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Chapter 5 Academic Biology PopulationsHow Populations GrowPopulation Density the number of individuals per unit area. Number can vary depending on the species and its ecosystem.
population size factors number of deaths, number of individuals that enter or leave, number of births
immigration the movement of individuals into an areaemigration the movement of individuals out of an area
exponential growth occurs when the individuals in a population reproduce at a constant
at first the number increases slowly, over time, population becomes larger, larger, larger infinitely large size*under ideal conditions with unlimited resources, a population will grow exponentially
logistic growth occurs when a population's growth slows or stops following a period of exponential growth S shaped curve
carrying capacity the largest number of individuals that a given environment can support
Exponential Growth Curve
• The rate of increase in the population under ideal conditions. This produces a J shaped curve.
Exponential Growth
Logistic Growth Curve
• Idealized population growth slowed by limiting factors as the population size increases.
Logistic Growth Curve
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• Density Dependent Limiting Factor – factors that limit the growth of a population as the population grows larger. • Includes competition (for food, water and space) predation, parasitism and disease • Does not impact small scattered populations as greatly.
Density Dependent Limiting FactorDensity Dependent: Decrease in song sparrow clutch sizes as population density increases.
• Density Dependent Limiting Factor
Predation = density dependent
• The regulation of a population size as one organism captures and feeds on another organism. This predator prey relationship is one of the bestknown mechanisms of population control.
Predator Prey Relationship
• Density Independent Limiting Factors – factors that limit the size of a population regardless of size.• Natural disasters, unusual weather, human activities.• These factors determine the Carrying Capacity – the maximum population size that an environment can support.
The effect of an abiotic factor (climate) on aphid population size.
Fluctuations in a song sparrow population, with periodic catastrophic reductions due to severe winter weather.
Human Population Growth the size of the human population tends to increase with time
about 500 years ago human population began growing more rapidly agriculture and industry made life easier and safer exponential growth curve
Patterns of Population Growth Demography scientific study of human populations examines the characteristics of human populations attempts to explain how those populations will change over time
* birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly
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Human PopulationDemographic Transition a dramatic change in birth and death rates as countries modernize nutrition, sanitation, medicine more children survive into adulthood and live to old age lower the death rate and begin the demographic transition as societies continue to modernize families have fewer children birth rate falls, population growth slows demographic transition is complete when birthrate falls to meet the death rate, and population growth stops US, Europe, Japan demographic transition worldwide human population is still growing exponentially
Mexico Demographic Transition Why?
age structure diagrams or population profiles graph the numbers of people in different age groups in a population Age Structure Diagrams
Future Population Growth current projections suggest by the year 2050 the population could be 9 billion
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Chapter 6 Academic Biology Humans in the Biosphere
Earth as an Island How??
Hawaii land reduction by 2/3 enormous number of land snails, plants, insects, hundreds of other native Hawaiian species are gone imported plants and animals have crowded out many remaining native species
among the human activities that have transformed the biosphere are hunting and gathering, agriculture, industry, and urban development
hunting and gathering gathered wild seeds, fruits, nuts
subsistence hunting hunting only to acquire basic necessities for survival, makes relatively few demands on the environment
agriculture began at the end of the last ice age, about 11,000 years ago combination of Latin words "ager" a field and "cultura" care science and art of farming which includes the cultivation of field soils, production of crops, and the raising of live stock
Domestication of Animals overgrazing changed the grassland ecosystems
green revolution introduction of intensive farming practices that lead to a substantial increase in crop yields central strategy was the development of new, highly productive varieties of major food crops developed "miracle strains" to improve harvests
monoculture farming strategy in which large fields are cleared, plowed, and planted with a single, highly productive crop year after year
benefits increased food production
problems can deplete energy and water supplies pest species can reproduce pesticides
industrial growth and urban development industrial revolution fossil fuels pollute air, water, soil. Dense human communities produce waste, suburban sprawl
nonrenewable resources is one that cannot be replenished by natural processes fossil fuels, population of trees in an ecosystem
renewable resources can regenerate and are therefore replaceable but not necessarily unlimited fresh water
Tragedy of the Commons
What was the tragedy?
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sustainable use using natural resources at a rate that does not deplete them sustainable practices are based on principles of ecology as well as economics
land resourcesdesertification dry climates, combination of farming, overgrazing, drought have turned productive areas into deserts
soil erosion wearing away of surface soil by water and wind contour plowing, leave stems and roots of previous year crop in place
forest resources old growth forestdeforestation loss of forests logged, soil erosion, grazing, plowing tropical soils laterite selective harvest, tree farms
ocean resources over fishingaquaculture farming of aquatic organisms
Oil Spill
deforestation loss of forests Oil Spill Sustainable Agriculture
air resources smog a mixture of chemicals that occurs as a graybrown haze in the atmosphere car exhausts and industrial emissions (e.g. Beijing)
pollutant a harmful material that can enter the biosphere through land, air, or water particulates
acid rain fossil fuels release acidic gases containing nitrogen and sulfur compounds nitric acid sulfuric acids
Formation of Acid Rain
Biological Magnification
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Biological Magnification water resources although water is a renewable resource, the total supply of fresh water is limited
biodiversity is the sum total of the genetically based variety of all organisms in the biosphere ecosystem diversity species diversity genetic diversity biodiversity is one of the earth's greatest natural resources. Species of many kinds have provided us with food, industrial products, and medicines antibiotics, heart drugs, and anticancer drugs "library" of genetic information upon which humans can draw for future use
conservation is used to describe the wise management of natural resources, including the preservation of habitats and wildlife
zoned reserves
Clearing Rainforest
Clearing Rainforest
zoned reserves
human activity can reduce biodiversity by altering habitats, hunting species to extinction, introducing toxic compounds into food webs, and introducing foreign species to new environmentsextinction endangered species
Species Diversity
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Fishery Collapse
Collapse of Northern Cod Fishery off Newfoundland
Fishery Collapse
Ecosystem Services