Transcript Factors Affecting Population Numbers

Factors Affecting
Population Numbers
Carrying capacity: the largest population of
a species that an environment can support.
• 4 factors that determine the carrying capacity:
1. materials and energy (energy, water, carbon, and
other essential nutrients
2. food chains: the population size is limited by the size
of the populations at lower trophic levels. (Prey are
limited by their predators and their food supply).
3. competition: each organism has the same need as
any other. They compete for resources such as
food, water, mates, space.
4. density: depending on their size, environment and
way of life, different species have different needs for
space.
Competition:
Two types of competition:
1. intraspecific: among
members of the
same species
2. interspecific: between
different species
Density:
• Two types of density factors can limit population sizes.
1. density-dependent factors: these are factors that increase as the
population gets bigger and then eventually lead to a decrease in the
population size by increasing death rate and lowering birth rate.
* overcrowding
*parasites/disease
*aggression amongst members
* neglect of offspring
• 2. density-independent factors:
can limit a population regardless of its original
size.
* forest fire
* flood
* volcano
Population Growth
• Since all organisms
reproduce, populations
tend to grow over time
• If unlimited resources are
present, growth will be
exponential
• It will increase very quickly
for rapidly reproducing
organisms and more slowly
for slowly reproducing ones
• The curve will be a “J”
curve or an exponential
growth curve
Generation
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
# of bacteria
1
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
16,384
32,768
65,536
131,072
262,144
524,288
1,048,576
2,097,152
4,194,304
8,388,608
16,777,216
time
0
15min
30min
45min
1hr
75min
90min
105min
2hrs
3hrs
4hrs
5hrs
6hrs
Population Growth 2
• Resources are never
unlimited in real life!
• As population rises,
resources decline.
• If the growth is too rapid,
resources are rapidly
depleted and a population
crash can occur
• This pattern occurs often
with many populations
(including humans)
Gypsy moth caterpillar
Population Growth 3
• More often what happens
is that the resources
slowly decrease, the
growth rate slowly
decreases, and they
meet.
• This results in an S shaped curve
• This sustainable
population number that
they keep returning to is
the carrying capacity of
the environment for that
particular organism
Predator Prey Populations
• Predator Prey
Populations means
that the two
populations are
linked- a change in
one population
causes a change
in the other
population.
The Rabbit - Wolf Example
• Year 1- 3000 rabbit and 5 wolves- the wolves have lots
of food so majority of their offspring survive
• Year 2- 2000 rabbits and 15 wolves- many rabbits were
eaten by the wolves and more young wolves survive.
(This is the closest we get to a perfect system- wolves
are fed and keeping the rabbit population in check.)
• Year 3- 2000 rabbits and 25 wolves- not enough rabbits
to feed the wolves. Rabbit population continues to drop
and wolves begin to starve. Wolf population also drops.
• Year 4- Rabbit population begins to recover.
• Year 5- Whole process repeats again.
Rabbit - Wolf Populations
As the population of rabbits grows, so does the population of wolves, until
there are so many wolves that they overeat the rabbits, whereupon the
wolf population begins to diminish. But once the wolf population
diminishes, the rabbit population is able to begin growing again, and of
course as it does so does the wolf population, in a cycle that never ends.
Human Growth Patterns
What are the causes of the rapid growth of human populations?
What are some possible consequences of this growth pattern?
What will our future look like? (Remember the Reindeer?)
Succession…
Changes in the structure of a
community of organisms; the
replacement of existing species by
more recently arriving species.
Before
After
Primary Succession :
After a major disturbance such as an ice
age, the rocks are bare, there isn’t even
soil, so it is with great difficultly that the
plants return and re-establish themselves.
Pioneer species: the
organisms that come
first…they will establish
themselves on bare rock
and start to change the
ecosystem!
Secondary Succession…
• This type of succession begins after a
disturbance which doesn’t remove all of
the vegetation. (Not down to the bare
rocks)
Examples:
forest fires
deforestation
construction
volcanos