Ant Community Changes Associated With Introduced Plant Species.  

Daniel S. Kjar and Edward M. BarrowsIntroduction

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.

Arthropods 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.

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 2002–2003).• 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.

A. B.

C. D.

Figure 2. (A) Soil core tool, (B) plant coverage grid, (C) pitfall trap, (D) modified Berlese-Tullgren funnel setup.

Images from the low forest in Dyke Marsh Wildlife Preserve: (A) a tree fall area dominated by Porcelainberry, (B, D) areas of relatively native forest, (C) an Asiatic bittersweet vine strangling a tree.

Percent Alien Plant Coverage

1.0.8.6.4.20.0

To

tal A

nt

Ab

un

da

nce

50

40

30

20

10

0

Figure 4a. Percent invasion, tree richness, and soil moisture account for nearly half the variance in ant abundance (Hierarchical Linear Regression).

Model Summary

.451a .204 .183 11.23765

.625b .391 .358 9.96071

.672c .451 .405 9.58545

Model1

2

3

R R SquareAdjustedR Square

Std. Error ofthe Estimate

Predictors: (Constant), Soil Moisturea.

Predictors: (Constant), Soil Moisture, Tree Richness,b.

Predictors: (Constant), Soil Moisture, Tree Richness,Percent Alien Plant Coverage

c.

Soil Moisture

.4.3.2.1

To

tal A

nt

Ab

un

da

nce

50

40

30

20

10

0

Table 2. Regression models for ant

community associations. a,b,c

Figure 4b. Ants and soil moisture.

Tree Richness

76543210-1

To

tal A

nt

Ab

un

da

nce

50

40

30

20

10

0

Figure 4c. Ants and tree richness.

ANOVAd

1227.575 1 1227.575 9.721 .003a

4798.825 38 126.285

6026.400 39

2355.416 2 1177.708 11.870 .000b

3670.984 37 99.216

6026.400 39

2718.692 3 906.231 9.863 .000c

3307.708 36 91.881

6026.400 39

Regression

Residual

Total

Regression

Residual

Total

Regression

Residual

Total

Model1

2

3

Sum ofSquares df Mean Square F Sig.

Predictors: (Constant), Soil Moisture (%)a.

Predictors: (Constant), Soil Moisture (%), Tree Richnessb.

Predictors: (Constant), Soil Moisture (%), Tree Richness, Alien Plant Coverage (%)c.

Dependent Variable: Ant Abundanced.

Table 3. ANOVA table for ant community associations. a,b,c,d

TreeRichness

AntsInvasive Plants

Soil Moisture-

+

+

A model of environmental factors significantly associated with changes in ant abundance. Arrow width represents amount of variance explained by the association. Arrow direction represents hypothesized direction of relationship.

Model Summaryc

.419a .176 .154 9.27474

.500b .250 .210 8.96340

Model1

2

R R SquareAdjustedR Square

Std. Error ofthe Estimate

Predictors: (Constant), Total Plant Richnessa.

Predictors: (Constant), Total Plant Richness, AlienPlant Coverage (%)

b.

Dependent Variable: Aphaenogaster rudisc.

ANOVAc

696.809 1 696.809 8.100 .007a

3268.791 38 86.021

3965.600 39

992.923 2 496.462 6.179 .005b

2972.677 37 80.343

3965.600 39

Regression

Residual

Total

Regression

Residual

Total

Model1

2

Sum ofSquares df Mean Square F Sig.

Predictors: (Constant), Total Plant Richnessa.

Predictors: (Constant), Total Plant Richness, Alien Plant Coverage (%)b.

Dependent Variable: Aphaenogaster rudisc.

Alien Plant Coverage (%)

1.0.8.6.4.20.0

Aph

aeno

gast

er r

udis

40

30

20

10

0

Table 4. Regression models for A. rudis

associations. a,b,c

Table 5. ANOVA table for A. rudis

associations. a,b,c

Total Plant Richness

1614121086420

Ap

ha

en

og

ast

er

rud

is

40

30

20

10

0

Figure 5a. Aphaenogaster rudis abundance and alien plant coverage.

Figure 5b. Aphaenogaster rudis abundance and total plant richness.

Trees

A. rudis

Invasive Plants

Plant Richness

Soil Moisture

-

+-

A model of environmental factors significantly associated with changes in A. rudis abundance. Soil moisture, tree richness, and abundance were not associated with A. rudis abundance. Arrow width represents amount of variance explained by the association. Arrow direction represents hypothesized direction of relationship.

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.

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.

