W09_L19_competitionII

W09_L19_competitionII - Competition II February 19, 2009...

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Unformatted text preview: Competition II February 19, 2009 Today Info on Midterm Finish competition Natural history of competition Early experiments testing outcomes of competition Mathematical models of competition Implications of natural communities BIS 2B - Section B Midterm 2 Monday, February 23rd Notes on Midterm Shorter: 21 Scantron Questions, 4 short answer questions (but only slightly) Content: Natural Selection through Predator Prey interactions (last Friday) No Chapter 55 questions: 10, 21, 22 NOT cumulative Problem set answers will be posted... DO NOT WAIT TO WORK ON THEM. NOTE: I WILL NOT BE in office hours TODAY 5:10 - 6:00 pm If your last name begins with: AL MS TZ go to go to go to Chem 194 Everson 176 Hunt 100 We begin with the fundamentals dN/dt = rN[1-(N/K)] dN/dt = rN[(K-N)/K] The logistic equation intraspecific competition Got mathy wit it Now we allow competitors to influence carrying capacity a12 = K1 N1 - N2 K1 Lotka-Volterra Equation 1 A zero net growth isocline (ZNGI) When K1 = N1 + N2 K1/ dN1/dt = 0 N2 K2 Now for species 2 dN2/dt = 0 When K2 = N2 + N1 N2 N1 K1 N1 K2/ dV/dt = rV - aVP dP/dt = baVP - d P p The dynamics this model predicts Now combine the two 4 options N2 N1 N2 N1 N2 Lotka-Volterra predator prey models N1 N2 N1 Option 1 K1/ K2 N2 dN1/dt = 0 Which species wins? Option 2 K2 K1/ N2 dN2/dt = 0 Which species wins? N1 K2/ K1 N1 K1 K2/ 2 Option 3 K1/ A) Stable? B) Unstable? K2 K1/ N2 dN2/dt = 0 Option 4 dN2/dt = 0 Stable: True or false? N2 K2 N1 K1 K2/ K2/ N1 K1 WHAT DO THESE GRAPHS TELL US? THE TWO POSSIBLE EQUILIBRIUM OUTCOMES: 1). Coexistence. When there is very little competitive overlap: If both Coexistence. aii are << 1 : species very likely to coexist 2) Competitive Exclusion. If aii is >> 1 for either species, one species Exclusion. will usually outcompete the other 3) Competitive Exclusion. If aii = 1, then the outcome will depend on: Exclusion. a) initial abundance, b) K of each species, and c) chance events a relates to how similar species are to one another.... another... Convince yourself: (recall = a12 and =a21) Coexistence among competitors occurs when: 1. Interspecific competition is weak relative to intraspecific competition. competition 2. Species are more self-limiting than selfother-species limiting. other3. When and < 1 . THESE ARE NOT 3 different criteria, they are the saying the same thing using three different sets of words. dN1/dt = r1N1[(K1-N1 - a12N2)/K1] dN2/dt = r2N2[(K2-N2 - a21N1)/K2] http://fisher.forestry.uga.edu/popdyn/LotkaVolterraCompetition.html LIMITING SIMILARITY AND THE NICHE Performance No niche overlap, no interspecific competition, a = 0 Performance Complete niche overlap, strong interspecific competition, a = 1 First, lets (re)define the concept of a niche: moisture predation competition moisture disease Niche axis (e.g., prey size) competition prey size Low niche overlap, weak interspecific competition, a << 1 Performance High niche overlap, strong interspecific competition, a close to, but less than 1 Performance nutrients Fundamental niche: defined by physical conditions under which a species can persist Realized niche: alteration of fundamental niche by species interactions nutrients Performance Lo nutrients Hi Lo Realized niche: species actually occurs over a narrower range of nutrients due to competition from other species nutrients Hi Performance Not enough to grow Too much becomes toxic Performance prey size Complete niche overlap, a > 1 for effect of blue species on the red one prey size 3 Linking the ecology of competition to evolution Performance How might interspecific competition cause the evolution of resource partitioning? Performance Time period 1 prey size Start with 2 species with high niche overlap and assume resource use is genetically controlled prey size Performance Time period 2 prey size How might interspecific competition cause the evolution of resource partitioning? Performance How might interspecific competition cause the evolution of resource partitioning? Performance Start with 2 species with high niche overlap and assume resource use is genetically controlled Start with 2 species with high niche overlap and assume resource use is genetically controlled prey size Individuals of the red species that eat small prey will have reduced fitness relative to those that eat large prey because they experience strong interspecific competition Individuals of the red species that eat large prey will have increased fitness relative to those that eat small prey because they experience