P1253296798uFWhZ

1
Insect herbivory on the leaf of Polygonum sp. in
relation to foliage height
By Ashley Ackerman (Biology), Brandon Aubry
(Exercise Science), Kelsey Berg (Biology)and
Emily Fullenkamp (Exercise Science)



Hypothesis The degree of insect herbivory is
proportional to leaf height from the ground as
well as stem length in the Polygonum sp. Null
Hypothesis There is no significant correlation
between the degree of insect herbivory and the
leaf height from the ground as well as stem
length in the Polygonum sp.

• Methods
• Seven plants were randomly selected as the
  experimental sample out of thirty-five total
  plants. These plants were chosen randomly by
  drawing seven numbers from a hat that contained
  pieces of paper numbered one through thirty-five.
  
• Leaves from each experimental plant were selected
  by identifying and collecting the lowest leaf on
  the plant and then every seventh leaf ascending
  the stem from the original position (Fig.2).
• Leaves were placed in bags identified by plant
  number and leaf position. In addition, the
  distance from the ground and the length of the
  stem was recorded on the bag.
• Most plants had multiple stems. In such
  situations, we numbered each individual stem and
  then drew a number from a hat to decide which
  stem to sample first. When the top of that stem
  was reached, we drew another number to determine
  the second sample.
• Leaves were then placed in a plant press prior to
  damage analysis. A digital image of each leaf was
  taken.
• The program Image J was used to measure the area
  of each leaf as well as the amount of damage to
  that leaf (Fig. 3). For more detail on this
  method, see Arnold, et all (2007).
• Correlation and regression analysis were used to
  examine any correlation between herbivory damage
  in relation to leaf height and stem length. Then
  we used descriptive statistics to calculate
  average percent of leaf damage, probability of
  leaf damage, the number of leaves damaged, and
  the average size of the leaf.

Graph 1
Graph 2
Background When an animal consumes plant
material, it is known as herbivory. Plant
material may consist of leaves, bud, bark, wood,
stem, sap, flowers, pollen, nectar, roots,
fruits, and seeds. Herbivores may be mammals,
insects, birds, etc, and are sometimes referred
to as miners, suckers, browsers, or grazers
(Trees for Life, 2008). Previous studies have
been completed in the area of herbivory that
relate to our present study of Polygonum. One
study showed a strong relationship between the
age of the foliage on the plant and the amount of
herbivory that ocurred. In most cases, foliage
that was younger in age was damaged by herbivory
more often than older foliage (Bach, 1990). In
addition, studies have been done to test the
amount of herbivory on a particular species in
relation to the distance the plant is to the next
plant of the same species. The results showed
that there is little correlation between the
amount of herbivory damage and the distance to
the closest neighbor (Geho, Campbell, Keddy,
2007). Related tests have been performed in
numerous environments on numerous different
species.


Discussion The results of our experiment failed
to support the hypothesis that height of a leaf
or the length of the stem on the Polygonum sp.
has a correlation with the percentage of damage
on the leaves. Our expectations were that leaf
position would affect how much damage was on the
leaf because of differences in accessibility to
herbivorous insects. If the lower leaves had more
percent damage, we speculated that it may have
been due to crawling insects eating the leaves.
However, if the higher leaves had more percent
damage, we speculated that it may have been due
to flying insects. Since there was no correlation
between plant height and leaf damage, we cannot
speculate which types of insects were causing the
damage.        Our statistical analysis shows
that there is no correlation between plant height
or stem length and percentage of leaf damage in
Polygonum. This is not the result that we
expected. This may be due to both flying and
crawling insects eating the plants leaves.
Therefore, it would not matter where the leaves
are located on the plant. If many different types
of insects are eating from the plant, most of the
leaves would have an equal probability of being
eaten and having damage. In a previous study,
there was also no correlation between the amount
of herbivory damage and the distance to the
closest neighboring plant (Geho, Campbell,
Keddy, 2007). This may have also been due to many
different types of insects eating from the
different plants.
Leaf processed by Image J
Random Selection of Leaves
Figure 2 The leaves indicated by the arrows are
the ones that would be randomly selected
according to our methods. Leaves from each
experimental plant were selected by identifying
and collecting the lowest leaf on the plant and
then every seventh leaf ascending the stem from
the original position.
Figure 3 The program Image J is used to measure
the area of each leaf as well as the amount of
damage to that leaf. This is an example of a leaf
processed by Image J.


Location of Test Plot Figure 1 Left Nahant
Marsh in Davenport (Star), Right Location of
Study Plot (Star)
Results The average size of a Polygonum leaf
was 9.621 cm2, for a sample of 68 Polygonum plant
leaves. Sixty-six out of sixty-eight sampled
leaves (97.1) showed signs of damage. The
average amount of leaf damage per leaf was 10.96
percent. We found in our observations of the
sixty-eight leaves that there are no significant
correlations between the height and percent
damage or the stem length and percent damage.
Graph 1 shows the relationship between the length
of the stem from the ground to the leaf and the
percent of damage. A test of the null hypothesis
shows no correlation between the length of the
stem from the ground to the leaf and the percent
of damage. This produced an r value of .18 (p gt
0.05). Graph 2 shows the relationship between the
height from ground to leaf and the percent of
damage. A test of the null hypothesis shows no
correlation between the height from ground to
leaf and the percent of damage. This produced an
r value of .19 (p gt 0.05).
References Arnold, N., Brock, K., Thurwanger, N.
(Decemeber 5, 2007). Comparing conspecific
distance to the nearest neighbor of Eupatorium
altissimum and average plant damage. Geho,
E.M., Campbell, D., Keddy, P.A. (2007).
Quantifying ecological filters the relative
impact of herbivory, neighbours, and sediment on
an oligohaline marsh. 116. Doi10.1111/j.2006.003
0-1299.15217.x Trees for life. (September 05,
2008). Retrieved November 3, 2008, from
www.treesforlife.org.uk/forest/ecological/herbivo
ry.html
Acknowledgments We would like to thank Dr. Paul
Koch and Dr. Rich Legg for their assistance in
the completion of this research project. We would
also like to thank the people at Nahant Marsh for
providing assistance and allowing us to conduct
our experiment at their location.
The total plot size is 41.4 m x 31.5 m.