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Species Interactions

Species Interactions. Lion Zebra. Tapeworm. Dandelion Gentian. Finch Cactus. Oak Gypsy moth. Shark Remora. Types of Interactions Between Organisms. I. The Niche. Each niche is occupied by only one species. Joseph Grinnell (1917) Charles Elton (1927)

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Species Interactions

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

  2. Types of Interactions Between Organisms

  3. I. The Niche • Each niche is occupied by only one species. • Joseph Grinnell (1917) • Charles Elton (1927) • G. Evelyn Hutchinson (1957)

  4. G.E. Hutchinson (1957) Uses range of tolerance for each resource

  5. Hutchinsonian Niche • We can continue to include resources until we have all possible resources • The niche is described as an • nth dimensional hypervolume

  6. Hutchison’s n-dimensional hypervolume

  7. Fundamental Niche Realized Niche Niche

  8. Niche Breadth The concept of niche breadth can then be employed to exam niche overlap

  9. Fundamental vs Realized Niche • Which one is greater for each species? • Is interspecific competition occurring? • Who wins?

  10. NICHE SPACE – No overlap No competition HUMIDITY SPECIES A SPECIES B LIGHT

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

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

  13. NICHE SPACE – Complete overlapSpecies A wins HUMIDITY SPECIES A SPECIES B LIGHT

  14. Exploitation Competition

  15. Types of Competition • Interference Competition (contest) • Diffuse Competition

  16. Competition • Intraspecific • Between individuals of the same species • Interspecific • Between individuals of different species

  17. Competitive Exclusion Gause’s Competitive Exclusion Principle Experiments with Paramecium

  18. III. How does one obtain evidence of competition? • Experimental studies • J.H. Connell 1961 - barnacles

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

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

  21. 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”

  22. Robert MacArthur - warbler study Niche partitioning

  23. 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

  24. 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.

  25. Lotka-Volterra Model of Competition Population size in the presence of intraspecific competiton How do we incorporate interspecific competiton?

  26. 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

  27. What would be the outcome of competition based on the Model? • Does one species have to win?

  28. Lotka-Volterra Model of Competition Population size in the presence of intraspecific competiton Intraspecific competition How do in incorporate interspecific competiton? We need to convert one species into the equivalent of another Interspecific competition

  29. Competition • 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 - α21 Amount of spp.2’s niche overlapped by spp 1’s niche, > or < 1

  30. 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

  31. K1/α12 K2 K2 N2 N2 K1 K1 K2/α21 K2/α21 N1 N1 Competition • Isoclines don’t cross? • One species excludes the other K1/α12 • Isoclines cross? • Coexistence possible Pp 331-332

  32. 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

  33. Competition • What happens to species 2 in the presence of species 1? K2 N2 dN2/dt =0 N1 K2/α21

  34. Competition K1/α12 K2 K2 K1/α12 N2 N2 K1 K2/α21 N1 K1 K2/α21 N1 Species 1 wins Species 2 wins

  35. Isocline Analysis Species 1 wins Species 2 wins K1/α12 K2 K1/α12 K2 N2 N2 K2/α21 K1 K2/α21 K1 N1 N1 • Sp. 1 isocline above • Sp. 2 most vulnerable to interspecific competition • Sp. 2 isocline above • Sp. 1 most vulnerable to interspecific competition

  36. Isocline Analysis Unstable Coexistence K2 K2 N2 K1/α12 K1/α12 N2 K2/α21 K1 N1 K1 K2/α21 N1 • K1 and K2 outside • Inter > Intra for both species

  37. Stable Coexistence K1/α12 K2 N2 K1 N1 • K1 and K2 inside • Intra > Inter for both species Isocline Analysis K1/α12 K2 N2 K2/α21 K1 K2/α21 N1 Intraspecific competition > interspecific competition

  38. 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

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