What Is: Invasive Species

Image Credit: Scientific Frontline / stock image

Scientific Frontline: Extended "At a Glance" Summary

The Core Concept: Invasive species are non-native organisms that, upon introduction to a new environment, escape the evolutionary checks of their native ranges to cause significant ecological, economic, or human health harm. This phenomenon represents a systemic disruption of biophysical systems rather than merely the presence of an unwanted plant or animal.

Key Distinction/Mechanism: The defining characteristic separating "invasive" from "non-native" is impact; while many non-native species (like agricultural crops) are beneficial, invasive species actively dismantle native ecosystems. They often succeed via the Enemy Release Hypothesis, flourishing because they have left behind natural predators and diseases, or through Priority Effects, such as leafing out earlier than native flora to monopolize resources.

Origin/History: While natural translocation has occurred for eons, the current crisis is driven by the "relentless engine of human globalization" in the Anthropocene. The concept is underscored by the "Ten Percent Rule," a statistical filter noting that roughly 10% of transported species survive, 10% of those establish, and 10% of those become destructive invaders.

Bringing back native predators to tackle invasive species crisis

Source: Queen's University Belfast

Invasive species are one of the greatest threats to biodiversity globally and are the main cause for the extinction of vertebrates in the last century, with an estimated cost of at least $162 billion (USD) a year.

Native predator populations have been depleted globally, despite being essential for the functioning of the ecosystem and biodiversity. The absence of native predators facilitates the spread of invasive species leading to the extinction of native species throughout the world.

The research, published today in Global Change Biology, found that restoring native predators could provide a solution to a variety of the most damaging invasive species globally. According to the study, the evolutionary naivety of invasive species to native predators, coupled with a lack of spatial refuges from predation could underpin the abilities of native predators to provide effective control of certain established invasive species.

The research team have previously shown how the recovery of the native pine marten in the UK and Ireland has resulted in landscape-scale declines of the invasive grey squirrel. Building on this research, the team have now evaluated native predator reintroduction and restoration as a viable nature-based solution to the invasive species crisis.

Insects are victims too, not just invaders, says study

Harlequin larva and moth eggs.
Photo Credit: Bill Phillips

Scientific Frontline: "At a Glance" Summary

• Main Discovery: A groundbreaking global analysis led by the UK Centre for Ecology & Hydrology (UKCEH) establishes that insects are major victims of invasive alien species (IAS), significantly exacerbating global population declines and compromising biodiversity.
• Specific Detail/Mechanism: The reduction in native insect populations is driven principally by invasive animals outcompeting or directly preying upon them, alongside invasive vegetation displacing the native flora that insects rely on for nutrition and habitat.
• Key Statistic or Data: The study, which analyzed data across six continents, indicates that invasive alien species reduce the abundance of terrestrial insects by an average of 31% and decrease species richness by 21%.
• Context or Comparison: Vulnerability varies significantly by order: Hemiptera (true bugs) experienced the steepest decline in abundance at 58%, followed by Hymenoptera (ants, bees, wasps) at 37%, while Coleoptera (beetles) were the least affected with a 12% reduction.
• Significance/Future Application: These findings highlight a critical risk to essential ecosystem services such as pollination and pest control, necessitating urgent prioritization of biosecurity measures and habitat management to mitigate the introduction and spread of damaging invasive species.
• Methodology: This research represents the first comprehensive study to quantify the impact of invasive alien species on insect populations on a global scale, filling a significant gap in the understanding of drivers of insect decline.

Study finds drought fuels invasive species after wildfires

Parry’s Phacelia, native to Southern California, grows beneath burnt brush, at the Loma Ridge site where UCI’s Sarah Kimball conducted the research.
Photo Credit: Jessica Rath / UCI

In a study recently published in the journal Ecology, University of California, Irvine scientists uncover the intricate dance between drought, wildfires and invasive species in Southern California’s coastal sage scrub ecosystems.

