What are invasive species? Invasive species refers to plants, animals, and microorganisms found outside of their natural range and whose presence poses an environmental, economic, or social threat (Government of Canada 2004). In collaboration with non-profit organizations in Ontario, the Ontario Ministry of Resources and Forestry is working hard to manage invasive species and monitor for new ones. Here is a list of some of today’s invasive plants in Ontario. You can find more information about these plants, as well as how to manage them on our Best Management Practices and Grow Me Instead Guide. Also, you can access technical documents through our Resources page. We are a non-profit, multi-sector group that is committed to collaborating with citizens and organizations to address the threat posed by invasive plants in Ontario.


An invasive species is an organism that has been introduced and becomes too numerous to be beneficial in its new environment. While they can be beneficial, invasive species can also negatively impact the bioregions and habitats of invading species, causing economic, ecological, and/or environmental damage. The term is sometimes used to describe native species that have become invasive in certain ecosystems because of human-induced changes to the environment. The purple sea urchin is an example of a native invasive species. It has decimated natural California kelp forests due to its natural predator, California sea otter. Invasive species pose a grave threat to the environment, economy, and society in the 21st century. Although invading long-established ecosystems is natural, human-facilitated introductions have significantly increased the pace, scale, geographic range, and frequency of such invasions. Humans have been dispersing organisms for millennia. They started with the earliest migrations and then accelerated with the advent of international trade.


The kudzu vine and Andean pampasgrass, English ivy, Japanese kneweed, and the yellow starthistle are all examples of invasive species. Examples of invasive animal species include the New Zealand mudsnail, European rabbit, feral pig and grey squirrel, as well as domestic cats, ferrets, ferrets, and carp. Popular reference sources have Homo sapiens as an invasive species. However, there is broad acceptance of humans’ learning potential, behavioral potential, and plasticity that argues against such a fixed classification. Naturalized or alien species are species that aren’t native to an area, but are established. Invasive species are species that pose a threat to biodiversity and native species. Although the term “invasive” can be difficult to define and is often subjective, it may include plants, animals, and microbes. Some also include native species that have infected humane habitats like farms and landscapes. Others expand the definition to include native or “native species” that have colonized natural areas. It is sometimes difficult to define “native”. The ancestors and descendants of Equus Ferus (modern horses), evolved in North America, then radiated to Eurasia.


Before becoming extinct locally, It is not clear whether the horses were indigenous or foreign to North America after their human-assisted migration in 1493. Although there are many areas of biology that can study invasive species, most of the research has been done in the field of ecology and geography. This is because the topic of biological invasions is of particular importance.


Charles Elton’s 1958 book The Ecology of Invasion by Animals and Plants has influenced a lot of the research on invasive species. This book drew from limited research in disparate fields to provide a generalized picture of how biological invasions are occurring. Research on invasive species was sparse up until the 1990s, when there was a lot of progress in the field. The majority of this research has been conducted through field observational studies and has focused disproportionately on terrestrial plants. Due to the rapid growth of this field, it is necessary to standardize the terminology used to describe invasive species. Although there is no official term for the study of invasive species, it is often called “invasion ecology” and “invasion biology”. This lack of standard terminology is a serious problem. It’s due to the interdisciplinarity of the field, which borrows terms and concepts from many disciplines, such as agriculture, zoology and pathology, and because studies on invasive species are often performed in isolation. Colautti and MacIsaac suggested a new nomenclature system that is based on biogeography and not taxa. This was in an effort to avoid the pejorative, subjective, and ambiguous terminology that often accompany discussion on invasive species in scientific papers.


