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Chap.8 Competition and coexistence

Chap.8 Competition and coexistence. 鄭先祐 生態主張者 Ayo Japalura@hotmail.com. Road Map. Forms of competition: Interspecific and intraspecific Intraspecific competition Common in nature Described by the 3/2 thinning law Interspecific competition Common in nature Outcome affected by

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Chap.8 Competition and coexistence

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  1. Chap.8 Competition and coexistence 鄭先祐 生態主張者 Ayo Japalura@hotmail.com

  2. Road Map • Forms of competition: Interspecific and intraspecific • Intraspecific competition • Common in nature • Described by the 3/2 thinning law • Interspecific competition • Common in nature • Outcome affected by • Physical environment • Other species chap08 Competition and coexistence

  3. Road Map • Competition • Exists among 55-75% of the species • Mechanism: over use of the same resource • Mathematical models, called Lotka-Volterra models, predict four outcomes of competition • One species eliminated • The other species is eliminated • Both species coexist • Either species is eliminated, depending on starting conditions • Competing species can coexist through partitioning of resources chap08 Competition and coexistence

  4. 8.1 Species Interactions • Herbivory, predation, parasitism(Table 8.1) • Positive for one population • Negative for the other population • Batesian mimicry • Mimicry of a non-palatable species by a palatable one • Positive for one population • Negative for the other population • Amensalism • One-sided competition • One species had a negative effect on another, but the reverse is not true. chap08 Competition and coexistence

  5. Species Interactions • Neutralism • Coexistence of noninteracting species • Probably rare • Mutualism and commensalisms • Less common • Symbiotic relationships • Species are intimately associated with one another • Both species may NOT benefit from relationship • Not harmful, as is the case with parasitism • Competition • Negative effect for both species chap08 Competition and coexistence

  6. Summary of biotic interactions chap08 Competition and coexistence

  7. Types of competition • Types of competition • Interspecific • Intraspecific • Characterizing competition • Resource competition • Organisms compete for a limiting resource • Interference competition • Individuals harm one another directly by physical force chap08 Competition and coexistence

  8. Intraspecific competition between members of the same species. Resource competiton: each caterpillar chews as much leaf as it can Interference competition: Each caterpillar physically intimidates the others Interspecific competition between different species. Aphid sucking leaf sap Fig.8.2 the different types of competition in nature Caterpillar chewing leaf chap08 Competition and coexistence

  9. 8.2 Intraspecific competition plants vs. animals • Quantifying competition in plants vs. animals • For plants, expressed as change in biomass • For animals, expressed as change in numbers • Plants can not escape competition • Animals can move away from competition • Yoda (1963) • Quantify competition between plants • Yoda's Law or self-thinning rule; 3/2 power rule chap08 Competition and coexistence

  10. Law or self-thinning • Yoda (1963) (cont.). • Describes the increase in biomass of individual plants as the number of plant competitors decrease. • Log w = -3/2 (log N) + log c • w = mean plant weight • N = plant density • C = constant • w = cN3/2 • Figure 8.3 chap08 Competition and coexistence

  11. 6 10 5 10 Fig. 8.3 Self-thinning in plants . 4 10 3 10 2 10 Mean dry weight per plant, g 1 10 1 -1 10 -2 10 -1 1 2 3 4 5 10 10 10 10 10 10 1 2 Number of plants per m chap08 Competition and coexistence

  12. 8.3 Interspecific competition • Field experiments • Organisms can interact with all other organisms • Natural variations in the abiotic environment is factored in • Laboratory experiments • All important factors can be controlled • Vary important factors systematically chap08 Competition and coexistence

  13. Thomas Park competition experiments • Tribolium castaneum and Tribolium confusum (Figure 8.4a) • Large colonies of beetles can be grown in small containers • Large number of replications • Observed changes in population sizes over two-three years • Waited until one species became extinct • Cultures were infested with a parasite Adelina • T. confusum won 89% of the time • Without the parasite, no clear winner • Microclimate effects (Figure 8.4) chap08 Competition and coexistence

  14. T. confusum generally wins in dry conditions 100 90 80 70 60 Percent wins 50 40 30 20 10 0 Temperate Wet Hot Temperate Dry Cold Hot Cold T. castaneum did better in moist environments T. castaneum T. confusum chap08 Competition and coexistence

  15. 100 90 80 70 60 Perfect wins 50 40 30 20 10 0 bII bIII bIV bII bIII bIV bI bI bII bIII bIV bII bIII bIV bI bI CIII CII CIV CI Genetic strain of beetle Fig. 8.5 Results of competition between different strains of flour beetles. T.castaneum T.confusum chap08 Competition and coexistence

  16. Interspecific competition: Natural systems • Assessing the importance of competition • Remove species A and measure the response of species B • Difficult to do outside of laboratory • Migration problems • Krebs or Cage effect (p.115) • Examples in nature • Parasitic wasps • Figure 8.6 chap08 Competition and coexistence

