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Surface active invertebrates

Aaron Randolph
Science Research Fellow, DePauw University
Summer 2004

Surface active invertebrates are an important factor in the forest ecosystem dynamics.  The goal of my project was to describe the composition of surface-active invertebrates in forests of the DePauw Nature Park. 

I hypothesized that the composition of surface-active invertebrates would vary depending on habitat characteristics. 

I constructed pitfall traps using 16-ounce plastic cups, propylene glycol, chicken wire, and Masonite.  I placed the traps at 30 meter intervals along 3 parallel transects in 3 locations in the DePauw Nature Park.  I sorted, identified, and counted the invertebrates caught in the traps.  I calculated the efficiency of traps (number of invertebrates caught per trap per day) and a diversity index for each location. 

I caught a total of 3,365 surface-active invertebrates.  The most abundant were isopods (690), millipedes (578), ants (426), springtails (267), beetles (250), and spiders (233).  The diversity index did not differ among the three locations.  The composition of captured invertebrates differed among the three locations.  Ants and isopods were most frequently caught in the Arboretum.  Millipedes were most frequently caught at Quarry Hillside and Quarry South.  Capture rates of springtails were highest at Quarry South and captures of crickets and spiders were highest at Quarry Hillside.

Differences in the composition of the surface-active invertebrate community may be due to differences in habitat structure.  Leaf litter cover and depth was higher at the Arboretum than the other two sites; leaf litter may provide shade and moisture for protection of invertebrates.  There were more logs at Quarry South and Quarry Hillside; logs may provide habitat for millipedes.  There was more understory vegetation at Quarry South, possibly contributing to higher capture rates of invertebrates.  Future research could address soil moisture, nutrients, and pH levels, and how each of these factors affect abundance and diversity of surface-active invertebrates.