This model focuses solely on ecological factors and omits taxonomy, economic factors, and human health. This model evaluated individual species rather than whole populations. Each population was classified based on how successful it has been in this environment. This model was equally applicable to both introduced and indigenous species. However, it did not automatically classify successful introductions as dangerous. The USDA’s National Invasive Species Information Center has a very narrow definition of invasive species. Executive Order 13112 defines an “invasive species” as an alien species whose introduction causes or is likely to cause harm to the environment or human health. A species that is introduced must survive in low populations before it can become invasive in another location. It can be difficult for introduced species to reproduce in new locations with low populations. This is why it might arrive at a place multiple times before becoming established. A high propagule pressure is a pattern of repeated human movement such as cars driving up and down roads or ships going to and from ports. Scientists consider ecosystem and species factors as the two mechanisms that can lead to invasiveness of a new species. The effects of new species on ecosystems are determined by the availability of resources and how they are used. Stable ecosystems have equilibrium in the utilization of resources. These mechanisms are used to describe an ecosystem that has been subjected to a disturbance that alters its fundamental nature.


Normal succession favors native grasses, forbs, and forest fires can cause changes. Introduced species can spread faster than native species and can take up resources that are not available to native species, thus squeezing them out. These species are often limited by phosphorus and nitrogen. Each species has a unique role in the ecosystem. Some species play large, varied and specialized roles. Invading species can fill in niches that aren’t used by native species and also create new niches. This is the case with the Lampropholis delicata skink species. Invasion is more common in ecosystems similar to the one where the potential invader originated. Changes in ecosystems can affect the distribution of species. Edge effects, for example, describe what happens to an ecosystem when it is disturbed or when land is cleared for agricultural purposes. The boundary between the unaltered habitat and newly cleared land creates a distinct habitat. This can lead to new winners and losers, and may even host species that are not able to thrive in the habitat. Charles S. Elton, a 1958 ecologist, claimed that ecosystems with greater species diversity are less susceptible to invasion because there are fewer niches.


Other ecologists pointed out highly diverse but heavily invading ecosystems, and suggested that ecosystems with higher species diversity were more vulnerable to invasion. The spatial scale of invasion studies was crucial to this debate. However, the question of how diversity impacts susceptibility remains unresolved. Studies on a small scale tend to show a negative correlation between invasion and diversity, while larger studies tend to show the opposite. This may be due to invasives’ ability capitalize on greater resource availability and weaker species interaction that are more prevalent when larger samples are taken into account. This spatially dependent pattern of the impacts of invasion on biodiversity does not hold when the invaders are vertebrates. Because their species are less likely to be harmed by predators and strong competitors, or because they live far from other species, island ecosystems could be more vulnerable to invasion.


This phenomenon can be seen in Guam’s decimation by the invasive brown-legged tree snake. Invaded ecosystems might lack natural predators and competitors that can stop invasive species from growing in their native ecosystems. Small islands may be home to native birds that have lost their ability to fly due the lack of predators. These birds are unable to escape the danger posed by introduced predators. Rails have a tendency to develop flightless forms on islands, which has resulted in a large number of species being extinct in this family. Many invasive species have been introduced to Hawaii’s islands, threatening the native plants and animals. Invasive insects, plants and hoofed animals like deer, goats, and pigs endanger the native plants. Rosy wolfsnails, which are native to the southeastern United States, feed on the island’s native snails. Plants such as Australian treefern and Miconia calvescens shade native plants. Introduced little fire ants can cause major damage to crops, animals and people in Hawaii. The ecology of Hawaii is greatly affected by the Jackson’s and veiled chameleons. The first invasive species in New Zealand were dogs and rats introduced by Polynesian settlers in around 1300. Europeans later introduced cats to New Zealand, which has had devastating effects on the birdlife, especially as many New Zealand birds have no flight.