Titled “Long-term drought promotes invasive species by reducing wildfire severity,” the research, led by Sarah Kimball, Ph.D., director of the Center for Environmental Biology at UCI, sheds light on the critical interplay of these factors and its profound implications for ecosystem health.

The research, conducted at the Loma Ridge Global Change Experiment, showcases how prolonged drought acts as a catalyst, influencing not only the severity of wildfires but also paving the way for invasive species to take center stage. By simulating drought conditions, the study clarifies connections between climate change, wildfire dynamics, and shifts in plant communities.

Reduced fire severity associated with drought creates an environment conducive to invasive species. Non-native grasses, in particular, thrive in these conditions, potentially leading to a transformation of the landscape and abundance and diversity of native species.

Researcher Aims to Uncover Plant Invasions in the Tropics

Invasive plants are invading all major ecosystems across Central America compromising the conservation of native species.
Photo Credit: Julissa Rojas-Sandoval

Invasive species of plants have a knack for settling in new settings and making big changes to an ecosystem, even leading to extinctions of native species.

Assistant Research Professor in UConn’s Institute of the Environment Julissa Rojas-Sandoval explains that invasive plants are non-native species that have been introduced into new areas generally as a result of human activities, and that they are actively spreading, causing harm to the environment, the economy, and human health. Invasive plants may have significant long-term implications for the conservation of native biodiversity, but to combat the problem, we need to know which plants are invasive, where they’re from, and how they got there.

Rojas-Sandoval leads an international collaboration including researchers from all Central American countries, working together to compile the most comprehensive databases of invasive plant species in Central America. The collaboration is called FINCA: Flora Introduced and Naturalized in Central America, and their first paper was published this week in Biological Invasions.

The collaboration arose to meet a need, says Rojas-Sandoval. “While we have a good understanding of the processes and mechanisms of plant invasions in temperate regions, there is a huge gap in our knowledge about biological invasions in the tropics, and this lack of information is limiting our ability to respond to invasive plants.”

Traded species have distinctive life histories with extended reproductive lifecycles

Chameleon
Invasive species can cause huge environmental problems and monetary costs
Photo Credit: Pierre Bamin

A new study by researchers from Durham University, UK, Queen’s University Belfast, UK, University of Extremadura, Spain and Swansea University, UK have revealed that vertebrate species involved in the live wildlife trade have distinctive life history traits, biological characteristics that determine the frequency and timing of reproduction.

Researchers discovered that traded species produce large numbers of offspring across long reproductive lifespans, an unusual profile that is likely financially advantageous for trades involving captive breeding such as the pet, food and fur/skin trades.

Traded species that have also been introduced into non-native areas have a more extreme version of this same life history profile, suggesting that species most likely to become problematic invaders are at a heightened risk of trade and release.

The study suggests that humans favor species with high reproductive output for trade and release, which are the very species likely to become problematic invaders in future.

Researchers point out that life history traits are therefore potentially useful for predicting future invasions.

Flipping the “genetic paradox of invasions”

A close-up look at a green crab. Image credit: Ted Grosholz

The green crab, Carcinus maenas, is considered a globally distributed invasive species, an organism introduced by humans that eventually becomes overpopulated, with increased potential to negatively alter its new environment. Traditionally, it’s been assumed that successful populations contain high genetic diversity, or a variety of characteristics allowing them to adapt and thrive. On the contrary, the green crab - like many successful invasive populations - has low genetic diversity, while still spreading rapidly in a new part of the world.

A new study led by Carolyn Tepolt, an associate scientist of biology at Woods Hole Oceanographic Institution, is investigating the adaptive mechanisms of the green crab along the west coast of North America, where it has shown extensive dispersal in the last decade despite minimal genetic diversity. The study was published recently in Molecular Ecology and is a collaboration between WHOI, the University of California at Davis, Portland State University, and the Smithsonian Environmental Research Center.

