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Population Ecology

Population Ecology. Chapter 13. Objectives. Define population Define exponential growth Understand the concept of carrying capacity Understand what factors may cause a population to fluctuate in numbers Understand the concept of environmental resistance. What Is a Population.

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Population Ecology

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  1. Population Ecology Chapter 13

  2. Objectives • Define population • Define exponential growth • Understand the concept of carrying capacity • Understand what factors may cause a population to fluctuate in numbers • Understand the concept of environmental resistance

  3. What Is a Population • The term population refers to the number of organisms of the same species residing in a given area • Population size = # of individuals • Population density = # of individuals/unit of area Populations may be clumped, uniformly distributed or randomly dispersed within a given area

  4. Change in Population Size • All populations change in size over time • Birth and immigration result in an increased population size if they outnumber death and emigration • Environmental factors play a key role in the increase or decrease of a population

  5. Exponential Growth • Exponential growth results when population growth increases by a constant proportion from one generation to the next • Doubling time is used to measure the rate of population growth

  6. Carrying Capacity • No population can increase in size indefinitely • Carrying capacity is reached when population growth reaches zero • Achieved when birth and immigration equals death and emigration • Carrying capacity limits result from resource availability

  7. What Factors Influence Population Growth • Growth factors are things that cause animals to flourish. • Food, space • Reduction factors are things that cause animals to die. • Food shortages, lack of space, disease, predation, deterioration of habitat, and natural disasters • Collectively, reduction factors constitute environmental resistance.

  8. Environmental resistance can be further grouped into: Density independent factors: limit growth of organisms irrespective of number. Storms, floods, most weather phenomena Density dependant factors: limit increase or decrease of organisms depending on the density (#/area) of the organism. Competition: for food Predation: Predators shift to most populated prey Parasitism: Increase # makes transfer easier Disease: like parasites, disease spreads more readily Environmental Resistance

  9. Species Interactions • Predator – Prey relationships demonstrate one species’ ability to influence another species’ population size

  10. So, Where Are We?

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