bsc201 week09

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Published on January 1, 2008

Author: Justine

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Ecology (BSC 201):  Ecology (BSC 201) Part 2. Steven Juliano Office: 335 FSA Hours: Wed 2:00PM, Thu 10:00AM, & by appointment Phone: 438-2642 sajulia@mail.bio.ilstu.edu Lectures on the web:  Lectures on the web http://www.bio.ilstu.edu/juliano/juliano.htm how to use lectures on the web Reading:  Reading Review chapters 19, 18 Read chapter 17 Competition:  Competition Negative effects of one individual on another: Resource competition: use and depletion of a shared resource Interference competition: direct harm to other individuals direct aggression, attack chemical interactions at population level, with increased N, competition lowers dN / Ndt Competition:  Competition intraspecific competition … among members of 1 species interspecific competition … between members of different species Interspecific competition mutually negative Assumptions of Lotka-Volterra Competition models:  Assumptions of Lotka-Volterra Competition models r1, r2, K1, K2, a, b are constants do not vary over time Effects of competition (inter- & intraspecific) are linear declines in dN / Ndt as N’s increase as opposed to nonlinear Either some resource(s) are limiting or there is interspecific interference Competitive Exclusion Principle:  Competitive Exclusion Principle Competitive Exclusion: local extinction of one species through interspecific competition Two species in continued direct competition cannot coexist unless interspecific competition is weak relative to intraspecific competition Weak interspecific competition? low a or b Use different resources Use different physical spaces Laboratory tests:  Laboratory tests Flour beetles Tribolium confusum & Tribolium castaneum Text pp. 368-369 Protozoans Paramecium aurelia, Paramecium caudatum, Paramecium burseria Interspecific competition: Paramecium:  Interspecific competition: Paramecium George Gause P. caudatum goes extinct Strong competitors, use the same resource (yeast) Competitve asymmetry Competitive exclusion Interspecific competition: Paramecium:  P. caudatum & P. burseria coexist Apparently stable What is different? Interspecific competition: Paramecium Mechanism of coexistence:  Mechanism of coexistence Paramecium caudatum nonphotosynthetic; feeds on yeasts only must be near surface (O2) Paramecium burseria photosynthetic; also feeds on yeasts endosymbiotic algae; photosynthesis; produce O2 can feed in the bottom of the test tube Two species used different resources weak interspecific competition; coexistence End 1st lecture:  End 1st lecture 2nd exam mean = 69.9 SD = 15.2:  2nd exam mean = 69.9 SD = 15.2 Resources:  Resources component of the environment availability increases population growth can be depleted or used up by organisms A resource is limiting if it determines the growth rate of the population Liebig’s law: resource in shortest supply determines growth Resources for 0 growth:  Resources for 0 growth Competition for 1 resource:  Competition for 1 resource Dynamics of competition for 1 resource:  Dynamics of competition for 1 resource Prediction for 2 species competing for 1 resource:  Prediction for 2 species competing for 1 resource The species with the lower R* will eliminate the other in competition Independent of initial numbers Coexistence not possible R* rule Competitive exclusion principle:  Competitive exclusion principle Two species in continued, direct competition for 1 limiting resource cannot coexist Focus on mechanism Coexistence requires 2 independently renewed resources Text: pp. 366-368 Interspecific competition in nature:  Interspecific competition in nature Interspecific competiton may affect distribution and abundance species’ resource use morphology and behavior (evolutionary time) community composition, species co-occurrence community: set of species living in one place at one time and potentially affecting each other Competition among barnacles Competitive exclusion affects distribution & abundance:  Competition among barnacles Competitive exclusion affects distribution & abundance Rocky intertidal zone adult barnacles immobile on rocks larvae settle on rocks from plankton Joseph Connell (1961) Ecology 42:710-723 Distributions of Balanus & Chthamalus:  Distributions of Balanus & Chthamalus Chthamalus & Balanus:  Chthamalus & Balanus Larvae settle throughout much of the intertidal Chthamalus adults only in the high intertidal Balanus adults only in the mid & low intertidal Hypothesis: Balanus excludes Chthamalus Resource? Space Hypothesis: Chthamalus cannot tolerate submergence Hypothesis: Balanus cannot tolerate desiccation Experiments:  Experiments Rocks with larvae and young adults remove Balanus control … count, no removal Rocks with young adults of one species transplant Balanus to high & low intertidal transplant Chthamalus to high & low intertidal Follow fates of marked individuals over years Experimental result #1:  Experimental result #1 Balanus individuals grow rapidly Shell undercuts or crushes adjacent Chthamalus Competition for space; Balanus wins Undercut Crushed End 2nd lecture:  End 2nd lecture Experimental result #2:  Experimental result #2 Chthamalus survives well in the low intertidal only if Balanus is removed With Balanus present, Chthamalus is completely eliminated Distribution of Chthamalus is limited by interspecific competition with Balanus Local competitive exclusion Experimental results #3:  Experimental results #3 Balanus does not survive in the high intertidal, regardless of Chthamalus Desiccation Chthamalus tolerates dry conditions Balanus upper limit set by physical environment Chthamalus has a refuge from competition, a place where it escapes effects of its competitor Barnacles: one example of