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Déjà Vu Communities When Invaders Meet
Again Melanie Northrup, Christy Cincotta, Mark
June-Wells, Jonathan Lansey, Kunj Patel, Apiwat
Romayanantakit, Claus Holzapfel Rutgers
University Newark, Dept. of Biological Sciences,
Newark NJ 07102-1811 contact holzapfe_at_andromeda.
rutgers.edu
Abstract

Grid Transect Data
Root Interaction Experiment
Methods
Methods
Fallopia japonica and Microstegium vimineum are
two sympatric northeast Asian plant species that
are non-native invaders in the Northeastern U.S.
In some areas these two species now co-occur and
very clear boundaries between populations of
these two species appear to be typical, while
overlap zones are typical when these species
interact with other species. We are studying the
interaction between these two species testing the
possibility that coevolved community level
interactions are involved when formerly sympatric
species meet again in déjà-vu communities. We
used a grid transect method to assess aboveground
interactions between 9 pairs of sympatric species
and 6 pairs of allopatric species. Additionally,
we conducted a greenhouse experiment to assess
belowground and aboveground interactions between
native and non-native co-occurring plants.
Results from the grid transect surveys showed
that allopatric pairs have significantly larger
overlap zones compared to sympatric species. The
root interaction experiment implied that Fallopia
produced less belowground growth and grew more
toward itself (intraspecific) when grown with
Artemisia vulgaris as opposed to Microstegium and
Solidago canadensis. We confirmed, with some
reservation, that direct competition with the
sympatric Microstegium is comparatively small.
Two parallel transects were taken perpendicular
to the border between pairs of sympatric and
allopatric species. Included in the study were 9
pairs of sympatric species and 6 pairs of
allopatric species across 5 sites in northern New
Jersey. Each transect was 3.5 x 0.5 m and
composed of 50 x 50 cm quadrats. Measurements
at the quadrat level included percentage
vegetation cover, average height, and density of
each species.
Interactions between three species pairs were
tested in this experiment, including Fallopia
vs. Microstegium, Fallopia vs. Artemisia, and
Fallopia vs. Solidago. Each arena type was
replicated 3 times, totaling 9 arenas.
Measurements included root mass at initiation,
shoot height and number of leaves weekly, root
cores extracted at week 11, and root and shoot
biomass upon harvest. Roots from root cores were
washed, scanned and then analyzed with WinRhizo
Pro software to calculate root length.
Results
Results
Allopatric pairs have significantly larger
overlap compared to sympatric pairs
Average Fallopia japonica root length toward
intra- or inter-specific neighbor
Average root length toward other plants or away
from plants
Fallopia had significantly (F 7.29 plt.0001
n6) more root length in the direction of other
plants (intra- or inter-specific) compared to
away from plants. Microstegium, Solidago, and
Artemisisa showed very little differentiation in
direction of growth.
Fallopia grown with Artemisia had significantly
(F 4.69 Plt.0001 n6) greater average root
length toward itself (intraspecific) than toward
Artemisia (interspecific). Fallopia grown with
Microstegium or Solidago showed no difference
between intra- and inter-specific neighbors.
Extent of overlap between bordering monotypic stands of different origin. Overlap percentages are based on scaled aboveground cover of each species along the transect. Shown are the means ( SE) of each pairing, the overall means of allopatric and sympatric pairs (shown as horizontal lines), and the p-value comparing overall means. There are 8 allopatric and 16 sympatric transects.
P0.0130
Fallopia overlaps with sympatric species
Microstegium less than with allopatric species
Artemisia
Fallopia japonica shoot height and number of
leaves by arena over 11 weeks
Introduction
Belowground growth of Fallopia is correlated
with biomass of other species
Belowground growth of Fallopia is positively
correlated (r0.9924) with belowground biomass of
other species in their respective arenas. For
example, Fallopia grew the least when grown with
Artemisia and Artemisia produced the least amount
of belowground biomass in that arena.
Although not statistically significant, Fallopia
showed the greatest total shoot height over time
when grown with Artemisia and the least with
Microstegium.
Fallopia japonica and Microstegium vimineum are
two non-native invaders in the Northeastern
United States. The former invaded the U.S. in
the eighteen century (Forman and Kesseli 2003)
and the later has become dominant much more
recently since its introduction in 1919
(Fairbrothers and Gray 1972). We have observed
sharp borders between these two sympatric species
where they co-occur, but found that these species
have larger overlap zones when they interact with
other allopatric species (.i.e., species that
originate from different geographic areas). These
differences might relate to studies by Turkington
and Mehrhoff (1990) that list several cases in
which plants perform better under interspecific
competition with their sympatric neighbors, as
compared to their allopatric neighbors. This
evidence has been interpreted as providing a
strong sign for co-evolution in communities
(Lawlor and Maynard-Smith 1976). Our field and
greenhouse studies investigate belowground
interactions and aboveground patterns between
pairs of sympatric and allopatric species.
Discussion
Belowground growth of Fallopia is least when
grown with Artemisia and most with Solidago, but
aboveground growth (total shoot height) of
Fallopia is greatest when grown with Artemisia.
It appears that when Fallopia and Artemisia are
paired, Fallopia is allocating more energy into
aboveground growth as opposed to belowground
growth. Our results also suggest that Fallopia
grows well above- and below-ground when paired
with Microstegium and Solidago. In general, this
confirms our hypothesis that direct competition
between Fallopia and Microstegium is
comparatively small, therefore possibly
suggesting recognition and cooperation between
these sympatric species. On the other hand,
belowground growth of Fallopia and Artemisia,
when grown together, was comparatively poor
possibly suggesting strong direct competition,
allelopathy or some other growth deterrents
between allopatric species.
Shown (above, left) is the area cover (average)
along 3.5m long grid transects (grid size 50x50
cm). These transects are centered at the
boundary of monotypic stands.
Future Directions
Discussion

