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Species Interactions: Competition (Ch. 13)
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Competition (Ch. 13) Definition: –Individuals attempt to gain more resource in limiting supply –(-,-) interaction: both participants get less Intraspecific: Within species. Interspecific: Between species.
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Competition Interference Competition: –Individuals interact with each other Resource (Exploitation) Competition: –Individuals interact with resource
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Competition: plants Ex: alfalfa
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Competition: plants Ex: alfalfa Type competition?
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Competition: plants Self-Thinning Rule: Biomass increases, mortality reduces density (size per survivor increases) Note log: log scale intraspecific competition Can plants do Interference?
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Interference competition: plants Allelopathy: Plant makes chemical reduces growth/survival (other plant) Ex, Salvia (sage)
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Animal Competition Plant hoppers (insects: Homoptera) –Tap plant vascular tissue –Experiment: density vs insect performance measure –Type competition?
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Intraspecific competition: animals Wood lice (isopod): Terrestrial crustacean
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Intraspecific competition: animals Study: high density & high mortality –Adding more food: no increase survival –Why?? Hint….
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Intraspecific competition: animals Study: high density & high mortality –Adding more food: no increase survival –Why??
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Interspecific competition Classic experiments: Gause –Demonstrated resource competition with Paramecium caudatum & Paramecium aurelia Q: Why was Gause always in a hurry??
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Paramecia Lab Experiments Grown alone: K determined by intraspecific competition. dN/dt = r max N (1-N/K)
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Paramecia Lab Experiments –Together, P. caudatum declined.
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Flour Beetle Experiments Classic experiments: Tribolium beetles (eat grain) –Park studied T. confusum and T. castaneum
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Flour Beetle Experiments Grown separately… Grown together: interspecific competition
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Field Experiments Connell: barnacles Removal experiment
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Field Experiments No effect Balanus removal upper intertidal
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Competition Between Barnacles Big effect middle intertidal
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Barnacles Chthamalus zonation also involved predation (lower intertidal) Tolerance, competition, predation involved!
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Competition of Small Rodents Brown studied competition: Chihuahuan Desert –Removal experiment
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Competition of Small Rodents Chihuahuan Desert.
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Competition of Small Rodents Chihuahuan Desert. Pocket mouse (Perognathus)
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Competition of Small Rodents Chihuahuan Desert. Grasshopper mouse
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Why does competition occur? Overlap in resource use: niche overlap Niche: Summarizes environmental factors that influence growth, survival, and reproduction.
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Niche (review) Hutchinson defined niche as: –n-dimensional hypervolume n = number environmental factors important to survival and reproduction –Fundamental niche - hypervolume –Realized niche - includes biotic factors (like competition!)
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Niche overlap Gause: Principle of Competitive Exclusion –2 species with identical niches cannot coexist indefinitely (niche overlap important!)
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Mathematical Models Scientific models: –Abstractions/simplifications –Provide insights into nature Example (male) model…
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Lotka Volterra Recall Logistic Growth Equation: –dN/dt=Nr max (1-N/K) –Same as: –dN/dt=Nr max (K-N)/K
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Lotka Volterra (K-N)/K contains effects intraspecific competition K reflects resource availability N reflects resource use
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Lotka Volterra Equations Competition between 2 species. Customize Logistic Growth Eqn. for sp. 1: dN 1 /dt=N 1 r max1 (K 1 -N 1 )/K 1 –dN 1 /dt=rate of change population sp. 1 –N 1 =number sp. 1 individuals –r max1 =intrinsic rate of increase sp. 1 –K 1 =carrying capacity for sp. 1
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Lotka Volterra dN 1 /dt=N 1 r max1 (K 1 -N 1 )/K 1 (K 1 -N 1 )/K 1 includes resource use sp. 1 How subtract resource use sp. 2 from that available to sp. 1? Imagination
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Lotka Volterra Convert resource use individual sp. 2 into sp. 1 units –Make “conversion factor” ( 12 ) –Multiplied by N 2 expresses sp. 2 resource use as sp. 1 individuals 12 N 2 = resources not available to sp. 1 because used by sp. 2 (K 1 -N 1 - 12 N 2 ) expresses total resource availability for sp. 1
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Lotka Volterra Equation: dN 1 /dt=N 1 r max1 (K 1 -N 1 - 12 N 2 )/K 1 Population growth rate species 1 No sp. 2: Logistic Growth Equation for sp. 1 –dN 1 /dt=N 1 r max1 (K 1 -N 1 )/K 1 Lots sp. 2, dN 1 /dt small
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Lotka Volterra dN 1 /dt=N 1 r max1 (K 1 -N 1 - 12 N 2 )/K 1 Alpha: competition coefficient. Expresses effect individual sp. 2 on individual sp. 1 If 12 >1, individual sp. 2 has greater effect than individual sp. 1
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Lotka Volterra Equation for sp. 2: dN 2 /dt=N 2 r max2 (K 2 -N 2 - 21 N 1 )/K 2 Note: 21 and 12 usually not equal: competition asymmetric
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Competition and Niches Interspecific competition should lead to directional selection (reduce niche overlap) Character displacement: shift in species traits
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Character Displacement Compare allopatric (non-overlapping) & sympatric (overlapping) populations
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Character Displacement Ex, Galapagos finches Geospiza fortis & Geospiza fuliginosa
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Character Displacement Shift documented
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Character Displacement Many cases suggested: hard to prove competition cause!
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Competition and Conservation Alien invasive species: may be better competitors
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Competition and Conservation Ex, mud snails: Cerithidea californica (native) vs. Batillaria attramentaria (introduced) “Homeboy” snail Asian invader
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Competition and Conservation Lots of alien snails…. Asian invader
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Competition and Conservation High densities reduce food supply (diatoms)
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Competition and Conservation Alien growth rate high
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Competition and Conservation Population models: competitive exclusion in 55- 70 years Who cares? –Native snail host of 17 species trematodes (mollusk parasites): live only in Cerithidea californica!
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Exploitation: Predation, Herbivory, Parasitism, and Disease (Ch. 14)
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5 main types of interactions among species: Effect on Effect on Type of interaction species A species B Competition - - Predation + - Parasitism + - Commensalism + 0 Mutualism + + Symbioses
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There are several types of exploiters! Exploitation: Interaction that enhances fitness of one while reducing fitness of another (+,-) interaction. Minus to “prey/host” Plus to: –Predators: Kill and consume MANY other organisms –Grazers: Consume MANY, kill FEW or none(Herbivores generally)
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There are several types of exploiters! Plus to: –Parasites: Live in/on ONE or FEW host(s) and reduce host fitness (usually do not kill host) Parasitoid: insect larva that consumes host (usually much smaller than host) Pathogens: induce disease (debilitating condition)
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