the role of interspecific competition:  Barnacles: one example of the role of interspecific competition Is interspecific competition common in nature? Is it often severe enough to cause competitive exclusion? How is exclusion avoided? Does competition cause natural selection? Role of interspecific competition:  Role of interspecific competition Competition experiments Remove a species  predict competitor  Add a species  predict competitor  control (no manipulation) Reviews Schoener 1983 Am. Naturalist 122:661-696 Connell 1983 Am. Naturalist 122:240-285 Prevalence of competition:  Prevalence of competition Schoener: 164 studies -- 90% find interspecific competition Connell: 69 studies -- 86% find interspecific competition Does NOT mean ~90% of all species compete Conclusion: When observations lead to the hypothesis of competition, that hypothesis is usually correct Likelihood of exclusion:  Likelihood of exclusion Competitive asymmetry - Competitive exclusion Schoener: 85 studies 60% asymmetrical 12% symmetrical 28% unclear Connell: 54 experiments 61% asymmetrical 39% symmetrical Conclusion: Exclusion should be very common Avoiding competitive exclusion:  Avoiding competitive exclusion Differences in resource use habitats, food, behavior Consider seed eating birds Morphology and resource use related Big bill  big seeds Small bill small seeds Quantitative traits: Resource use:  Quantitative traits: Resource use Selection and competition:  Selection and competition TIME Differences in resource use:  Differences in resource use Low overlap can originate in 2 ways 1) Evolution in response to selection by competition 2) Independent of competition, pre-existing differences enable 2 species to coexist when they meet Resource partitioning: use of different resources by potential competitors; facilitates coexistence Includes both 1) and 2) Character displacement: evolution of morphological differences where two species co-occurr Includes only 1) Morphology & Resource use:  Morphology & Resource use Evidence that species with different morphology: use different resources? compete less intensely? Example: Anolis lizards Insectivorous, arboreal Evidence for resource partitioning Probably not character displacement Caribbean Anolis:  Caribbean Anolis St. Maarten A. gingivinus SVL=41 mm A. wattsi SVL=38 mm Competition experiment A. gingivinus + A. wattsi less food in stomach lower growth rate compared to A. gingivinus alone St. Eustatius A. bimaculatus SVL=53 mm A. wattsi SVL=40 mm Competition experiment A. bimaculatus + A. wattsi same amount in stomach same growth rate compared to A. bimaculatus alone End 3rd lecture:  End 3rd lecture Character displacement:  Character displacement Birds Large Bill Size … crack large seeds Small Bill Size … crack small seeds Ch. 16, pp. 311-312 Selection for resource partitioning examine 2 species where they are: together (sympatry) separate (allopatry) Predict species DIFFER more in sympatry Darwin’s Finches:  Darwin’s Finches Galapagos Islands Different seed-eating finches on different islands Recently evolved from a common South American ancestor Ch. 20, pp. 389-390 Bill sizes of Darwin’s Finches:  Bill sizes of Darwin’s Finches Bill sizes of Darwin’s Finches:  Bill sizes of Darwin’s Finches Character displacement:  Character displacement Evolution of morphological divergence in places where two otherwise similar species occur together Hypothesis: natural selection due to competition For finches, presumably competition for seeds Evidence that seeds are a limiting resource and that changes in seed availability select for bill size (pp. 311-312) Species interactions:  Species interactions Interspecific competition interspecific competition is mutually negative (-,-) dN/N dt  by competition Exploitation (predation, parasitism, herbivory) One species benefits, one harmed (+,-) dN/N dt of consumer , dN/N dt of victim  Mutualism Both species benefit (+,+) dN/N dt  by mutualism Exploitation - specifically predation:  Exploitation - specifically predation Predator: kills and eats victim snake, wolf, fish, lion, spider, seed weevil, etc. Parasite: lives intimately with victim and usually does not necessarily kill victim tapeworm, flea, louse, aphid, malaria, etc. Herbivore/Carnivore distinction not that important for dynamics Ch. 17, 18 Predictions of  logistic:  Predictions of  logistic 1. Inefficient predator isoclines don’t cross predicts predator extinction 2. Intermediate predator efficiency #1 isoclines cross to right of peak predicts stable coexistence with damped oscillations Predictions of  logistic:  Predictions of  logistic 3. Intermediate predator efficiency #2 isoclines cross near peak predicts stable oscillations 2.Highly efficient predator isoclines cross to left of peak predicts expanding oscillations & extinction Predator (P) Prey (N) 4 Predictions of  logistic:  Predictions of  logistic Implications of improved predator-prey models:  Implications of improved predator-prey models Different patterns of dynamics are possible Stable cycles are only one special case Prey may be exterminated (efficient predators) Prey may be reduced to stable populations below K Biological control: Introduce enemies to reduce or eliminate pests Gause’s predator-prey experiments:  Gause’s predator-prey experiments Paramecium Prey Didinium Predatory ciliate Didinium - Paramecium predator-prey experiment:  Didinium - Paramecium predator-prey experiment Time (t ) Density (N or P) Paramecium Didinium Gause’s Predator-Prey experiments:  Gause’s Predator-Prey experiments No cycles (stable or otherwise) Predator exterminates prey Predator dies out shortly after Inconsistent with Lotka-Volterra predator-prey models Consistent with more realistic models (e.g.,  logistic) End 4th lecture:  End 4th lecture

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