Plan – Week 3

Plan – Week 3• Test on 5.1 – Today or Tuesday…• Test on 5.2 (Greenhouse Effect, Carbon Cycle

and Climate Change) : Friday• In between….5.3 and Topic G.3:Population Ecology and Invasive Species

5.3 Population Ecology

What you need to know about populations (Topic 5.3, SL and HL)

• Key Factors which determine population size

• You must know how to draw, and interpret, a classical population growth curve

• Factors which set limits to population increase

What ELSE you need to know about populations (Topic G, SL and HL)

• You must understand the impacts of alien species

• You must be able to give three examples of alien species in ecosystems

• You must outline one example of biological control of an invasive species

What ELSE you need to know about populations (Topic G, HL, NEXT YEAR)

• You must understand and distinguish between r-strategies and K-strategies

• You must understand environmental conditions that favour r- or K-strategies

• You must understand a method to estimate population size (catch and release)

WHAT IS A POPULATION?...

Let’s start simple…

Human Population• At what point in human history did the

population reach 1 billion people?

• It took all of human history up to the early 1800s for world population to reach 1 billion people, and until 1960 to reach 3 billion. Today, the world gains 1 billion people every 11 years.

Let’s Review: What is a population? (5.1.1)

A group of organisms of one species that interbreed and live in the same place at the same time

Key Characteristics of Populations 1: Geographic Distribution

Characteristics of Populations 2: Population density

The number of individuals per unit area

Population Density• Can vary tremendously depending on the

species and its ecosystemA few saguro cactusA field of sunflowers

A flock of birds

Turtles grouped to sun

Population DensityWhat are some benefits of living close together

or in a clumped population?1. Help finding food2. Protection from predators

or wind3. Easier to find species

Population DensityWhat are some drawbacks (negatives) of living

in a clumped population?1. Crowded living areas2. Battles over food/shelter3. Easier for disease to spread

Characteristics of Populations: Evaluating Growth Rate

The amount by which a population’s size changes in a given time

Let’s imagine a brand new population of….

• Let’s think about how it changes over time….

• How does it arrive in its new habitat?• Which factors will affect population size over

time?• You have two minutes…

www.SummitStudies.com

Time Remaining

5.3.1 What are the four factors that affect populations?

What affects population size? Number of births (natality)Number of deaths (mortality)Number of individuals

that enter (immigration)or leave (emigration)

Population Growth• Migration- periodic movements of populations

away from and back to their place of origin (not what we are talking about here)• Irregular movements of some

individuals out of an area, into a new area, with no return - affects population size

• Immigration – movement of individuals into an areaPopulation increases in size

• Emigration – movement of individuals out of an areaPopulation decreases in size

Population Growth• Why would an animal immigrate to or emigrate

from a population? • Competitive pressures on some individuals

– To find food, better living conditions, or a mate

Evaluating population growth…doing the mathematics…

If a population has unlimited food and space

and is protected from predators and disease, what will happen to the size of the population?

What would population growth looks like on a graph when an population colonizes a new habitat?

Draw a graph and explain the shape.Work with a partner.

You have five minutes.

Time Remaining

It will increase exponentially!

Under ideal conditions with unlimited resources and no predation, a population will grow

exponentially

Some formulae (you don’t need to know these!)

(Reference:http://www.nature.com/scitable/knowledge/library/how-populations-grow-the-exponential-and-logistic-13240157• Exponential growth:

• Logistic Growth (Transitional phase):

Exponential Growth• Example: Bacteria reproduce in ~20 minutes by

splitting in half– 1 bacteria after 20 min = 2 bacteria– 2 bacteria after 40 min = 4 bacteria– 4 bacteria after 60 min = 8 bacteria– In 180 min (3 hours) = 512 bacteria– In one day = 4,720,000,000,000,000,000,000 bacteria

Exponential Growth• Exponential growth occurs when the

individuals in a population reproduce at a constant rate– Creates a “J” shaped

curve– Under ideal conditions

with unlimited resources and no predation, a population will grow exponentially

This is what a graph of bacterial growth would look like if the growth went unchecked

Can exponential growth continue for ever?

Write down the factors that set limits to population size

You have two minutes…

What are factors that set limits to population size?

• Competition for resources• Build up of toxic by-products of metabolism• Increased predation• Incidence of disease.

Birth and Death Rates• Affected by

– Biotic factors• Disease, predators, food, competitors

– Abiotic factors• Rainfall, temperature, light, pollution

– Can be density dependent or density independent

– Can be extrinsic or intrinsic

Limits to Growth

• Medium Galapagos finch• Droughts (fewer seeds)

– Death rate increases– Birth rate decreases

• High rainfall (more seeds and caterpillars)– Death rate decreases– Birth rate increases

Logistic (Transitional) Growth Phase

• Do bacteria cover the planet?• Exponential growth does not continue in

populations very long.• As resources become less available, the

growth of a population slows or stops• What might cause population growth to stop

or slow down?– Predators, loss of habitat, disease, competition

for resources: less food, less space etc.

Logistic Growth (Transitional Phase)• Logistic growth (transition phase)

occurs when population growth slows or stops following a period of exponential growth– Creates an “S” shaped curve

• Population growth may slow or stopfor a number of reasons:– Birthrate ↓ death rate ↑

immigration ↓ emigration ↑• At some point, the growth of a

population will level off (stabilise, plateau phase)

Comparing Exponential and Logistic Growth

Carrying Capacity

Carrying Capacity (K)• The maximum number of individuals that a

particular habitat can support

The classical ‘Sigmoid’ Population growth curve

Most plant and animal populations follow this type of growth

What is happening in this population graph?

Finches & Rainfall

Some formulae (you don’t need to know these!)

(Reference:http://www.nature.com/scitable/knowledge/library/how-populations-grow-the-exponential-and-logistic-13240157• Exponential growth:

• Logistic Growth (Transitional phase):

Alien Species

What is an alien species?• An alien species is one which

arrives in a non-native habitat, usually as a result of intentional or accidental human activity

• Often, they are not well adapted to their new habitat and don’t survive (too far outside their ‘niche’

• MANY have been hugely successful in their new habitat, causing huge ecological and economic damage

The Classic Examples:• Zebra Mussels in

American Great Lakes• Cane Toads in Australia• Rabbits in Australia• Japanese Knotweed in

Europe• Bamboo in EuropeThere are literally hundreds

of thousands more…

Example of an Alien Species: The Cane Toad

• http://www.youtube.com/watch?v=gYUHnf7Uy1k&feature=player_embedded

• http://www.youtube.com/watch?v=8q77CIQodVw

Homework (2)http://www.issg.org/database/welcome/• The Global Invasive

Species DataBase• Use the database to

build a factsheet about one invasive species, EITHER from your home country, OR Switzerland

You must provide:• Common name and Binomial

nomenclature• Native and introduced habitat

range• Introductory pathway/vectors• Local dispersal methods• Impacts on local ecosystem

and environment• Management strategies• Images

Draw a graph and explain the shape.Work with a partner.

You have five minutes.

5.3.2, 5.3.3

K = carrying capacity

r = rate of reproduction

N0 = starting population

Population Growth

Population Stability

Population Decline

Make the shape of a Sigmoid graph

with your hand in the air.

Homework (1): Zebra Mussel Webquest (Population Study)

http://ats.doit.wisc.edu/biology/ec/pd/t1_a1_b.htm

Population Growth

Population Stability

Population Decline

Make the shape of a Sigmoid graph

with your hand in the air.

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