  17. A. chrysomphalidisplaced by A. lagnanensison oranges 100 (a) Orange County 80 60 40 20 0 No competitive displacement 100 (b) Santa Barbara (mild) A. chrysomphali 80 A. lagnanensis A. melinus 60 Percent of individuals 40 20 0 100 Competitive displacement of A. lagnanensis Fig. 8.6 interspecific competition: replacement of one parasite by another in the orange gwoves of California (c) San Fernando Valley (hot) 80 60 40 20 0 1 2 3 chap08 Competition and coexistence Year

  18. The Frequency of Competition • Joe Connell (1983) • Competition was found in 55% of 215 species surveyed (Figure 8.7) • Effects of number of competing species • Single pairs: competition was almost always reported (90%) • Multiple species, competition was reported in 50% of the studies chap08 Competition and coexistence

  19. 倘若有ABCD四種，其可能的互動有c(4,2)=6個，但實質會有重疊到的互動只有3個，所以可能發生competition的機率是50% (3/6)。 a) AB AC AD BC BD CD AB BC CD B D A C Ant Beetle Mouse Bird Resource utilization Resource supply 倘若只有兩種，互動的可能就只有一個。 b) A C Ant Mouse Fig. 8.7 Resource spectrum, (for example grain size) chap08 Competition and coexistence

  20. Differing opinions - Schoener (1983) • Common flaws of studies • Positive results tend to be more readily • Scientists do not study systems at random - may work in systems where competition is more likely to occur • Failure to reveal the true importance of competition in evolution and ecological time • Most organisms have evolved to escape competition and lack of fitness it may confer • Competition may only occur infrequently and in years where resources are scarce chap08 Competition and coexistence

  21. Freshwater Marine Habitat Terrestrial Vertebrates Invertebrates Taxa Carnivores Herbivores Plants 30 20 10 0 70 60 50 40 Fig. 8.8 Percent competition chap08 Competition and coexistence

  22. Mechanisms of interspecific competition • Consumptive (exploitative) • Preemptive • Overgrowth • Chemical • Territorial • Encounter P.120-121 chap08 Competition and coexistence

  23. Table 6.2 Mechanisms of interspecific competition Consumptive competition is the most common form of competition, occurring in 37.8% of cases. chap08 Competition and coexistence

  24. Amensalism • Asymmetric competition is often called amensalism and may be particularly important in plants, wherein one species might secrete chemicals from its roots which inhibit the growth of other plants that do not secrete such chemicals. • Allelopathy chap08 Competition and coexistence

  25. Differing views of competition • Gurevitch et al. 1992 • Examined on 93 species • Primary producers and carnivores did not show strong effects of competition as did filter feeders and herbivores. (fig. 8.9) • No differences in the effects of competition in terrestrial, freshwater, or marine systems, for plants or carnivores, or in high-productivity versus low-productivity systems. chap08 Competition and coexistence

  26. Fig. 8.9 mean size of the effect of competition on biomass for carnivores, filter feeders, herbivores, and primary producers. chap08 Competition and coexistence

  27. Grime-Tilman debate • Grime 1979 • Competition unimportant for plants in unproductive environments • Tilman 1988 • Competition occurs across all productivity gradients • Gurevitch’s result supports Tilman chap08 Competition and coexistence

  28. 8.5 Modeling Competition • Based on logistic equations for population growth • Growth equations for two populations coexisting independently • For species 1; dN1 /dt = r1N1 [(K1- N1) / K1] • For species 2; dN2 /dt = r2N2 [(K2 - N2) / K2] • r = per capita rate of population growth • N = population size • K = carrying capacity chap08 Competition and coexistence

  29. Modeling Competition • For species 1; dN1 /dt = r1N1 [(K1 - N1 - aN2) / K1] • For species 2; dN2/dt = r2N2 [(K2 - N2 - bN1)/ K2] • a = per capita competitive effect of species 2 on species 1 • b = per capita competitive effect of species 1 on species 2 • dN1/dt = 0: zero-growth isocline • Four possible outcomes (Figure 8.12) chap08 Competition and coexistence

  30. Fig. 8.10 conceptualization of conversion factors a and b chap08 Competition and coexistence

  31. Fig. 8.11 changes in the population size of species 1 when competing with species 2. chap08 Competition and coexistence

  32. Species 1 eliminated Species 2 eliminated N N 2 2 k k 1 2 k > 2 a dN 1 k dN = 0 k 2 1 = 0 dt 2 < k a dt 1 b k dN 1 1 k = 0 a 2 dt dN 1 = 0 dt N N 1 1 0 0 k k k k 1 1 2 2 b b N N 2 2 Either species 1 or species 2 eliminated Both species coexist k 1 k a 2 dN 1 = 0 dt k k 2 1 a dN 1 = 0 dt N N 1 1 0 k k k k 0 1 2 1 2 b b Region of increase of N only 1. 1 2. Region of increase of N only Fig. 8.12 2 3. Region of increase of N and N chap08 Competition and coexistence 1 2

