MANAGEMENT OF INVASIVE PLANTS IN THE WESTERN USA
  • Defining the Problem
    • What is a Weed? >
      • Federal Definitions of Noxious Weeds
    • Costs of invasive plants
    • Human Factor
    • Challenges of Invasive Plants
    • Wildfires in the Western USA >
      • Forest Fires: Structure
      • Bark Beetles & Forest Ecosystems
      • Rangeland Fires
    • Climate Change Impacts on Plants >
      • Climate Change: CO2, NO, UV, Ozone Impacts on Plants
      • Climate Change Impacts on Crops
      • Climate Change Impacts on C4 Plants
      • Climate Change Impacts on Rangelands
      • Climate Change Impacts on Forests
    • What are we doing?
  • Focus of this Project
    • Why Western States? >
      • Audience for these reports
    • History: Are we doomed to repeat it? >
      • Dust Bowl Re-visited >
        • China: Past & Present
        • UN Biodiversity Report
    • Policy vs. Practice
    • Ecosystems & Economics >
      • Reductionist Approach to science
      • Ecology & Feminism
      • Systems View of Life
      • Ecosystems Health
      • Economic Growth
      • Impact of the Petrochemical Industry
      • Interrelation of Economics & Ecology
    • Federal Agencies >
      • Federal Agencies and Invasive Species
      • History of Coordination with States
      • Challenges of Coordination between Federal Agencies
      • Collaboration or Confusion
    • Organizations to assist landowners
    • Federal Legislation on Invasive Species >
      • 1930s Federal Laws on Invasive Species
      • Federal Seed Act 1939
      • 1940s-1960s Federal Laws on Invasive Species
      • 1970s Federal Laws on Invasive Species
      • 1980s Federal Laws on Invasive Species
      • 1990s Federal Laws on Invasive Species
      • 2000-2010 Federal Laws on Invasive Species
      • 2011-2022 Federal Laws on Invasive Species
      • Federal Bills on Invasive Species not passed
      • Executive Orders on Invasive Species
      • Federal Excise Taxes
    • State Laws and Lists of Noxious Weeds
  • Why we need plants
    • Native Plants
    • Plant Resources
  • Invasive Success Hypotheses
    • Unified Framework
    • Role of Diversity >
      • How Ecosystems Maintain Diversity
      • Fluctuation Dependent Mechanisms
      • Competition-based coexistence mechanisms
      • Niche Differences
      • Species Richness
    • Enemy Release Hypothesis
    • Constitutive Defense Mechanisms
    • Evolution of Increased Competitive Ability
    • Role of Microbes
    • Indirect Defense Mechanisms
    • Novel weapons hypothesis
    • Evolutionary Shifts
    • Resource Allocation
    • Evolutionary Dynamics >
      • Pre-introduction evolutionary history
      • Sampling Effect
      • Founder Effect
      • Admixture, hybridization and polyploidization
      • Rapid Evolution
      • Epigenetics
      • Second Genomes
    • Role of Hybridization
    • Role of Native Plant Neighbors
    • Species Performance
    • Role of Herbivory
    • Evolutionary Reduced Competitive Ability
    • Summary Thoughts on Research
  • Historical Record
    • Regional Conferences
    • Timeline
  • Innovative Solutions
    • Grazing Solutions >
      • Sheep, Goat & Chicken Grazing
      • Cattle & Sheep Grazing
      • Cattle and Bison Grazing
      • Grazing and Revegetation
    • Agricultural Best Practices >
      • Ecologically based Successional Management >
        • Regenerative Agriculture
        • Sustainable Agriculture
      • Perennial Crops, Intercropping, beneficial insects
      • Soil Solarization
      • Natural Farming
      • Permaculture
      • Organic Farming
      • Embedding Natural Habitats
      • Conservation Tillage
      • Crop Rotation
      • Water Use Practices
      • Tree Planting: Pros & Cons
    • Rangeland Restoration >
      • Federal Goals for Rangelands
      • Novel Ecosystems
      • Prairie Restoration >
