populations honors biology – chapter 5. what is a population? a group of the same species living...
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Populations
Honors Biology – Chapter 5
What is a Population?
A group of the same species living in a given area
It is populations of organisms that interact in ecosystems
Example:
An Introduction – Sea Otters of the Pacific Northwest
Life in kelp forest community
An Introduction – Sea Otters of the Pacific Northwest
Sea urchins as food Sea urchins eat kelp
Sea otters nearly eliminated due to hunting
Sea urchin populations rise
Kelp forests decline Restoring balance: Sea
otters declared endangered – protected from hunting
Predator/Prey Population Relationships
Hare / Lynx Hare population goes up
Lynx population goes up Lots of food (hares) available
Causes hare population to go down More lynx = more predation on hares
Causes lynx population to go down Hare population decrease means less food
for lynx and they die
Hare/Lynx
4 Characteristics of Populations
Geographic distribution Range Area inhabited by a population
Density Number of individuals per unit area
Growth rate Age structure
Population Growth
3 factors affect population size Number of births
natality Number of deaths
mortality Number of individuals that enter or leave a
population Immigration - enter Emigration - leave
Population Growth
A population will increase or decrease in size depending on how many individuals are added to it or removed from it
Growth occurs if More individuals are born than die If birth rate equals death rate the
population will stay near the same size
Movement into or out of a population
May be caused by Young animals mature and leave the area Shortage of food in an area
Exponential Growth
Individuals in a population reproduce at a constant rate Initially, growth is slow Overtime the population
becomes larger and large until it approaches an infinitely large size
Ideal conditions with unlimited resources required
Bacteria
Fastest rates of reproduction among living things
20 minutes for population to double
Why don’t they take over the Earth? NOT unlimited
resources
Logistic Growth
Growth pattern that occurs when a population’s growth slows or stops following a period of exponential growth.
Things that slow a population’s growth Natality (birth rate) decreases Mortality (death rate) increases Rate of immigration decreases Rate of emigration increases
Logistic Growth
Also, when birth and death rates are the same, the population growth will slow or even stop for a time
Even when a population stops “growing”, the population is still rising and falling somewhat – though the ups and downs average out to the same population size.
Logistic Growth Curve
Slow growth Exponential growth Growth levels off Carrying Capacity
K Dotted line The maximum
number of individuals that an environment can support
Limits to Growth
Limiting Factors Factors that cause population growth to
decrease Competition Predation Parasitism Drought Human disturbance
There are TWO types of limiting factors
Density Dependent Density Independent
Density Dependent Limiting Factors
Depends on the size of a population Usually greatest impact when the
population is large and dense Include
Competition Predation Parasitism Disease
Density Independent Limiting Factors
Affects all populations (large or small) in similar ways. Unusual weather Natural disasters Human activities
Like Habitat Destruction
Human Population Growth
Like other populations of organisms, the human population tends to increase with time.
Human Population Growth Curve Initially slow
Food scarce Life harsh
500 years ago More rapid growth
Currently EXPONENTIAL Why?
Agriculture and industry advances Food supply increased Improved sanitation Medicine
Human Population Growth Curve
Demography
The study of human populations Examines human populations and tries
to predict how they will change over time.
Demographic Transition
Population growth in some countries has slowed U.S. Japan Much of Europe
Why? Hypothesis: These countries have
completed the “demographic transition
Demographic Transition
A dramatic change in birth and death rates What happens
Initially both birth and death rates high Advances in nutrition, etc. lower death rate Population increases rapidly Societies modernize – increase education, etc. Families have fewer children Birthrate falls to meet the death rate Population growth stops
Populations that have NOT completed the demographic transition Most countries
India China
Age Structure Diagrams
Shows how many people of different ages and genders are in a population
Useful in predicting future population growth
Age Structure Diagram
Predicting Future Population Growth
Factors to consider Age structure of each country Prevalence of life-threatening diseases
Predictions for 2050 9 billion people on Earth
Effects of Human Population Growth
Some scientists suggest if human population growth rate does not become LESS than 0 (deaths outnumber births) Serious damage to environment Serious damage to global economy
Some economists say that technology advances and changes in societies can control negative impacts
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