  33. 1.8 (a) K = 13.0 14 1 Pure populations Pure populations 12 10 Alcohol concentration (%) 1.0 8 6 Mixed populations 4 2 0.2 Saccharomyces 10 20 30 40 50 60 70 Volume of yeast, pure populations Volume of yeast Volume of yeast, mixed populations Alcohol concentration, pure populations K = 5.8 Pure populations 2 6 (b) 5 4 Test of equations 3 2 Mixed populations 1 Schizosaccharomyces 140 20 40 60 80 100 120 chap08 Competition and coexistence Time (hr)

  34. Lotka-Volterra 公式的缺陷 • The maximal rate of increase, the competition coefficients, and the carrying capacity are all assumed to be constant • There are no time lags • Field tests of these equations have rarely been performed • Laboratory tests have shown divergence • Figure 8.14 • Mechanisms that drive competition are not specified chap08 Competition and coexistence

  35. N increase 1 K 1/a N increase 2 N and N increase 1 2 K 2 Equilibrium Fig. 8.14 Nonlinear Lotka-Volterra isoclines. N 2 K K 2/b 1 N chap08 Competition and coexistence 1

  36. R star concept • R* - Tilman (1982, 1987) alternative • Need to know the dependence of an organism's growth on the availability of resources • Figure 8.15 chap08 Competition and coexistence

  37. (a) Species A Growth Fig. 8.15 Tilman’s R star concept of competition between two species A and B, based on their resource utilization curves. Growth or loss rate Loss R* 0 10 A Species B (b) Growth Growth or loss rate Initially grows faster than species B Outcompetes species A, as resources become more scarce. Loss 0 R* 10 B Resource level (R) (c) 100 Species A Resource level (R) Species B Population size R* R* B 0 0 Time chap08 Competition and coexistence

  38. 8.6 Coexistence of species • Niche • Grinnell (1918): a subdivision of a habitat that contains an organism's' dietary needs, its temperature, moisture, pH, and other requirements • Elton (1927) and Hutchinson (1958): an organism's role within the community • Gause: two species with similar requirements could not live together in the same place • Hardin (1960): Gause's principle, known as competitive exclusion principle, where direct competitors cannot coexist chap08 Competition and coexistence

  39. Coexistence of species • David Lack: Competition and coexistence in about 40 pairs of birds, mediated by habitat segregation. • Figure 8.16 • Examples of coexistence • Darwin's finches on the Galapagos • Terns on Christmas Island (Ashmole 1968) chap08 Competition and coexistence

  40. Fig. 8.16 Type of separation among 40 species. By habitat 20 Number of species pairs Segregating across different axes 10 No separation By feeding habitat By size By geography By winter range 0 chap08 Competition and coexistence

  41. Resource partitioning • Ranks for resource partitioning • (Schoener 1974) • Macrohabitat (55%) • Food type (40%) • Time of day or year (5%) • Habitat was of most importance in separation species. chap08 Competition and coexistence

  42. Hutchinson (1959) • Seminal paper, "Homage to Santa Rosalia, or why are there so many kinds of animals?" • Examined size differences for • Sympatric species (species occurring together) • Allopatric species (occurring alone) • Table 8.3 • Hutchinson's ratio, 1.3 chap08 Competition and coexistence

  43. chap08 Competition and coexistence

  44. Criticism of Hutchinson • Studies that supported Hutchinson - inappropriate statistics • Further tests showed no differences between species than would occur by chance alone. • Size-ratio differences could have evolved for other reasons • Biological significance cannot always be attached to ratios, particularly to structures not used to gather food. Figure 8.17 chap08 Competition and coexistence

  45. Fig. 8.17 A ratio of 1:1.3 has been found to occur between members of sets of kitchen knives, skillets, musical recorders, and children’s bicycles. chap08 Competition and coexistence

  46. Support of Hutchinson • Figure 8.18 d/w analysis for separation on continuous resource sets • Figure 8.19 • Figure 8.20 • Discontinuous resource distribution • Figure 8.21 • Figure 8.22 chap08 Competition and coexistence

  47. d= distance apart of means. w=standard deviation of resource utilization, d/w= resource separation ratio Resource availability, K d A B C Resource utilization w Resource spectrum (x) Fig. 8.19 Resource partitioning. Three species with similar, normal resource utilization curves utillization curves utilize a resource supply K. chap08 Competition and coexistence

  48. 1 a a a 1 b 2 a b b 1 c Second niche dimension 2 b c c 2 c A B C 1 1 1 2 2 2 A A B C B C Fig. 8.20 First niche dimension chap08 Competition and coexistence

  49. Leaf pairs N 2 50 1 N 1 Distribution of insect A 2 50 20 3 20 50 4 20 Distribution of insect B 5 20 6 20 20 7 Fig. 8.21 8 P.S. = 0 + 0.166 + 0.166 + 0 + 0 + 0 + 0 + 0 = 0.333 chap08 Competition and coexistence

  50. 0.4 Species A 0.3 0.2 Proportion Species B 0.1 0 1 2 3 4 5 6 7 8 Resource set Fig. 8.22 chap08 Competition and coexistence

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