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
Root Interaction Experiment
Methods
Methods
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.
150
100
50
(F
S)
)
M
lid
ag
o
(F
M
icr
So
os
te
gi
um
te
m
pi
a
isi
a
(F
S)
(F
A)
0
)
As
i
Pairing
200
Ar
As
i
an
-E
ur
op
As
ea
ia
n
nNa
tiv
e
Eu an
ro
pe
an
Na
tiv
e
0
Toward other plant
Toward wall
Fa
llo
5
250
M
10
Fallopia had significantly
(F = 7.29; p<.0001; n=6)
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.
300
(F
15
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.
Fa
llo
pi
a
20
(F
A)
P=0.0130
Average Fallopia japonica root length toward
intra- or inter-specific neighbor
Average root length toward other plants
or away from plants
pi
a
25
Results
Fa
llo
Allopatric pairs have significantly larger overlap compared to sympatric
pairs
Average Root Length (cm)
Results
Overlap (% of transect)
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.
Grid Transect Data
Species/Arena
350
Toward Interspecific
Toward Intraspecific
300
Average Root Length (cm)
Abstract
contact: holzapfe@andromeda.rutgers.edu
250
200
150
100
50
0
Fallopia (FA)
Fallopia (FM)
Fallopia (FS)
Species/Arena
Fallopia grown with
Artemisia had significantly
(F= 4.69; P<.0001; n=6)
greater average root length
toward itself (intraspecific)
than toward Artemisia
(interspecific). Fallopia
grown with Microstegium or
Solidago showed no difference
between intra- and interspecific neighbors.
Fallopia overlaps with sympatric species Microstegium less than with
allopatric species Artemisia
180
100
80
60
40
20
0
Fallopia (FA)
Fallopia (FM)
Fallopia (FS)
160
2
3
4
5
6
7
140
120
100
80
60
40
20
Transect
0
1
Fallopia
Artemisia
100
80
60
40
20
0
2
3
4
5
6
7
8
9
10
11
Belowground growth of Fallopia is correlated
with biomass of other species
Although not
statistically
significant,
Fallopia showed
the greatest total
shoot height over
time when grown
with Artemisia
and the least with
Microstegium.
8
Belowground Biomass (Other
Species)
Cover (scaled %)
Microstegium
1
Cover (scaled %)
Fallopia japonica and Microstegium vimineum are two nonnative 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.
Fallopia
Total Height (cm)
Introduction
Fallopia japonica shoot height and number
of leaves by arena over 11 weeks
7
Solidago
6
5
4
3
Microstegium
2
Artemisia
1
0
0
20
40
60
80
Belowground growth (Fallopia )
Measurement Number (Weekly)
Belowground growth of
Fallopia is positively
correlated (r=0.9924)
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.
Discussion
1
2
3
4
5
6
7
Transect
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.
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.
Future Directions
Discussion
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.
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.
• 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.
References
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.