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Ecology. Part 4. Populations Part 5. Communities Part 6. Biodiversity and Conservation. Population Ecology: Population Characteristics. Population Characteristics. Population Density: The number of organisms per unit area Spatial Distribution: - PowerPoint PPT Presentation
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Ecology
Part 4. PopulationsPart 5. Communities
Part 6. Biodiversity and Conservation
Population Characteristics
1. Population Density: – The number of organisms per unit area
2. Spatial Distribution:– Dispersion: The pattern of spacing a population
within an area– 3 main types of dispersion
• Clumped• Uniform• Random
– The primary cause of dispersion is resource availability
Population Ecology: Population Characteristics
Population Limiting Factors
3. Population growth rate– How fast a given population grows– Factors that influence this are:
• Natality (____ rate)• Mortality (_____ rate)• Emigration (the number of individuals moving
_________ a population)• Immigration (the number of individuals _________ a
population)
Population Ecology: Population Characteristics
birthdeath
away frommoving to
Population Limiting Factors
• Density-independent factors– Factors that limit population size, regardless of
population density.– These are usually abiotic factors– They include natural phenomena, such as weather
events• Drought, flooding, extreme
heat or cold, tornadoes, hurricanes, fires, etc.
Population Ecology: Density-independent factors
Population Limiting Factors
• Density-dependent factors– Any factor in the environment that depends on
the number of members in a population per unit area
– Usually biotic factors– These include
• Predation• Disease• Parasites• Competition
Population Ecology: Density-dependent factors
Understanding Exponentials
• Put your pens down for a minute & think about this:– An employer offers you two equal jobs for one hour
each day for fourteen days. – The first pays $10 an hour.– The second pays only 1 cent a day, but the rate
doubles each day.– Which job will you accept?
Population Ecology: Population Growth Rate
Understanding ExponentialsPopulation Ecology: Population Growth Rate
0102030405060708090
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Job 1 Job 2
Job 2 lags for a long time before
exponential growth kicks in!
Now, how much would your employer owe you if you stayed at this job for another 2 weeks?
What would happen if this type of growth took place
within a population?
What population do you think this is?Population Ecology: Population Growth Rate
What letter does this curve resemble?
The USCB estimates that the world population exceeded 7 billion on March 12, 2012
• Population growth models– Exponential growth model
• Also called geometric growth or J-shaped growth.
• First growth phase is slow and called the lag phase
• Second growth phase is rapid and called the exponential growth phase
• Bacteria can grow at this rate, so why aren’t we up to our ears in bacterial cells?
• Population growth models– Limits to exponential growth
• Population Density (the number of individuals per unit of land area or water volume) increases as well
• Competition follows as nutrients and resources are used up
• The limit to population size that a particular environment can support is called carrying capacity (k)
Population Limiting Factors
So, what do you think is going to happen to the human population?
• We will probably reach our carrying capacity.• Our growth rate will start to look like most
organisms, which is the Logistic Growth Model
Carrying Capacity (k)
What letter does this curve kind of look like?
http://en.wikipedia.org/wiki/Overpopulation
• Population growth models– Logistic Growth Model
• Often called the S-shaped growth curve• Occurs when a population’s growth slows or stops
following exponential growth.• Growth stops at the population’s carrying capacity• Populations stop increasing when:
– Birth rate is less than death rate(Birth rate < Death rate)
– Emigration exceeds Immigration (Emigration > Immigration)
Population Limiting Factors
Population Limiting Factors
• Population growth models– Logistic Growth Model
The S-curve is not as pretty as the image looks1. Carrying capacity can be raised or lowered. How?
Example 1: Artificial fertilizers have raised kExample 2: Decreased habitat can lower k
2. Populations don’t reach k as smoothly as in the logistic graph.• Boom-and-Bust Cycles• Predator-Prey Cycles
Population Ecology: Population Growth Models
r and K strategists• A logistic equation can describe the self-limiting growth of a
biological population.• where r is the maximum growth rate of the population (N),
and K is the carrying capacity of its local environmental setting, d stands for derivative, and t for time.
In r/K selection theory, selective pressures drive evolution in one of two generalized directions: r- or K-selection
Traits that are thought to be characteristic of r-selection include: • high fecundity• small body size• early maturity onset• short generation time• ability to disperse offspring widely
Traits that are thought to be characteristic of K-selection include: large body size• long life expectancy• production of fewer offspring• extensive parental care until they
mature
r and K strategists
Evolved to take advantage in unstable environment, density independent
Evolved to take advantage in stable environment, density dependent interactions
Communities
• Review:– A community is a group of interacting populations
that occupy the same area at the same time.
