BIOLOGY CHAPTER 5 POPULATIONS

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BIOLOGY CHAPTER 5 POPULATIONS
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5-1 How Populations Grow

• (Otter introduction page 119- Read)

Sea otters are important to populations of kelp,
sea urchins, killer whales.
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CHARACTERISTICS OF POPULATIONS1-Geographic
distribution or range- the area inhabited by a
population.
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EX A few cubic cm (bacteria in a rotting
apple)to millions of square km (Migrating
whales)
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2-Population Density- of individuals per unit
area.Density refers to HOW MANYnot
where!!3-Growth Rate4-Age Structure- of
people in different age groups in the population.
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AGE STRUCTURE
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POPULATION GROWTH 3 Factors That Affect
Population Size 1- of births 2- of deaths 3-
of individuals that enter or leave a population
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A population will increase or decrease depending
on how many individuals are added to it or
removed from it. When birth rate death
ratepopulation stays the same size
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When birthrate is GREATER than death ratethe
population grows. When DEATHRATE is greater than
birthratethe population shrinks.
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IMMIGRATION-(INTO a population) movement of
individuals into an area occupied by an existing
population. Immigration can cause a population to
grow. EX Animals come into a territory in search
of mates or food.
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EMIGRATION-(EXIT from a population) movement of
individuals out of a population. Emigration can
cause a population to decrease in size. EX Young
animals leave the area where they were born to
find mates establish territories. EX shortage
of food
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EXPONENTIAL GROWTH- growth pattern in which the
individuals in a population reproduce at a
constant rate. At first, the of individuals
increases slowly. Over time the population
becomes larger larger at a very rapid rate!
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Under IDEAL conditionsplenty of food, water,
space protected from predators diseasea
population will continue to grow Under ideal
conditions with unlimited resources, a population
will grow exponentially.
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See Exponential Growth Curves on page
121J-Shaped! How are these graphs alike? Besides
showing different types of organisms, how do they
differ? What do these differences indicate? What
is another major difference between the
reproduction of bacteria that of elephants?
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How are these graphs alike?Both plot time on the
x axis of organisms on the y axiscurve on
graph is j shaped. Besides showing different
types of organisms, how do they
differ? Population size is given in hundreds of
thousands for bacteria in millions for
elephants. The elapsed time is in hours for
bacteria in hundreds of years for elephants.

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What do these differences indicate?Bacteria
reproduce very rapidly in a short period of time,
but elephants reproduce much more slowly over a
longer period of time.
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What is another major difference between the
reproduction of bacteria that of
elephants?Bacteria reproduce asexually, every
bacterium is capable of producing 2 offspring.
Elephants reproduce sexually- 2 parents- male
female- so two parents are needed to produce one
offspring.
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Bacteria double every 20 minutes under ideal
conditions! ?Do ideal conditions usually exist in
nature??
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BIOTIC POTENTIAL- the size a population would
reach if all offspring were to survive and
produce young. In order for this to happen- ideal
conditions would have to exist! 2 Elephants under
ideal conditions would produce more than 20
million descendents after 750 years.
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In reality- no population ever reaches its biotic
potential. The factors that prevent this ideal
growth are called Limiting Factors or
Environmental Resistance
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LOGISTIC GROWTH THE LOGISTIC GROWTH CURVE As
resources become less available, the growth of a
population slows or stops. Logistic Growth-
growth pattern in which a populations growth
rate slows or stops following a period of
exponential growth.
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A logistic growth curve has a general s
shape. Growth starts out slow, then hits a period
of exponential growth. Exponential growth
continues until the population reaches the
carrying capacity.
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Carrying Capacity- largest of individuals of a
population that a given environment can
support. A horizontal line is drawn through the
part of the graph where the population growth has
leveled offthis is how carrying capacity is
indicated on a logistic growth curve.
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The average growth rate is to zero at the
carrying capacity. Complete population trends
on page 123.graphing analyzing data.
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5-2 Limits to Growth Page 124 LIMITING FACTOR- a
factor that causes the growth of a population to
decrease.
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2 Types Of Limiting Factors 1-
Density-Dependent Factors-a limiting factor that
depends on population size. EX competition,
predation, parasitism, disease 2-Density-Indepen
dent Factors-limiting factors that affect all
populations regardless of population size. EX
unusual weather, natural disasters, seasonal
cycles, certain human activities.
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COMPETITION- when organisms compete/struggle with
one another for food, water, space, sunlight, or
other essentials of life. Competition usually
occurs when populations become crowded. Competitio
n is the major force behind evolutionary change!
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PREDATION- interaction in which one organism
captures feeds on another organism. PREDATOR-PRE
Y RELATIONSHIP mechanism of population control in
which a population is regulated by
predation. (See figure 5-7 page 126)
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Periodic increases in the moose population are
quickly followed by increases in the wolf
population (predators!).
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Predator-Prey Graphs
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PARASITISM DISEASE Parasites are similar to
predators in many ways.they take nourishment
from hosts and can cause them to become sick or
die.
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HEARTWORMS
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Nematods- Roundworms
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DENSITY INDEPENDENT FACTORS tend to be abiotic.
They affect all populations the same way
regardless of size.
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5-3 HUMAN POPULATION GROWTHpage 129 The human
population tends to increase with time. A long
time ago, when life was harshlimiting factors
kept the human population sizes low.
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Many years ago childhood diseases kept half of
the children from surviving to adulthood. People
would have several children because death rates
were so highthis was to assure that some would
survive!
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Agriculture industry made life safer
easier -more reliable food sources -better
sanitation -better healthcare -better
medicine Birth rates remained high we
experienced exponential growth.
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See Figure 5-10 page 129 What would the graph
look like if we were to extend the graph to
thousands of years in the future? Why?
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PATTERNS OF POPULATION GROWTH. Demography-the
scientific study of human populations. Demography
examines characteristics of human populations
attempts to explain how these populations change
over time.
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Birth rates, death rates, age structure of a
population help predict why some countries have
high growth rates why others grow more
slowly. DEMOGRAPHIC TRANSITION- change in a
population from high birth rate death rates to
low birth death rates.
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The demographic transition is complete when the
birthrate falls to meet the death rate
population growth stops. This has happened only
in a few countries.
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AGE STRUCTURE Population growth depends on how
many people of different ages makes up a
population. AGE-STRUCTURE DIAGRAMS- population
profiles which graph the s of people in
different age groups in the population.
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See figure 5-13.Page 131
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Future Population Growth Page 132 Independent
student reading! END OF CHAPTER 5 NOTES!