Chap 8 Competition and coexistence Ayo Japalurahotmail com

Chap. 8 Competition and coexistence 鄭先祐 生態主張者 Ayo Japalura@hotmail. com chap 08 Competition and coexistence

Road Map 1. Forms of competition: Interspecific and intraspecific 2. Intraspecific competition – Common in nature – Described by the 3/2 thinning law 3. Interspecific competition – Common in nature – Outcome affected by • • Physical environment Other species chap 08 Competition and coexistence 2

4. Competition Road Map – Exists among 55 -75% of the species – Mechanism: over use of the same resource 5. 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 6. Competing species can coexist through partitioning of resources chap 08 Competition and coexistence 3

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. chap 08 Competition and coexistence 4

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 chap 08 Competition and coexistence 5

Summary of biotic interactions chap 08 Competition and coexistence 6

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 chap 08 Competition and coexistence 7

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 chap 08 Competition and coexistence 8

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 chap 08 Competition and coexistence 9

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 = c. N 3/2 – Figure 8. 3 chap 08 Competition and coexistence 10

Mean dry weight per plant, g 10 6 10 5 Fig. 8. 3 Self-thinning in plants. 10 4 10 3 10 2 10 1 1 10 -2 10 -1 1 102 103 104 Number of plants per m 2 chap 08 Competition and coexistence 105 11

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 chap 08 Competition and coexistence 12

Thomas Park competition experiments – Tribolium castaneum and Tribolium confusum (Figure 8. 4 a) – 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) chap 08 Competition and coexistence 13

T. confusum generally wins in dry conditions 100 90 Percent wins 80 70 60 50 40 30 20 10 0 Hot Temperate Cold Hot Temperate Wet T. castaneum T. confusum Cold Dry T. castaneum did better in moist environments chap 08 Competition and coexistence 14

100 90 80 Perfect wins 70 60 50 40 30 20 10 0 b. III b. IV CI b. II b. IV b. III b. IV CII b. II CIII b. IV CIV Genetic strain of beetle Fig. 8. 5 Results of competition between different strains of flour beetles. chap 08 Competition and coexistence T. castaneum T. confusum 15

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 chap 08 Competition and coexistence 16

(a) Orange County 100 A. chrysomphali displaced by A. lagnanensis on oranges 80 60 40 20 (b) Santa Barbara (mild) (c) San Percent of individuals 0 Fernando Valley (hot) 100 No competitive displacement A. chrysomphali A. lagnanensis A. melinus 80 60 40 20 0 100 80 60 40 20 Competitive displacement of A. lagnanensis Fig. 8. 6 interspecific competition: replacement of one parasite by another in the orange gwoves of California 0 1 2 3 chap 08 Competition and coexistence Year 17

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 chap 08 Competition and coexistence 18

• 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)。 Resource utilization b) Resource supply a) A B C D Ant Beetle Mouse Bird AB AC AD BC BD CD 倘若只有兩種，互動的可能就只有一個。 A Ant Fig. 8. 7 AB BC CD C Mouse Resource spectrum, (for example grain size) chap 08 Competition and coexistence 19

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 chap 08 Competition and coexistence 20

Freshwater Marine Habitat Terrestrial Vertebrates Invertebrates Taxa Carnivores Herbivores Plants 70 60 50 40 30 20 10 Percent competition chap 08 Competition and coexistence 0 Fig. 8. 8 21

Mechanisms of interspecific competition 1. Consumptive (exploitative) 2. Preemptive 3. Overgrowth 4. Chemical 5. Territorial 6. Encounter • P. 120 -121 chap 08 Competition and coexistence 22

Table 6. 2 Mechanisms of interspecific competition Consumptive competition is the most common form of competition, occurring in 37. 8% of cases. chap 08 Competition and coexistence 23

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 chap 08 Competition and coexistence 24

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. chap 08 Competition and coexistence 25

Fig. 8. 9 mean size of the effect of competition on biomass for carnivores, filter feeders, herbivores, and primary producers. chap 08 Competition and coexistence 26

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 chap 08 Competition and coexistence 27

8. 5 Modeling Competition • Based on logistic equations for population growth • Growth equations for two populations coexisting independently – For species 1; d. N 1 /dt = r 1 N 1 [(K 1 - N 1) / K 1] – For species 2; d. N 2 /dt = r 2 N 2 [(K 2 - N 2) / K 2] • r = per capita rate of population growth • N = population size • K = carrying capacity chap 08 Competition and coexistence 28

Modeling Competition – For species 1; d. N 1 /dt = r 1 N 1 [(K 1 - N 1 - a. N 2) / K 1] – For species 2; d. N 2/dt = r 2 N 2 [(K 2 - N 2 - b. N 1)/ K 2] • a = per capita competitive effect of species 2 on species 1 • b = per capita competitive effect of species 1 on species 2 • d. N 1 /dt = 0: zero-growth isocline • Four possible outcomes (Figure 8. 12) chap 08 Competition and coexistence 29

Fig. 8. 10 conceptualization of conversion factors a and b chap 08 Competition and coexistence 30

Fig. 8. 11 changes in the population size of species 1 whenchap 08 competing with species 2. Competition and coexistence 31

