Distribution of a plant parasite
on its host
and
Reproductive and Somatic Effort
BIOL 3060
Distribution of a plant parasite on its
host: gall distribution on the flowering
dogwood, Cornus florida
Flowering dogwood, Cornus florida
Midge fly, Resseliella clavula
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 # or distribution of galls be related to:
• Size/age of the plant? Nearest neighbor distance?
Sunny versus shady microhabitat?
P1: Random Distribution
• Parasites are randomly distributed within
the environment. If midges flew until they
“hit” a dogwood haphazardly …
20
30
14
12
# Trees
20
20
16
40
10
30
20
40
20
20
20
8
30
6
20
2
0
0
10
20
# Parasites
30
40
30
40
30
4
30
30
20
10
40
20
P2: Even Distribution
# Trees
• “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
16
14
12
10
8
6
4
2
0
10
10
10
10
10
10
10
10
10
0
10
20
# Parasites
30
10
10
40
10
P3: Clumped Distribution
• Most trees have few parasites, and some a lot.
• Typically associated with:
– disease outbreaks
– tree densities (“contagious”)
– age-related effects
0
16
0
0
14
30
# Trees
12
0
10
8
30
30
6
0
0
0
0
0
30
4
0
2
0
0
10
20
# Parasites
30
40
0
0
0
0
30
0
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.
Flower buds
(reproductive)
Both
Leaf bud
(somatic)
Bark: dark brown
with squarish,
scaly blocks.
Young trees will be
smooth and not as
distinctive.
Examples of different numbers of bud scales
Dogwood with two bud scales. Twigs are slender, green or purple.
Terminal bud
Opposite leaf scars
Dogwood leaf scars are
opposite, small, and encircle
twig.
Example of alternate leaf scars
Fruit: bright red,
in clusters (late
summer, fall)
Flowers: white,
four petals (spring)
Leaves: opposite,
veins curved