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BIOL3060

Distribution of a plant parasite on its host: gall distribution on the flowering dogwood, Cornus florida. BIOL3060. Overview. (A) Parasite: Gall Midge Fly ( Resseliella clavula ) (B) Host: Flowering dogwood ( Cornus floria ) Process Female fly lays eggs near terminal dogwood bud

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BIOL3060

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  1. Distribution of a plant parasite on its host: gall distribution on the flowering dogwood, Cornusflorida BIOL3060

  2. Overview (A) Parasite: Gall Midge Fly (Resseliellaclavula) (B) Host: Flowering dogwood (Cornusfloria) • Process • Female fly lays eggs near terminal dogwood bud • Eggs hatch & larvae enter dogwood shoots • Abnormal swelling (galls) form on twig ends • Larvae get protection and food source • Plants expend more energy regenerating tissue

  3. 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) Could gall number or distribution be related to: • Size/age of the plant? Nearest neighbor distance? Sunny versus shady microhabitat?

  4. P1: Random Distribution • Parasites are randomly distributed within the environment. If midges flew until they “hit” a dogwood haphazardly … 20 20 20 30 30 20 40 40 20 20 20 30 30 30 40 30 20 20 10 20 30 40

  5. P2: Even Distribution • “Regular”: Organisms are evenly spaced in the environment. In our case, every tree would have the same number of galls. This would suggest that the parasites are competing for the trees. 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

  6. P3: Clumped Distribution • Most trees have few parasites, and some a lot. • Typically associated with: • disease outbreaks • tree densities (“contagious”) • age-related effects 0 0 0 0 30 0 0 30 30 0 0 0 30 0 0 0 0 0 30 0

  7. Question 2) Number of galls per tree related to the environment? 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 “catch” galls. • Collect data in two habitats • Some microhabitats might be better for galls than others.

  8. Hypotheses 1) HO: Dogwood galls are distributed randomly. HA: Dogwood galls are not distributed randomly. prediction: Galls are either like a disease to dogwoods and they will be clumped, or there will be competition between them and their distribution will be even.. 2) HO: The number of dogwood galls per twig on trees is the same between sunny areas and shady areas HA: The number of dogwood galls per twig on trees is not the same between sunny areas and shady areas prediction: There is an environmental factor (possibly sunlight) that differs between the two habitats that causes the number of galls to differ between habitats. 3) HO: The number of dogwood galls per twig on trees is not correlated with tree size. HA: The number of dogwood galls per twig on trees is correlated with tree size. prediction: Part of the biology of the dogwood midge involves choosing or avoiding larger trees. 4) HO: The number of dogwood galls per twig on a tree is not correlated with distance to nearest neighbor. HA: The number of dogwood galls per twig on a tree is correlated with distance to nearest neighbor. prediction: Dogwood midges are more likely to lay eggs on trees closer to the ones they developed in.

  9. Task 1. Student’s T-test1) # galls2) dbh3) dnnAlso use the excel function TTEST Degrees of Freedom: Df = (n1-1) + (n2-1) P=0.05

  10. Probability Levels for Student’s t-Distribution (Two-sided Probability Level)

  11. Task 2. HistogramUse countif statements

  12. Task 3. What is the distribution of galls in the forest? • Index of Dispersion (Id)

  13. Critical Values of the Chi-Square Distribution For p = 0.05 Degrees of FreedomLowerUpper 10 3.94 18.31 15 7.26 25.00 18 9.39 28.90 19 10.10 30.14 20 10.85 31.41 25 14.61 37.65 30 18.49 43.77 35 22.47 49.80 40 26.51 55.76 45 30.61 61.66 50 even 34.76 rand 67.51 clump 55 38.96 73.31 60 43.19 79.08 65 47.45 84.82 70 51.74 90.53 75 56.05 96.22

  14. Task 4. Correlations1) dbh2) dnn • Degrees of Freedom: • Df= (n-2) • P=0.05

  15. Task 5. Scatter plots (2)

  16. Before you leave today: • Fill out chart on Pg 39 • 3 graphs (histogram, 2 correlation plots)

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