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Unformatted text preview: Competition Today's questions: (one more topic in behavioral ecology kin selection) (one more topic in behavioral ecology = kin selection) I. How does competition work? (theory) II. Observational studies of competition II Observational studies of competition III. Experimental studies of competition How does kin selection work? Question: When do alleles that lead to altruism increase in frequency in a population? Answer: When they increase the fitness of related individuals. l Direct fitness = Direct fitness = Indirect fitness = Inclusive fitness = I. How does competition work? (theory) A. Why are fundamental and realized niches different? % % used low Range of resources high B. Niche differentiation (resource partitioning) B Niche differentiation (resource partitioning) Start of competition: Species A Species B % % used small Size of nesting cavity large After many generations: Species A Species B % % used small Size of nesting cavity large B. Symmetric and asymmetric competition Av verage f fitness Species A A+B Species B Species A A+B Species B only only Populati ion size e D. Competitive exclusion Time P Populat tion size e Time G. fuliginosa on Los Hermanos G f li i L H II. Observational studies of competition studies of competition A. Character displacement in Galpagos finches
The species g p graphed here feed on seeds; large beaks = large seeds large seeds 60 40 20 0
G. fortis G f i on Daphne Major D h M j 60 40 20 0 60 40 20 0
Both species (Santa Mara, San Cristbal) 6 8 10 12 14 16 Beak depth (mm) B. Criticisms of observational studies Name two other plausible hypotheses--other than competition--that could explain this pattern. III. Experimental studies of competition Connell's study of barnacles growing in intertidal habitats Adults are sessile; find adult Chthamalus i Ad lt il fi d d lt Chth l in upper intertidal; adult Semibalanus in lower intertidal Larvae are motile; found in both habitats L til f d i b th h bit t H1: Adult Chthamalus are absent from the lower intertidal because Semibalanus exclude them. H2: Adult Chthamalus are absent from the lower intertidal : Adult Chthamalus are absent from the lower intertidal because they cannot grow there. Experimental test: 1) Take rocks from the upper interidal that are colonized by Chthamalus. 2) Transfer these rocks to the lower intertidal and allow Semibalanus to colonize them. to colonize them. 3) Divide each rock into two treatments: Remove Semibalanus f S ib l from one half, leave both species on the other h lf l b th i th th half. 4) Measure survivorship, over time. Questions: 1) Why did Connell split each rock into two treatments? 2) Would it be important to place each rock into random locations (versus all clumped) in the lower intertidal? 3) Why was it important for him to do many replicates (many rocks)? Question: How would you test the hypothesis that Semibalanus can't grow in the upper intertidal? ...
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