Interspecies Competition from Ch. 13

1. Interspecies Competition from Ch. 13

2. Interspecies Competition • Populations of 2+ species: • Compete for common resource w/limited supply (may combine with intraspecific comp.) • Both are affected adversely • Like intraspecific: • Two general competition forms- • exploitation & interference

3. Schoener proposed 6 different Interspecific interactions: • Consumption • Preemption • Overgrowth • Chemical interaction • Territorial • Encounter

4. Schoener interactions (cont.) • Consumption: • based on the utilization of some renewable resources • (eg. Consumption of shared resource by one spec. inhibits another) • Preemption: • based on the occupation of open space • usually sessile organisms • eg. occupation on one organism precludes another • Overgrowth: • one individual grows upon/over another, depriving the other of resource. • eg. oysters, trees….

5. Schoener interactions (cont.) • Chemical interactions: • based on the production of a toxin that acts at a distance after diffusing through the environment. (Allelopathy in plants). • Territorial:the defense of space • Encounter competition: • non-territorial/ chance meetings between individuals cause negative result for one or both • physical harm, • loss of time or energy, or • theft of food. • etc. • eg. Scavengers fighting over carcass, eagle robbing osprey

6. These red slides were not covered in class & are not on the test

7. Lotka Volterra Equations • Predict Four outcomes from: • 2 species competing for common resource • Begin with Logistic equation • Then Modified to account for competitive effect of other species

8. Lotka Volterra Equations • Species 1: • Species 2: • If competition is 0: • Each species would stabilize at K

9. N1 = Number of individuals of species 1 • N2 = Number of individuals of species 2 • r1 = intrinsic rate of increase of species 1 • r2 = intrinsic rate of increase of species 2 • t = time & Key to determining outcome: • K1 = carrying capacity of species 1 • K2 = carrying capacity of species 2 • α = the competition coefficient, the effect of species 2 on species 1 • β = the competition coefficient, the effect of species 1 on species 2

10. Lotka Volterra Equations: Predicted outcomes Four different predicted outcomes: • Species 1 inhibit growth of species 2, while continuing to increase. - Species 2 goes extinct • Species 2 inhibits growth of species 1, while continuing to increase. - Species 1 goes extinct

11. Both species inhibit the growth of each other more than its own growth. • Eventually, one species will win • the loser will go extinct. (Which winner depends on initial pop. Densities) • Each species inhibits its own growth more that each other. - Neither eliminates the other. - Both coexist.

12. Y- axis • pop. Species 2 • X- axis • pop. species 1 • Line represents • population density • at zero growth (K) Zero growth isoclines dN= 0dt

13. Controlled competition experiments • (Eliminates unknown factors) E.G. Next slide

15. Controlled competition experiments • Eliminates unknown factors • G.F. Gause - Looked at competition in two species of Paramecium: P. aurelia and P. caudatum • P. aurelia- Higher r value and can tolerate higher density. Always won in competition with P. caudatum

16. Controlled competition experiments • Park- flour beetles • Winner was dependent on environment

18. Controlled competition experiments • Tilman- two species of diatoms: Asterionella formosa & Synedra ulna. • Synedra was able to maintain growth at lower levels of silica • thus driving Asterionella extinct

19. Af= Asterionella formosa Su= Synedra ulna Si= Silica

20. Competitive Exclusion Principle • “complete competitors” cannot coexist. • Compete competitors: • are two species • live in the same place • have the exact same ecological requirements • constant environmental conditions. • However…

21. Non-resource factors • Environmental factors can limit growth rates in a species aside from resources • Environmental conditions can prevent one species from reaching a critical density. • & can affect which is better competitor

22. 5 species of annual plant: germination vs. temp. & affects on colonization

23. Peter Dye- • African grasslands. • Variation in rainfall led to shift in dominant grass

24. Competition for multiple resources • Unlike controlled experiments natural populations compete on many levels • Groves & Williams • looked at above-ground, below-ground and combined competition in clover & skeleton weed. • species with a lower growth rate was always neg. affected. • Biomass reductions for skeleton weed (clover not affected ): • control 35% reduction 53% red. 69% red.

25. Environmental gradients • Resource & environmental gradients showed: • changes in relative competitive abilities of species along the gradient. • The response of individual species to changes is controlled by the presence of other species

26. Relative performance of 3 thistle sps. under exp. nutrient gradients • in mixed pop.

27. 6 thistle sps. under exp. nutrient gradients • monoculture mixed pop.

29. Competitive Exclusion • Species distribution is determined by • Interspecific competition • Tolerance of environmental conditions

32. Chipmunk Competitive Exclusion • E. slope of Sierra Nevada • 4 species of chipmunk, each in different alt. zone: • Species: Alpine, Lodgepole-pine, Yellow-pine & Least. • Least • can occupy entire range-highly tolerant • limited in elevation due to aggression in sagebrush environment. • When yellow pine sp. is removed • Least moves up-not vice versa • Lodgepole sp. limits elevational movement both neighbors

33. Interspecific CompetitionInfluences Niche of a species • Fundamental niche- • the full range of conditions and resources an organism could use with no interference by other species • i.e. Habitat that can potentially be used. • Realized niche- actual niche used • the portion of the fundamental niche used as a result of interactions with other species

34. Fig. 13-12 Fundamental & Realized niches

35. Realized niche ←Fundamental niche (dashes) Realized niche (shaded)

36. Niche overlap- two (or more) species use a portion of the resources simultaneously • food, habitat, etc. • Competitive release-when a species expands its niche in response to the removal of a competitor • Eg. Least chipmunk when Yellowpine chipmunk removed

37. Competitive Exclusion redefined • “Species which are complete competitors, that is whose niches overlap completely, cannot coexist indefinitely.”

38. Field Studies of Competition • The classic study on competition in the field was done by Joseph Connell (1961) • He studied the distribution of two species of barnacles found in the intertidal zone. • He observed that most intertidal zones show a striking vertical zonation.

40. Field Studies of Competition • For the two species of barnacles of interest, there is a great deal of overlap in the portions of the intertidal where the larval stages settle. • But the adults have a completely non-overlapping distribution.

41. Field Studies of Competition • Balanusoccupies most of the intertidal zone from the high water neap tide to the low water spring tide. • Chthalamusis only found from the high water neap to the high water spring tide zones. • (Higher Desiccating zone)

43. Mean High Spring Tide Mean High Neap Tide Mean Tide Level Mean Low Neap Tide Mean Low Spring Tide

44. Skip to next Red slide

45. Field Studies of Competition What explains this non-overlapping distribution of adults? • Differences in Fundamental Niches? • Interspecific Competition? • Both?

46. Barnacle Competitive Exclusion- reasons • Chthalamus upper limit set by desiccation, lower limit by Balanus • Remove Balanus and and Chthalamus grows • Remove Chthalamus and and Balanus does not invade • Balanus upper limit set set by desiccation, lower by starfish predation • Remove predators and Balanus invades

47. Field Studies of Competition The answer is: Both. • Competition. In all areas below the mean high neap tide zone, Balanusis the superior competitor. It either overgrows or undercuts Chthalamus,eliminating it.

48. Field Studies of Competition • Balanusis unable to survive long w/ drying winds & sun • zone between high neap & high spring tide zones. • The fundamental niche of Balanus does not include that zone.

49. Field Studies of Competition • For Chthalamus, however, the fundamental niche includes the entire intertidal zone. • When exposed to competition with Balanus, however, the realized niche is only the high tide zone between the neap and spring tides.