gall distribution on the flowering dogwood Cornus florida BIOL3060 Overview A Parasite Gall Midge Fly Resseliella clavula B Host Flowering dogwood Cornus floria ID: 292577
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Slide1
Distribution of a plant parasite on its host: gall distribution on the flowering dogwood, Cornus florida
BIOL3060Slide2
Overview(A) Parasite: Gall Midge Fly (Resseliella clavula
)(B) Host:
Flowering dogwood (Cornus floria)
Process
Female fly lays eggs near terminal dogwood bud (late spring).
Eggs hatch & larvae enter dogwood shoots.Abnormal swelling (galls) form on twig ends (summer).Larvae exit galls and overwinter in soil. Pupate in early spring. Become adults in late spring.Larvae get protection and food source.Plants expend more energy regenerating tissue.Slide3
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) Could gall distribution be related to:
Size/age of the plant? Nearest neighbor distance? Sunny versus shady microhabitat?Slide4
Question 2. Could gall distribution be related to:
Tree sizeO
lder and infirm trees might be more likely to be attacked by the midge parasite. How could this affect distribution?
Distance to nearest neighbor
If trees are close together, they might be more likely to “catch” galls
. How could this affect distribution?Collect data in two habitatsWarmer environments might be better for midges. Environments with more vigorous trees might affect midge choices. How could this affect distribution?Slide5
Clumped DistributionMost trees have few parasites, and some a lot.Typically associated with:disease outbreakstree densities (“contagious”)age-related effects
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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.
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Random DistributionParasites are randomly distributed within the environment. If midges flew until they “hit” a dogwood haphazardly …
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Hypotheses and predictionsH1 Midge galls are like a disease for dogwoods, some are attacked while others are not. prediction: the distribution of galls on dogwoods is clumped. H2 Gall midges compete for laying sites, and larvae cannot survive if they are too close to each other.
prediction: the distribution of galls on dogwoods is regular (even).
Slide9
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 Slide10
Probability Levels for Student’s t-Distribution (Two-sided Probability Level)
Degrees
of Freedom
Sample Size
Value of
p
0.5
0.2
0.1
0.05
0.01
3
5
0.77
1.64
2.35
3.18
5.84
5
7
0.73
1.48
2.02
2.57
3.36
10
12
0.70
1.37
1.81
2.23
3.17
15
17
0.69
1.34
1.75
2.13
2.95
30
32
0.68
1.31
1.70
2.04
2.75
38
40
0.68
1.30
1.69
2.03
2.71
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0.68
1.30
1.68
2.02
2.70
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52
0.68
1.30
1.68
2.01
2.68
100
102
0.68
1.29
1.66
1.98
2.63
1000
1002
0.67
1.28
1.65
1.96
2.53Slide11
Task 2. HistogramUse countif statements# galls/ tree
# trees in edge habitat
# trees in canopy habitat
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Slide12
Task 3. What is the distribution of galls in the forest?Index of Dispersion (Id)Slide13
Critical Values of the Chi-Square Distribution For p = 0.05 Degrees of Freedom Lower Upper10 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 clump55 38.96 73.31 60 43.19 79.08 65 47.45 84.82 70 51.74 90.53 75 56.05 96.22 Slide14
Task 4. Correlations1) dbh vs. # galls2) dnn vs. # gallsDegrees of Freedom:Df= (n-2)P=0.05 Slide15
Task 5. Scatter plots (2)Slide16Slide17
Before you leave today:Fill out chart on Pg 513 graphs (histogram, 2 correlation plots)Slide18
Before you leave today:Transfer your data to spreadsheet on TA’s computer.