        • Prairie Restoration Workshop
        • Weed Prevention Areas
        • California grassland restoration
        • Selah: Bamberger Ranch Preserve
      • Sagebrush Steppe Restoration >
        • Low Nitrogen in Sagebrush Steppe
      • Revegetation with Native Plants
      • Dogs as detectors of noxious weeds
    • Habitat Conservation
    • Technology solutions
    • Nudges
  • Biological Control
    • Insects as Biocontrol >
      • Impacts of Biocontrol Agents on Non-Target Species
      • Indirect Impact of Biocontrol on Native Species
    • Challenges of Using Biocontrols >
      • DNA studies on Biocontrol Insects
      • Biocontrol takes time
    • Prioritization process for Biocontrol Programs
    • Evolutionary changes impact Biocontrol
    • Vertebrates as Biocontrol Agents
  • Herbicides: History and Impacts
    • Effectiveness of Herbicides in Agricultural Lands
    • Effectiveness of Herbicides in Rangelands
    • History of Use of Herbicides and Pesticides Prior to and During WWII
    • Herbicide use during and post-World War II >
      • 2,4-D Herbicide Use
      • 2,4-D and 2,4,5-T, post-World War II
    • Modern use of Herbicides >
      • Atrazine Herbicide
      • Dacthal, DCPA
      • Dicamba Herbicide
      • Glyphosate Herbicide
      • Paraquat Dichloride
      • Picolinic acid family of herbicides >
        • Picloram (Tordon 22K) Herbicide
        • Triclopyr Herbicide
    • Herbicide Resistance in Invasive Plants >
      • Herbicide Resistant Crops
      • Controlling herbicide-resistant weeds in herbicide-resistant crops
      • Best Management Practices
    • Myth of the Silver Bullet
    • Myth of Eradication
    • Merging of Agrochemical Companies
    • Funding for Research on Pesticides
    • Impacts of Pesticides on Environment and Human Health >
      • Pesticide Drift
      • Impacts of Pesticides on Biological Diversity
      • Impacts of Herbicides on Native Plants
      • Pesticide Impacts on Insects >
        • Butterflies: The Impacts of Herbicides
        • Monarch Butterflies: Impacts of Herbicides
      • Impacts of Pesticides on Wildlife >
        • Reptiles & Amphibians: Pesticide Impacts
      • Pesticide Residue in Foods
      • Commentary on Herbicide Use
  • Interviews
    • Interviews Biocontrol >
      • Biocontrol Wyoming
      • Montana Biocontrol Interview Maggio
      • Montana Biocontrol Interview Breitenfeldt
    • California Interviews >
      • Robert Price
      • Doug Johnson
    • Colorado Interviews >
      • George Beck Interview
      • Scott Nissen Interview
    • Idaho Interviews >
      • Purple Sage Organic Farms in Idaho
    • Montana Interviews >
      • Jasmine Reimer Interview Montana
      • Organic Farms Montana Interviews
    • Texas Interviews
    • Washington Interviews >
      • Ray Willard
    • Wyoming Interviews >
      • Slade Franklin Interview
      • John Samson Interview
    • Wyoming Weed and Pest Districts >
      • Josh Shorb Interview
      • Slade Franklin Interview 2
      • Lars Baker Interview
      • Steve Brill Interview
      • George Hittle Interview
      • Peter Illoway Interview
      • Robert Jenn Interview
      • Sharon Johnson Interview
      • Larry Justesen Interview
      • Gale Lamb Interview
      • Stephen McNamee Interview
      • Allen Mooney Interview
      • Rob Orchard Interview
      • Robert Parsons Interview
      • Dick Sackett Interview
      • Comments by Delena
    • NRCS Interviews: Wyoming
  • Western Weed Control Conference 1940s Minutes
    • 1942 Conference
    • 1945 Conference
    • 1946 Conference
  • Who am I?
    • My Work
    • My Inspirations
    • My Adventures
    • Contact Page
  • Road Logs
    • Colorado Road Logs
    • Idaho Road Logs
    • Montana Road Logs
    • New Mexico Road Logs
    • Texas Road Logs
    • Wyoming Road Logs
  • Bibliography

