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 Rangeland
    • 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
    • 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
    • My Inspirations
  • 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
    • Agricultural Best Practices >
      • Ecologically based Successional Management
      • Perennial Crops, Intercropping, beneficial insects
      • Natural Farming
      • Permaculture
      • Organic Farming
      • Embedding Natural Habitats
      • Conservation Tillage
      • Crop Rotation
      • Water Use Practices
      • Tree Planting: Pros & Cons
    • Grazing Solutions >
      • Sheep and Goat Grazing
      • Cattle & Sheep Grazing
      • Cattle and Bison Grazing
      • Grazing and Revegetation
    • 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
    • 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
      • Dicamba Herbicide
      • Glyphosate Herbicide
      • 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
    • 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
    • Funding for Research on Pesticides
    • 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 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

The Role of Diversity
​​in Preventing Invasions

Photo: Native prairie, East Texas. © 2017 Delena Norris-Tull

The Role of Diversity in Invasive Success or Failure

Summary of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, 
July 2020.
​
​ 
The study of the impact of invasive species is based on the assumption that most invasive non-native species out-perform their neighboring native species, and that they spread more rapidly in the non-native range than in their native environment. Most hypotheses, regarding factors that facilitate the success of invasive species, assume “that success is acquired as a result of novel ecological and environmental dynamics” the species encounters in the introduced range (Levine, Adler, & Yelenik, Sept., 2004).
 
In reality, relatively few non-native species become invasive in their introduced ranges. So what, then, are the factors that cause non-native species to become invasive, and what factors restrict the spread of non-native species?
 
Levine, et al., 2004, conducted a meta-analysis on biotic resistance research, research that examines the factors that contribute to successful non-native plant invasions. Quite a bit of that research has focused on biotic resistance, defined as “the reduction in invasion success caused by the resident [native plant] community…. Biotic resistance can arise from any effect of resident species on colonizing invaders, including predation, herbivory, and disease… In addition, abiotic factors, such as high temperature or salinity can also make an ecosystem difficult to colonize…. An understanding of biotic resistance might be used to predict which communities are most susceptible to invasions or where invasions are most likely to occur… Similarly, restorative ecologists need to design communities that will best resist invasion (Levine, et al., 2004).”
 
Of the 52 research studies Levine, et al., 2004, reviewed in their meta-analysis, 24 examined competition as a factor in resistance to non-native plant invasion. These studies “revealed strong and significant effects of resident [native] competitors on both the establishment and individual performance of exotic invaders.” The higher density of native plants in the study plots did show an effect in reducing the success of the invader species. The studies also indicated that “for invader performance, but not establishment, [invasive] grasses, forbs and woody plants differed significantly in their susceptibility to biotic resistance from competition [from native plants], with grasses and forbs showing greater sensitivity than woody species (Levine, et al, 2004).”
 
Levine, et al., 2004, found that, of the seven studies on the effects of species diversity, the research does support the conclusion that higher native plant diversity in an ecosystem constrains invasion by non-native plants species. “Resident species diversity had a significant negative effect on both invader establishment and individual performance” (Levine, et al., 2004). But even high plant diversity within a community has not been shown to entirely prevent infiltration by invader species. However, only one study effectively tackled that question by introducing an invader not already present in the study habitat (a treatment that would be unethical in most contexts). Other evidence indicates that, “The most diverse natural communities contain the greatest number of exotic species” (Levine, et al., 2004). For example, there are many more exotic species established in the highly diverse California coastal areas and foothill grasslands, than in the harsh environments of the Western States desert, chaparral, and alpine environments.
 
Levine, et al., 2004, point out that “it is still possible that in the absence of the diversity effect, many more invaders would be found in these communities.” Unfortunately, once a non-native species has invaded, if it is able to outproduce the native plants in seed production, it may continue further invasion. The research indicates that successful invaders are often better at seed production than the native plant community.
 
