Native plant diversity and introduced earthworms have contrasting effects on the success of

invasive plants

Timothy J. S. Whitfeld1*, Alexander M. Roth1, Alexandra G. Lodge1, Nico Eisenhauer2, Lee E.

Frelich1, Peter B. Reich1, 3

1University of Minnesota, Department of Forest Resources, 1530 Cleveland Avenue North, St.

Paul, Minnesota, 55108-6112, USA

2Institute of Ecology, Friedrich-Schiller-University Jena, Dornburger Str. 159, 07743 Jena,

Germany

3Hawkesbury Institute for the Environment, University of Western Sydney, Penrith, NSW 2751,

Australia

*Corresponding author: Email: whitf015@umn.edu, Phone: (612) 624-6709,

Fax: (612) 625-5212

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Supplementary Figure S1. (A) Initial path analysis model showing all tested causal influences

of earthworm presence/absence and resident species functional diversity (exogenous variables;

grey rectangles) on soil moisture, litter biomass, light transmittance, total resident species

biomass, total invasive species biomass (endogenous variables; white rectangles). Circles

indicate error terms (E1-E5).

(B) Best-fit path analysis of causal influences of earthworm presence/absence and resident plant

species functional diversity (exogenous variables) on aboveground buckthorn biomass, soil

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moisture, and total resident plant species biomass (endogenous variables). Numbers on arrows

are standardized path coefficients (equivalent to correlation coefficients). Solid and dashed lines

indicate negative and positive relationships respectively. Bold lines indicate significant

standardized path coefficients (P < 0.05), fine dashed line indicates non-significant path

coefficient (P > 0.05). Circles indicate error terms (E1-E3). Model fitted the data: Chi-square =

0.106, probability level = 0.948, AIC = 26.106

Supplementary Figure S2. Mean biomass, by earthworm treatment, of all resident and invasive

species (error bars represent one standard error).

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Supplementary Figure S3. Invasive species biomass versus (A) net biodiversity effect, (B)

complementarity effect, and (C) selection effect. Circles and the solid line represent earthworms

absent. Crosses and the dashed line represent earthworms present. ns = non significant

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Supplementary Figure S4. Resident species biomass versus (A) net biodiversity effect, (B)

complementarity effect, and (C) selection effect. Circles and solid lines represent earthworms

absent. Crosses and dashed lines represent earthworms present.

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Worms absent: R2 = 0.12, F(1, 46) = 6.19, p = 0.02

Worms present: R2 = 0.20, F(1, 46) = 11.77, p = 0.001

Worms absent: R2 = 0.007, F(1, 46) = 0.37, p = 0.54

Worms present: R2 = 0.08, F(1, 46) = 3.76, p = 0.06

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Worms absent: R2 = 0.16, F(1, 46) = 8.90, p = 0.005

Worms present: R2 = 0.13, F(1, 46) = 7.19, p = 0.01

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Supplementary Table 1. Experimental design indicating the number of microcosms for each of

the three native species diversity levels. EM = (Eurybia macrophylla (L.) Cass, AE = Asclepias

exaltata L., CB = Carex blanda Dewey, DG = Desmodium glutinosum (Muhl. ex Willd.) Alph.

Wood, EH = Elymus hystrix L., LA = Lathyrus sp.

Diversity treatment

Species mix Number of microcosms

Number of species

Number of functional groups

Monoculture EM 6 1 1Monoculture AE 6 1 1Monoculture CB 6 1 1Monoculture DG 6 1 1Monoculture EH 6 1 1Monoculture LA 12 1 1Two species CB, EH 6 2 1Two species EM, AE 6 2 1Two species DG, LA 4 2 1Two species CB, EM 6 2 2Two species CB, AE 6 2 2Two species EH, EM 6 2 2Two species EH, AE 6 2 2Two species CB, DG 6 2 2Two species CB, LA 4 2 2Two species EH, DG 6 2 2Two species EH, LA 4 2 2Two species EM, DG 6 2 2Two species EM, LA 4 2 2Two species AE, DG 6 2 2Two species AE, LA 4 2 2Six species EM, AE, CB,

DG, EH, LA16 6 3

Total 138

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