“Invasive species like these are generally unwelcome. Green crabs can compete with native species, rip up eelgrass ‘nurseries’, and eat small shellfish before they have a chance to be harvested. Green crabs can be an ecological menace and an economic burden,” Tepolt said. “In this study, we found that one of the world's most serious marine invasive species has evolved specific genetic variation that likely helps it adapt to new environments really quickly, even when it's lost a lot of genetic diversity overall.”

Genetic diversity refers to small individual-to-individual differences in DNA, and often translates into a range of different inherited traits within a species. A population with high genetic diversity is more likely to include individuals with a wide range of different traits. In order for a population to adjust to changing environments, this variation can be crucial - or so scientists have often thought. Invasive species often challenge this assumption, successfully spreading in new regions despite low genetic diversity caused by descending from a small number of initial colonists.

This study focuses on a northwest Pacific population of green crab that has spread within the last 35 years from a single source. High-profile marine invasive species, such as green crabs, often live across thousands of kilometers of ocean, spanning countless environmental differences, both small and large. Using six U.S. west coast locations spanning over 900 miles from central California to British Columbia, Tepolt and her team examined the species’ genetic structure at thousands of places across its genome. While this population has lost a large amount of overall genetic diversity relative to its European source, a piece of DNA associated with cold tolerance in a prior study appears to be under strong selection from north to south across its invasive West Coast range.

This may represent a type of genetic feature - a balanced polymorphism - that evolved to promote rapid adaptation in variable environments despite high gene flow, and which now contributes to successful invasion and spread in a novel environment. Researchers do occasionally find incredibly successful populations that have passed through severe bottlenecks, dramatically decreasing their genetic diversity relative to their source. This study is amplifying the need to consider that diversity at specific parts of the genome (rather than genome-wide diversity) may play a critical role in resilience in new or changing environments.

“This is exciting for two main reasons. First, the study tests a partial resolution to ‘the genetic paradox of invasions’, demonstrating that variation at key parts of the genome permits rapid adaptation even in a population with low overall genetic diversity. Second, it suggests that high gene flow in a widespread species’ native range may generate evolutionary mechanisms, like this one, which provide that species with the substrate for rapid adaptive change as it spreads across new environments,” Tepolt explained.

Identifying invasive species spread can also be a job for non-scientists. As the climate changes and as humans get better and better at moving stuff around the globe, there’s more potential for species to come along for the ride and expand into new environments. Tepolt says it’s important to keep an eye out for cues, changes in the environment and possible new species in places they haven’t been before. She recommends seizing the opportunity to tell officials and researchers if there is something unusual at the coastline. There may be signs at beaches and boat ramps asking people to keep a lookout for particular species and giving contact information. If there are suddenly green crabs in an area for the first time, for example, on the West Coast in the Salish Sea and in Alaska, they likely should not be there and should be reported.

Source/Credit: Woods Hole Oceanographic Institution

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Understanding mutualism can help control the spread of invasive species

The subalpine fir has a mutualistic relationship with belowground fungi.
Photo Credit: Khilav Majmudar, University of Minnesota

Cooperation between species to help each other's survival is known as mutualism. It is seen among many types of organisms, such as plants and fungi that exchange nutrients with one another, plants that provide bees with nectar in exchange for pollination, and sea anemones that provide protection for clown-fish in exchange for excreted nutrients. Recently, scientists have found evidence that some invasive plants become even more invasive in the presence of helpful partners, as can happen with certain pine trees and fungi or fig trees and wasps. But other studies have suggested that species that didn't rely on mutualist partners were more invasive. 

Recent research at the University of Minnesota, published in the journal Ecology, attempted to identify the conditions under which a mutualistic partner could make a species more or less invasive. To study this, they built mathematical models called integro-difference equations (IDEs). IDEs take into account the effects of mutualism on growth and dispersal of species and are useful tools to model spatial processes. Mathematical models are helpful in understanding ecological processes like invasion that occur over many years and can be difficult to study in the field.

