Species Interactions Dandelion Gentian Finch Cactus Shark Remora Oak Gypsy moth Lion Zebra Tapeworm

Types of Interactions Between Organisms

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

Niche Fundamental NicheRealized 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 HUMIDITY

NICHE SPACE – Overlap; Species B wins SPECIES A SPECIES B LIGHT HUMIDITY Region of Overlap

SPECIES A SPECIES B LIGHT HUMIDITY Region of Overlap NICHE SPACE – Overlap; Species A wins

NICHE SPACE – Complete overlap Species A wins SPECIES B LIGHT HUMIDITY SPECIES A

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 barnacles

Connell Results: Middle Intertidal Fundamental vs. Realized Niche Interspecific Competition

IV. Effects of Competition Niche Shifting One species shifts its niche. 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”

Robert MacArthur - warbler study Niche partitioning

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 intraspecific competiton How do we incorporate interspecific competiton?

Lotka-Volterra Model of Competition 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

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 intraspecific competiton How do in incorporate interspecific competiton? We need to convert one species into the equivalent of another Intraspecific competition Interspecific competition

Competition 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 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 K 1 / α 12 K2K2 N2N2 K 2 / α 21 K1K1 N1N1 Isoclines don’t cross? –One species excludes the other K 1 / α 12 K2K2 N2N2 K 2 / α 21 K1K1 N1N1 Isoclines cross? –Coexistence possible Pp

Competition * = all sp 1, no sp 2 ** = all sp 2, no sp 1 What happens to species 1 in the presence of species 2? K1K1 N1N1 N2N2 K 1 / α 12 dN 1 /dt =0 ** *

Competition What happens to species 2 in the presence of species 1? K2K2 N1N1 N2N2 K 2 / α 21 dN 2 /dt =0

Competition K2K2 N2N2 K 1 / α 12 K 2 / α 21 K1K1 N1N1 Species 1 wins K2K2 N2N2 K 2 / α 21 K1K1 N1N1 K 1 / α 12 Species 2 wins

Isocline Analysis N2N2 N1N1 K1K1 K2K2 N2N2 N1N1 K1K1 K2K2 Species 1 winsSpecies 2 wins Sp. 1 isocline above Sp. 2 most vulnerable to interspecific competition Sp. 2 isocline above Sp. 1 most vulnerable to interspecific competition K 2 / α 21 K 1 / α 12

Isocline Analysis N2N2 N1N1 K1K1 K2K2 Unstable Coexistence K 1 and K 2 outside Inter > Intra for both species K 2 / α 21 K 1 / α 12 N2N2 K2K2 K 2 / α 21 K1K1 N1N1 K 1 / α 12

Isocline Analysis K 2 / α 21 N2N2 N1N1 K1K1 K2K2 Stable Coexistence K 1 and K 2 inside Intra > Inter for both species K 1 / α 12 K2K2 N2N2 K 2 / α 21 K1K1 N1N1 Intraspecific competition > interspecific competition

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