Photo: Russian Olive, southwest Montana. © 2020 Delena Norris-Tull
Summary thoughts on research on causes of the success or failure of biological invasions
Commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020, updated November 2024.
A wide array of theories/hypotheses have emerged, in attempts to understand what factors, or combinations of factors, enable some plant species to become invasive, while most other nonnative species do not. Theories are validated by research. If research lends support to a particular theory, that theory becomes more widely recognized. Some of the theories described here conflict with other theories, and some complement each other.
For a number of those theories, the evidence supporting or refuting it are mixed. And some plant species seem to respond as predicted, while others do not. I believe we are in the infancy of understanding the mechanisms that result in a nonnative plant becoming invasive and destructive.
It is clear from the literature review that not enough research has been conducted to reach a clear understanding of the various factors that contribute to the success or the failure of introduced species in a nonnative range. For each species, are there multiple factors that interact with each other, to result in either success of failure? Are the factors so specific to individual species that no general approach to plant management can be successful? Or is it more accurate to say that there are multiple factors that interact with each other, to result in either success or failure?
In their study of performance differences from genoptypes of invasive tallow trees, comparing growth and survival rates of seedlings from trees that have been present in four states in the southeastern USA for different lengths of time (ranging from 100 to 233 years), Siemann, Rogers, & Dewalt (2006) state that their results indicate "a complex interaction of native herbivores and introduced plants in which low levels of herbivory at first may promote invasion success but then accumulation of herbivores over a period of centuries eventually equalizes invasive and native plant performance."
This suggests the possibility that nonnative species, over centuries, become naturalized into local ecosystems and potentially become less invasive over time. Some nonnative species that are invasive in some areas of North America are not invasive in other areas, where they have become part of the local ecosystem and naturalized.
It seems clear that it will remain challenging to determine which combination of factors contribute to the success or failure of each species.
Within this website, the sections on Herbicide Resistance discuss the reality that many invasive species evolve to become resistant to the herbicides and pesticides designed to keep them under control. Chemical manufacturing companies keep inventing new chemicals in what may be a useless attempt to come up with chemicals for which invasive species will not develop resistance.
The sections on Biocontrol and the other research cited in these webpage summaries point to the possibility that plant species evolve in the introduced range and can become resistant to the same specialist herbivores that controlled them in their native range.
Are we fighting a losing battle to control invasive species?
And we must remember that the vast majority of nonnative plants that we now condemn with the labels, "invasive" or "noxious," were originally brought to North America because of their value as agricultural crops, or their use in soil stabilization, as medicines, and for many additional uses.
Human beings do not have a good track record when it comes to attempting to protect agricultural crops or the environment. Rather than pumping billions of dollars annually into eradication of introduced species that have become economic or ecological problems, shouldn’t we be putting those dollars into much more research, to ensure that our management practices have a greater chance of being effective?
Reference:
Link to return to the research on Invasive Success Hypotheses:
Summary thoughts on research on causes of the success or failure of biological invasions
Commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020, updated November 2024.
A wide array of theories/hypotheses have emerged, in attempts to understand what factors, or combinations of factors, enable some plant species to become invasive, while most other nonnative species do not. Theories are validated by research. If research lends support to a particular theory, that theory becomes more widely recognized. Some of the theories described here conflict with other theories, and some complement each other.
For a number of those theories, the evidence supporting or refuting it are mixed. And some plant species seem to respond as predicted, while others do not. I believe we are in the infancy of understanding the mechanisms that result in a nonnative plant becoming invasive and destructive.
It is clear from the literature review that not enough research has been conducted to reach a clear understanding of the various factors that contribute to the success or the failure of introduced species in a nonnative range. For each species, are there multiple factors that interact with each other, to result in either success of failure? Are the factors so specific to individual species that no general approach to plant management can be successful? Or is it more accurate to say that there are multiple factors that interact with each other, to result in either success or failure?
In their study of performance differences from genoptypes of invasive tallow trees, comparing growth and survival rates of seedlings from trees that have been present in four states in the southeastern USA for different lengths of time (ranging from 100 to 233 years), Siemann, Rogers, & Dewalt (2006) state that their results indicate "a complex interaction of native herbivores and introduced plants in which low levels of herbivory at first may promote invasion success but then accumulation of herbivores over a period of centuries eventually equalizes invasive and native plant performance."
This suggests the possibility that nonnative species, over centuries, become naturalized into local ecosystems and potentially become less invasive over time. Some nonnative species that are invasive in some areas of North America are not invasive in other areas, where they have become part of the local ecosystem and naturalized.
It seems clear that it will remain challenging to determine which combination of factors contribute to the success or failure of each species.
Within this website, the sections on Herbicide Resistance discuss the reality that many invasive species evolve to become resistant to the herbicides and pesticides designed to keep them under control. Chemical manufacturing companies keep inventing new chemicals in what may be a useless attempt to come up with chemicals for which invasive species will not develop resistance.
The sections on Biocontrol and the other research cited in these webpage summaries point to the possibility that plant species evolve in the introduced range and can become resistant to the same specialist herbivores that controlled them in their native range.
Are we fighting a losing battle to control invasive species?
And we must remember that the vast majority of nonnative plants that we now condemn with the labels, "invasive" or "noxious," were originally brought to North America because of their value as agricultural crops, or their use in soil stabilization, as medicines, and for many additional uses.
Human beings do not have a good track record when it comes to attempting to protect agricultural crops or the environment. Rather than pumping billions of dollars annually into eradication of introduced species that have become economic or ecological problems, shouldn’t we be putting those dollars into much more research, to ensure that our management practices have a greater chance of being effective?
Reference:
- Siemann, E., Rogers, W.E., & Dewalt, S.J. (August 1, 2006). Rapid adaptation of insect herbivores to an invasive plant. Proceedings of the Royal Society, 273, 2763-2769.
Link to return to the research on Invasive Success Hypotheses:
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