Episode 78: Invasive Species with Leigh Greenwood (The Nature Conservancy)

Episode Intro Notes

Outline

• What are invasive species?

• Why are invasive species a problem?

• How do invasive species travel?

• How has the issue evolved (i.e., gotten worse, more complex) over time, and is it set to get worse?

• Who is leading efforts to combat invasive species?

• What policies are being pursued to address invasive species?

• What can Definers do to help address invasive species?

• Expert Guest, Leigh Greenwood, Forest Pest and Pathogen Program Director at The Nature Conservancy

What are invasive species?

• The National Wildlife Federation defines an invasive species as “any living organism that is not native to an ecosystem and causes harm.” Plants, animals, insects, fish, fungi, bacteria, or really any living thing or its parts, like seeds or eggs can be called invasive if they harm the environment or even the economy or human health. These species have negative impacts on native animals and plants, which in turn affect the natural balance of the ecosystem. 

• Contrary to popular belief, these species don’t have to come from another country to be considered invasive, they just need to be from outside of their traditional habitat. 

• Further, not all non-native species are invasive species. For example, food that is grown in the United States like wheat, tomatoes, and rice, are not native to North American habitats, but are not considered invasive because they do not harm the native species in the area. However, it is important to note that it is extremely difficult to predict which species will become invasive within an area and what negative effects they could have within a new geography. It could take years before a population grows large enough to be deemed invasive.

Why are invasive species a problem?

• Invasive species can cause extinction of native plants and animals and can significantly alter local habitats by outcompeting the native species for limited resources. As these new species will have no natural predators, parasites, or competitors in their new area, they can often grow in numbers rapidly! This rapid or significant population growth results in the displacement or eradication of native species by significantly reducing their natural habitats and/or food sources.

• One example of an invasive species causing extensive damage to ecosystems is the zebra mussel. These mussels attach themselves to boats gaining a free ride to other ecosystems. Once there, they outcompete the native species for space and food, and once established, they are very hard to remove. They reproduce rapidly and often eat all of the microorganisms, like plankton from the area. This causes the entire ecosystem to suffer. As the zebra mussels take food and space from the other animals, those native populations shrink and the entire ecosystem is ultimately altered. This is the pattern that is followed by most invasive species - they outcompete, overpopulate, and overtake. 

• In the process of overpopulating and overtaking a region, these species can have detrimental effects. In September 2023, the United Nations’ Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) released an assessment report on “Invasive Alien Species.” The main takeaway from the report was that these invasive species pose major global threats to “nature, economies, food security, and human health.” The report not only provides details on how invasive species have affected various regions across the globe; it also offers tools and solutions to help governments work towards mitigating these negative effects and create a path forward.

• Notably, this report mentioned that nearly 85% of the impacts these invasions have on native species are negative! So let’s dive a little bit deeper into each of these threats - nature, food security, economy, and human health - to better understand why invasive species are a problem.

• First, let’s look at how invasive species affect nature. We briefly talked about invasive species within Episode 72: Biodiversity, because invasive species are one the the top factors contributing to biodiversity loss! In 2019, the Global Assessment report from the United Nations found that invasive species were one of the top 5 direct drivers of biodiversity loss - right along with climate change, pollution, exploitation, and changes in land and sea use. The report noted that these organisms can cause irreversible damage to our ecosystems contributing to extinction. According to the 2023 report, invasive species have been a “major factor” to 60% of all recorded animal and plant extinctions.   

• This also goes hand in hand with these species affecting food security by damaging our food supplies. Invasive species affect food security in two main ways according to the Pacific Invasives Initiative. First, they decrease the production within agriculture, forestry, fishing, and other sectors that are critical to food production. Second, the biodiversity loss and degradation of the native ecosystem services within an area as a result of invasives, can further directly affect production and harvests of our foods. 

• The fish tilapia, for example, is a native species to Africa and the Middle East, but it has been introduced into many other regions in the world due to the rise of aquaculture and the demand for the fish as a food source. However, this popularity has resulted in tilapia becoming one of the world’s most globalized fish, as they have found their way from aquaculture into natural habitats and even into biodiversity hotspots, posing serious threat to native species. 

