Transcript Chapter 14 “Populations”

Chapter 14
“Populations”


14.1 “Populations and How They
Grow”
Objective:
– Describe the different ways that
populations may change.
Populations
A
group of
organisms of
a single
species that
live in a
given area.
Changes in Population Size
 In
nature populations
will stay relatively the
same in number.
 HOWEVER, sometimes
those numbers will
change dramatically.
Growth Rate
A
change in population
size. (+ or -)
 Depends on how many
organisms are added and
removed (immigration &
emigration).
 AND
interaction between
organisms.
Why do Populations Grow?
 Ideal
conditions
(adequate food supply,
shelter, protection from
predators) = growth.
 Birth
rates are higher
than death rates.
Mexican Population Growth
Baby Boom
 If
ideal conditions
continue, the larger the
population gets, the faster
it grows.
 Exponential Growth =
constant growth that takes
place under ideal
conditions.
Exponential Growth in Bacteria
Growth with Limits
 In
nature, exponential
growth does not
continue forever.
 Growth slows down
because resources are
limited.
Growth with Limits
Carrying Capacity
Growth Limits continued...

Zero Population Growth
– birth rate and death rate are the
same
– population stays the same =
steady-state

Carrying Capacity
– the largest # of individuals of a
population that a given
environment can support
Boom & Bust
 In
nature species
increase in # until they
reach their carrying
capacity.
 Some however reach a
“boom” and then crash
in size “the bust”.
Boom and Bust
14.2 “Why Populations Stop
Growing”
 Objective:
–Identify the factors that
control population
growth in nature.
Population Growth
 Limited
by the size and
density of a population.
 Population Density = the # of
organisms in a given area.
 Limiting Factor = a factor that
causes a population to
decrease.
Density-Dependent Limiting
Factors


Depends on population size, affects
large & dense pops more.
Include:
– Competition
– Predation
– Parasitism
– Disease
– Crowding & Stress
Competition
 When
populations become
too crowded, organisms will
compete for resources.
 Can occur between different
species = evolutionary
change.
 Increases death rates.
Predation
 Predator-Prey
relationship
controls populations.
 Defenses for both predator
& prey.
Predator Prey Graph
Parasitism
 Range
in size from
microscopic (bacteria)
to tapeworms (30+ cm).
 Like predators, parasites
take nourishment at the
expense of their hosts.
 Host-specific.
Parasites – tapeworm
Crowding and Stress
 Most
organisms need a
certain amount of space.
 Overcrowding causes
disturbances among
organisms leading to
weakening.
Density-Independent Limiting
Factors
 Affects
populations
regardless of size.
 Some examples include:
unusual weather
 seasonal cycles
 human activities:
–damming rivers
–clear-cutting forests

Clear Cut Forest