The nuisance of rabbits has been a problem for farmers in South Island, where they were introduced by sailors as food in 1800s. Common gorse is a native hedge plant from Western Europe. It was brought to New Zealand to serve the same purpose, but it grows aggressively and threatens native plants. Many species of deer, both from North America and Europe, and the Australian brushtail posesum are heavily impacting native forests. All of these exotic species have thrived in New Zealand. Exotic plant and animal species have been introduced to Madagascar by colonization. This has significantly changed the island’s landscape. This is due to man-made disturbances of the ecosystems. Extensive logging is the most prominent disturbance. This allows non-native species to invade the space created. Prickly pear (Opuntia species) is one example of an invasive plant species found in Madagascar. and silver wattle (Acacia dealbata). Over the past few decades, Madagascar has been affected by the water hyacinth Eichhornia crepes (one of the most invasive species of plants in the world). The spread of this plant has a negative impact on Madagascar’s finances. It is found in basins of lakes and other bodies of water. It forms dense mats of roots that cover the water surface. This limits light penetration, which can impact aquatic organisms. This plant can be used to make fertilizers, paper bags, and clean up biological waste. Invaded ecosystems might have been subject to disturbances, most often human-caused.


This disturbance could give invading species the opportunity to establish themselves, with less competition from native species less able to adapt to disturbed ecosystems. Bioconstruction and bioprotection are the main geomorphological effects caused by invasive plants. To control soil erosion, the vine Pueraria montana (kudzu) was introduced to the United States. Bioturbation and bioerosion are the main geomorphological effects that invasive animals have on soil. Invasion of the Chinese mitten crab Eriocheir sinensis (Chinese mitten crab) has resulted in higher rates of bioturbation, and bioerosion. Although all species are in competition for survival, some invasive species have certain traits or combinations of traits that enable them to outcompete the native species. Sometimes, it is about growth and reproduction. Other species interact more directly with one another. Researchers differ on the utility of traits as invasiveness markers. A study showed that traits alone could identify 86% of the invasive species from a list of noninvasive and invasive species. Another study showed that invasive species tend to only have a subset of the predicated traits. Many similar traits were also found in noninvasive species. This suggests other explanations.


The following are common traits of invasive species: A species that is introduced can become an invasive species if it outcompetes native species for resources like nutrients, light, space, water or food. These species may have evolved in a hostile environment, which could lead to fewer viable competitors and a faster spread of the invader. An ecosystem that is being utilized to its fullest extent by native species can be described as a zero-sum system in which any gain for an invader is a loss to the native. This unilateral competitive advantage (and the extinction of native species due to increased invader populations) is not the norm. For a long time, invasive species can coexist with native species. Gradually, however, the superior competitive abilities of an invading species become apparent as its population increases and adapts to its new environment.


Invasive species may be able access resources previously unavailable to native species. This could include deep water sources that can be accessed via a long taproot or the ability to survive on soils previously unknown. Barbed goatgrass (Aegilops Triuncialis), was introduced to California in serpentine soils. These soils have low water-retention and low nutrient levels. They also have high magnesium/calcium ratios and can be toxic for heavy metals. These soils have low plant populations, but goatgrass can make dense stands and crowd out native species. Invasive species can alter the environment by releasing chemical compound, altering abiotic factors or changing the behaviour of herbivores. This could have a positive or detrimental impact on other species. Kalanchoe digremontana produces allelopathic chemicals, which might have an inhibitory impact on other species and affect some soil processes, such as carbon and nitrogen mineralization. Stapelia gigantea, another species, facilitates the recruitment and development of seedlings in dry environments. It provides appropriate microclimatic conditions that prevent herbivory at its early stages. Centaurea dilute (diffuse knapweed) and Centaurea solstitialis, which are both yellow starthistle (yellow starch), are two other examples. These noxious weeds from Eastern Europe have been spreading through the West Coast.


