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Species Interactions Lion Tapeworm Zebra Oak Gypsy moth Dandelion Gentian Finch Cactus Shark Remora 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) • 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 – nth dimensional hypervolume Hutchison’s n-dimensional hypervolume Niche • Fundamental 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 intraspecific competiton K1 N1 dN1 r1 N1 dt K1 for species1 K2 N2 dN2 for species 2 r2 N 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 species1 K N2 dN2 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 competition coefficients, α K1N1 12 N 2 dN1 r1N1 dt K1 for species 1 K 2 N 2 21N1 dN2 r2 N 2 for species 2 dt K2 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 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 K N N dN1 1 1 12 2 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. -α12 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 K N1 12 N 2 dN1 0 r1 N1 1 dt K1 K N 2 21 N1 dN2 0 r2 N 2 2 dt K2 N1 K1 12 N 2 N 2 K 2 21 N1 • 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? N2 K1/α12 N1 K1 K2/α21 K1/α12 K2 N2 – One species excludes the other • Isoclines cross? – Coexistence possible N1 K1 K2/α21 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? K1/α12** dN1/dt =0 N2 N1 * K1 Competition • What happens to species 2 in the presence of species 1? K2 N2 dN2/dt =0 N1 K2/α21 Competition K1/α12 K2 K2 K1/α12 N2 N2 N1 K2/α21 Species 1 wins K1 K1 N1 Species 2 wins 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 • K1 and K2 outside • Inter > Intra for both species N1 K2/α21 K1 Isocline Analysis Stable Coexistence K1/α12 K2 K1/α12 K2 N2 N2 N1 K1 K2/α21 •K1 and K2 inside •Intra > Inter for both species N1 K1 K2/α21 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