weak interspecific competition prey size Individuals of the blue species that eat small prey will have greater fitness relative to those that eat large prey because they experience weak interspecific competition Individuals of the blue species that eat large prey will have reduced fitness relative to those that eat small prey because they experience strong interspecific competition How might interspecific competition cause the evolution of resource partitioning? Performance Start with 2 species with high niche overlap and assume resource use is genetically controlled Nice idea, but does that really work? prey size Individuals of both species that eat prey more like their competitors will have reduced fitness relative to those that eat more different prey because they experience strong interspecific competition Individuals of both species that eat more different prey will have greater fitness relative to those that similar prey because they experience weak interspecific competition Because individuals that eat more differently left more offspring than those that eat more similarly, the mean phenotype has shifted to a lower and higher prey size in the next generation prey size Performance 4 Nice idea, but does that really work? Character displacement is the process of evolution toward niche divergence as a result of interspecific competition. Compare populations living in the same location as another species (sympatry) vs. those living in an area without the other species (allopatry). Geospiza fortis in sympatry SPECIES L W Green heron Cattle egret Snowy egret Black crowned night heron Great egret Great Blue Heron 18 20 24 25 39 46 26 36 41 44 51 72 Geospiza fuliginosa Character displacement in beak size of populations of Galapagos finches The "ghost of competition past"... The following minimum criteria must be met for character displacement to have occurred: 1. 2. 3. 4. 5. 6. Morphological differences between a pair of sympatric species are greater than the difference between allopatric populations of the same species These morphological differences have a genetic basis Variation in the character has a measurable effect on resource use There must be competition for the resource in question and competition must be directly correlated with the character Differences in the character cannot be explained by differences in the resources available to sympatric vs. allopatric populations (habitat differences). Differences must have evolved in place and not be the result of sympatric and allopatric populations arising from different founder stock (founder effects). Galapagos finches - partitioning of food resources is manifested in the evolution of different beak sizes... leading to reduced competition. Lacking a time machine, these have been difficult prove definitively, but ecologists hypothesize this frequently Species packing: adding new species shrinks the niche width of all species. To compensate species often become more specialized, and more efficient at using a narrower range of resources. Is there a limit to the number of species that can be "packed" into an area? If resources are finite (the niche axis can't be expanded), then adding species will increase the competition coefficent between pairs of species, decreasing the likelihood of coexistence Corollary: as you add species, the probability of establishment of new species should decrease: Invasion success should decrease with increasing numbers of resident species, and successful invaders should be those that are most different from established species (least overlap). Few species = Many "empty niches", susceptible to invasion. Resource Performance Islands might be a good place to look for this effect Why islands? High potential for empty niches: ---Low native species richness. ---High endemicity Performance Diet proportion Numerous examples of invasions Many species = Few "empty niches" resistant to invasion. Resource And, we find both examples of species packing (community enrichment) and competitive exclusion 5 BUT, there may be numerous resource axes operating at once.... Species can also coexist a number of other ways due to life history tradeoffs. The niche of an organism includes not only its resource utilization and competition with other species, but its response to environmental conditions, predators, etc. More issues in competition moisture predation competition disease competition nutrients July 2007 6 ...
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This note was uploaded on 10/08/2009 for the course BIS 2 taught by Professor Schwartzandkeen during the Spring '09 term at UC Davis.

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