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Population Ecology I. Attributes II.Distribution III. Population Growth – changes in size through time IV. Species Interactions V. Dynamics of Consumer-Resource Interactions VI. Competition

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VI. COMPETITION A. Empirical Tests of Competition 1. Gause P. aurelia vs. P. caudatum P. aurelia outcompetes P. caudatum.

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VI. COMPETITION A. Empirical Tests of Competition 1. Gause P. aurelia vs. P. bursaria ):

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VI. COMPETITION A. Empirical Tests of Competition 1. Gause P. aurelia vs. P. bursaria: coexistence ):

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VI. COMPETITION A. Empirical Tests of Competition 1. Gause 2. Park ): Tribolium castaneum Competition between two species of flour beetle: Tribolium castaneum and T. confusum. TEMPHUM T. casteum won (%) T. confusum won (%) COOLdry COOLmoist WARMdry WARMmoist HOTdry HOTmoist

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VI. COMPETITION A. Empirical Tests of Competition 1. Gause 2. Park ): TEMPHUM T. casteum won (%) T. confusum won (%) COOLdry COOLmoist WARMdry WARMmoist HOTdry HOTmoist Competitive outcomes are dependent on complex environmental conditions Basically, T. confusum wins when it's dry, regardless of temp.

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VI. COMPETITION A. Empirical Tests of Competition 1. Gause 2. Park ): TEMPHUM T. casteum won (%) T. confusum won (%) COOLdry COOLmoist WARMdry WARMmoist HOTdry HOTmoist Competitive outcomes are dependent on complex environmental conditions But when it's moist, outcome depends on temperature

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VI. COMPETITION A. Empirical Tests of Competition 1. Gause 2. Park 3. Connell ): Intertidal organisms show a zonation pattern... those that can tolerate more desiccation occur higher in the intertidal.

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3. Connell - reciprocal transplant experiments ): Fundamental Niches defined by physiological tolerances increasing desiccation stress

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3. Connell - reciprocal transplant experiments ): Realized Niches defined by competition Balanus competitively excludes Chthamalus from the "best" habitat, and limits it to more stressful habitat

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VI. COMPETITION B. Modeling Competition 1. Intraspecific competition

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition The effect of 10 individuals of species 2 on species 1, in terms of 1, requires a "conversion term" called a competition coefficient (α).

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition We can create an "isocline" that described the effect of species 2 on the abundance of species 1 across all abundances of species 2. For example, as we just showed, 10 individuals of species 2 reduces species 1 by 20 individuals, so species 1 will equilibrate at N1 = 60.

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition and when N2 = 20 (exerting a competitive effect equal to 40 N1 individuals), then N1 will equilibrate at N1 = 40.

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition And, when species 2 reaches an abundance of 40 (N2 = K 1 /α 12 ) it drives species 1 from the environment (competitive exclusion). In this case, species 1 equilibrates at N1 = 0. So, this line describes the density at which N1 will equilibrate given a particular number of N2 competitors in the environment. This is the isocline describing dN/dt = 0.

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition Generalized isocline for species 1.

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition And for two competing species, describing their effects on one another.

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition Now, if we put these isocline together, we can describe the possible outcomes of pairwise competition. If the isoclines align like this, then species 1 always wins.We hit species 2's isocline first, and then as abundances increase, species 2 must decline while species 1 can continue to increase. Eventually, species 2 will be driven to extinction and species 1 will increase to its carrying capacity.

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition Now, if we put these isocline together, we can describe the possible outcomes of pairwise competition. If the isoclines align like this, then species 2 always wins. We hit species 1's isocline first, and then as abundances increase, species 1 must decline while species 1 can continue to increase. Eventually, species 1 will be driven to extinction and species 2 will increase to its carrying capacity.

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition Now, if we put these isocline together, we can describe the possible outcomes of pairwise competition. The effects are more interesting if the isoclines cross. There is now a point of intersection, where BOTH populations have a non- zero equilibrium. This is competitive coexistence. And it is stable - a departure from this point drives the dynamics back to this point. Essentially, each species reaches it's own carrying capacity before it can reach a density at which it would exclude the other species.

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VI. COMPETITION B. Modeling Competition 2. Interspecific competition Now, if we put these isocline together, we can describe the possible outcomes of pairwise competition. Here the isocline cross, too. But each species reaches a density at which it would exclude the other species before it reaches its own carrying capacity. So, although an equilibrium is possible (intersection), it is unstable... any deviation will result in the eventual exclusion of one species or the other.

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