Download Understanding Populations

Objective
 Explain
how population sizes are
regulated.
Key Terms
Population
Dispersion
Growth rate
Reproductive potential
Carrying capacity
What Is a Population?

Group of organisms of the same species



live in the same area
interbreed
Organisms usually breed with members of
their own population.
Populations
 “Population”
refers to the group as a
whole or the size - number of individuals
(members) in the group.
Populations
 Population
Density - number of
members that live in a specific area.
Populations
 Dispersion
distribution of
organisms in a
population



Clumped
Uniform
Random
Growth Rate
 Population
change over time can be
represented by:
Growth Rate
 Changes
when birth rates and death
rates increase or decrease.
 Can be positive, negative, or zero.
Growth Rate
 Positive
– average number of
births > average number of
deaths
 Negative - average number of
births < average number of
deaths
 Zero - average number of
births = average number of
deaths
Growth Rate
 Population
sizes usually stay
the same
 Certain factors control the
sizes of populations (limiting
factors).
•
•
•
•
space
disease
immigration/emigration
predators and parasites
Reproductive Potential
 The
maximum number of offspring a
specific organism can produce.
 Depends upon



fecundity
fertility
gestation
Reproductive Potential
 Increases



when individuals
produce more offspring at a time
reproduce more often
reproduce earlier in life
• shortens generation time – average age of
reproduction
Reproductive Potential
 Small
times


organisms have short generation
can reproduce after few hours/few days
populations grow quickly
Reproductive Potential
 Large
organisms reach reproductive age
after years


have a much lower reproductive potential
populations grow slowly
Exponential Growth
A large number of
individuals is added
to the population
each generation.
 Numbers increase by
a certain factor
(usu. 2).
 Occurs in nature
with plenty of
resources and no
predators.

Limits to Population Growth
 Only
the best adapted members of a
population will survive and reproduce.
 Characteristics of a population may
evolve over time.
Carrying Capacity
 Largest
population an environment can
support at any time.
 Population can increase beyond this
number but cannot stay elevated
Carrying Capacity
Estimated
by average population sizes or
by observing population crashes after a
certain size has been exceeded.
Resource Limits
Resource Limits
 Carrying
capacity is reached when
species consume a resource at the same
rate that the resource is produced.

resource consumption = resource creation
 That
natural resource is called a limiting
resource.



Food
Water
Light
Competition Within a
Population
 Resource
competition
increases as
population
approaches carrying
capacity.
 Competition within a
population is part of
the pressure of
natural selection.
Competition Within a
Population
Members of a species may compete indirectly
for social dominance or for a territory.
 A territory is an area defended by one or
more individuals against other individuals.






space
shelter
food
mates
breeding sites
Population Regulation
 Causes
of death in a population may be
density dependent or density
independent.
Population Regulation

Density dependent
cause of death deaths occur more
quickly in a crowded
population than in a
sparse population.



Limiting factors
Predation
Emigration
Population Regulation
Population Regulation
 Density
independent cause of death –
some of the population can die
regardless of the population’s density.


Severe weather
Natural disasters
Do Now/Objective – separate
paper…Hand In (4 min)
 Do
all living organisms interact in the
same way?
 List the different ways organisms
interact with each other.
Niche
 Ecological



A

role of an organism
where it makes its home
resources it needs to survive
how it interacts with other organisms
niche includes an organism’s habitat.
habitat is an area within an ecosystem.
Niche Map
All organisms use their habitats in a unique way.
Think about your niche (where you fit into your
community) and answer:
• Where do you gather your favorite resources?
• Who do you compete or cooperate with?
• Where do you live and where do you hang out?
• Do you spend certain parts of the day in certain places?
Draw a niche bubble map that shows how your use your
habitat. INCLUDE 4+ interactions and describe
those interactions on your maps.
Key Terms
Niche
Competition
Predation
Parasitism
Mutualism
Comensalism
Symbiosis
Species Interaction
 Five
•
•
•
•
•
main types of interactions:
Competition
Predation
Parasitism
Mutualism
Commensalism
Competition
 Organisms
try to use the same limited
resource
 Members of the same species compete


they require the same resources
they occupy the same niche
Indirect Competition

Species can compete
even if they never
come into direct
contact with each
other.
Adaptations to Competition
 Members
of different species
sometimes compete (niche overlap)

each species use some of the same
resources in a habitat.
Adaptations to Competition
 Law

of Competitive Exclusion
No two species can occupy the same niche
(competing for the same resources) at the
same time indefinitely
Adaptations to Competition
The
niche
species will often divide up the

by area

by time of use
Adaptations to Competition
 Niche
restriction - each species uses
less of the niche than they are capable
of using.

Actual niche may be smaller than potential
niche.
Adaptations to Competition
Predation
 One
species kills and eats the other
species


predator
prey
Predators

Some predators eat
only specific types
of prey.

sizes of both
populations have a
direct relationship
Parasitism

An organism lives in
or on another
organism to feed on
the other organism


parasite
host
Parasitism vs. Predation
 Parasites
depend on their hosts; usually
don’t kill them.
 The host is often weakened or diseased
by the parasite.
Symbiosis
 Relationship
where two different
organisms benefit from each other


Mutualism
Commensalism
Mutualism

Relationship between two species where
both species benefit.
Commensalism
 Relationship
between two organisms
where one organism benefits and the
other is unaffected.
Coevolution
 Can
occur with species in symbiotic
relationships.

species may evolve adaptations that
improve the benefits to each member.
Species Interactions
Interaction
Type
1.
2.
3.
4.
5.
Competition
Species A Species B
(harmed or (harmed or
benefited) benefited)
Harmed
Harmed
Description
Your own
example
Both parties
struggle for a
limited resource
Coyote and kit fox
both hunting
kangaroo rat