Levine, et al., 2004, examined 12 studies, including 27 experiments, of “the impact of native herbivores in natural ecosystems on the establishment and performance of exotic invaders.” Most of the studies examined mammalian herbivores, or the combined effect of mammals and insects, two studies examined only insect herbivores, and one study examined birds as seed predators. All but three of the studies concluded that “herbivory has a significant and strong negative effect on invader establishment.” Herbaceous invading plant species were more susceptible to herbivory than woody plants. But, “although herbivory had a strong negative effect on survivorship and individual plant performance,… whether this was strong enough to reverse the course of an invasion is difficult to infer… Even when herbivory negatively affects an invader population, its relative abundance increases if herbivory impacts other species to a greater extent” (Levine, et al., 2004). Eight of the 27 experiments “showed that herbivory could reduce invader establishment or fecundity to zero.” These were studies on mammalian herbivory. However, it is unlikely that even mammalian herbivores could completely prevent or eliminate an invader species. The studies also indicated that “herbivory is more destructive to perennials than annuals because perennials have a longer period of vulnerability prior to reproduction.”
 
Levine, et al., 2004, also examined research on soil fungal communities on invasive plant success. All but one of the nine experiments they reviewed were conducted in greenhouses, and most “examined performance measures (biomass, number of leaves and growth) rather than establishment.” In some studies, “native fungal communities increased plant biomass.” In some studies, fungi had differential effects on invader species, in different treatments. Levine, et al., 2004, found these greenhouse experiments difficult to generalize to environments in the field. Even when examining the seven studies on soil or foliar fungal pathogens, the results were variable. “The effect of fungal pathogens in individual cases is strong, but on average, positive and negative effects cancel out.” Based on the limited research available, Levine, et al., 2004, agreed with “the emerging view that depending on the identity of the plant and fungal species, mycorrhizal fungi can be either mutualistic or parasitic.”
 
Levine, et al., 2004, found “no significant difference between the reduction in invader establishment and individual performance caused by competition vs. herbivory.”
 
Overall, Levine, et al., 2004, concluded that the available research does support the Enemies Release Hypothesis, described below, more so than the idea that biotic factors within the native plant community are the dominant factors in resistance to invasion. Abiotic factors (e.g., temperature, precipitation, soil type, salinity) may be more important in regulating invasions, than biotic factors. “If biotic resistance does not deterministically drive colonizing invaders to extinction, it may still cause invasions to fail if the invaders have a limited number of arriving seeds… Although in theory the invader would eventually colonize, limited seed arrival coupled with biotic resistance could dramatically alter the course of an invasion… Interactions between different sources of biotic resistance and between biotic and abiotic factors have the potential to more strongly inhibit invasions than each ecological process in isolation” (Levine, et al., 2004). They suggested that more research is needed to examine the role of abiotic factors, and the interplay between biotic and abiotic factors, in invasive success or failure.
 
Levine, et al., 2004, concluded their meta-analysis with a call for much more research. They point out that, “If species interactions do not completely repel invaders, but rather, constrain their abundance within communities, new questions gain prominence. Among the most interesting is what factors allow native species to persist with invaders once the latter have established… Only a small fraction of invaders ever reach high abundance or exert large impacts… Understanding the ecological dynamics enabling native species to persist in these communities is critical to preserving their diversity.”

Reference:
  • Levine, J.M., Adler, P.B., & Yelenik, S.G. (Sept., 2004). A meta-analysis of biotic resistance to exotic plant invasions. Ecology Letters, 7, 975-989.​

Research topics on the roll of diversity:
  • How Ecosystems Maintain Diversity
  • Fluctuation Dependent Mechanisms
  • Competition-based coexistence mechanisms
  • Niche Differences
  • Species Richness
​
Additional Research topics on the success of invasive species:
creating a unified framework
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
hybridization
the role of native plant neighbors
species performance
the role of herbivory
evolutionary reduced competitive ability
summary thoughts on the research
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 Rangeland
    • 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
    • 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
    • My Inspirations
  • 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
    • Agricultural Best Practices >
      • Ecologically based Successional Management
      • Perennial Crops, Intercropping, beneficial insects
      • Natural Farming
      • Permaculture
      • Organic Farming
      • Embedding Natural Habitats
      • Conservation Tillage
      • Crop Rotation
      • Water Use Practices
      • Tree Planting: Pros & Cons
    • Grazing Solutions >
      • Sheep and Goat Grazing
      • Cattle & Sheep Grazing
      • Cattle and Bison Grazing
      • Grazing and Revegetation
    • 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
    • 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
      • Dicamba Herbicide
      • Glyphosate Herbicide
      • 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
    • 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
    • Funding for Research on Pesticides
    • 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 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