Left top: Healthy Senecio vulgaris growing in Calif. where it was introduced approximately 100 yrs ago. Left bottom: Dying Senecio vulgaris covered in Puccinia and Albugo pathogens, growing in part of its native range in the UK (from Calif. seed). Center top: Senecio squalidus growing in the UK where it invaded nearly 400 years ago, with some Puccinia infection. Center bottom: Senecio ciliocarpa growing in the UK where it was introduced less than 10 years ago with no infection. Right top: Albugo. Right bottom: Puccinia. Photos by: Christine V. Hawkes.
One way invasive plants can get a leg up in their new environment is through an absence of natural enemies, but their escape doesn’t last long, according to a new study by biologist Dr. Christine Hawkes.
In a meta-analysis of 67 introduced plant species, Hawkes found that invasive plants start-out escaping natural enemies, but they become just as susceptible to herbivores and pathogens as natives over time.
“They eventually experience the same enemy damage as native plants,” says Hawkes, assistant professor of integrative biology, “and once the invasive plants are more like the natives, we may need to use different approaches for eradication.”
Invasive plants are thought to succeed in their new environments for a number of reasons, including escape from natural herbivores, a lack of competition, and increase in size and reproduction. This is the first quantitative review of invasive plants showing how they can change over time.
Hawkes looked at published records that were mainly studies of herbaceous dicots that invaded North America from Eurasia as few as five years and up to 377 years ago.
She compared the invaders to others of the same species in their home range (called “conspecifics”) and to similar native species in their introduced range.
Hawkes’ analysis confirmed that invaders do escape herbivores and pathogens, and the more noxious the weed, the more they escape.
Most revealing, she found that invasive plants evade enemies less and less over time.
“There’s definitely escape from natural enemies, but escape is largely limited to those species that have been in the introduced environment for less than 50 to 100 years,” says Hawkes.
“This is just a first step in a long pathway towards thinking about invasive plants as something changeable,” she says. “There are all sorts of ecological and evolutionary changes happening over time that make invaders a moving target in regards to management.
“If these patterns hold up for individual species followed through time, we may be able to use time-based strategies to improve control efforts.”
Hawkes study was published in The American Naturalist.
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