Invasive Species Misconceptions, Denialism, and the Need for Universal Terminology

Erin Brennan

Western Kentucky University

BIOL 516 Research - Plant Ecology

25 February 2022


In this paper, I will examine misconceptions and confusion surrounding invasive species terminology, along with invasive species denialism. First, I will explain the main reasons that invasive species, more so now than ever before, are a major ecological, economic, and human health threat, the effects of which cannot be minimized. Then I will analyze some of the misunderstandings and misconceptions represented in literature and media in particular. Next, I will examine invasive species denial and address arguments against invasion biology. Finally, I will scrutinize the currently used terminology describing biological invasions and propose suggestions for universal terminology on the subject.

A Growing Threat

The threat from invasive species is real, well-documented, and growing. As global commerce continues to grow, so too does the threat of invasions by non-native species. The harmful effects of invasions are now globally recognized with programs to reduce both current and future impacts in place in many parts of the world (Pyšek & Richardson 2010). Invasive species have caused devastating ecological and economic impacts globally (Wainright et al. 2021). Invasions can have significant impacts on native species and ecosystems and have critical, sometimes dire, consequences for biodiversity (Wainright et al. 2021). Invasive species eat, compete with, and often hybridize with the native species, resulting in a loss of native species and a decline in biodiversity (Lockwood et al. 2013). Invasive species are responsible for the decline of approximately half of the species on the International Union for Conservation of Nature Red List and are protected by the US Endangered Species Act (Wainright et al. 2021).

Effectively predicting the long-term ecological impacts of invasions can be challenging because complex ecological changes compound over time, especially when combined with other environmental pressures (Wainright et al. 2021) Invasive species disrupt native food webs through trophic dispersion and displacement (Wainright et al. 2021). This leads to fundamental changes and the formation of divergent biological communities. Wainwright et al. (2021) found that over time, the establishment of an invasive predator species can destabilize food webs through trophic disruptions that result in the formation of a new ecological regime dominated by the invasive predator.

Invasive species represent an extremely damaging and costly environmental problem. There is ample evidence that invasive species cause grave economic problems (Lockwood et al. 2013). The negative impacts of invasions on ecosystem services far outweigh any potential positive impacts (Charles & Dukes 2007). Invasive species negatively impact ecosystem services, including the natural pest control, soil stabilization, and water filtration that humans depend upon (Lockwood et al. 2013). Most of the agricultural pests in the United States are invasive species (Lockwood et al. 2013). Additionally, invasive species congest our waterways, hinder navigation, destroy homes, and kill livestock and fisheries (Lockwood et al. 2013). Invasive species cause nearly US$120 billion in annual damages in just the United States (Crystal-Ornelas et al. 2021).

Invasive species lead to human health impacts as well. Many human diseases are non-native (Lockwood et al. 2013). Many vectors of disease and parasites are also invasive (Mazza et al. 2014), (Lockwood et al. 2013). The negative impacts of such invasions are predicted to increase in the future due to increased opportunities attributed to globalization, habitat fragmentation and destruction, and the direct and synergistic effects of climate change (Mazza et al. 2014). To develop effective policies for mitigating the negative impacts of invasive species and preventing future invasions, we must improve our understanding of the introductions of species impacting human health and their pathways to invasion (Mazza et al. 2014). When ecosystems are invaded, the effects on human health can be devastating. The cost of these invasions in human lives cannot be understated, nor can the danger of future invasive diseases and disease vectors.

The scope and cost of the ecological, economic, and human health damages have provoked attempts at predicting the vulnerability of ecosystems to invasions and prioritizing them for management. Difficult to predict, the effects of invasive species on ecosystems can grow over time, making the prevention of invasions imperative. The prediction process is greatly dependent upon our understanding of the mechanisms by which invaders alter food webs and how these invasions change trophic interactions over time (Wainright et al. 2021). The importance of biological invasions is demonstrated by the growing costs of invasions to industries such as agriculture, forestry, aquaculture, and apiculture, water and energy supply systems, and human health, as well as myriad effects on ecosystem services (Richardson & Ricciardi 2013). Given the significant demonstrable cost, invasions are increasingly seen as a national security issue (Richardson & Ricciardi 2013).

