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BIOL 302 Lecture 25 Competition

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Queen's University
BIOL 302
Laurene M Ratcliffe

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 - Figure 13.27 - take 2 ponds and divide it in half with a barrier - took an intermediate stickleback species and put the same number in each half of both ponds - added limnetic species to only half of both ponds - fed them for 3 months, harvest and measure growth rates - PREDICTION: if competition for food between limnetic and intermediate species ,directional selection should move the intermediate species towards benthic species morphology (ie. Intermediates most similar to limnetics should have lowest fitness) - fish similar to limnetics have the lowest fitness because they are competing without the same efficient morphology - Figure 13.28 - look at the distribution of the intermediate species and their growth rate - when grown alone, growth rates are independent of phenotype - when grown in competition, fish with phenotypes more similar to the competitors grow the slowest - resource related character displacement!!! Predation a) 5 kinds of consume-resource exploitation: herbivores, carnivores, parasites, parasitoids and cannibals - carnivores: kill and consume prey, remove from populatoin - parasites: consume live host, but don't remove -
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