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Scales of Ecological Organization
Population Dynamics
•Distribution and Abundance
•Relationships between
Populations
Populations
• A population is a group of individuals of
the same species living in the same area.
• Species features are important to their
location
Populations
• Distribution is the area that one or more
members of the same species are found
• Three patterns found: uniform, clumped,
and random.
Random
Uniform
Clumped
Population Growth
• All populations undergo three distinct phases
of their life cycle:
– growth
– stability
– decline
• Growth - when available resources exceed the
number of individuals using them.
Reproduction is rapid, and death rates are low,
producing an increase in population size.
• Population stability is often followed by a
"crash"
• Stability is longest phase
• Decline is the decrease in the number of
individuals in a population can lead to
extinction.
Competition
• The main density-dependent factor
• Compete for resources
• Can be interspecific or intraspecific
Competitive Exclusion Principle
•
Two species cannot occupy the same
niche, in the same place, at the same
time
• If there are 2 species with very similar
requirements there are 2 outcomes:
1. One species out competes the other
2. Species undergo evolution and therefore
occupy different niches.
Factors Influencing Population
Growth
• Nearly all populations will tend to grow
exponentially if resources are available.
• Most populations have the potential to
expand at an exponential rate, since
reproduction is generally a multiplicative
process.
• Two of the most basic factors that affect
the rate of population growth are the birth
rate, and the death rate.
Two modes of population growth.
• The Exponential curve (also known as a J-curve) occurs when
there is no limit to population size.
• The Logistic curve (also known as an S-curve) shows the effect of
a limiting factor (in this case the carrying capacity of the
environment).
Relationships in Communities
between Populations PREDATION
An interaction where an
individual of one species
(predator) eats all or most
of an individual of another
species (prey).
Possible Outcomes of Predation
• 1. Predator population has little effect on
abundance of prey.
• 2. Predator population eradicates prey
population;
• 3. Predator and prey populations coexist.
Prey Population Living Alone
• Assume a constant
rate of increase in
absence of predators.
18
16
16
Number (N)
14
12
10
8
8
6
4
4
2
2
1
0
0
1
2
3
Time (t)
4
5
Predator Population Living
Alone
• Assume a constant
rate of decline in
absence of predators.
18
16
16
Number (N)
14
12
10
8
8
6
4
4
2
2
1
0
0
1
2
3
Time (t)
4
5
A Model Predator/Prey Cycle
Number of Individuals (N)
250
200
150
P re da to r
P re y
100
50
0
0
20
40
60
80
Time (t)
This graph shows a limit cycle of predators and prey.
The Hare & Lynx Predator/Prey
Relationship
• Snowshoe hare and
Canadian lynx show
classic population cycles
with a 10-11 year cycle.
• Hare are herbivores and
feed on twigs under the
snow in winter; lynx feed
primarily on snowshoe
hare.
The Hare/Lynx Cycle
Based on Pelt Sales
Similar data is provided in Figure 53.10 (Freeman, 2005).