Ant Community Changes Associated With Introduced Plant Species.

1
Ant Community Changes Associated With Introduced
Plant Species.  
Daniel S. Kjar and Edward M. Barrows
Introduction Since colonial times, biodiversity
has markedly changed in the Washington, D.C.,
area as a result of disturbances from humans.
Unlike direct human threats such as encroachment,
frag-mentation, overuse, and pollution,
introduced organisms cannot be stopped by simply
passing legislation or by lawsuits against
parties guilty of introducing these organisms.
Alien, invasive organisms will continue to grow,
fill our natural areas, and consume resources
needed to support our native populations. Arthrop
ods are ideal for studying changes in eastern
deciduous forests. Arthropods are abundant, have
short generation times, and are sensitive to
local changes. We have caught and identified (to
various taxonomic levels) nearly 300 species in
over 90 families of arthropods in this study.
For this poster we concentrate on the ant
community (Insecta Hymenoptera Formici-dae).
Ants are attractive indicators of change as they
are easy to catch and identify, are diverse,
generally do not travel more than a few meters
from their nests, and move nests away from areas
which are no longer suitable. The aim of this
research is to quantify changes in the arthropod
community associated with the invasion of alien
plants in the low forest of Dyke Marsh Wildlife
Preserve (DMWP). Associations among plant
coverage and richness, soil moisture and
structure, tree abundance and richness, and the
arthropod community are examined using several
methods. We hypothesize that increased alien
invasive plant coverage decreases native plant
richness and changes the abundance and diversity
of native arthropods.
Aphaenogaster rudis (a common ant
species) Increased abundance of A. rudis
is associated with increased levels of alien
plant coverage and total plant species richness.
Figure 4c. Ants and tree richness.
Table 3. ANOVA table for ant community
associations. a,b,c,d

• Preliminary Results
• The study plots had 55 plant species of
  different abundances, including 10 invasive
  species. We found that the average level of
  coverage by invasive plant species for the DMWP
  forest was 45, ranging from 0-94 at each site.
  Lonicera japonica and Celastrus orbiculatus were
  the more common alien plants (Table 1).
• Invasive plant coverage is correlated with
  decreasing native plant richness (Figure 3,
  Appendix Table 1).
• Increasing alien plant coverage is associated
  with increasing abundances in the native ant
  community. Tree richness and soil moisture are
  also highly correlated with ant abundance (ANOVA,
  P lt 0.05, Figures 4a, 4b, 4c, Tables 2 and 3).
• Aphaenogaster rudis may be a good indicator of
  ecological change caused by invasion of alien
  plants (ANOVA, P lt 0.05, Figures 5a, 5b,
  Appendix Table 3).

• Conclusions
• Preliminary data show that alien plants are
  associated with changes in native plant richness
  and ant abundance in the low forest of the Dyke
  Marsh Wildlife Preserve. Lonicera japonica and
  Celastrus orbiculatus appear to present the
  larger threats to native plant species and the
  terrestrial arthropod community within the
  forest.
• Modern computer software and GPS provide an
  effective method of randomly sampling a large
  area without the use of transects, haphazard
  sampling, or other potentially flawed forms of
  site selection.

• Materials and Methods
• We utilized satellite imagery and Geographic
  Imaging System data (GIS) with ArcView and the
  AlaskaPak to generate 60 random sites within the
  DMWP. We used a Global Positioning System (GPS)
  to locate these sites (Figure 1).
• We placed a pitfall trap at the center of each
  1-m2 site (Figure 2). Pitfalls were run for 24
  hr during a warm night at the end of each
  trapping month (June, August, October during
  20022003).
• We recorded all plant species and relative
  coverage for each site during early August of
  2002 and 2003 (Figure 2). We recorded the dbh
  and species of all trees within a 6-m diameter
  circle of each site.
• We took one soil core (40 x 80 mm) from each
  site at the end of each trapping period. We used
  a modified Berlese-Tullgren design to extract
  arthropods from the 60 soil cores (Figure 2).
  Soil cores were used to determine soil moisture
  and soil structure.
• The results presented here are preliminary.
  These data are from 40 sites, do not include soil
  core samples, and do not include the 2003
  trapping year.