• That was nature and food security. Next, let’s look at the economic costs of invasive species. The 2023 UN report we mentioned a bit ago found that invasive species cost more than $423 billion a year. In fact, the costs of invasive species have quadrupled each decade since 1970. As invasive species have become more prevalent over time and continue to grow, for reasons we'll get into here in a bit, the dollar amount of impact is set to grow as well. The majority of the economic impact of these species is due to their contribution to damaging ecosystems, people, and our quality of life. 

• Additional costs are associated with the control and management of invasive species and these costs can add up quickly. Consider the oriental fruit fly, which has become invasive in the states of Florida, Hawaii, and many other parts of the world. It is known to attack more than 400 different fruits and vegetables including citrus fruits, peaches, tomatoes, and apricots. The fruit flies lay their eggs within the produce, using it as a host, and once the eggs hatch, the produce is inedible. Even though a fruit fly outbreak was spotted quickly in Florida, it was estimated that farmers lost an estimated $10 million over the time it took to remediate. In addition, the government likely spent over $3 million in remediation. 

• These flies were spotted once again in Florida in 2022, which prompted a quarantine order that halted the movement of fruits and vegetables that did not have a compliance agreement from the Florida Department of Agriculture and Consumer Services. This was in an effort to protect the crops in the areas from being exposed and to take the time to eradicate the existing flies using bait and insecticide. Back in 2015, when the oriental fruit fly was last seen prior to 2022, a quarantine of over 85 square miles of farmland in Miami-Dade was established in an effort to stop the spread and eradicate the invasive population.

• Zooming out, in fiscal year 2015, U.S. federal agencies invested almost $2.3 billion in the management of invasive species, a funding level rivaling the entire budget of the U.S. National Park Service.

• In addition, like many environmental and sustainability impacts, it is often the most marginalized that bear the brunt of the impacts. People with the greatest reliance on nature, like Indigenous Peoples and smaller communities, are at the greatest risk of feeling the effects of these impacts. The UN IPBES study reports that more than 2,300 invasive species are found on Indigenous lands, which could threaten their quality of life and their cultural practices. 

• Lastly, invasive species can affect human health. Invasives can have a direct effect on spreading pathogens and as vectors for disease. For example, diseases like Malaria and the Zika virus are spread by invasive mosquito species! 

• The zebra mussel, which we talked about earlier, causes damage to local ecosystems by outcompeting the native animals and plants, causing an imbalance in the ecosystem that can increase the numbers of blue-green algae, which is what causes toxic algal blooms that can be detrimental to public health. Studies from the University of Michigan found that in lakes that have these zebra mussels, this algae is about 3 times more prevalent than in lakes that do not have the invasive mussels.

How do invasive species travel?

• At this point, you may be wondering, how do invasive species get introduced to an area in the first place? There is not a simple answer to this question, there are a few main ways that these organisms move from place to place. 

• First, many species that end up being invasive are originally brought to areas for specific reasons as they may serve agricultural or other important purposes, but end up becoming established in these non-native habitats.

• Cane toads, for example, were brought to Australia from South and Central America in the 1930s as a way to control beetle populations around sugar cane crops. As these toads are carnivores, the initial intent was that they would be perfect to eat the beetles around the crops, lessening the use of pesticides. Unfortunately, these toads ended up not only eating the beatles, they also were eating a lot of other native wildlife including other native insects and even bird eggs! The toads are also poisonous, and can harm the animals who would have been the predators of these frogs, making it difficult to control the populations once introduced in the wild without human intervention.

• The second way invasive species can be introduced are when they are originally  intended to be used as pets or could be ornamental plants or flowers that were intended to be used indoors, but are then somehow introduced into the wild. Once these non-native organisms are introduced into the wild, they then establish themselves into the ecosystem. 

• One study estimates that almost 85% of the non-native reptiles and amphibians on Florida’s coastal waters have been introduced by the exotic pet trade. One of these, the burmese python, a large constrictor snake, is an invasive species that is found within the Florida Everglades. The snakes, which average 6 to 9 feet in length, initially arrived in Florida in the late 1970s, when they were initially sold as exotic pets from parts of India, the East Indies, and China. When they were accidentally or intentionally released from people's homes, they were able to easily establish themselves within the region after acclimating to the new warm climate.