Conservation paradox: Invasive species are often threatened in their native range

The wild rabbit is endangered in its native Europe. In other parts of the world, such as Australia, this species has been introduced and has large populations.
Photo Credit: ©Alexis Lours

Non-native animals are a threat to biodiversity, yet many are themselves threatened with extinction in their areas of origin

Non-native species introduced by humans are among the main causes of global species decline – they were partly responsible for 60 percent of the species that have become extinct worldwide in recent decades. In Central Europe, non-native mammals include species such as the Norway rat, the mouflon and the mink. Now a study led by biologists from the University of Vienna and La Sapienza University in Rome shows that some of these species introduced by humans are themselves endangered in their native range. The study has been published in the current issue of the journal Conservation Letters.

The globalization of the earth is contributing to the introduction of many animal and plant species into new parts of the world. Invasive species can displace native species through competition or transmit new diseases. At the same time, however, some of these non-native species are threatened with extinction in their native ranges. This creates a conservation paradox – because the question now is, should non-native occurrences of species that are endangered in their native range be protected or controlled? However, it was previously unknown how many non-native mammal species this paradox actually applies to. In the new study, the scientists have now quantified this in order to come one step closer to an answer to this paradox.

Twenty species of sea lettuce found along the coasts

Sea lettuce, which is a type of green alga, grows along the coasts and is interesting as potential food source. A new survey shows that there are 20 different species of sea lettuce along the Swedish coast.
Photo Credit: Sophie Steinhagen

The number of species of the green alga sea lettuce in the Baltic Sea region and Skagerak and is much larger than what was previously known. Researchers at the University of Gothenburg have surveyed 10,000 kilometers of coast and found twenty species of sea lettuce.

Green macroalgae of the genus Ulva, also known as sea lettuce, are almost ubiquitous in the wider Baltic Sea region and can be found from the Atlantic waters all the way up to the Bay of Bothnia in the Baltic Sea. Sea lettuce reproduces easily and grows quickly, which makes it interesting for an expanding aquaculture industry. Research is ongoing both in Sweden and abroad for utilizing sea lettuce in the food industry and for different biochemical applications.

There are multiple species, but until now it has not been known how many there are and previously only a handful had been identified.

Invasive Species Increasingly Threaten Protected Areas Worldwide

China's famous Red Marshes, a protected area and vital shorebird
habitat that is increasingly being overrun by invasive grasses
that are smothering the red plants.
Photo credit: Hong'an Ding

Scientific Frontline: "At a Glance" Summary

• Main Discovery: Invasive species, specifically non-native cordgrass, are aggressively displacing native flora in protected coastal wetlands, effectively converting critical habitats into "green deserts" despite successful mitigation of human disturbances.
• Methodology: Researchers utilized remote sensing technology to analyze a 30-year time series of satellite imagery from Google Earth Engine, comparing rates of wetland loss and cordgrass invasion across seven major protected areas and unprotected control sites along China’s Yellow Sea.
• Key Data: While wetland loss caused by human activities was significantly slower in protected zones, the expansion of invasive plants was substantially higher in four of the protected areas compared to their unprotected counterparts.
• Significance: The study challenges the prevailing ecological theory that human disturbance is the primary driver of biological invasion, demonstrating that protected areas remain highly vulnerable to invasive species even when human impact is minimized.
• Future Application: Conservation management protocols must be updated to include active defense mechanisms against biological invaders in low-elevation mudflats, rather than relying solely on the restriction of human activity to maintain ecosystem health.
• Branch of Science: Marine Conservation Biology and Coastal Ecology
• Additional Detail: The research specifically highlighted the degradation of China's "Red Beach" marshes, a vital migratory bird stopover where iconic native red succulent plants are being smothered by invasive grasses.

New invasive, weedy grasses discovered across Hawaiʻi, some pose major fire risk

Enneapogon cenchroides is the most flammable grass species that Faccenda discovered. It was found in Mākaha.
Photo Credit: Courtesy of University of Hawaiʻi

New species of flammable invasive grasses have been discovered and identified across most Hawaiian islands by a University of Hawaiʻi at Mānoa School of Life Sciences PhD student.

