Testing hypotheses for exotic plant success: parallel experiments in the native and introduced ranges

Area of Science:

• Ecology
• Invasive Species Biology
• Plant Population Dynamics

Background:

• Understanding why some exotic plants become abundant invaders while rare in their native range is a key ecological question.
• Factors like herbivory and disturbance are hypothesized to influence plant population success across biogeographic ranges.
• Previous research often lacks comparative experimental data from both native and introduced ranges.

Purpose of the Study:

• To test the hypotheses that "enemy escape" from specialist herbivores and a greater response to disturbance contribute to the success of exotic plants.
• To experimentally assess the impact of herbivory and disturbance on the performance of houndstongue (Cynoglossum officinale) in its native (Germany) and introduced (USA) ranges.
• To model the demographic consequences of these factors on population growth rates in different ranges.

Main Methods:

• Field experiments manipulating insect herbivore exclusion and small-scale disturbances in native and introduced populations of Cynoglossum officinale.
• Assessment of plant size and fecundity responses to experimental treatments in both ranges.
• Parameterization of integral projection population models using experimental and demographic data to compare population growth rates (lambda).

Main Results:

• Insect herbivores negatively impacted plant size and fecundity in the native range but had minimal effects in the introduced range.
• Small-scale disturbances increased seedling recruitment in both ranges, with a stronger positive effect on subsequent survival in the introduced range.
• Population models indicated that a greater response to disturbance in the introduced range had a larger positive effect on population growth rate (lambda) than enemy escape.

Conclusions:

• The enhanced response to small-scale disturbances in the introduced range appears to be a more significant driver of higher houndstongue abundance than escape from specialist herbivores.
• This study underscores the importance of considering interactions with the abiotic environment, particularly disturbance, in understanding plant invasions.
• Biogeographic experiments comparing native and introduced ranges are crucial for elucidating the complex factors governing the success of exotic plants.