N 2 k 1 a Species 2 eliminated k 1 >k 2 a k 2 <k 1 d. N 2 =0 dt b k 2 d. N 1 dt 0 N 2 k 2 d. N 1 =0 dt k 1 N 1 0 b Either species 1 or species 2 eliminated N 2 k 1 a k 2 Species 1 eliminated d. N 1 =0 dt a =0 k 1 N 2 k 1 k 2 N 1 b Both species coexist d. N 1 =0 dt 0 1. k 2 k 1 N 1 0 b Region of increase of N 1 only 2. Region of increase of N 2 only 3. Region ofchap 08 increase of N 1 and N 2 Competition and coexistence k 1 k 2 N 1 b Fig. 8. 12 32

1. 8 K 1 = 13. 0 Pure populations 10 1. 0 8 6 Mixed populations 4 2 10 Volume of yeast (b) Saccharomyces 20 30 40 50 60 0. 2 Alcohol concentration (%) (a) 14 12 70 Volume of yeast, pure populations Volume of yeast, mixed populations Alcohol concentration, pure populations 6 Pure populations K 2 = 5. 8 5 4 3 2 1 Mixed populations Test of equations Schizosaccharomyces 20 40 60 80 100 120 140 Time (hr) chap 08 Competition and coexistence 33

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 chap 08 Competition and coexistence 34

N 1 increase K 1/a N 2 increase N 1 and N 2 increase K 2 Equilibrium N 2 K 1 N 1 chap 08 Competition and coexistence • Fig. 8. 14 Nonlinear Lotka. Volterra isoclines. K 2/b 35

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 chap 08 Competition and coexistence 36

• Outcompetes species A, as resources become more scarce. (c) Growth Loss 0 R*A 10 Species B Growth Loss 0 R*B 10 Resource level (R) 100 Population size • Initially grows faster than species B Species A Species B R* 0 Time Resource level (R) (b) Growth or loss rate (a) • Fig. 8. 15 Tilman’s R star concept of competition between two species A and B, based on their resource utilization curves. R*B 0 chap 08 Competition and coexistence 37

8. 6 Coexistence of species • Niche – Grinnell (1918): a subdivision of a habitat that contains an organism's' dietary needs, its temperature, moisture, p. H, 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 chap 08 Competition and coexistence 38

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) chap 08 Competition and coexistence 39

10 chap 08 Competition and coexistence No separation By winter range By size By feeding habitat By geography By habitat Number of species pairs Segregating across different axes 20 • Fig. 8. 16 Type of separation among 40 species. 0 40

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. chap 08 Competition and coexistence 41

• 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 chap 08 Competition and coexistence 42

chap 08 Competition and coexistence 43

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 chap 08 Competition and coexistence 44

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. chap 08 Competition and coexistence 45

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 chap 08 Competition and coexistence 46

• d= distance apart of means. • w=standard deviation of resource utilization, Resource utilization • d/w= resource separation ratio Resource availability, K d A B C w Resource spectrum (x) Fig. 8. 19 Resource partitioning. Three species with similar, normal resource utilization curves utilize a resource supply K. chap 08 Competition and coexistence 47

Second niche dimension a 1 b 1 a a a 2 c 1 b 2 b b c c c 2 A A 1 • Fig. 8. 20 B 1 B C 1 A 2 C B 2 First and niche dimension chap 08 Competition coexistence C 2 48

Leaf pairs N 2 50 1 N 1 2 20 50 3 20 50 4 20 5 20 6 20 7 20 8 Distribution of insect A Distribution of insect B • Fig. 8. 21 P. S. = 0 + 0. 166 + 0 + 0 + 0 = 0. 333 chap 08 Competition and coexistence 49

0. 4 Species A Proportion 0. 3 0. 2 Species B 0. 1 0 1 2 3 4 Resource set 5 chap 08 Competition and coexistence 6 7 • Fig. 8. 22 8 50

Coexistence of Species • Niche overlap between two insect species that feed on a shrub – Measured quantity • • • PS = Spi PS = proportional similarity S = sum of all units, 1 to n, in resource set pi = proportion of least abundant member of pair PS < 0. 70 indicates coexistence for single resource PS > 0. 70 indicates competitive exclusion for single resource chap 08 Competition and coexistence 51

Coexistence of Species • Proportional similarity indices for two or more resources can be combined – Multiply separate PS values to determine overall PS value – Coexistence for two resources – 0. 7 x 0. 7 = 0. 49 or less – chap 08 Competition and coexistence 52

Applied Ecology • Is the release of multiple species of biological control agents beneficial? – Control of pests in agriculture is of paramount importance – Biological control is seen as a preferable alternative to chemical control • Release a variety of enemies against a pest • Observe which enemy does the best job chap 08 Competition and coexistence 53

Biological control • Is this the best strategy? – Intensive competition for the prey leads to lower effectiveness of the biological agents – Greater population establishment rate with fewer enemy species (Figure 1) – Establishment rate of single-species releases were significantly greater than the simultaneous release of two or more species (76% vs. 50%) chap 08 Competition and coexistence 54

v 問題與討論！ Japalura@hotmail. com Ayo 台南站： http: //mail. nutn. edu. tw/~hycheng/ chap 08 Competition and coexistence 55