Post on 16-Dec-2015
Types of Interactions Between Organisms
- 0 +
- - - (Competition)
- 0 (Amensalism)
- + (Predation Parasitism Herbivory)
0 0 – (Amensalism)
0 0 0 + (Commensalsim)
+ + - (Predation
Parasitism Herbivory)
+ 0 (Commensalsim)
+ + (Mutualism)
I. The Niche
• Each niche is occupied by only one species.
• Joseph Grinnell (1917)
• Charles Elton (1927)
• G. Evelyn Hutchinson (1957)
Hutchinsonian Niche
• We can continue to include resources until we have all possible resources
• The niche is described as an – nth dimensional
hypervolume
• Fundamental vs Realized Niche
• Which one is greater for each species?
• Is interspecific competition occurring?
• Who wins?
Competition
• Intraspecific– Between individuals of
the same species
• Interspecific– Between individuals of
different species
III. How does one obtain evidence of competition?
• Experimental studies– J.H. Connell 1961 - barnacles
IV. Effects of CompetitionNiche Shifting
One species shifts its niche.
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
Lack – “Ghost of competition past”
IV. Effects of CompetitionCharacter Displacement
a morphological (or physiological) change in areas of sympatry
We are assuming that competition for a resource is the only thing which effects this character
Character Displacement
Beak size in Darwin’s finches from the Galapagos Islands. Beak sizes given for Geospiza fortis and G. fuliginosa on islands where these two species occur together (upper three sets of islands) and alone (lower two islands). Geospiza magnirostris is a large finch that occurs on some islands.
Lotka-Volterra Model of Competition
2 speciesfor
1 speciesfor
2
2222
2
1
1111
1
K
NKNr
dt
dN
K
NKNr
dt
dN
Population size in the presence of intraspecific competiton
How do we incorporate interspecific competiton?
Lotka-Volterra Model of Competition
2 speciesfor
1 speciesfor
2
2222
2
1
1111
1
K
NKNr
dt
dN
K
NKNr
dt
dN
dN1dt
r1N1K1N1 12N2
K1
for species 1
dN2dt
r2N2K2N2 21N1
K2
for species 2
Population size in the presence of intraspecific competiton
How do in incorporate interspecific competiton?
We need to convert one species into the equivalent of another – add competition coefficients, α
Lotka-Volterra Model of Competition
dN1dt
r1N1K1 N1
K1
for species 1
dN2dt
r2N2K2 N2
K2
for species 2
dN1dt
r1N1K1 N1 12N2
K1
for species 1
dN2dt
r2N2K2 N2 21N1
K2
for species 2
Population size in the presence of intraspecific competiton
How do in incorporate interspecific competiton?
We need to convert one species into the equivalent of another
Intraspecific competition
Interspecific competition
Competition
dN1
dtr1N1
K1 N1 12N2
K1
dN2
dtr2N2
K2 N2 21N1
K2
• Lotka-Voltera Interspecific competiton– Convert individuals of species 1
into species 2 equivalents.
-α12 Amount of spp.1’s nicheoverlapped by spp 2’s niche, > or < 1
- α 21 Amount of spp.2’s niche overlapped by spp 1’s niche, > or < 1
Competition – Isocline Analysis
0
0
2
1212222
2
1
2121111
1
K
NNKNr
dt
dN
K
NNKNr
dt
dN
• 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
12122
21211
NKN
NKN
Competition
K1/α12
K2
N2
K2/α21K1N1
• Isoclines don’t cross?– One species
excludes the other
K1/α12
K2
N2
K2/α21K1N1
• Isoclines cross?– Coexistence
possible
Pp 331-332
Competition
• * = all sp 1, no sp 2• ** = all sp 2, no sp 1• What happens to
species 1 in the presence of species 2?
K1N1
N2
K1/α12
dN1/dt =0
**
*
Isocline Analysis
N2
N1K1
K2
N2
N1K1
K2
Species 1 wins Species 2 wins
• Sp. 1 isocline above
• Sp. 2 most vulnerable to interspecific competition
• Sp. 2 isocline above
• Sp. 1 most vulnerable to interspecific competition
K2/α21K2/α21
K1/α12
K1/α12
Isocline Analysis
N2
N1K1
K2
Unstable Coexistence
• K1 and K2 outside
• Inter > Intra for both species
K2/α21
K1/α12
N2
K2
K2/α21 K1N1
K1/α12
Isocline Analysis
K2/α21
N2
N1K1
K2
Stable Coexistence
•K1 and K2 inside
•Intra > Inter for both species
K1/α12K1/α12
K2
N2
K2/α21K1N1
Intraspecific competition > interspecific competition