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Populations Slide 2 Population density = the number of individuals per unit area. Examples: 33 oak trees per acre 5 goldfish per aquarium 2 bears per square kilometer Slide 3 Population size is affected by Births Deaths Immigration Emigration Slide 4 Types of growth Exponential growth occurs when individuals in a population reproduce at a constant rate J shaped curve Slide 5 Exponential growth graph Slide 6 Populations will grow exponentially when there are unlimited resources. Slide 7 Logistic growth occurs when a populations growth slows or stops following a period of exponential growth. Slide 8 Resourses become less available S-shaped curve of graph Slide 9 Logistic growth graph Slide 10 Carrying capacity is the largest number of individuals an environment can support. Slide 11 Limits to Growth A limiting factor is something that causes population growth to decrease. Slide 12 Limiting factors that depend on population size are called density dependent. Examples: disease, predation, competition, parasitism, waste build-up, Slide 13 Like competition Slide 14 Populations are often kept in check by the predator-prey relationship Slide 15 Lynx and hare populations Slide 16 Density independent limiting factors affect all populations in similar ways. Examples are weather and climate extremes Slide 17 Density independent example: weather Slide 18 Or climate extremes Slide 19 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 Slide 20 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 Slide 21 Pollution DDT, a pesticide, became more concentrated as it moved up the food web biological magnification Slide 22 Biological Magnification of DDT Fish-Eating Birds Magnification of DDT Concentration 10,000,000 100,000 10,000 1,000,000 1 1000 Large Fish Small Fish Zooplankton Producers Water Slide 23 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 Slide 24 Causes of ozone depletion include: Aerosol sprays that contain chlorofluorcarbons (CFCs), the coolants in air conditioners and production of plastic foams CFCs are banned in US