Transcript Ecology Part 2

Population Dynamics
Day 4
Population Characteristics
• Population Density:
– The number of organisms per unit area
• Dispersion:
– The pattern of spacing a population within an area
– 3 main types of dispersion
• Clumped
• Uniform
• Random
– Resource availability
determines dispersion patterns
Population Limiting Factors
1) Density-independent factors
– Factors that limit population size, regardless of
population density.
– usually abiotic
– include natural phenomena
• Ex. drought, flood, fire
extreme temperature,
tornadoes, etc.
Population Limiting Factors (cont.)
2) Density-dependent factors
– Any environmental factor that depends on the
density of the population
– Usually biotic
– For ex.
•
•
•
•
Predation
Disease
Parasites
Competition
Population Limiting Factors (cont.)
3) Population growth rate
– How fast a population grows
– Factors that influence this are:
birthrate)
• Natality (____
death rate)
• Mortality (_____
away from
• Emigration (the number of individuals moving _________
a population)
moving to
• Immigration (the number of individuals _________
a
population)
Break here
Understanding Exponentials
• Put your pens down for a minute & think about
this:
– An employer offers you two equal jobs for one hour
each day for fourteen days.
– The first pays $10 an hour.
– The second pays only 1 cent a hour, but the rate
doubles each hour.
– Which job will you accept?
Understanding Exponentials
Job 1
90
80
70
60
50
40
30
20
10
0
Job 2
Now, how much would
your employer owe you
if you stayed at this job
for another 2 weeks?
Job 2 lags for a long
time before
exponential growth
kicks in!
1
2
3
4
5
What would happen if this
type of growth took place
within a population?
6
7
8
9
10 11 12 13 14
Population Growth Models
1) Exponential growth model
• Also called geometric growth or J-shaped growth.
• First growth phase is slow and called the lag phase
• Second growth phase is rapid and called the exponential
growth phase
• Bacteria can grow at this rate, so why aren’t we up to our
ears in bacterial cells?
Population Growth Models (cont.)
• Limits to exponential growth
– As population density increases, competition
follows as nutrients and resources are used up
– The limit to population size that a particular
environment can support is called carrying capacity
(k)
– When you’re done writing, put your pens down…
What population do you think this is?
So, what do you think is going to
happen to the human population?
• We will probably reach our carrying capacity.
• Our growth rate will start to look like most
organisms, which is the Logistic Growth Model
Carrying Capacity (k)
What letter does this curve
kind of look like?
Population Growth Models (cont.)
2) Logistical growth model
–
–
–
Often called the S-shaped growth curve
Growth slows or stops following exponential growth at the
population’s carrying capacity
Populations stop increasing when:
Birth rate < Death rate
Emigration > Immigration
–
Carrying capacity can be raised or lowered. How?
Ex. 1: Artificial fertilizers have raised
Ex. 2: Decreased habitat can lower k
Community Dynamics
Day 5
Communities
• Review:
– A community is a group of interacting populations
that occupy the same area at the same time.
Limiting Factors of Communities
Any abiotic or biotic factor that restricts the
numbers, reproduction, or distribution of
organisms.
Range of Tolerance
Upper and lower limit of conditions in which an
organism can survive.
Ex. Temperature, Salinity, pH
Ecological Succession
The change in an ecosystem that happens when
one community replaces another as a result of
changing biotic and abiotic factors
Ecological Succession (cont.)
2 types:
10 Primary Succession
20 Secondary Succession
Primary Succession
– In primary succession (10), the community
establishes in an area of exposed rock (no soil)
It occurs very slowly at first
Primary Succession (cont.)
– Pioneer species, or the first organisms to arrive,
are usually lichens or mosses
– They secrete acids that can break down rock,
creating soil.
Primary Succession (cont.)
– Small weedy plants and other organisms become
established.
– As they die, more soil is made
Primary Succession (cont.)
– Animals, water and wind bring seeds that sprout
– Eventually there is enough soil for shrubs and
trees to grow.
Primary Succession (cont.)
– The stable, mature community that eventually
develops from bare rock
is called a climax community.
Secondary (20) Succession
– Disturbances (fire, flood, windstorms) can disrupt
a community.
– After a disturbance,
new species of plants
and animals might
occupy the habitat.
Secondary Succession (cont.)
– Pioneer species in 20 succession are usually plants
that grow in disturbed area.
– Much faster
than 10
succession
Succession End point?
– Cannot be predicted
– Different rates of growth &
human involvement
make it impossible to
know if a true climax
community has been
reached.