Ecology

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


• 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


• 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?


• 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)

– When you’re done writing, put your pens down…


What population do you think this is?Population Ecology: Population Growth Rate

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?


• 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 Ecology: Population Growth Models


• 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

Communities

• Review:– A community is a group of interacting populations

that occupy the same area at the same time.

Community Ecology: Communities

Communities

• Range of Tolerance– The limits within which an organism can exist.

Community Ecology: Communities

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– Consists of 2 types:

• Primary Succession• Secondary Succession

Community Ecology: 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.



• Ecological Succession: Primary– Small weedy plants and other organisms become

established.– As these organisms die, additional soil is created



• 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.



• Ecological Succession: Primary– The stable, mature community that eventually

develops from bare rock is called a climax community.


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.

On the left side of your IntNB, address the following:

• 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

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.

• 250 MYA: Over90% 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

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Ecology