gall distribution on the flowering dogwood Cornus florida Purpose To determine the distribution of midge galls on dogwood trees and to investigate some environmental factors that might influence distribution ID: 541822
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Distribution of a plant parasite on its host: gall distribution on the flowering dogwood, Cornus floridaSlide2
PurposeTo determine the distribution of midge galls on dogwood trees and to investigate some environmental factors that might influence distribution.
Questions
1) How are the galls distributed spatially?
Random vs. clumped vs. uniform
2)
Number or
distribution of galls influenced by:Size/age of the plant? Nearest neighbor distance? Sunny versus shady microhabitat?Slide3
Midge fly, Resseliella clavulaSlide4
Random DistributionParasites are randomly distributed within the environment. If midges flew until they “hit” a dogwood haphazardly …Predict:
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40Slide5
Even Distribution“Regular”: Organisms are evenly spaced in the environment. Then every tree would have the same number of galls. This would suggest that the parasites are competing for the trees.Predict:
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10Slide6
Clumped DistributionMost trees have few parasites, and some a lot.Typically associated with:disease outbreaks, tree densities (“contagious”), agePredict:
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30Slide7
Tree sizeOlder and infirm trees might be more likely to be attacked by the midge parasite.Distance to nearest neighbor
If trees are close together, they might be more likely to attract
galls.
Collect gall data in two habitats
Some microhabitats might be better for galls than others.
Environmental Factors We are MeasuringSlide8
Dogwood (Cornus florida) IdentificationSlide9
Dogwood IdentificationFlowers: white, four petals (spring)
Fruit: bright red, in clusters (late summer, fall)
Leaves: opposite, veins curvedSlide10
Dogwood Identification (Winter)Flower buds(reproductive)
Leaf bud(somatic)
BothSlide11
Bark: dark brown with squarish, scaly blocks.Young trees will be smooth and not as distinctive. Slide12
Terminal BudsExamples of different numbers of bud scales Dogwood with two bud scales.
Twigs are slender, green or purple.Slide13
Leaf ScarsDogwood leaf scars are opposite, small, and encircle twig. Example of alternate leaf scars
Opposite leaf scars
Terminal budSlide14
MethodsGroups of 4Go to 2 sites and survey 20 trees each1) Record how many galls on 100 branch nodes per tree
2)
Measure the DBH (cm) of each tree trunk
DBH = “Diameter at breast height”
3)
Measure the distance (m) of the three closest dogwood neighbors (
DNN = nearest neighbor dist.)Slide15
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Dogwood Branch
Galls
…so this branch is good for 13 out of the 100 counts you need for each tree, and the number of galls is 2