Download Population Dynamics

Scales of Ecological Organization
Population Dynamics
•Distribution and Abundance
•Relationships between
Populations
Population – group of individuals of the same species
living in the same area, potentially interacting
Community – group of populations of different species
living in the same area, potentially interacting
What are some ecological interactions?
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.
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.
• The size of a population depends on the rates of
birth, death, immigration and emigration
r = (b+i) – (d-e)
• Factors that influence population growth as the
numbers increase are called DENSITY
DEPENDENT eg food supply
• Birth rates and death rates may vary regardless
of population density. Factors which make this
happen are called DENSITY – INDEPENDENT
eg environmental changes
Types of ecological interactions
competition
predation
parasitism
mutualism
commensalism
symbiosis
Competition – two species share a requirement for a
limited resource  reduces fitness of one or both species
Predation – one species feeds on another  enhances
fitness of predator but reduces fitness of prey
herbivory is a form of
predation
Parasitism – one species feeds on another  enhances
fitness of parasite but reduces fitness of host
Mutualism – two species provide resources or services
to each other  enhances fitness of both species
Commensalism – one species receives a benefit from
another species  enhances fitness of one species; no
effect on fitness of the other species
Symbiosis – two species live together  can include
parasitism, mutualism, and commensalism
Organizing ecological interactions
effect on species 1
+
effect on
species 2
+
mutualism
0
commensalism
-
predation
herbivory
parasitism
0
-
commensalism
predation
herbivory
parasitism
competition
competition
competition
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.
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).
Interaction between Populations
can influence population numbersPREDATION
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).
Human Population
•Has been 3 population explosions
–20 000yrs ago due to tools
–6000yrs ago increase in farming
–300yrs ago improvement in medicine etc
• Humans unlike other species populations have created
environmental changes to raise the normal population
carrying ability
• To what extent can the human species can continue to
change the environment to sustain an ever increasing
population?