Evolutionary Changes
​in the New Environment:
Impacts on Biocontrol Agents

Photo: Kochia in Southwestern Montana. © 2020 Delena Norris-Tull

Evolutionary Changes in the New Environment: Potential impacts on the effectiveness of biocontrol agents

Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, September 2020.

​Müller-Scharer, et al., 2004, conducted a review of the research on evolution that may occur in invasive plants within their new non-native range. They found that, “Two contrasting, but mutually non-exclusive hypotheses address the relationship between phenotype and invasion success; the first assumes that invaders are pre-adapted with traits that make them successful invaders, whereas the second postulates successful invasion as the outcome of rapid evolutionary change once the species has become established in the new habitat.”
 
They also found that, “Many of the best examples of rapid evolution involve invasive plants, possibly because of the genetic processes involved during invasion that enhance genetic variation (on which selection can act; including hybridization), or to strong directional selection exerted by abiotic and/or biotic factors. Interactions with competitors and natural enemies differs strongly between the native and introduced range. If evolutionary change does occur, knowledge of its pace and direction might help to improve our predictions of the impact of subsequent biological control attempts.”
 
[Within this website, refer to the section on Herbicide Resistance, for description of the rapid evolution of invasive plant species in response to the selective pressure resulting from the use of herbicides.]
 
Müller-Scharer, et al., 2004, also found that, “The enemy release hypothesis posits that introduced plants experience a decrease in regulation by herbivores and other natural enemies, and, therefore, can spread rapidly. It has been shown that invasive exotic plants do suffer a reduced overall amount of herbivore damage, or are attacked by fewer herbivorous invertebrates, fungal and viral pathogens compared with the same species in their native range.” This reduction of damage is primarily due to the fact that the plants no longer can be attacked by their specialist enemies from their home range. “However, the level of attack by local [native] generalists can vary considerably, and can even hinder the invasion of certain communities.” Müller-Scharer, et al., 2004, propose that “the most prominent change experienced by introduced plants in terms of natural enemies is a shift in the composition toward an assemblage that is dominated by generalists. Attack by specialists is restricted to those cases in which natural enemies feeding on closely related natives colonize the introduced plant, or where specialist herbivores have been co-introduced. The shift in the composition of the natural enemy complex in the exotic range, along with changes in the competitive environment and in resource availability, is expected to incur altered selection on traits in invasive plants.”
 
Müller-Scharer, et al., 2004, also noted that, “The EICA [evolution of increased competitive ability] hypothesis assumes that plant defence chemicals incur fitness costs. For qualitative defense (toxins such as alkaloids and glucosinolates), only a few of the many experimental studies on this topic found significant direct (allocation) costs. By contrast, quantitative defence compounds (e.g. lignins and tannins) appear to incur high costs because they constrain the inherit relative growth rate of plants… In the native range, different antagonists are expected, based on optimal defence theory, to impose differential selection on both the qualitative and quantitative defence traits of plants. First, high concentrations of plant toxins might deter generalists while attracting specialists that either use them as a cue to locate or to accept the host plant for oviposition and/or feeding or that sequester the toxins and use them for their own defence… As a result of opposite selection imposed by specialist and generalist herbivores, we expect plants to evolve intermediate levels of toxins….
 
“Second, plant species or genotypes that have lower quantitative defence are more susceptible to specialists and to those generalists that have adapted to the toxins of the plant, but… such defenses constrain the growth of the plant. Furthermore, interspecific studies revealed relative growth rate to be positively correlated with competitive ability and the risk of invasiveness. Thus, in the native range, selection exerted primarily by specialist natural enemies and plant competitors is expected to favour intermediate levels of quantitative defences.”
 
“In the introduced range, where specialist herbivores are largely absent, but plants might be attacked by native generalist herbivores, we expect that plant toxins will increase in concentration, rather than decrease as predicted by the EICA hypothesis. This is because high concentrations of toxins no longer have fitness costs associated with attracting or increasing the survival of specialist herbivores. Furthermore, there is increasing evidence that some plant toxins, including glucosinolates, also function to benefit plants in competitive interactions through allelopathic effects. Thus, an increase in their concentration might further enhance the potential of a population to become invasive. However, concentrations of lignins and/or tannins are expected to decrease, particularly when generalists in the introduced range are repelled by the plant toxins.
 