Community Ecology: Communities
Communities• Limiting Factors
– Any abiotic or biotic factor that restricts the numbers, reproduction, or distribution of organisms.
Community Ecology: Communities
Name some…
Communities• Range of Tolerance
– The limits within which an organism can exist.
Community Ecology: Communities
Think: Effects of global warming/climate change?
Ecological Succession• Ecological Succession
– The change in an ecosystem that happens when one community replaces another as a result of changing biotic and abiotic factors
Community Ecology: Ecological Succession
Ecological Succession
• Ecological Succession– Consists of 2 types:
• Primary Succession• Secondary Succession
Community Ecology: Ecological Succession
Ecological Succession• Ecological Succession: Primary
– The establishment of a community in an area of exposed rock that does not have topsoil is called Primary Succession.
• It occurs very slowly at first
Community Ecology: Ecological Succession: Primary Succession
• Ecological Succession: Primary– The first organisms to arrive
are usually lichens or mosses, which are called pioneer species.
• They secrete acids that can break down rock
• Their dead, decaying organic materials, along with bits of sediment from the rock make up soil.
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary– Small weedy plants and other organisms become
established; dispersal– As these organisms die, additional soil is created
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary– Seeds brought in by animals, water and wind
begin to grow in the soil.– Eventually enough soil is present for shrubs and
trees to grow.
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary– The stable, mature community that eventually
develops from bare rock is called a climax community.
Community Ecology: Ecological Succession: Primary Succession
Ecological SuccessionCommunity Ecology: Ecological Succession: Secondary Succession
• Ecological Succession: Secondary– Disturbances (fire, flood, windstorms) can
disrupt a community.– After a disturbance,
new species of plants and animals might occupy the habitat.
Ecological SuccessionCommunity Ecology: Ecological Succession: Secondary Succession
• Ecological Succession: Secondary– Pioneer species in secondary succession are
usually plants that begin to grow in the disturbed area.
– This is much fasterthan primarysuccession
Ecological SuccessionCommunity Ecology: Ecological Succession
• Ecological Succession: End point?– Cannot be predicted– Different rates of growth &
human involvementmake it impossible toknow if a true climaxcommunity has beenreached.
• What would happen if all of the jackrabbits in a food web died suddenly?
• Is the disappearance of one species from Earth important, or will another species fill its niche?
Biodiversity and Conservation: Introduction
“Keystone” species…is a species that has a disproportionately
large effect on its environment relative to its abundance.
• Play a critical role in maintaining the structure of an ecological community
• Affect many other organisms in an ecosystem
Examples:1) Pacific Coast: purple sea urchin can damage kelp forests by chewing through kelp holdfastsThe sea otter is an important predator of sea urchins.
2) Grey wolves in Yellowstone
3) Can you think of any other examples?
Biodiversity• What is Biodiversity?
The variety of life in an area that is determined by the number of different species in that area.
• There are 2 main types:
Biodiversity and Conservation: What is biodiversity?
Genetic Diversity Species Diversity
BiodiversityBiodiversity and Conservation: Why is biodiversity important?
Teosinte: A distant relative of corn
Domestic corn plant
Penicillin: Derived from bread mold
Madagascar Periwinkle: Used to treat childhood forms of leukemia
Extinction Rates• The gradual process of becoming extinct is known as background
extinction.• Mass extinctions: When a large percentage of all living species
become extinct in a relatively short period of time.• Ex: 250 MYA: Over
90% of species died
Biodiversity and Conservation: Extinctions
Estimated number of Extinctions since 1600
Biodiversity and Conservation: Extinctions
Group Main-land
Island Ocean Total Approximate Number of Species
Percent of Group Extinct
Mammals 30 51 4 85 4000 2.1
Birds 21 92 0 113 9000 1.3
Reptiles 1 20 0 21 6300 0.3
Amphibians 2 0 0 2 4200 0.05
Fish 22 1 0 23 19,100 0.1
Invertebrates 49 48 1 98 1,000,000+ 0.01
Flowering Plants
245 139 0 384 250,000 0.2
Five Most Recent Mass ExtinctionsBiodiversity and Conservation: Extinctions
Ordovician Period (444 MYA)
Devonian Period (360 MYA)
Permian Period (250 MYA)
Triassic Period (200 MYA)
Cretaceous Period (65 MYA)
Activity: Understanding Geological Time
• Working in your groups, you will get the following supplies:– A meter stick– A roll of 5 meters of paper– Colored pencils
• Using the worksheet, plot out the dates. – 1 million years is a millimeter– 1 billion years is a meter