Title: Population Ecology
1Population Ecology
- Elizabeth Petrie
- Jill Stittleburg
- Sherry Wiedman
2Todays objectives
- Define 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 - Analyze human causes of extinction
3Changes in Population Size
- What causes populations to change in size?
- What are some factors that may limit population
growth? - Is there a point at which the population cannot
grow anymore? Why or why not?
4- Population growth is a function of birth rate and
death rate-
If birth rate gt death rate, population
increases
If death rate gt birth rate, population
decreases
If birth rate death rate, then the
population stablizes
5Limiting Factors-
- An environmental factor that prevents a
population from increasing.
Lack of food water shelter space
6- There are 2 types of limiting factors
- Density dependent factors
- Density independent factors
7Density- dependent factors
- Limiting factors that increase in intensity as
the population increases in size. - Will reduce birth rates or increase death rates
Ex. limited food supplies increased risk
of infectious disease toxins due to
increased waste levels
8Density-independent factors
- Influence population rates regardless of their
density
Ex. weather events drought,
floods, extreme temperatures human
interventions
9Carrying capacity
- The maximum population that can be supported
indefinitely in a given environment - Populations that are experiencing exponential
growth eventually reach carrying capacity
10Fruit Fly Population Growth
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12Population Growth
- When conditions are good, a population can grow
exponentially - The effects of declining resources gradually slow
growth rate - Growth rate declines to zero as it approaches
carrying capacity - If a population grows beyond the carrying
capacity, a population crash may occur
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1414.1 The Sixth Extinction
- 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
15Endangered Species Act (ESA)
- 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 - The 10 million species living today represent
only 1 of all species that have ever existed
16Measuring Extinction Rates
- Earths 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 http//www.jkaneart.com/massextinctiongraph.h
tm
17Causes 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
formscontinental drift, asteroid impact - The sixth mass extinction (that scientists
currently believe we are experiencing) is being
caused by human activity
18Human causes of extinction
- Habitat Destruction
- Habitat Fragmentation
- Introduced Species
- Overexploitation
- Pollution