“Therefore, we propose that the evolved increased vigour documented in the introduced range for a few plant species is best explained by a reallocation of resources from costly quantitative defences to growth, whereas the toxin concentrations might well evolve in the opposite direction than that predicted by the EICA hypothesis. We suggest that such plants will be particularly amenable to biological control, because target weeds with increased digestibility are likely to support a faster population build-up of specialist biocontrol agents.”
 
Müller-Scharer, et al., 2004, found that little research had been conducted to study whether invasive plant populations are evolving tolerance as a response to attack. “What evolutionary trajectory do we expect in the introduced range where the intensity of competition and herbivory can be altered compared with the native range? Tolerance might be a defence mechanism that is particularly important for plant species that lack efficient chemical defence. Assuming that tolerance incurs fitness costs…, we might expect the evolution of decreased tolerance but increased competitive ability when plants are introduced into a new range… However, various factors might limit such an evolutionary response. First, selection imposed by generalist insect herbivores might be strong enough to maintain high tolerance in the introduced range. Second, it is likely that other stress and disturbance factors (e.g. fire, frost, or drought), which also operate in the introduced range, will lead to the maintenance of tolerance due to herbivory, because similar compensatory mechanisms might be activated after the destruction of apical meristems… by various abiotic stress and disturbance factors. Third, many introduced plants invade grassland habitats, where they are browsed by cattle. Thus, although in such habitats invasive plants might face lower levels of insect herbivory compared with their native range, browsing by cattle might nevertheless be common and impose strong selection on plant tolerance.”
 
Müller-Scharer, et al., 2004, stated that, “Therefore, effective tolerance mechanisms could be common in plant invaders. We propose that this can help explain why most introductions of insect biological control agents exhibit only weak negative effects on their hosts. It might further explain the resulting super-abundance of some of the biological control agents over extended time periods because tolerance, unlike resistance, is generally not expected to regulate the population dynamics of its consumers.” Müller-Scharer, et al., 2004, included, as one example, the two introduced gallfies that have failed to control Centaurea maculosa but now occur at a very high density compared to their native range.
 
Zenni, et al., 2017, conducted an extensive review of the research on the evolutionary processes that may impact the success of biological invasions by trees, to better understand the importance of the changes that invasive species undergo after being introduced to a new environment.
 
Ellstrand and Schierenbeck, 2000, point out that the fact that some species are readily controlled by biological agents brought over from their home environment is an indicator that evolution occurring after introduction is not a factor for those species. But the fact that various invasive species do not respond well to biocontrol presents the possibility that evolutionary changes occurring within the species within the new environment are an important factor, particularly among plant species.
 
[Within this website, refer to the section, Invasive Success Hypotheses, for details of the EICA, evolution of increased competitive ability hypothesis, and for more details of the research on hybridization.]

References:
  • Ellstrand, N.C., & Schierenbeck, K.A. (Jan. 27-29, 2000). Hybridization as a stimulus for the evolution of invasiveness in plants? Paper presented at the National Academy of Sciences, Irvine, CA. Reprinted in Euphytica (2006), 148, 35-46.
  • Müller-Scharer, H., Schaffner, U., & Steinger, T. (August, 2004). Evolution in invasive plants: Implications for biological control. Trends in Ecology and Evolution, 19 (8), 417-422.
  • Zenni, R.D., Dickie, I.A., Wingfield, M.J., Hirsch, H., Crous, C.J., Meyerson, L.A., Burgess, T.I., Zimmermann, T.G., Klock, M.M., Siemann, E., Erfmeier, A., Aragon, R., Montti, L, & LeRoux, J.J. (Jan., 2017). Evolutionary dynamics of tree invasions: Complementing the unified framework for biological invasions. AoB Plants, 9 (1), 1-14.

Next Sections on Biocontrol Agents:
Vertebrates as Biocontrol Agents
Biocontrol Interviews
Copyright: Dr. Delena Norris-Tull, July 2020. Management of Invasive Plants in the Western USA.