Invasive Species Misconceptions

Awareness of invasive species has grown along with the risk of invasions. However, information regarding invasive species shared with the general public is not always accurate and is often rife with misconceptions. Coverage of invasive species and their impacts is expanding in mainstream media and literature (Russell & Blackburn 2017). At first, much of this coverage was in alignment with the scientific tenets that invasive species have negative ecological, social, health, and economic impacts and lead to declining biodiversity (Russell & Blackburn 2017). However, many recent stories from major media outlets have challenged the scientific consensus on invasive species. Sometimes scientific evidence about the impact of invasive species has been misunderstood, misinterpreted, or even misrepresented (Russell & Blackburn 2017). Some of these stories highlight common misconceptions regarding invasive species and confuse social and scientific terminology.

For example, a 2015 article in The Economist argued that “most campaigns against foreign plants and animals are pointless, and some are worse than that,” (The Economist 2015). The article goes on to erroneously state that “most invasive species are neither terribly successful nor very harmful” and that “new arrivals often turn out to be useful, even lovely.” (The Economist 2015). The article misrepresents the invasion of cane toads in Australia as an example of invasive animals “helping” native species by killing their predators, which shows a fundamental lack of understanding of the functioning of food webs (The Economist 2015). The cane toad, native to Central and South America, is one of the world’s most infamous invasive species and has been introduced to over 30 countries (Dubey & Shine 2008). This amphibian is a voracious predator purposely introduced to Australia in 1935 to reduce damage to sugarcane crops by beetles (Dubey & Shine 2008). However, with no predators capable of consuming them, the toxic toads quickly spread out of control and now occupy over a million square kilometers in Australia (Dubey & Shine 2008; Phillips et al. 2007; Dubey & Shine 2008). They are widely known to have caused ecological devastation and negatively impacted biodiversity (Phillips et al. 2007). The toad spread rapidly throughout much of tropical Australia since its introduction and has continued to expand its range almost a century later (Phillips et al. 2007). The cane toad even brought with it another invader, a South American lungworm, highlighting the complexity of invasions and the need for understanding their impacts (Phillips et al. 2007; Dubey & Shine 2008; Phillips et al. 2007). Unfortunately, no factual information about the cane toad invasion is shared in the article, so readers are left thinking that cane toads are helpful rather than harmful. There is little to no scientific basis to most of the claims in this misleading and inaccurate article that is written for the general public who may not have the background scientific knowledge to discern such misinformation.

A 2016 article published in the New York Times claims that “a growing number of scientists are challenging” the view that invasive species are always unwanted. This article demonstrates a misunderstanding of terminology, confusing non-native or naturalized species with those causing damaging invasions. The International Union for the Conservation of Nature (IUCN) defines invasive species as “introduced by man into places out of their natural range of distribution, where they become established and disperse, generating a negative impact” (Russell & Blackburn 2017). Most scientific definitions of invasive species acknowledge that they have harmful impacts, and therefore, are not welcomed by scientists. Alternatively, non-native naturalized species, while well established, are not generally harmful and can even serve as desirable replacements for native species which have gone extinct. An example of this is the introduction of the Aldabra giant tortoise Aldabrachelys gigantea on the islands of Mauritius (Marris 2014). The Mauritius islands lost their large tortoise species, and as a consequence, the fruiting plants that depended upon the fruit-eating tortoises to disperse their seeds had been declining (Marris 2014). The Aldabra tortoise, a non-native species from the Seychelles that is closely related to those native to the islands that was intentionally introduced in 2004 to ensure the survival of the fruiting plants, and ultimately, the entire ecosystem (Marris 2014). The Aldabara tortoise, despite being an introduced, non-native species, is not invasive in the Mauritius islands. Its similarity and close relationship to the original tortoise species allowed it to fill a necessary role in the ecosystem while maintaining balance in the food web. This example reveals an important distinction between non-native and introduced species and invasive species.