• A 2012 study of the region found since 1997 the populations of raccoons, opossums, and bobcats showed over 87% drops in population due to the introduction of the pythons. Other animals, like rabbits and foxes had basically disappeared within the same time frame. This is largely due to the fact that these animals forage for food near bodies of water, in the same habitats that the pythons frequent to look for prey.

• By the way, there’s actually a state-run Florida Python Challenge each year where people sign up to remove pythons from the Everglades and the person who removes the most wins money. In 2023, it was over 10 days with over 840 participants, and the winner got $10,000. 

• While some species are introduced on purpose, there are many more examples of species that have been introduced unintentionally. One of the main ways invasive species are introduced is by accident. This often occurs via contaminated freight or movement of wood products, plants, or food. Individual animals and plants, or their seeds, eggs, or spores, can “hitchhike” their way into these shipments and move from place to place. 

• You may remember the Asian Giant Hornet making headlines in 2020, when the invasive giant insect was spotted for the first time in the US, in Washington State. These hornets, nicknamed ‘murder hornets,’ are the largest hornets in the world. Most notably, they are predatory and are capable of killing humans if stung multiple times and can absolutely devastate a local bee population by infiltrating their hives and attacking bees directly, killing them and driving any survivors away from their homes. This discovery sent scientists on a years-long hunt to locate where the hornets could have worked to establish themselves in the region and crews were successful in locating and eliminating a few newly established nests.

How has the issue evolved (i.e., gotten worse, more complex) over time, and is it set to get worse?

• Unfortunately, the issues with invasive species have only increased over time and much of this increase can be attributed to one key explanation - globalization. As levels of global trade and travel have increased, the ability for these invasive species to be spread and introduced has increased. Globalization ultimately facilitates the spread of these species, whether intentionally or unintentionally. It is predicted that as globalization continues to expand in conjunction with changes in how we use the land and sea, coupled with other demographic changes, the numbers of invasive species, and the subsequent impacts, will also continue to increase and species that have already been introduced into areas will continue to thrive by expanding into new regions. 

• Anibal Pauchard, a professor who helped to co-chair the previously mentioned IPBES report, has stated that while it is normal and common for species to move, we are currently living in the unprecedented era where organisms are jumping “big barriers” and moving between continents more easily than before. So while it would be normal for species to travel within a country, we are now seeing that they have the ability to cross entire oceans due to the fact that humans and our technologies travel across continents.

• The second key factor contributing to the expansion of invasive species in some regions is climate change. Warming temperatures are helping some plants and animals thrive and expand their habitats to regions where they have not been found historically, creating new opportunities for species to become invasive. 

• The burmese python, which we just mentioned, is one of the species that is set to expand their habitats due to climate change. A January 2023 study determined that these snakes are currently expanding their habitats further north in Florida and their range will continue to expand in the next 5 to 10 years as climates start to heat up elsewhere, potentially expanding their reach beyond Florida and into more states within the southern US. 

• In addition, extreme climate events like hurricanes and floods can actually play a role in transporting these invasive species from one area to another while also decreasing the built in-defenses that native ecosystems have against a potential invasion. Further, some of the control tools that are used, like aquatic barriers, to keep invasive species out of other habitats can be made less effective due to the impacts of climate change. As these invasive species already play a major role in changing ecosystems, if you couple this impact with other climate change impacts, this can be a recipe for disaster for many ecosystems to be significantly altered. 

• A 2020 study predicts that the number of established invasive species will increase by 36% between 2005 to 2050. This study applied a model based on historic invasive species data and then looked into how this data could predict the future. The results of the model showed that strong increases are projected to occur in Europe, parts of Asia, North America, and South America and the potential for invasive species decline in Australia and some other parts of Asia. Of course, this scenario is dependent on many factors, including any mitigation and prevention policies or programs. However, wide scale efforts will be needed to make significant progress in this area due to the impacts of globalization and climate change.