These webpages are always under construction. I welcome corrections and additions to any page.
​Send me an email, and I can send you the original Word format version of any page you wish to correct.
contact Dr. Norris-Tull
Bibliography
who am i?
My work
my inspirations
my adventures
  • Defining the Problem
    • What is a Weed? >
      • Federal Definitions of Noxious Weeds
    • Costs of invasive plants
    • Human Factor
    • Challenges of Invasive Plants
    • Wildfires in the Western USA >
      • Forest Fires: Structure
      • Bark Beetles & Forest Ecosystems
      • Rangeland Fires
    • Climate Change Impacts on Plants >
      • Climate Change: CO2, NO, UV, Ozone Impacts on Plants
      • Climate Change Impacts on Crops
      • Climate Change Impacts on C4 Plants
      • Climate Change Impacts on Rangelands
      • Climate Change Impacts on Forests
    • What are we doing?
  • Focus of this Project
    • Why Western States? >
      • Audience for these reports
    • History: Are we doomed to repeat it? >
      • Dust Bowl Re-visited >
        • China: Past & Present
        • UN Biodiversity Report
    • Policy vs. Practice
    • Ecosystems & Economics >
      • Reductionist Approach to science
      • Ecology & Feminism
      • Systems View of Life
      • Ecosystems Health
      • Economic Growth
      • Impact of the Petrochemical Industry
      • Interrelation of Economics & Ecology
    • Federal Agencies >
      • Federal Agencies and Invasive Species
      • History of Coordination with States
      • Challenges of Coordination between Federal Agencies
      • Collaboration or Confusion
    • Organizations to assist landowners
    • Federal Legislation on Invasive Species >
      • 1930s Federal Laws on Invasive Species
      • Federal Seed Act 1939
      • 1940s-1960s Federal Laws on Invasive Species
      • 1970s Federal Laws on Invasive Species
      • 1980s Federal Laws on Invasive Species
      • 1990s Federal Laws on Invasive Species
      • 2000-2010 Federal Laws on Invasive Species
      • 2011-2022 Federal Laws on Invasive Species
      • Federal Bills on Invasive Species not passed
      • Executive Orders on Invasive Species
      • Federal Excise Taxes
    • State Laws and Lists of Noxious Weeds
  • Why we need plants
    • Native Plants
    • Plant Resources
  • Invasive Success Hypotheses
    • Unified Framework
    • Role of Diversity >
      • How Ecosystems Maintain Diversity
      • Fluctuation Dependent Mechanisms
      • Competition-based coexistence mechanisms
      • Niche Differences
      • Species Richness
    • Enemy Release Hypothesis
    • Constitutive Defense Mechanisms
    • Evolution of Increased Competitive Ability
    • Role of Microbes
    • Indirect Defense Mechanisms
    • Novel weapons hypothesis
    • Evolutionary Shifts
    • Resource Allocation
    • Evolutionary Dynamics >
      • Pre-introduction evolutionary history
      • Sampling Effect
      • Founder Effect
      • Admixture, hybridization and polyploidization
      • Rapid Evolution
      • Epigenetics
      • Second Genomes
    • Role of Hybridization
    • Role of Native Plant Neighbors
    • Species Performance
    • Role of Herbivory
    • Evolutionary Reduced Competitive Ability
    • Summary Thoughts on Research
  • Historical Record
    • Regional Conferences
    • Timeline
  • Innovative Solutions
    • Grazing Solutions >
      • Sheep, Goat & Chicken Grazing
      • Cattle & Sheep Grazing
      • Cattle and Bison Grazing
      • Grazing and Revegetation
    • Agricultural Best Practices >
      • Ecologically based Successional Management >
        • Regenerative Agriculture
        • Sustainable Agriculture
      • Perennial Crops, Intercropping, beneficial insects
      • Soil Solarization
      • Natural Farming
      • Permaculture
      • Organic Farming
      • Embedding Natural Habitats
      • Conservation Tillage
      • Crop Rotation
      • Water Use Practices
      • Tree Planting: Pros & Cons