A recent article published by Vox titled “It’s time to stop demonizing ‘invasive’ species” declared that because climate change is forcing some animals to move, we shouldn’t call them “invasives” (Bolotnikova 2021). ​​While this does acknowledge the escalating issue of range-shifting organisms moving in response to climate change, organisms are not automatically labeled as invasive when shifting their range. Recent research into range-shifting species shows that compared to those introduced by humans, native species are less likely to cause negative ecological impacts when shifting to nearby habitats (Wallingford et al. 2020). Bolotnikova argues that the term invasive species has “taken on a life of its own,” influencing the way we judge the health of ecosystems and “dividing life on Earth into native and invasive,” again demonstrating a misunderstanding of invasive species terminology (Bolotnikova 2021). The fact remains that invasive species can have a devastating impact on the health of an ecosystem that a native species would not. To suggest that using the term ‘invasive’ somehow vilifies an organism or labels it as ‘evil’ fails to acknowledge that invasive species generally are not harmful in their native range. A recent Smithsonian Magazine article questioned the use of the terms invasive and non-native, suggesting connotations of xenophobia and war (Crawford 2018). These media pieces seem to unknowingly misrepresent scientific terminology and theory. This misuse of terminology demonstrates how a lack of a universal definition and public education of invasive species can lead to the spread of misconceptions, with the potential to impact invasive species research, programs to identify potential invaders and mitigate the effects of current invaders, and even conservation efforts.

There are unfortunately plenty more articles with similar misconceptions and misrepresentations of the impacts of invasive species. An article published in New Scientist in 2015 called the data pointing to invasive species as a major cause of extinctions “hearsay” and “scanty and overused” (Pearce 2015). Invasive species are directly linked with population declines and extinctions around the world, and invasions can complicate conservation efforts for threatened and endangered species by compounding the issues they face (Bellard et al. 2016). The most harmful invaders tend to be predators and pathogens (Bellard et al. 2016). An example of the devastation caused by an invading pathogen, chytrid fungus Batrachochytrium dendrobatidis has ravaged amphibian populations with species going extinct shortly after being observed for the first time (Bellard et al. 2016). In a 2009 Global Amphibian Extinction Risk Assessment, Rödder et al. identified 833 anuran amphibian species that demonstrate a high predicted susceptibility to chytrid fungus based on their life history and biology (Rödder et al. 2009). Of those species, 379 were identified as high risk due to chytridiomycosis (Rödder et al. 2009). For at least 40% of the 379 species, scientists did not yet have sufficient data to make an accurate assessment under the IUCN Red List of Threatened Species (Rödder et al. 2009). Of the species with sufficient information for assessment, 94% are categorized as threatened with extinction. Likely, many more of the identified species would eventually be categorized as such (Rödder et al. 2009). Further, researchers have already identified 90 species of amphibians the chytrid fungus has caused to go extinct and more than 500 species that have experienced declines due to the fungus over the past 50 years (Frey 2019). Most of the currently affected species are still declining and the losses are much greater than scientists previously thought (Frey 2019). This is one example of the direct correlation between invasions and extinctions misrepresented by authors and refuted by invasive species deniers, but ample evidence of this link can be found in threatened and endangered species around the world.

Scientific Debate or Invasive Species Denial?

Science denialism is the refutation of accepted and agreed-upon scientific facts (Russell & Blackburn 2017). This differs from scientific debate, which is inherent in and crucial to the scientific process. Ideas that pass through this scientific process do so because they have been proven, are repeatable and provide the most likely explanation consistent with previously existing scientific knowledge (Russell & Blackburn 2017). The scientific process is reliant upon criticisms and skepticism to guide it and challenges to scientific consensus succeed only when they provide a better, more accurate answer to a question or explanation of a phenomenon (Russell & Blackburn 2017). Denialism relies heavily on fabricated uncertainty and takes advantage of the element of change that accompanies the scientific process, explaining that change as the science being “wrong” rather than adding to our body of knowledge (Russell & Blackburn 2017).

