Biology Department

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The Study of Population Locations of Epimecis Caterpillars

( Demographic Study of Epimecis hortaria )

The purpose of this experiment is to better understand the cycling (highs and lows of young and adult) of the populations of the main caterpillar (Epimecis hortaria) that feeds on spicebush ( Lindera benzoin).

 

STATE THE PROBLEM :

How does the population of herbivores (caterpillars) vary with the season and between habitats?

MAKE OBSERVATIONS:

  • There appeared to be a large population of adult caterpillars (Epemicis hortaria) at the beginning of the summer with little difference in number between the interior and edge of the forest.

Background Information (What questions were you trying to answer?):

  • When are the caterpillars at their highest numbers?
  • Where are the caterpillars found most often (edge/interior)?

FORM A HYPOTHESIS :

  • The caterpillars have two peaks in their populations and they are found more frequently in the interior because there is more herbivory in the interior.

EXPERIMENT:

Materials:

  • Tape Measure
  • 2 Locations with Spicebush
  • Aluminum Tree Tags
  • Flagging Tape
  • Beatsheet (1 sq. meter)
  • Sharpie
  • Ziplocks (many)
  • Tape (labeling)

Method:

  1. Choose two field locations which both contain spicebush on the interior (inside the trees) and on the edge (where forest meets field).
  2. You will need to mark 2 interior transects and 2 edge transects at each location. To mark your transects:
    1. Choose a spicebush plant to start with.
    2. Choose a branch on the plant that looks healthy.
    3. Label it at the base with an aluminum tree tag that has your name and identifying number for that plant. Also tie flagging tape to the branch so it is easier to see.
    4. From your starting plant, walk a straight line. Every 5m stop and label the closest spicebush as you did above.
    5. Each transect should have 5 plants labeled.
  3. You will then need to use the beat sheet. Hold beat sheet under plant (with cross bar frame up).
  4. Grab marked branches so that as much of selected branch material is bent over beat sheet as possible.
  5. Give 5 swift vertical strikes.
  6. Look at the insects that are on your beat sheet.
  7. Count and record the number of Epimecis and Papilio larvae.
  8. Replace all collected organisms back on the plant.

Data:

Example of a data table

Example of a Graph

 

DRAW A CONCLUSION :

Analysis of Data:

The data has shown that there are greater rates of model larva attack and higher model mortality risk at the forest edge. Coincidentally, there is greater herbivore damage to L. benzoin (Spicebush) in forest interior compared to edge environments.

Conclusion:

Landscape edges are known to affect a multitude of environmental variables that may directly or indirectly affect herbivory. Previous studies of L. benzoin have demonstrated that edges may affect “bottom-up” factors that influence herbivory via altered plant characteristics. The current study provides evidence that the “top-down” factor of bird predation may act in concert with these “bottom-up” effects in producing the observed pattern of decreased herbivory in edge habitats.

 

 

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This material is based upon work supported by the National Science Foundation under Grant No. 0442049.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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