Who is leading efforts to combat invasive species?

• Because invasives touch nearly every corner of the world, there are many organizations leading efforts to combat invasive species and minimize their impacts. From government agencies to international organizations, non-profits, and academic institutions, invasive species are a key topic in conservation around the world. 

• For example in the United States, the United States Department of Agriculture (USDA), is one of the leading agencies that is collaborating with other groups, both internal and external to the government, to prevent, control, and eradicate these species. The Wildlife Services arm of the USDA specifically has invasive species activities and works to create control plans and programs around certain key invasive species including the brown tree snake, european starling, feral swine, and nutria. If you're curious, you can actually go online and see the action plans they have created around these specific species in the U.S. and the progress they have made on those plans. Additionally, USDA’s Wildlife Service has provided help to the public to fix the damages that have been caused by invasives.

• The National Wildlife Federation, one of America’s largest conservation organizations, is also leading the charge to prevent invasive species from spreading. The organization has programs and works to support and advocate for policy to take action on controlling the spread of these organisms.

• For example, the organization has a program that advocates for the treatment of ballast water, the fresh or salt waters that is held in the ballast tanks of ships, as this is often a main way that invasive organisms are introduced into new marine ecosystems. They also have educational programs for the public to help underscore the importance of using native plants and removing invasive ones. 

• One group working globally on invasive species is the International Union for Conservation of Nature (IUCN). The IUCN Secretariat and Species Survival Commission Invasive Species Specialist Group work together to tackle invasive alien species and their impacts at all stages, from providing essential data and expertise to guide policy-making through to action on the ground.

What policies are being pursued to address invasive species?

• Globally, the IPBES report highlights that while the impacts of invasive species are complex, they can be prevented and managed through effective tools and governance options. The IPBES report found that 80% of 196 countries have targets within their national strategies and action plans to manage biological invasions; further, in the past 10 years, more countries have developed these policies. Though there is still significant policy work to do globally, having a biodiversity plan is a key step in the right direction.

• Because invasive species cross all boundaries and legislative jurisdictions, controlling them can be difficult to coordinate and action often needs to be orchestrated by many different levels. Globally, these policies are still evolving, but the role of policy in this area will likely increase as the problem worsens.

• In the U.S., state and federal policy to combat these issues has been limited due to the lack of resources and lack of concern from the public. However, in 1999, an Executive Order established the National Invasive Species Council, or NISC. This council is co-chaired by the United States Secretaries of the Interior, Commerce, and Agriculture alongside other key members of federal agencies like the U.S. Environmental Protection Agency, Health and Human Services, and Homeland Security. Members are tasked with coordinating, planning, and leading the federal invasive species program working with local and state governments along with smaller private organizations and tribal partners. The council also works to not only prevent, eradicate, and control invasive species, but also hopes to restore ecosystems that are negatively impacted by these invasives. 

• This executive order also allowed for the development of a National Invasive Species Management Plan and allowed for the creation of the Invasive Species Advisory Committee. The Invasive Species Advisory Committee helps to provide information and advice for the NISC’s consideration and has helped since 1999 (minus a couple years of defunding in the Trump Administration) to provide input on federal policies and emerging topics of interest. This committee is composed of members at all levels of representation - state, territorial, tribal, and local governments, as well as academic institutions, non-governmental organizations, and the private sector.

• For aquatic life specifically in the United States, the National Invasive Species Act (NISA) grants $4 million annually for states to implement their state aquatic nuisance species plans. But like many policy actions, this Act has yet to be fully funded. 

• In the EU, there is the EU Biodiversity Strategy for 2030, which contains the commitment to manage established invasive alien species and decrease the number of Red List species they threaten by 50% by 2030. The Invasive Alien Species Regulation includes a set of measures to be taken across the EU in relation to invasive alien species. The core of the Regulation is the list of Invasive Alien Species of Union concern that currently has 88 species on it. The species included on this list are subject to restrictions and measures set out in the Regulation. These include restrictions on keeping, importing, selling, breeding, growing and releasing into the environment.