In this manner, the field of invasion biology and the consensus by the scientific community on the negative impacts of invasive species is increasingly being challenged (Russell & Blackburn 2017). While skepticism is important, denialism is ineffectual. Invasion biology has been the target of criticism from a small yet vocal group of scientists for some years now, despite ample, rigorous, scientifically-accepted evidence of the importance of the field not only to science but society at large (Richardson & Riccardi 2013). Many of the common criticisms against invasion biology do not stand firm against scrutiny. Some of the critics of invasion biology question research agendas, dispute the connections between the results of studies and their implications for the management of invasions or even question the need for the field (Richardson & Riccardi 2013). Despite ample evidence, some deny that non-native species play a major role in extinction (Ricciardi & Ryan 2018). Some even go as far as to call for the end of invasion biology as a field (Richardson & Riccardi 2013, Ricciardi & Ryan 2018).

One common claim against invasion biology is that the origin of a species is irrelevant to its impact, and therefore, should have no bearing on its management (Simberloff 2010). Similarly, critics claim that the native/non-native distinction holds no scientific value, thus negating the entire field (Richardson & Riccardi 2013). Yet another claim is that invasive species increase, not decrease biodiversity. Although unlikely, local and/or regional species richness could increase, however, the population declines and extinctions caused by invasive species reduce species richness on a global level faster than it can be recovered (Russell & Blackburn 2017). This demonstrates the need to look at invasions not only through a local or regional lens but to measure global impacts as well.

All of these claims ignore the documented importance of the role of evolutionary history when examining the impact of invasions. Such research demonstrates community-level interactions involving invaders, such as a greater occurrence of pests among non-native plants than native plants or why non-native consumers cause greater damage to native populations, and ultimately why invasive species are more likely to cause ecological disruptions (Richardson & Riccardi 2013). The origins of species can and do matter when it comes to understanding why some invasions have a greater impact than others (Richardson & Riccardi 2013).

Another claim is that most invasions are benign, and therefore do not necessitate management, and that management effort are wasted on innocuous species simply because they are non-native (Richardson & Riccardi 2013). The reality is that management is extremely constrained already by a lack of resources and prioritizes and allocates resources to the most problematic species (Richardson & Riccardi 2013). Management efforts are limited by several facts ignored by denialists. Studies have not been conducted on the impacts of most invasive species, the impacts of invaders can vary from region to region, impacts may seem subtle at first but can cause massive ecosystem changes over time, and many non-native species that are not immediately harmful may become so years later when eradication is no longer feasible (Richardson & Riccardi 2013). If anything, management efforts need to be increased.

This recently emerging opposition to policy, research, and management of invasive species is attempting to change the terminology so that impact is narrowly defined and includes only extinction. Extinction is an extreme potential outcome but there is a wide range of subtle, long-term impacts caused by invasive species (Russell & Blackburn 2017). The arguments against invasion biology continue to be reformulated and subsequently republished, despite being challenged and refuted many times. This escalation past denialism and into calling for the end of the field of invasion biology is undermining scientific practice and the management of invasive species and invaded ecosystems at a time when understanding the impacts of rapidly increasing invasions is greatly needed (Richardson & Riccardi 2013).