Kevin Faccenda discovered 34 invasive and/or weedy species never before reported in Hawaiʻi during more than 50 days of fieldwork conducted across Kauaʻi, Oʻahu, Maui, Molokaʻi and Hawaiʻi Island over the past year. Six of these species have never been found outside of their native range before, making Hawaiʻi the first place worldwide to experience naturalizations by these species. Faccenda says controlling the spread of these grass species and others is critical to avoid future wildfires, like the one that devastated Lahaina on August 8.

How rapid temperature changes influence biodiversity

Image Credit: Scientific Frontline stock image

Biodiversity has changed faster in places where temperatures have also changed quickly. This is the result of a new study published in the scientific journal Nature. Researchers from the Martin Luther University Halle-Wittenberg (MLU), the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig and Friedrich Schiller University Jena were also involved in the work.

The study focused on how the composition of species in an ecosystem - rather than the number of species - has shifted over time. The researchers found that faster temperature changes sped up shifts in species composition, meaning species identities changed more rapidly in those areas.

The results also suggest that behavioral adaptation and changing species interactions are not enough to preserve species composition in the face of higher rates of temperature fluctuations. 

"It's like shuffling a deck of cards, and temperature change now is shuffling that deck faster and faster," said lead author Dr Malin Pinsky, associate professor of ecology and evolutionary biology at UC Santa Cruz. Pinsky was hosted at iDiv as a sabbatical researcher in 2020. "The worry is that eventually you start to lose some cards," he said.

Pets or threats? Goldfish might be harmful for biodiversity

Invasive species are one of the leading causes of global biodiversity loss, and the pet trade is responsible for a third of all aquatic invasive species. Pet owners releasing unwanted pets into the wild is a major problem. Whilst many believe this is a humane option, new research suggests that attempting to ‘save’ the life of a goldfish could in fact lead to catastrophic outcomes for native biodiversity.

To better understand the ecological risks posed by species within the pet trade, the researchers focused on the two most commonly traded fish species in Northern Ireland: goldfish and the white cloud mountain minnow.

The globally popular goldfish was first domesticated over a thousand years ago and has since established non-native populations around the world. The white cloud mountain minnow on the other hand is a species with a limited invasion history to date.

Will renaming carp help control them?

Joseph Parkos directs the Illinois Natural History Survey’s Kaskaskia, Ridge Lake and Sam Parr biological stations in Illinois.
Photo Credit: B. Gallo-Parkos

Illinois officials this month announced that Asian carp would now be called “copi” in an attempt to make the fish more desirable for eating. Joseph Parkos, the director of the Illinois Natural History Survey’s Kaskaskia, Ridge Lake and Sam Parr biological stations in Illinois, spoke with News Bureau life sciences editor Diana Yates about scientific initiatives to study and control carp/copi fish populations and the potential for rebranding to aid those efforts.

What are Asian carp/copi and where in Illinois are their populations a problem?

Silver carp produce more offspring than other carp species. 
Photo Credit: USGS

New damselfly sharing habitat with UK natives

A male small red-eyed damselfly.
Photo Credit Pam Taylor

A damselfly species that came to the UK from Europe poses a minimal risk to native damselflies and dragonflies; new research shows.

As tens of thousands of species shift their “range” (the areas they live in) due to climate change, the small red-eyed damselfly has spread northwards from the Mediterranean. It was first observed in the UK in 1999 and has since established itself.

The new study – by the University of Exeter and the UK Centre for Ecology & Hydrology – used data from the British Dragonfly Society to see if it had caused native damselflies and dragonflies to decline.

The results showed most native dragonflies and damselflies were either found more often or were unchanged in areas colonized by the small red-eyed damselfly.

However, two damselfly species might have been negatively affected, and more research is needed to investigate this.

“With range-shifting increasing globally, we need to understand what impact newly arrived species have on ecosystems,” said Dr Regan Early, of the Centre for Ecology and Conservation on Exeter's Penryn Campus in Cornwall.