• Looking globally, the Convention on Biological Diversity (CBD) and its members have stressed the importance of invasive species control as a way to prevent biodiversity loss. In 2002, the Convention released the “Guiding Principles for the Prevention, Introduction and Mitigation of Impacts of Alien Species that Threaten Ecosystems, Habitats and Species.” This guidance seeks to minimize the risk of biological invasions from crossing borders and emphasizes the need for collaboration to minimize the associated risks.

• Invasive species are also a focus of one of the targets in The Kunming-Montreal Global Biodiversity Framework. This Framework was adopted in December 2022 at the CBD’s 15th Conference of Parties. It has been referred to as a “Paris Agreement for Nature.” Target 6 says, “Eliminate, minimize, reduce, and/or mitigate the impacts of invasive alien species on biodiversity and ecosystem services by identifying and managing pathways of the introduction of alien species, preventing the introduction and establishment of priority invasive alien species, reducing the rates of introduction and establishment of other known or potential invasive alien species by at least 50 percent by 2030, and eradicating or controlling invasive alien species, especially in priority sites, such as islands.”

• To end this section on a positive note, we want to mention that a review of 1,550 eradications on nearly 1,000 islands since 1872 found an 88% success rate using methods such as hunting, trapping, and targeted poisoning to help restore the islands’ biodiversity.

• For example, in 2011, rats were eradicated from Palmyra Atoll in the mid-Pacific; the germination of native plant seedlings increased by more than 5,000%, two previously undocumented crab species became abundant, and coral began to recover.

What can definers do to help address invasive species?

• The Nature Conservancy lists 6 main ways we as individuals can help stop the introduction and spread of invasive species. 

• First, we can verify that the plants in our yards and gardens are non-invasive. We can also take steps to remove any non-native plants in our gardens and focus our landscaping on native plants, as many common exotic or ornamental plants, while they can be beautiful, can harm natural ecosystems.

• Second, if you’re boating, make sure to clean your boat thoroughly before moving into different bodies of water. 

• Next, regularly clean and inspect your shoes, tires, boat, or any other equipment that is used outdoors and remove any insects or plant parts that may have tagged along with you and are unintentionally being spread.

• Fourth, we should be mindful to not “pack a pest” when we are traveling. Many fruits, vegetables, plants, and animals can be invasive or carry pests, so it is important to be mindful of when we may be unintentionally harboring an invasive species without knowing it.

• Fifth, we cannot release anything into the wild! This is especially important if you are a person who likes to keep exotic or non-native pets, you should never unleash them into any non-native habitats.

• Many pet owners do not ever plan to release their pets, but when their pet alligators, aquarium fish, or reptiles become too big, difficult, or aggressive, these once loved pets are often released into the wild rather than properly transitioned into a new home. It is important to find proper channels to rehome your pet as this can turn into a serious issue or reconsider having these animals as pets if you cannot commit to looking after them. This also goes for aquarium fish, plants, and live bait.

• Lastly, we can become engaged in learning more about species that are non-native in our area and volunteer at local parks to work directly on the issues and/or educate others about the issues. The National Wildlife Federation suggests learning how to identify the species that are invasive around us, so that you can identify and report any sightings to your local wildlife officials. You can also join local groups in removing invasive species from your local parks. 

Expert Guest: Leigh Greenwood, Forest Pest and Pathogen Program Director at The Nature Conservancy (TNC)

Leigh is the Director of TNC’s Forest Pest and Pathogen Program, which sits within the North America Natural Climate Solutions team. Leigh works to bring stakeholders together to achieve common goals in support of forest health from the forest pest and pathogen perspective. Her projects include: managing the Don’t Move Firewood campaign, convening the Continental Dialogue on Non-native Forest Insects and Diseases, working to improve the international biosecurity measures in place for solid wood packaging, and leading partnership efforts to accelerate the development of pest- and pathogen-resistant native trees. Leigh’s leadership of the Don’t Move Firewood campaign has led to its being widely regarded as one of the most innovative public outreach arms of TNC. 

Leigh earned her B.A. in biology at Williams College and her M.S. in wildlife biology at the University of Montana in Missoula, where she studied the intersection of native wildlife, invasive plants, and biological control insects.