Universal Terminology

A lack of universally accepted terminology leads to much confusion, lack of consensus, and disagreement regarding invasive species on the part of ecologists, organizations, governments, and the general public. Terms used in this context should be explicit and specific because the use of overly simplistic terms to communicate complex ecological concepts can undermine management efforts, and lead to skepticism and debate (Colautti & MacIsaac 2004). This problem is particularly evident in studies of invasive species as they have also been called non-indigenous, non-native, exotic, introduced, and naturalized (Colautti & MacIsaac 2004). The terms alien, exotic, foreign, introduced, invasive, naturalized, non-native, non-indigenous, domesticated, weed, and pest can all be found in various scientific literature. These terms are often used interchangeably yet sometimes have different meanings, typically referring to non-native species that may or may not be invasive (Courchamp et al. 2017; Poland et al. 2021). Terms such as pests and weeds are still sometimes used and can apply to both native and non-native organisms (Poland et al. 2021; Richardson et al. 2000). There is a need for a universally agreed-upon definition of invasive species, yet redefining commonly used terminology has proved difficult because organizations, governments, and even individual authors are partial to the particular definitions with which they are already familiar (Colautti & MacIsaac 2004; Poland et al. 2021).

This lack of universal invasion terminology created issues such that the Federal Government of the United States now utilizes a set of terminology established by Executive Order (“Executive Order 13112 - Invasive Species” n.d.). This Executive Order established a universal set of key terms in hopes that public and private organizations would adopt the definitions as well (Poland et al. 2021). However, many sectors continue to use other definitions, and debates regarding terminology persist in scientific literature (Poland et al. 2021).

Executive Order 13112 defines invasive species as "an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health" and specifies that this includes only species for which the introduction and movement is “a result of human activity.” (Poland et al. 2021; “Executive Order 13112 - Invasive Species” n.d.). This definition intentionally included anthropogenic causes and excluded the background rates of introductions of species that occur naturally by non-human means such as animal movement, range shifting, and natural disasters (Poland et al. 2021). The specificity of this definition was met with both support and opposition. Many argued against an unconditional definition as it could overlap with processes that are not driven by human activities, such as the movement of species onto new islands, volcanic areas, fire-ravaged areas, and natural succession (Poland et al. 2021).

Definitions of invasive species that lack an explicit statement about their impact have been met with disagreement as well. Many scientists argue that the impact of invasive species must be considered in defining them. Richardson et al. (2000) state that the term ‘invasive’ must only be used for species that cause or have the potential to cause obvious damage to ecological and/or economic systems. Russell and Blackburn (2017) argue that invasive species must be defined by the negative impact they create because there is an overwhelming amount of evidence that invasive species are one of the major global challenges to the conservation of biodiversity in our time. The IUCN defines invasive species as those species introduced by humans outside of their natural range, that then become established and spread, causing a negative impact (Russell & Blackburn 2017). However, determining the negative impact of invasive species is dependent upon a combination of objective scientific research along with definitions of impact which can often be subjective and can vary greatly depending upon a variety of factors including the species in question, the habitat, proximity to humans, level of disturbance in the ecosystem, and more (Russell & Blackburn 2017). The inherent subjectivity of defining impacts can lead to disagreement over these impacts and therefore the classification of species as invasive, potentially delaying or limiting the availability of programs and funding to prevent the spread and mitigate the impact of such species (Russell & Blackburn 2017).

Many important terms used in invasion biology vary greatly and have traditionally been quite subjective. The terms ‘weed’, ‘pest’, and ‘invasive’ have been used to mean a variety of things from displeasing to nuisance to a vector of disease (Colautti & MacIsaac 2004). Sometimes species are labeled as ‘weed’ simply because they are not wanted in a particular area despite being important to an ecosystem or as a ‘nuisance’ or ‘pest’ because they were labeled as such elsewhere (Colautti & MacIsaac 2004). In these cases, the terms are not only extremely subjective but are tied to human emotions and perceptions about the species rather than scientific evidence or ecological impacts. Because of this ambiguity in terminology, ‘invasive’ has been used as a taxonomic description rather than as a term that describes the ecological phenomenon of invasion (Colautti & MacIsaac 2004). Subjective terms can lead to misconceptions and can even complicate investigations into invasions and management of invasive species (Colautti & MacIsaac 2004).