    • Rangeland Restoration >
      • Federal Goals for Rangelands
      • Novel Ecosystems
      • Prairie Restoration >
        • Prairie Restoration Workshop
        • Weed Prevention Areas
        • California grassland restoration
        • Selah: Bamberger Ranch Preserve
      • Sagebrush Steppe Restoration >
        • Low Nitrogen in Sagebrush Steppe
      • Revegetation with Native Plants
      • Dogs as detectors of noxious weeds
    • Habitat Conservation
    • Technology solutions
    • Nudges
  • Biological Control
    • Insects as Biocontrol >
      • Impacts of Biocontrol Agents on Non-Target Species
      • Indirect Impact of Biocontrol on Native Species
    • Challenges of Using Biocontrols >
      • DNA studies on Biocontrol Insects
      • Biocontrol takes time
    • Prioritization process for Biocontrol Programs
    • Evolutionary changes impact Biocontrol
    • Vertebrates as Biocontrol Agents
  • Herbicides: History and Impacts
    • Effectiveness of Herbicides in Agricultural Lands
    • Effectiveness of Herbicides in Rangelands
    • History of Use of Herbicides and Pesticides Prior to and During WWII
    • Herbicide use during and post-World War II >
      • 2,4-D Herbicide Use
      • 2,4-D and 2,4,5-T, post-World War II
    • Modern use of Herbicides >
      • Atrazine Herbicide
      • Dacthal, DCPA
      • Dicamba Herbicide
      • Glyphosate Herbicide
      • Paraquat Dichloride
      • Picolinic acid family of herbicides >
        • Picloram (Tordon 22K) Herbicide
        • Triclopyr Herbicide
    • Herbicide Resistance in Invasive Plants >
      • Herbicide Resistant Crops
      • Controlling herbicide-resistant weeds in herbicide-resistant crops
      • Best Management Practices
    • Myth of the Silver Bullet
    • Myth of Eradication
    • Merging of Agrochemical Companies
    • Funding for Research on Pesticides
    • Impacts of Pesticides on Environment and Human Health >
      • Pesticide Drift
      • Impacts of Pesticides on Biological Diversity
      • Impacts of Herbicides on Native Plants
      • Pesticide Impacts on Insects >
        • Butterflies: The Impacts of Herbicides
        • Monarch Butterflies: Impacts of Herbicides
      • Impacts of Pesticides on Wildlife >
        • Reptiles & Amphibians: Pesticide Impacts
      • Pesticide Residue in Foods
      • Commentary on Herbicide Use
  • Interviews
    • Interviews Biocontrol >
      • Biocontrol Wyoming
      • Montana Biocontrol Interview Maggio
      • Montana Biocontrol Interview Breitenfeldt
    • California Interviews >
      • Robert Price
      • Doug Johnson
    • Colorado Interviews >
      • George Beck Interview
      • Scott Nissen Interview
    • Idaho Interviews >
      • Purple Sage Organic Farms in Idaho
    • Montana Interviews >
      • Jasmine Reimer Interview Montana
      • Organic Farms Montana Interviews
    • Texas Interviews
    • Washington Interviews >
      • Ray Willard
    • Wyoming Interviews >
      • Slade Franklin Interview
      • John Samson Interview
    • Wyoming Weed and Pest Districts >
      • Josh Shorb Interview
      • Slade Franklin Interview 2
      • Lars Baker Interview
      • Steve Brill Interview
      • George Hittle Interview
      • Peter Illoway Interview
      • Robert Jenn Interview
      • Sharon Johnson Interview
      • Larry Justesen Interview
      • Gale Lamb Interview
      • Stephen McNamee Interview
      • Allen Mooney Interview
      • Rob Orchard Interview
      • Robert Parsons Interview
      • Dick Sackett Interview
      • Comments by Delena
    • NRCS Interviews: Wyoming
  • Western Weed Control Conference 1940s Minutes
    • 1942 Conference
    • 1945 Conference
    • 1946 Conference
  • Who am I?
    • My Work
    • My Inspirations
    • My Adventures
    • Contact Page
  • Road Logs
    • Colorado Road Logs
    • Idaho Road Logs
    • Montana Road Logs
    • New Mexico Road Logs
    • Texas Road Logs
    • Wyoming Road Logs
  • Bibliography