Experiments have shown that 8-hydroxyquinoline (a chemical that is produced at the root C. diffusa) has a negative impact only on plants that are not co-evolved. These co-evolved native species have developed defenses. C. diffusa or C. solstitialis are not found in their native habitats as overwhelmingly successful rivals. Failure in one habitat does NOT necessarily mean success in another. However, it is possible to find new weapons against invasiveness by studying habitats where a species is less successful. Another form of facilitation is the alteration in fire regimes. Bromus tectorum is a highly adaptable fireweed, originally from Eurasia. Bromus tectorum spreads quickly after being burned and also increases the intensity (heat) fires by providing large quantities of dry debris during the fire season in western North America. It has caused changes in the fire regime of many local areas. Native plants are unable to survive frequent fires. This allows B. Tectorum to expand and retain its dominance within its original range. Research on invasive species has shown that they are capable of rapid adaptation. This is why introduced species can establish themselves and become invasive in new places. Biologists may not be able to determine the spread rate of an invasive species because population growth is not linear but geometric. Individuals begin to exhibit additive variance instead of epistatic variance when there are founder effects and bottlenecks. This can lead to an increase in variance among the founding populations, which allows for rapid adaptive development. Selection may be based on both the ability to disperse and the physiological tolerance to new environmental stressors. The adaptive response to the environment’s selective pressures is then what happens. These changes would be most likely due to climate change and temperature, as well as the presence of predators or prey species. Adaptations can be described as changes in morphology and physiology. These species exhibit rapid adaptive evolution, which results in offspring with higher fitness and better adaptations to their environment. Pre-adaptation, intraspecific phenotypic and post-introduction evolutionary factors are all important components of adaptive evolution.


The ability to adapt to the environment allows for plasticity within populations. This is a key aspect of adaptive evolution, as the goal is to be the best fit for the environment in which the species was introduced. A population that is able to achieve this goal as quickly as possible will have a high level of fitness. The success of introduced species depends on their ability to adapt and evolve quickly. It is more likely that the introduced species will adapt to a similar environment or have traits that are well-suited to the new environment. These factors, along with evolution after introduction, determine whether the species can establish itself in the new environment and if it will reproduce or thrive. Ballast water is another vector that allows for non-native aquatic species to be transported. The main vector for the invasion of non-native aquatic species is ballast water, which is taken at sea and then released into port by transoceanic vessels. Ballast water is used to transport 10,000 species each day, many of them non-indigenous. Many of these species can be harmful to their environment and are therefore considered dangerous. Freshwater zebra mussels are a species that is native to the Azov, Caspian, and Black seas. They most likely arrived in the Great Lakes via ballast water, which was transported by transoceanic vessels. Zebra mussels are more efficient than other native organisms in terms of oxygen and food, including algae. Although the first zebra mussel infestation was noted in 1988, a mitigation plan was implemented soon thereafter. However, there was a major flaw to the plan. Ships carrying cargo were not tested for oxygen and food because the ballast water tanks on their ships were empty. Even if a ballast tank is empty, there is still a puddle of water that contains organisms that can be released at the next port. After unloading cargo, ships take on ballast water, which then mixes with the puddles, and everything, including any living organisms, is discharged at next port.


The current regulations for the Great Lakes use’salinity shock to kill freshwater organisms in ballast tanks. Ballast water regulations exist to protect against potentially invasive species. However, there is a loophole that allows organisms between 10 and 50 microns to be killed in ballast tanks. Current regulations permit less than 10 cells per liter to be discharged from treatment systems for organisms that are between 10-50 microns. This includes certain types of phytoplankton. Ships carrying cargo to ports discharge water. The discharge water may not be the same as the water that is being received. Many species of phytoplankton have a small size and can reproduce sexually. This means that one cell could multiply exponentially into thousands over a short time. This loophole could lead to environmental damage. Some species of the genus Pseudo–nitzschia have a width less than 10 microns and contain domoic Acid, a neurotoxin.


Pseudonitzschia species can cause poisoning. Ballast discharge can contain domoic acid, which could lead to domoic acid poisoning of shellfish, marine mammals, and birds. Due to stringent monitoring programs established after the 1987 domoic acid epidemic in Canada, human deaths from domoic acid poisoning were prevented. To prevent the release of toxic and invasive phytoplankton, ballast water regulations must be made more stringent. Non-native species also provide ecosystem services. Non-native species also have the potential to act as biocontrol agents, limiting the impact of invasive species. For example, they can be used to control pests in agriculture. For example, Asian oysters filter water pollutants more effectively than native oysters to Chesapeake Bay. The Johns Hopkins School of Public Health has found that the Asian oyster could help improve the bay’s declining water quality. Naturalisation is a term that describes species that have invaded an area for so long they have created their own niche in the environment.


