Types of Interactions Between Organisms
-
-
0
+
--
-0
-+
(Amensalism)
(Predation
Parasitism
Herbivory)
(Competition)
0
0–
00
(Commensalsim)
(Amensalism)
+
0+
+-
+0
++
(Predation
Parasitism
Herbivory)
(Commensalsim)
(Mutualism)
I. The Niche
• Each niche is occupied by only one species.
• Joseph Grinnell (1917)
– The niche is a subdivision of habitat.
• Physical location in the environment.
• Charles Elton (1927)
– The "role" of the species in the community.
• The functional role of the species.
• G. Evelyn Hutchinson (1957)
– The range of resources and factors tolerated by an organism
• What does a species need to survive, grow, and reproduce
G.E. Hutchinson (1957)
Uses range of tolerance for each resource
Hutchinsonian Niche
• We can continue to
include resources until
we have all possible
resources
• The niche is described
as an
Niche
• Fundamental Niche
• Realized Niche
Niche Breadth
The concept of niche breadth can then be
employed to exam niche overlap
• Fundamental vs
Realized Niche
NICHE SPACE – No overlap
No competition
SPECIES
A
SPECIES B
LIGHT
NICHE SPACE – Overlap; Species B wins
Region of Overlap
SPECIES
A
SPECIES B
LIGHT
NICHE SPACE – Overlap; Species A wins
Region of Overlap
SPECIES
A
SPECIES B
LIGHT
NICHE SPACE – Complete overlap
Species A wins
SPECIES
A
SPECIES B
LIGHT
• Exploitation Competition
– Use up resources available to other species by intaking
the resources
Types of Competition
• Interference Competition (contest)
– Prevent other organisms from getting
resources by interfering with consumption
• Allelopathy
• Antibiotics
Types of Competition
• Diffuse Competition
– Competition can occur for a variety of
resources from multiple other species
Competition
• Intraspecific
– Between individuals of
the same species
• Interspecific
– Between individuals of
different species
Competitive Exclusion
Gause’s Competitive
Exclusion Principle
Experiments with
Paramecium
No two species with the
same niches can
coexist.
III. How does one obtain evidence of competition?
• Experimental studies
– J.H. Connell 1961 - barnacles
Connell Results: Middle Intertidal
Fundamental vs. Realized Niche
Interspecific Competition
IV. Effects of Competition
Niche Shifting
Niche variable
Niche variable
Observational studies
Manipulation is not
always possible
J.M. Diamond 1975
Inferred competition
resulted in the
distributional
patterns he
observed for dove
species
Niche partitioning
Robert MacArthur
- warbler study
IV. Effects of Competition
Character Displacement
We are assuming that
competition for a
resource is the only
thing which effects this
character
Character
Displacement
Character
Displacement
King, C.M. 1989. in Carnivore behavior, ecology, and evolution
Lotka-Volterra Model of
Competition
Population size in the presence of intraspecific competiton
 K 1  N1 
dN1

 r1 N1 
dt
 K1 
for species 1
 K  N2 
dN 2
 for species 2
 r2 N 2  2
dt
 K2 
How do we incorporate interspecific competiton?
Lotka-Volterra Model of
Competition
Population size in the presence of intraspecific competiton
 K  N1 
dN1

 r1 N1  1
dt
 K1 
for species 1
 K  N2 
dN 2
 for species 2
 r2 N 2  2
dt
 K2 
How do in incorporate interspecific competiton?
We need to convert one
species into the
equivalent of another –
add
 K  N1  12 N 2 
dN1

 r1 N1  1
dt
K1


for species 1
 K  N 2   21 N1 
dN 2
 for species 2
 r2 N 2  2
dt
K2


Lotka-Volterra Model of
Competition
Population size in the presence of intraspecific competiton
K1  N1 
dN1
 r1N1

dt
 K1 
for species 1
Intraspecific competition
K 2  N 2 
dN2
 r2 N 2 
 for species 2
dt
 K 2 
How do in incorporate interspecific competiton?

We need to convert one
species into the
equivalent of another
K1  N1  12 N 2 
dN1
 r1N1

dt
K1


for species 1
Interspecific
competition
K 2  N 2  21N1 
dN2
 r2 N 2 
 for species 2
dt
K2


Competition
K1  N1  12 N 2 
dN1
 r1N1



dt
K1


K2  N 2   21N1 
dN2
 r2 N 2 



dt
K2


• Lotka-Voltera Interspecific
competiton
– Convert individuals of species 1
into species 2 equivalents.
Competition – Isocline Analysis
 K  N1  12 N 2 
dN1
  0
 r1 N1  1
dt
K1


 K  N 2   21 N1 
dN 2
  0
 r2 N 2  2
dt
K2


N1  K1  12 N 2
N 2  K 2   21N1
• Rearrange equations when = 0
• Predict population growth for
the two species will stop
– Graph of these = straight
lines = isoclines = dN/dt = 0
– Zero Growth Isoclines
– Above: Population
decreasing
– Below: Population
increasing
Competition
K2
• Isoclines don’t
cross?
K1/α12
N2
N1
K1 K2/α21
N1
K1
K1/α12
• Isoclines
cross?
K2
N2
K2/α21
*Pp 257-260
Competition
• * = all sp 1, no sp 2
• ** = all sp 2, no sp 1
K1/α12**
dN1/dt =0
N2
N1
*
K1
Competition
K2
N2
dN2/dt =0
N1
K2/α21
Competition
K1/α12
K2
K2
K1/α12
N2
N2
N1
K2/α21
K1
N1
K1
K2/α21
Isocline Analysis
Species 1 wins
K1/α12
Species 2 wins
K2
K1/α12
K2
N2
N2
N1
K2/α21
K1
N1 K1
K2/α21
• Sp. 1 isocline above
• Sp. 2 isocline above
• Sp. 2 most vulnerable to
interspecific competition
• Sp. 1 most vulnerable to
interspecific competition
Isocline Analysis
Unstable Coexistence
K2
K2
N2
K1/α12
K1/α12
N2
K2/α21
N1
K1
N1
K2/α21
K1
Isocline Analysis
Stable Coexistence
K1/α12
K2
K1/α12
K2
N2
N2
N1
K1
K2/α21
N1
K1
K2/α21
What would be the outcome of
competition based on the Model?
• Species 1 wins
– Species 2 goes extinct
• Species 2 wins
– Species 1 goes extinct
• Both species win
– A stable equilibrium is reached
• Neither species goes extinct
• Because the species have a greater competitive effect on themselves
than on each other.
– Intraspecific competition > interspecific competition
• We don’t know who is going to win, but one species goes extinct
– An unstable equilibrium exists
• Either species 1 reaches K1 and species 2 becomes extinct or vice
versa.
• Because both species compete more strongly with individuals of the
other species than they do among themselves.
– Interspecific competition > intraspecific competition