Population Ecology Elizabeth Petrie Jill Stittleburg Sherry Wiedman

Today’s objectives: Define carrying capacity Define carrying capacity Describe how and why population growth rates change as the population approaches carrying capacity Describe how and why population growth rates change as the population approaches carrying capacity Discuss the “sixth extinction” and measurement of extinction rates Discuss the “sixth extinction” and measurement of extinction rates Analyze human causes of extinction Analyze human causes of extinction

Changes in Population Size What causes populations to change in size? What causes populations to change in size? What are some factors that may limit population growth? What are some factors that may limit population growth? Is there a point at which the population cannot grow anymore? Why or why not? Is there a point at which the population cannot grow anymore? Why or why not?

Population growth is a function of birth rate and death rate- Population growth is a function of birth rate and death rate- If birth rate > death rate, population increases increases If death rate > birth rate, population decreases decreases If birth rate = death rate, then the population stablizes population stablizes

Limiting Factors- An environmental factor that prevents a population from increasing. An environmental factor that prevents a population from increasing. Lack of : food water shelter space

There are 2 types of limiting factors: Density dependent factors Density dependent factors Density independent factors Density independent factors

Density- dependent factors Limiting factors that increase in intensity as the population increases in size. Limiting factors that increase in intensity as the population increases in size. Will reduce birth rates or increase death rates Will reduce birth rates or increase death rates Ex. limited food supplies increased risk of infectious disease increased risk of infectious disease toxins due to increased waste levels toxins due to increased waste levels

Density-independent factors Influence population rates regardless of their density Influence population rates regardless of their density Ex. weather events: drought, floods, extreme temperatures floods, extreme temperatures human interventions human interventions

Carrying capacity The maximum population that can be supported indefinitely in a given environment The maximum population that can be supported indefinitely in a given environment Populations that are experiencing exponential growth eventually reach carrying capacity Populations that are experiencing exponential growth eventually reach carrying capacity

Fruit Fly Population Growth

Population Growth When conditions are good, a population can grow exponentially When conditions are good, a population can grow exponentially The effects of declining resources gradually slow growth rate The effects of declining resources gradually slow growth rate Growth rate declines to zero as it approaches carrying capacity Growth rate declines to zero as it approaches carrying capacity If a population grows beyond the carrying capacity, a population crash may occur If a population grows beyond the carrying capacity, a population crash may occur

14.1: The Sixth Extinction Vocabulary Vocabulary –Extinction: complete loss of a species –Biodiversity: entire variety of living organisms –Endangered Species Act: law passed in 1973 with the purpose of protecting and encouraging the population growth of threatened and endangered species

Endangered Species Act (ESA) Written and passed because humans seemed to be triggering the rapid rate at which species were being lost Written and passed because humans seemed to be triggering the rapid rate at which species were being lost –Ex: passenger pigeon, whooping crane, bald eagles, elephant seals Critics of ESA say that saving all species is unrealistic goal because extinction is a natural process Critics of ESA say that saving all species is unrealistic goal because extinction is a natural process –The 10 million species living today represent only 1% of all species that have ever existed

Measuring Extinction Rates Earth’s history highlighted by 5 mass extinctions thus far Earth’s history highlighted by 5 mass extinctions thus far –Mass extinction: period of a few thousand or few hundred years in which 50%-90% of living species lost From

Causes of Mass Extinction First five thought to be caused by natural global changes: changes in sea level and climate fluctuations, changes in ocean and land forms—continental drift, asteroid impact First five thought to be caused by natural global changes: changes in sea level and climate fluctuations, changes in ocean and land forms—continental drift, asteroid impact The sixth mass extinction (that scientists currently believe we are experiencing) is being caused by human activity The sixth mass extinction (that scientists currently believe we are experiencing) is being caused by human activity

Human causes of extinction: Habitat Destruction Habitat Destruction Habitat Fragmentation Habitat Fragmentation Introduced Species Introduced Species Overexploitation Overexploitation Pollution Pollution