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.

Questions1) 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 …

4020

20

30

30

20

2020

10

2030

4030

20

20

30

30

30 20

20

40

40

0 10 20 30 4002468

10121416

# Parasites

# Tr

ees

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.

0 10 20 30 4002468

10121416

# Parasites

# Tr

ees

10

10

10

101010

1010

10

10

10

1010

10

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 10 20 30 400

2

4

6

8

10

12

14

16

# Parasites

# Tr

ees

030

30

3030

0

0

00

0

0

0

0

0

00

0

0 030

• 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.

Environmental Factors We are Measuring

Dogwood Identification (Winter)

Flower buds(reproductive)

Leaf bud(somatic)

Both

Bark: dark brown with squarish, scaly blocks.

Young trees will be smooth and not as distinctive.

Terminal Buds

Examples of different numbers of bud scales

Dogwood with two bud scales. Twigs are slender, green or purple.

Leaf Scars

Dogwood leaf scars are opposite, small, and encircle twig.

Example of alternate leaf scars

Opposite leaf scars

Terminal bud

Dogwood Identification

Flowers: white, four petals (spring)

Fruit: bright red, in clusters (late summer, fall)

Leaves: opposite, veins curved