• The root interaction experiment will be
  redesigned to assess one on one interactions
  between pairs of species and include a
• greater number of replicates to obtain more
  conclusive results.
• Initiation of a root chamber experiment to
  assess root interactions when plant roots are
  forced to grow into one another due to
• gravitational forces. Root interactions
  between plants can be observed over time as they
  grow along a Plexiglas viewing pane.

Pairs of sympatric species species that
originate from similar geographic areas tend to
have smaller overlap zones between them compared
to species pairs in which each originate from
different areas. This difference, though
significant, is based on a fairly small data set.
For instance it is not clear to us whether
different subgroups of sympatric species (e.g.
Asian, European or native North American species)
show similar low levels of overlap avoidance.
Moreover, the mechanisms underlying such
cooperation are unclear and may be case
specific.
References
Acknowledgements We are grateful to a number of
people who guided us to research sites and
provided access Betty Ann Kelly (Union County
Dept. Parks Recreation, New Jersey), Frank
Gallagher (Liberty State Park) and Martin Rapp
(New Jersey Natural Lands Trust) and to Amitabha
Bose (New Jersey Institute of Technology, UBM
program) who was instrumental in keeping the
undergraduates on the mathematical track.
Fairbrothers, D.E. and J.R. Gray. 1972.
Microstegium vimineum (Trin.) A. Camus
(Gramineae) in the United States. Bulletin of
the Torrey Botanical Club 99(2)
97-100. Forman, J. and R.V. Kesseli. 2003.
Sexual reproduction in the invasive species
Fallopia japonica (Polygonaceae). American
Journal of Botany 90(4) 586-592. Lawlor, L.R.
and J. Maynard-Smith. 1976. The co-evolution
and stability of competing species. American
Naturalist 110 79-99. Turkington, R. and L.A.
Mehrhoff. 1990. The role of competition in
structuring pasture communities. In Grace,
J.B., Tilman, D. (Eds.) Perspectives on Plant
Competition, Academic, San Diego.