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Lecture 12

BIO220H1 Lecture Notes - Lecture 12: Genetic Variation, Polyculture, Species Richness

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John Stinchcombe

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Lecture 12: Ecological Consequences of Genetic Variation
Re-ordering our thinking
So far our thinking is:
oEcology produces selection
oLeads to changes in allele frequency
Recall dairy agriculture, crops we grow
Human imposed artificial selection to make crops more nutritious
oLeads to evolutionary response
Today, think about opposite chain of causation:
oWithin any population will have multiple Alleles in Focal Population that will
produce genetic variation
oInteracting species and process respond differentially to these alleles
oEX: Response of a herbivore depends on which alleles the plant it consumes has
oEX: Predator will respond to different alleles in the herbivores that they
oConsequence: Changes in Ecological Processes
Aspects of nutrient cycling, species composition
Break into several questions:
(1) Ecological effects of genetic diversity:
oDo genetically diverse communities have different fundamental structure?
(2) What are the effects of genetic diversity on disturbance recovery?
(3) Close: Are effects of species diversity and genetic diversity the same?
Biodiversity results in resistance to environmental perturbation and higher productivity
Top graph:
oVertical: Biomass remaining after drought
oHorizontal: Plant species richness before drought
oSaturating curve:
Plots that started out with higher species richness before drought
retained more biomass after drought
Bottom graph:
oSame conclusion true for number of guilds (functional diversity)
oGuild: Grasses in one category, legumes in another, shrubs in one category
oPlots with more guilds had higher biomass
Evidence that diverse communities with lots of species have more resilience than less
diverse communities
Questions: Do these effects hold for Genetic Diversity?
Do these ecological consequences hold true for effects of genetic diversity as well?
oi.e. Is effect of ecological diversity sae as effects of genetic diversity?
Say we had “genetic variation in a focal species before drought” (instead of species
richness) would we get same effects

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oAre the forces governing species diversity and genetic diversity the same?
oAre the consequences the same?
Are plant patches that are more genetically diverse able to support more insects?
Establish whether or not genetic diversity in plant community supports more insects
(1) Grow groups of plants that are either monocultures or polycultures
oMonoculture: Grow just 1 genotype (say genotype A)
Every individual on this plot is genotype A
Repeat for 8 separate genotypes
i.e. make on plot of all genotype B
oPolyculture: In each plot of land plant mixture of genotypes
Say if we plant 8 individuals, might choose 2 individuals of 4 genotypes
= Plot of land with 4 genotypes
Or do with 9 genotypes
At the end, if planted same number of plants in each plot will see:
oDifferences among plots of number of plants are due to genetic composition
(2) Measure:
oNumber and identity of herbivores/omnivores/predators that recruit patches of
oHow does variation in genetic composition of plot affect identity and composition
of species that colonize it?
Do more genetically diverse plots contain greater richness of diversity of species?
Infer mechanisms behind this:
oInfer whether or not this is a sampling artifact (random chance)
oOr is there biological interactions among genotypes of plant that feeds into insect
Experiment performed at UofT’s Koffler Scientific Reserve
More genetically diverse plant communities do support more predatory insects
First result:
Horizontal: Number of genotypes (plots of 1, 4, 8 genotypes)
Vertical: Cumulative predator richness
oIn plots of 1 genotypes average number of predators is around 6.5
oIn plots of 4, average predators is 7.5
oIn plots of 8, average predators is 8.5
By planting different genotypes together, get more predators that come to plots
What is the mechanism?
Distinguish between 2 possibilities:
o(1) Genotypes in mixture react additively
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