Transcript species a
Lion Zebra Species Interactions Tapeworm Finch Dandelion Gentian Oak Gypsy moth Cactus Shark Remora
Types of Interactions Between Organisms 0 + - 0 + - - (Competition) 0 – (Amensalism) + - (Predation Parasitism Herbivory) - 0 (Amensalism) 0 0 - + (Predation Parasitism Herbivory) 0 + (Commensalsim) + 0 (Commensalsim) + + (Mutualism)
I. The Niche
• Each niche is occupied by only one species.
• Joseph Grinnell (1917) • Charles Elton (1927) • G. Evelyn Hutchinson (1957)
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 –
n th dimensional hypervolume
Hutchison’s n-dimensional hypervolume
• Fundamental Niche
Niche
• Realized Niche
Niche Breadth
The concept of niche breadth can then be employed to exam niche overlap
• Fundamental vs Realized Niche • Which one is greater for each species?
• Is interspecific competition occurring?
• Who wins?
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
Types of Competition
• Interference Competition (contest) • Diffuse Competition
Competition
• Intraspecific – Between individuals of the same species • Interspecific – Between individuals of different species
Competitive Exclusion
Gause’s Competitive Exclusion Principle Experiments with
Paramecium
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 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”
Niche partitioning Robert MacArthur - warbler study
IV. Effects of Competition
Character 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
Population size in the presence of intra specific competiton
dN
1
dt
r
1
N
1
K
1
N
1
K
1 for species 1
dN
2
dt
r
2
N
2
K
2
K
2
N
2 for species 2 How do we incorporate inter specific competiton?
Lotka-Volterra Model of Competition
Population size in the presence of intra specific competiton
dN
1
dt
r
1
N
1
K
1
K
1
N
1 for species 1
dN
2
dt
r
2
N
2
K
2
K
2
N
2 for species 2 How do in incorporate inter specific competiton?
We need to convert one species into the equivalent of another – add competition coefficients , α
dN
1
dt
r
1
N
1
K
1
N
1
K
1 12
N
2 for species 1
dN
2
dt
r
2
N
2
K
2
N
2
K
2 21
N
1 for species 2
What would be the outcome of competition based on the Model?
• Does one species have to win?
Lotka-Volterra Model of Competition
Population size in the presence of intra specific competiton
dN
1
dt
r
1
N
1
K
1
K
1
N
1 for species 1 Intraspecific competition
dN
2
dt
r
2
N
2
K
2
K
2
N
2 for species 2 How do in incorporate inter specific competiton?
We need to convert one species into the equivalent of another
dN
1
dt
r
1
N
1
K
1
N
1
K
1 12
N
2 for species 1 Interspecific
dN
2
dt
r
2
N
2
K
2
N
2
K
2 21
N
1 competition for species 2
Competition
dN
1
dt dN
2
dt
r
1
N
1
K
1
r
2
N
2
K
2
N
1
K
1 12
N
2
N
2
K
2 21
N
1 • Lotka-Voltera Interspecific competiton – Convert individuals of species 1 into species 2 equivalents.
-α 12 Amount of spp.1’s niche overlapped 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
dN
1
dt dN
2
dt
r
1
N
1
K
1
N
1
K
1 12
N
2 0
r
2
N
2
K
2
N
2
K
2 21
N
1 0
N N
2 1
K
1
K
2 12
N
2 21
N
1 • 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
K 2 N 2 K 1 / α 12 K 1 / α 12 N 1 K 2 N 2
Competition
• Isoclines don’t cross?
– One species excludes the other K 1 K 2 / α 21 • Isoclines cross?
– Coexistence possible Pp 331-332 N 1 K 1 K 2 / α 21
Competition
• * = all sp 1, no sp 2 • ** = all sp 2, no sp 1 • What happens to species 1 in the presence of species 2?
K 1 / α 12
**
N 2 dN 1 /dt =0 N 1
*
K 1
Competition
• What happens to species 2 in the presence of species 1?
K 2 N 2 N 1 dN 2 /dt =0 K 2 / α 21
K 1 / α 12 K 2
Competition
K 2 K 1 / α 12 N 2 N 1 K 2 / α 21 Species 1 wins K 1 N 2 N 1 K Species 2 wins 1 K 2 / α 21
K 1 / α 12 K 2 Isocline Analysis Species 1 wins Species 2 wins K 2 K 1 / α 12 N 2 N 2 N 1 K 2 / α 21 K 1 • Sp. 1 isocline above • Sp. 2 most vulnerable to interspecific competition N 1 K 1 K 2 • Sp. 2 isocline above • Sp. 1 most vulnerable to interspecific competition / α 21
K 2 Isocline Analysis Unstable Coexistence K 2 K 1 / N 2 α 12 N 2 K 1 / α 12 K 2 / α 21 N 1 K 1 • K 1 and K 2 outside • Inter > Intra for both species N 1 K 2 / α 21 K 1
Isocline Analysis K 1 / α 12 Stable Coexistence K 1 / α 12 K 2 N 2 K 2 N 2 N 1 K 1 K 2 / α 21 •K 1 and K 2 inside •Intra > Inter for both species N 1 K 1 K 2 / α Intraspecific competition > interspecific competition 21
What would be the outcome of competition based on the Model?
• Species 1 wins • Species 2 wins • Both species win • We don’t know who is going to win, but one species goes extinct