that contain chlorofluorcarbons (CFC’s), the coolants in air conditioners and production of plastic foams CFCs are banned in US