The Biology and Ecology of Garlic Mustard Dr. Kevin Gibson Purdue - - PowerPoint PPT Presentation

The Biology and Ecology

• f

Garlic Mustard

• Dr. Kevin Gibson

Purdue University

Outline

• Life cycle and distribution
• Why is it invasive?
• Impact on native plant communities
• Role in forest change

– Earthworms – Potential adaptation by native species

• Management implications

Garlic Mustard Life Cycle()

Photo by Doug Landis Photo by Doug Landis

Distribution

Why is it invasive?

• Release from natural enemies
• Phenology
• Reproduction
• It produces nasty compounds

Why is it invasive?

• Release from natural enemies

– Many more herbivores (69 insect spp.) in native range (Szentesi 1991) and herbivory is greater in native range. – However, garlic mustard does not have greater growth or reduced allocation to defense in invaded range than in native range (Bossdorf et al. 2004) – White‐tailed deer may reduce competition by consuming native plant species and disturbing the soil with their hooves (Nuzzo 2000).

Why is it invasive?

• Phenology

– Maximum photosynthetic rates achieved before many native species emerge (Myers and Anderson 2003). – Overwinters as green rosette

• Reproduction

– 3,500 seeds per plant, 9500 seeds m‐2 in northern Illinois (Nuzzo 1993) – Adapted to generalist pollinators – Virtually all pollinated ovules develop into seed – High levels of population cross‐pollination maintains high level of genetic variability – Virtually all second year plants produce flowers

Emergence and survival

Cohorts

1 2 3 4 5 6 7 8 9 10

Plant density (individuals m

• 2)

10 20 30 40 50 60 70 80

44% 25% 18% 28% 8% 0%

Why is it invasive?

• It produces nasty compounds

– Glucosinolates – Cyanide (Cipollini and Gruner 2007)

• It suppresses soil pathogens and pests

(Klironomos 2002), facilitating its own invasion.

• It suppresses mycorrhizal fungi, accelerates

decomposition, and increases N availability (Rodgers et al. 2008).

– Many native forest species are AMF dependent – Garlic mustard establishment is reduced by leaf litter (Bartsuzevige et al. 2007)

Impact!

Stinson et al. (2007)

Impact

• McCarthy (1997)

– Removal of garlic mustard increased native annuals, vines, and tree seedlings within first year

• Meekins and McCarthy (1999)

– Box elder (Acer negundo) and jewelweed (Impatiens capensis) biomass greater with garlic mustard than in monoculture – Chestnut oak (Quercus prinus) had opposite response.

• Hochstedler et al. (2007)

– Cover of native spring perennials and graminoids increased within two years of herbicide applications – Cover of annuals decreased slightly after five years of applications

Additional impact

• West Virginia white butterfly (Pieris virginiensis)

lays eggs on garlic mustard. Hatching is lower on garlic mustard than on native species (Porter 1994).

• Mustard white butterfly (Pieris napi oleracea)

– Field mustard and wild radish are primary hosts – Garlic mustard can serve as alternate hosts – Larvae have lower survivorship on garlic mustard than

• n native plant hosts

– Models suggest that garlic mustard is a major factor in the decline of this butterfly species.

Forest change

• Garlic mustard is one

among many plant and animal invaders.

• Earthworms may

facilitate garlic mustard invasion

– Garlic mustard dominant

• n sites with earthworms

(Hale 2004) – Fewer herbaceous species, lower cover, reduced litter layer – Shift from slower cycling fungal dominated system to rapid bacterial dominated system

Bohlen et al. (2004)

Site without earthworms Site with earthworms

Adaptation

• Keeler et al. (2008). Escaping an evolutionary trap:

preference and performance of a native insect on an exotic invasive host. Oecologia 156:559‐568.

• Compared oviposition

preference and larval performance

• f P. oleracea
• n garlic mustard in areas with and without

garlic mustard.

• Females preferred GM and larval survivorship was

positively correlated with mother’s preference in area with GM.

• Females had wide range of preference of host preference

in area without GM and very low larval survival on GM.

• P. oleracea

may be adapting to GM in areas where the weed is well‐established

Management Implications

• Garlic mustard has a suite of adaptations that

contribute to its ability to invade and substantially alter forest systems.

• Garlic mustard may be as much a symptom as

cause of forest change.

• Eradication is not possible at the regional

level; local control will require a sustained effort.

Management Implications

• Garlic mustard phenology

may allow local management without damaging native species.

• Biocontrol

may allow regional control that reduces garlic mustard impact.