The population genetic analysis has shown that Lasioglossum Leucozonium is an invasive species in North America. It has been a major pollinator for blueberry bushes, cucurbits, apple trees and cucurbits. Any female who laid her eggs on ribwort plantsain, an invasive plant, had the advantage of the checkerspot butterfly. The plantain leaves were green enough to allow the caterpillars survive in dry summers. This was despite the fact that the climate is changing and the plants seem to have become drier. The caterpillars became starved and desiccated as the native plants that they used to eat began to die. The difference in survival led to the butterflies developing a preference for plantains as a place to lay their eggs. In fact, in 1984 the percentage of female butterflies who chose to lay their eggs there rose from less than a third to three-quarters. The switch was made a few years later. Federally endangered Taylor’s Checkerspot Euphydryas Editha taylori is so dependent on it, that conservationists actively plant plantains into the wild. In Washington state, Mission Creek Corrections Centre for Women prisoners breed checkerspots in greenhouses so they can be released into new habitats.


It may seem strange, but encouraging an alien plant (increasing profits) is helping to preserve a beloved native insect (reducing losses). Balsam wooly Adelgid is small sap-sucking insect that eats true firs. It is an invasive species in North America, including BC. The black slug, also known by the red or chocolate name, is a native species of Europe. They have been introduced to many countries via human activity. Since the 1940s, this slug is well-established in British Columbia. It is also common throughout Southern BC as well as Haida Gwaii. Blueweed is a noxious and dangerous weed in BC. It is toxic to horses, cattle, and reduces the quality of forage in rangelands and pastures. This can lead to economic losses. In 2016, brown marmorated stink bugs first appeared in BC. They have since spread to all of the Lower Mainland, the Okanagan Valley and Brentwood Bay, Vancouver Island. They are considered a nuisance pest in humans’ homes and have been a major pest to many crops. They are an invasive species in British Columbia. They are larger than any other species of turtle found in BC and can be a threat to native turtles. The first introduction of Eastern cottontail rabbits to BC was in Sooke, in 1964. They have spread all over Eastern Vancouver Island, from Victoria to Campbell River.


They pose a threat to the fragile Garry Oak habitats of Vancouver Island. They also feed on many at-risk species. They compete with native squirrel species for habitat and feed on nestlings and eggs of birds. They are found in the Lower Mainland, Vancouver Island and the Southern Interior. The European brown garden snail can be found in Southern BC, Vancouver Island and the Lower Mainland. The snail will eat a variety of ornamental and agricultural crops, and compete with native snails and slugs for food and habitat. The European Chafer Beetle was introduced to BC for the first time in 2001. Infested turf was likely the reason they were introduced to BC in 2001. Because they infest lawns and attract predators like skunks and crows to eat them, they can be a nuisance pest for homeowners. The European green crab is a highly-invasive species that has been found in many areas of the globe, including on the BC coast.


They can outcompete native crabs in food and habitat, and they could be a threat to other marine species. Leafy spurge was originally introduced to BC in the form of a perennial. However, it has since escaped into nature. It can be found in fields, fields, grasslands and open forests. It is a native European weed and is a common weed in BC. It can survive as an annual or biennial. One plant can produce thousands upon thousands of seeds that remain viable in the soil for many years. It can also spread by root and stem fragments. The invasive Rosy Red Minnow can be found in BC waterways, most likely because it was intentionally dumped by pet owners. These fish are able to breed easily in BC waters and could compete with small fish for food or habitat if they spread. The strawberry blossom weevil, which is a pest of strawberries in Europe, is a native species. This new arrival to BC has the potential to disrupt BC’s berry-growing industry.