Biology DepartmentGeorgetown UniversityWashington, D.C.20057

ANOVAb

35.142 1 35.142 7.504 .009a

177.958 38 4.683

213.100 39

Regression

Residual

Total

Model1

Sum ofSquares df Mean Square F Sig.

Predictors: (Constant), Invasive Plant Coveragea.

Dependent Variable: Native Plant Richnessb.

Model Summary

.406a .165 .143 2.164Model1

R R SquareAdjustedR Square

Std. Error ofthe Estimate

Predictors: (Constant), Invasive Plant Coveragea.

Table 1. Increased alien plant coverage is associated with decreased native plant richness.a,b

Appendix

Coefficientsa

54.624 9.919 5.507 .000

-126.351 40.526 -.451 -3.118 .003

44.296 9.310 4.758 .000

-110.769 36.217 -.396 -3.059 .004

4.175 1.238 .436 3.372 .002

32.316 10.797 2.993 .005

-90.450 36.319 -.323 -2.490 .018

4.446 1.199 .464 3.707 .001

13.552 6.816 .257 1.988 .054

(Constant)

Soil Moisture

(Constant)

Soil Moisture

Tree Richness

(Constant)

Soil Moisture

Tree Richness

Percent AlienPlant Coverage

Model1

2

3

B Std. Error

UnstandardizedCoefficients

Beta

StandardizedCoefficients

t Sig.

Dependent Variable: Total Ant Abundancea.

Table 2. Increased alien plant coverage is associated with increased ant abundance.a

Coefficientsa

22.209 4.235 5.244 .000

-1.694 .595 -.419 -2.846 .007

14.161 5.859 2.417 .021

-1.384 .598 -.342 -2.316 .026

12.162 6.335 .284 1.920 .063

(Constant)

Total Plant Richness

(Constant)

Total Plant Richness

Alien Plant Coverage (%)

Model1

2

B Std. Error

UnstandardizedCoefficients

Beta

StandardizedCoefficients

t Sig.

Dependent Variable: Aphaenogaster rudisa.

Table 3. Increased alien plant coverage is associated with increased A. rudis abundance.a

Statistical AnalysisEach site’s trap catches are summed across all trapping dates (n=40). Hierarchical Linear Regression was used for analysis where appropriate. Simple regression was used for the analysis of invasive plant coverage and native plant richness.

AcknowledgmentsWe greatly appreciate help from Maya Patel, Philip Sze, Martha Weiss, John Sauer, Barry Wood (NPS), Smithsonian and USDA specialists, and support from Friends of Dyke Marsh, Georgetown University, the National Park Service, and the Washington Biologists’ Field Club.

ReferencesCrisp, P. N., K. J. M. Dickinson, and G. W. Gibbs.

1998. Does native invertebrate diversity reflect native plant diversity? A case study from New Zealand and implications for conservation. Biological Conservation 83: 209–220.Gremmen, N. J. M., S. L. Chown, et al. 1998. Impact

of the introduced grass Agrostis stolonifera on vegetation and soil fauna communities at Marion Island, sub-Antarctic. Biological

Conservation 85(3): 223–231.Panzer, R. and M. W. Schwartz. 1998. Effectiveness

of a vegetation-based approach to insect conservation. Conservation Biology 12: 693–702.Perfecto, I. and R. Snelling 1995. Biodiversity and the

transformation of a tropical agroecosystem: Ants in coffee plantations. Ecological

Applications 5: 1084–1097.

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 < 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 < 0.05, Figures 5a, 5b, Appendix: Table 3).

Invasive plant coverage is associated with decreasing native plant richness. In our model of coverage, increasing coverage by one species does not require decreasing coverage of other species. Coverage was determined by the presence of a species in a grid of nine subplots. Maximum coverage of a species at a single site is nine; many species may have a score of 9 at any one site.

Invasive Plant Coverage

3020100

Na

tive

Pla

nt

Ric

hn

ess

12

10

8

6

4

2

0

2.09%Rosa multiflora

0.70%Lonicera maackii

56.38%Lonicera japonica

0.23%Ligustrum sp.

3.25%Hedera helix

0.93%Euonymus fortunei

< 0 .01%Duchesnea indica

2.55%Clemitis terniflora

24.59%Celastrus orbiculatus

9.28%Ampelopsis brevipedunculata

Table 1. Invasive alien plant species found in this study and their contribution to the total alien plant species coverage.

Figure 3. Decreasing native plant species richness is associated with increasing alien plant coverage.

Figure 1. (A) To locate sites we used a Trimble® GPS unit (left, Keith Post with GPS). (B) Satellite imagery and ArcView® with AlaskaPak were used to generate random field site loactions in the Dyke Marsh Wildlife Preserve low forest.

A. B.