Download 5-1 How Populations Grow

How Populations Grow
3 important characteristics of a
population
1. Its geographic distribution
2. Its density
3. Its growth rate
Geographic distribution
 Is the area inhabited by a population.
 This can vary in size
- A few cm for bacteria living on a rotting apple
- Millions of kilometers for a population of
whales.
Population Density
 The number of individuals per unit area.
http://2fm9xz2drvqemrbu.zippykid.netdna-cdn.com/wp-content/uploads/2012/10/population-density.jpg
3 factors that affect population size
1. # births
2. # deaths
3. # of migrations (entering or leaving)

A population will increase or decrease in
size depending on how many individuals are
added or removed from it.
Population Growth
 Birth rate > death rate = Growth
 Birth rate < death rate = Pop shrinks
 Birth rate = death rate = Pop stays the same
 Immigration- the movement of individuals into
an area.
 Emigration- the movement of individuals out
of a population.
Exponential Growth
 Occurs when the individuals in a pop
reproduce at a constant rate.
- At 1st the growth is slow
- Over time the growth increases at a faster
rate.
- Under ideal conditions with unlimited
resources, a pop will grow exponentially.
Rabbit Population
140000
Rabbit
population
after 10
years
shows
exponential
growth
120000
# Rabbits
100000
80000
60000
40000
20000
0
1
2
3
4
5
6
Time in years
7
8
9
10
Series1
Series2
Looking back
 Look at your graph from the deer population
activity.
 At which point did the deer, lion, and resource
populations grow exponentially?
Logistic Growth
(S shaped curve)
 Occurs when a pop’s growth slows (or
stops growing exponentially)
-As resources become less available, the
growth of population slows or stops.
Fruit Flies
350
300
# of fruit flies
250
200
Rabbit
150
100
50
0
0
10
20
30
Generations
40
50
Looking back
 Look at your graph from the deer population
activity.
 At which point did the deer, lion, and resource
populations show logistic growth?
Carrying Capacity
 This is the largest # of individuals an
environment can support.
 This is where the growth levels off
 When the carrying capacity is reached
the growth rate is zero.
Looking back
 Look at your graph from the deer population
activity.
 At which point did the deer, lion, and resource
populations reach carrying capacity?
Biotic Factors
 Biotic factors are the biological
influences on organisms within an
ecosystem.
 These are living influences, such as
prey, predators, producers, and
other cohabitating organisms.
Density-dependent factors
 Factors that influence the growth rate of a
population
 Density of the population matters
 Usually biotic factors
 Examples: predation, disease, food
availability, migration, & parasitism
Abiotic Factors
 Abiotic factors are physical
nonliving factors that shape an
ecosystem.
 Ex. Climate (temperature,
precipitation), sunlight, wind,
limiting nutrients, etc.
Density-independent factors
 Any factor limiting the size of a population
whose effect is not dependent on the number
of individuals in the population
 Usually abiotic factors
 Examples: natural disasters, climate,
precipitation
A Habitat
 A habitat is the area where an organism
lives.
 A habitat includes both the biotic, and
abiotic factors.
 Together biotic and abiotic factors
determine the survival of both an
organism and the productivity of the
organism’s ecosystem.
Community Interactions
1. Competition
2. Predation
3. Symbiosis
a.
b.
c.
Mutualism
Commensalism
Parasitism
Competition
 Competition occurs when two
organism (of the same or diff
species) attempt to use a resource
in the same space at the same
time.
 A resource is any life necessity.
(food, water, light, shelter, etc.)
Competitive Expulsion Principle
(CEP)
 CEP states that no 2 species can
occupy the same niche in the same
habitat at the same time.
Predation
 Predation is when one organism
captures and feeds on another
organism.
 The organism that does the killing
is called the predator.
 The organism that gets killed is
called the prey.
Symbiosis
 Symbiosis is any relationship in which
2 species live closely together.
 There are 3 main types of symbiosis.
1. Mutualism- both species benefit from
the relationship.
2. Commensalism- One organism is
helped by the relationship, the other, is
neither helped nor harmed.
3. Parasitism- One organism lives on or
inside another organism, and harms it.
• The parasite receives all or part of its
nutrition from the host organism.
• The host is weakened, but not usually
killed. Ex. tapeworm