Effects of Simulated Herbivory on Alliaria petiolata

Ashley Paschal, Brian Scott,

Kyle Burns, and Tyler McPheters

Background

• Problems with invasive species– Cause a decline in native populations– Leads to a loss of biodiversity

• Difficult and expensive to manage

Garlic mustard invasion

• Eradication might be nearly impossible for colonized sites– Autogamous breeding system, high seed

production, and rapid growing season (Anderson et al. 1996)

– Successful in outcompeting other plants (Meekins and McCarthy 1999)

– High tolerance to environmental variation (Meekins and McCarthy 2001)

How do we get rid of them?

• Non-biological eradication– Fires, herbicides, floods, and mowing– Possibly effective, but damaging to

surrounding environment

• Biological controls– Host-specific herbivores might be a suitable

solution (Blossey et al. 2001)

Deciding on a control

• Simulated herbivory– Benefit from controlling multiple variables– Better understanding what types of herbivores

are effective (Baldwin 1990)

• Rebek and O’Neil (2005)– Simulated herbivory shortens lifespan and

decreases biomass of garlic mustard

Our study

• How does simulated herbivory affect garlic mustard populations in the DePauw Nature Park?

• Hypothesis: Increased herbivory will reduce survival, growth, and reproduction of garlic mustard

• Indicated by differences in height, above-ground biomass, and flower number

Methods

• Location: DePauw Nature Park – Creekside Trail.

• Initially labeled 40 plots that contained at least three (3) rosettes of garlic mustard

(Hula-hoop sized plots)

• Labeled one plant in each plot as control, low, and high.

• Counted leaves on each plant and then performed treatments.

Methods – Treatment

• Standard hole–punch• Half of leaves from

the two treatment levels were punched

• Low – One fourth of leaf area removed.

• High – Half of leaf area removed

Methods

• Measured light intensity using a light meter

• Measured soil moisture levels

• Post-treatment:– Number of flowers,

height of plants, and above-ground biomass.

Methods

• Statistical Analysis:– Pearson Correlations– ANOVA

ResultsResultsTreatment Effect on Final Height

0

20

40

60

80

100

120

140

Fin

al H

eig

ht

(cm

)

Control

Low Treatment

High Treatment

F = 0.530 P > 0.05

Treatment Effect on Biomass

0

2

4

6

8

10

Bio

mas

s (g

) Control

Low Treatment

High Treatment

F = 2.861 P > 0.05

Treatment Effect on Number of Flowers

0

20

40

60

80

100

120

Nu

mb

er o

f F

low

ers

Control

Low Treatment

High Treatment

F = 0.229 P > 0.05

Correlation Data

Significant Correlations• Initial height was correlated with density, total

number of leaves, number of flowers, final height, and biomass.

• Final height was correlated with number of flowers, and biomass.

• Biomass was correlated with number of flowers.• There was also a correlation between initial

number of leaves and amount of sunlight.• Flowering date was not correlated with the

different treatments. Most plants had flowered by March 20, 2006 and the remainder had flowered by March 27, 2006.

Discussion

• Our low herbivory and high herbivory treatments showed no significant effects on garlic mustard plant height, biomass, or number of flowers (p>0.05)

• No significant ANOVA tests, so plants started off comparably and treatments did not detectably affect growth or reproduction

Discussion

• Many obvious correlations between response variables and initial variables

– i.e. initial number of leaves and initial height

– Less expected but significant correlation seen between plant density and height

Discussion

• Published results have used different methods

• Rebek and O’Neil 2005 – Effects of simulated herbivory on A. petiolata. – Study on manual flower shoot damage– Led to decreased plant size and reproduction.

• Bossdorf et al. 2004 – Leaf removal led to reduced production of seeds and fruits.– 75% of leaf removal reduced fitness to 81% of that of

controls.

Implications

• Results imply that the level of simulated herbivory used was not effective– Currently there are no herbivores in the

Nature Park that eat garlic mustard– If we were to introduce an herbivore, it would

have to more drastically affect garlic mustard to be successful in controlling the garlic mustard population

Implications

• Garlic mustard is currently affecting the native species of plants at the DePauw Nature Park, so it is important to control garlic mustard

• Control of garlic mustard important also for regeneration of forest

New York Times article (May 2, 2006) says that GM disrupts interactions between tree seedlings and soil mycorrhizae

Recommendations

• Other strategies for removal of garlic mustard:

pulls, herbicides, controlled fire• Small, isolated patches that are more

manageable should be controlled to prevent spread– Rim trail patches in contrast to rail trail

flourishing populations

Works CitedBaldwin, I.T. 1990. Herbivory simulations in ecological research. TREE 5: 91-

93.Bossdorf, O., S. Schroder, D. Prati, and H. Auge. 2004. Palatability and

tolerance to simulated herbivory in native and introduced populations of Alliaria petiolata (Brassicaceae). American Journal of Botany 91 (6):856-862.

Blossey, B., V. Nuzzo, H. Hinz, E. Gerber. 2001. Developing biological control of Alliaria petiolata (M. Bieb.) Cavara and Grande (garlic mustard). Natural Areas Journal 21: 357-367.

Meekins, J.F., and B.C. McCarthy. 1999. Competitive ability of Alliaria petiolata (garlic mustard, Brassicaceae), an invasive, nonindigenous forest herb. International Journal of Plant Sciences 160: 743-752.

Meekins, J.F., and B.C. McCarthy. 2001. Effect of environmental variation on the invasive success of a nonindigenous forest herb. Ecological Applications 11: 1336-1347.

Rebek, K.A., and R.J. O’Neil. 2005. Impact of simulated herbivory on Alliaria petiolata survival, growth and reproduction. Biological Control 34:283-289.