BIO220H1 Lecture Notes - Lecture 16: Polyculture, Genetic Variation, Species Richness

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19 Apr 2012
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Lecture 16 BIO220 Ecological Consequences of Genetic Variation
Biodiversity resistance to perturbation, increased productivity
e.g. High species richness, high biomass after drought
Are plant patches that are more genetically diverse able to support more insects?
Grow groups of monocultures (only 1 genotype), or polycultures (mixture)
Measure # and identify herbivores, omnivores, predators
Result: more genetically diverse plant communities support more predatory insects.
Increased number of genotypes, predator richness
Mechanism:
Genotypes in mixture react additively
oGenotypes independent
oPredator abundance on a genotype in monoculture = abundance on that
genotype in polyculture
oCommunities: whole is sum of parts
Genotypes in mixture react non-additively
oProperties of genotype depend on other surrounding genotypes
oAbundance of predators on genotype in monoculture do not predict that in
polyculture
oCommunities: whole is > or < than sum of parts
Whole > sum of parts
Plant genotypes differ in nutritional qualities, growth, defensive compounds,
flowering phonologies
More diverse patches, more spatial, temporal niches for insects
Once insects find a patch, they may be more likely to stay and visit other nearby
genotypes
Polycultures recover from severe disturbances faster, are more resilient to natural
disturbance
Mechanism:
Polycultures: more tolerant genotypes, can regrow quickly
Overperformance of polycultures: interaction between genotypes
oDifferent resource uptake strategies of genotypes
oMore micro-niches, less competition
Galled plants decompose slower, have greater retention of C/N compared to ungalled.
Genetic variation affects nutrition cycling
Chain of causation
oGenotypes differ in chemical properties
oDifferent attack by insects
oGenotypes differ in chemical responses to attack
oCombined set of chemical differences alter decomposition, nutrition cycling
Coyote Bush
Facilitates colonization of other species
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