BIOL 302 Lecture Notes - Littoral Zone, Limnetic Zone, Character Displacement
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22 Nov 2012
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Lecture 25: Competition (cont.)/Predation
November-15-12
8:28 AM
2. Why is competition an important ecological process?
- the most compelling evidence for competition is demonstration character displacement
- competition should lead to divergence in characters of species in areas where they co-occur
(sympatry), compared to areas where each lives alone (allopatry)
- character displacement may be reproductive or ecological; both required for speciation
- avoid interbreeding which lead to selection of sexual signals and ability to recognize those signals
- characters may have similar values in areas where species are separated but in areas of divergence,
there should be a difference in character value
- infers that the two s
pecies diverges which is a result of evolutionary character displacement
- criteria necessary to show character displacement:
- chance should be ruled out
- phenotypic differences must have genetic basis
- phenotypic differences in sympatry should result from evolutionary shifts
- phenotypic differences should related to resource use
- sites of symatry and allopatry should be similar
- environment is not very different between those two sites
- should be evidence that that similar phenotypes compete for resources
- replicate tests to eliminate any local effects
*Competition and Character Displacement in Stickleback (Schluter 1994)
- morphology reflects feeding niche (efficiency in feeding on inverts)
Benthic
- littoral zone bottom feeders
- wide gape (vacuuming the ocean floor)
- few short gill rakers
- large, deep-bodied
Limentic
- phytoplankton open water eaters
- narrow gape
- many long gill rakers
- small, slender
- when the two species are in allopatry, they can feed in either zone (although not as efficient in their
own zone)
- when found together, each specialize in their own zone of feeding
- differences in characteristics are heritable