Further, the term ‘invasive’ is often dynamic (Courchamp et al. 2017). A species can have both beneficial and harmful effects. An example of this is the introduction of the mosquitofish Gambusia affinis in many parts of the world because of its appetite for mosquito larvae. While the fish controls the mosquito population, depending on the ecosystem, it can also have a negative impact on native fish, amphibians, and other insects (Colautti & MacIsaac 2004). Because species can become invasive in one habitat and not another, analyses done at the species level can help identify potential invaders. However, the proclivity toward invasion depends on a variety of factors and not just the traits of the species, as invasions occur at the population level, not the species level (Colautti & MacIsaac 2004; Mack et al. 2000; Lockwood et al. 2013). By focusing on invasion as a series of stages, we can view invasions as biogeographical rather than taxonomic phenomena (Colautti & MacIsaac 2004). That being said, problems have arisen in deciding whether a species should be labeled as ‘naturalized’ or ‘invasive’ as the stages of invasion are not discrete (Richardson et al. 2000). A species may move from stage to stage over time and space and as ecosystems change. A species might move from ‘naturalized’ to ‘invasive’ if limiting factors and opportunities in an ecosystem change in their favor (Richardson et al. 2000). This fluidity between the stages of the invasion process further demonstrates the need for early recognition and monitoring efforts so that species can be properly managed or eradicated early while still possible.

For all the previously mentioned reasons, the scientific messaging surrounding invasions can be complex, unclear, and even contradictory (Courchamp et al. 2017). A set of clear, standard definitions would make the understanding of invasive species more efficient and effective (Courchamp et al. 2017). Terminology stemming from the invasion process and its impacts, rather than the origin of the species or specific genetic traits could lead to a universal understanding of invasions and reduce confusion related to invasion terms and concepts (Colautti & MacIsaac 2004). A consensus on terminology is necessary to dispel misconceptions about invasive species and bring clarity to both the field of invasion ecology and the general public. Lack of strong consensus and debate among scientists leaves space for denialism to take root at a time when strong action against harmful invasions is necessary to protect biodiversity, ecosystem services, economic interests, and human health.


The recent rise in invasive species denialism is alarming, especially because it is not only coming from outside of the scientific field but from within as well (Russell & Blackburn 2017). However, this skepticism represents a level of confusion and uncertainty and requires a discourse with the public on the changing role of invasive species alongside our understanding of rapid global change.

Despite the arguments of invasive species denialists, the threat from invasive species is real, well-documented, and growing. Science denialism in general typically arises from groups with interest in opposition to the scientific consensus on a topic and is characterized by downplaying the severity and scope of the threat, such as is commonly done with climate change (Russell & Blackburn 2017). This tends to happen when science and policy collide and policy has the potential to impact the behavior, freedom, even profits of people (Russell & Blackburn 2017). It is no coincidence that the original opposition to invasion biology came from outside of science and that those opposed to it continue to perpetuate misconceptions and misrepresent information (Russell & Blackburn 2017).

The lack of succinct, easily understood, and universally accepted terminology feeds this skepticism and fuels confusion, leading to flawed and misleading messages from media outlets. Because terminology matters and has a significant impact on the messaging and public education regarding invasive species, universal terminology must be used to describe invasive species. The terminology used must be up to date and based on the latest science to meet the realities of the modern ecological issues we face (Richardson et al. 2000). For example, the scale and magnitude of invasions have changed dramatically since the term ‘naturalized’ was first used. Darwin used variations of the term 35 times in his book ‘On the Origin of Species’ written in 1859 and yet many are still using the same definition today (Richardson et al. 2000).

The United States Government sought to create a universal set of definitions in Executive Order 13112, as did the IUCN. Both of these sets of definitions are clear, concise, and include human impacts and the recognition of the negative impacts of invasive species. Such definitions lay down a framework for universal terminology that could eliminate much of the confusion, skepticism, and denialism surrounding invasion biology and bring clarity to our understanding of invasive species in a changing world.

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