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Purpose

Distribution of a plant parasite on its host: 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. Questions.

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Purpose

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  1. Distribution of a plant parasite on its host: gall distribution on the flowering dogwood, Cornusflorida

  2. Purpose • To 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?

  3. Midge fly, Resseliellaclavula

  4. RandomDistribution • Parasites are randomly distributed within the environment. If midges flew until they “hit” a dogwood haphazardly … • Predict: 20 20 20 30 30 20 40 40 20 20 20 30 30 30 40 30 20 20 10 20 30 40

  5. EvenDistribution • “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: 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

  6. ClumpedDistribution • Most trees have few parasites, and some a lot. • Typically associated with: • disease outbreaks, tree densities (“contagious”), age • Predict: 0 0 0 0 30 0 0 30 30 0 0 0 30 0 0 0 0 0 30 0

  7. Environmental Factors We are Measuring • Tree size • Older 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.

  8. Dogwood (Cornus florida) Identification

  9. Dogwood Identification Fruit: bright red, in clusters (late summer, fall) Flowers: white, four petals (spring) Leaves: opposite, veins curved

  10. Dogwood Identification (Winter) Both Flower buds (reproductive) Leaf bud (somatic)

  11. Bark: dark brown with squarish, scaly blocks. Young trees will be smooth and not as distinctive.

  12. Terminal Buds Examples of different numbers of bud scales Dogwood with two bud scales. Twigs are slender, green or purple.

  13. Leaf Scars Terminal bud Opposite leaf scars Dogwood leaf scars are opposite, small, and encircle twig. Example of alternate leaf scars

  14. Methods • Groups of 4 • Go to 2 sites and survey 20 trees each 1) 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.)

  15. Dogwood Branch 4 9 8 2 10 5 11 3 7 1 13 6 12 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

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