Conservation: In-Depth Description

Photo Credit: Tomáš Malík

Conservation is the scientific discipline and practice dedicated to the protection, management, and restoration of Earth's biological diversity—including species, their habitats, and ecosystems—to prevent their decline, extinction, and degradation, while ensuring the sustainable use of natural resources. The primary goals of conservation are to maintain the planet's ecological health, preserve evolutionary processes, and secure the vital ecosystem services upon which all life, including humanity, depends.

Mussel survey reveals alarming degradation of River Thames ecosystem since the 1960s

Photo Credit: Gil Ndjouwou

The detailed study measured the change in size and number of all species of mussel in a stretch of the River Thames near Reading between 1964 and 2020.

The results were striking: not only had native populations severely declined, but the mussels that remained were much smaller for their age – reflecting slower growth.

Mussels are important in freshwater ecosystems because they filter the water and remove algae. As filter feeders they’re exposed to everything in the water, and this makes them a valuable indicator of ecosystem health. Mussel shells also provide places for other aquatic species to live.

“Mussels are a great indicator of the health of the river ecosystem. Such a massive decline in mussel biomass in the river is also likely to have a knock-on effect for other species, reducing the overall biodiversity,” said Isobel Ollard, a PhD student in the University of Cambridge’s Department of Zoology and first author of the report.

She added: “The depressed river mussel used to be quite widespread in the Thames, but this survey didn’t find a single one - which also raises concerns for the survival of this species.”

Rare, endangered insects illegally for sale online

Brazilian salmon pink bird-eating tarantula (Lasiodora Parahybana) in the lab of Linda Rayor, senior research associate in CALS.
Credit: Jason Koski/Cornell University 

A survey has found that endangered and threatened insects and spiders, as well as common species that provide valuable ecological services, can be easily purchased– without adequate oversight – through basic internet searches, according to a new Cornell study.

For example, the Luzon peacock swallowtail, one of the rarest butterflies, which is listed as endangered both internationally and, in the U.S., and is illegal to trade, was found for sale at Amazon.com pinned in a display box for around $110.

Many species of live tarantulas, which are not threatened with extinction but whose trade is strictly controlled, were also readily discovered for sale as pets without any oversight or enforcement.

These results are concerning given that insects are in steep decline globally due to habitat loss, pesticides, invasive species, urbanization, pollution, and climate change. Some entomologists have estimated that the Earth is losing about 10 to 20% of all insect species every decade, and researchers said an insect or spider species’ survival can be greatly impacted when it is collected and sold.

John Losey, professor of entomology and the lead author of the paper, “Insects and Spiders on the Web: Monitoring and Mitigating Online Exploitation of Species and Services,” which published in the journal Global Ecology and Conservation, said the study began as a project for his Insect Conservation Biology course. The paper included 18 student co-authors who were undergraduates in 2019 when the research was done. Paul Curtis, extension wildlife specialist in the Department of Natural Resources and the Environment, is a senior co-author.

The barred owl’s westward migration threatens other species and a whole ecosystem

Barred owls, native to the eastern United States and Canada but invasive to the west, prey on a wide range of species with special conservation status.
Photo Credit: Lane Wintermute/USFWS

A new study of nearly 800 barred owls on the West Coast shows the invasive predator feeds on 29 species given special conservation status by federal and state governments.

The list includes mammals, birds, fish, amphibians and reptiles, according to an analysis led by researchers at the University of Wisconsin–Madison, who describe the wide-ranging pressure the owl’s advance into new territory is putting on native prey and predator species alike.

In 2024, the federal Fish and Wildlife Service adopted plans to reduce the number of barred owls in California, Oregon and Washington to protect a pair of threatened owls, the northern spotted owl and California spotted owl.

The new findings, published before peer review as a preprint on bioRxiv, suggest that the barred owl — which arrived recently in the western United States — is a danger to the survival of more than just competing owls, according to Daniela Arenas-Viveros, a lead author of the study.