Invasive Species vs. The Global Economy

As humans have spread across the globe, other species have followed. The domestication of animals and the advent of agriculture helped speed up this process, but species have been traveling around with humans long before that. Presently, our ability to move species from one corner of the globe to another is unprecedented. As more countries join the global economy, the risk of outsider species establishing themselves in uncharted territory increases. Species introductions via globalization are not likely to decrease, and so the question must be asked: Are we, as a global community, equipped to address this?

A review published in Nature Communications in August 2016 warns that “most countries have limited capacity to act against invasions.” The authors come to this conclusion after analyzing available data about invasive species across the globe and developing a “global, spatial forecast for emerging invasions throughout the twenty-first century.” National responses to invasive species were assessed based on reports to the Convention on Biological Diversity (CBD).

As part of the 2011-2020 CBD Strategic Plan for Biodiversity, nations or states that are parties of the CBD agreed to work towards a series of goals called Aichi Biodiversity Targets. Target 9 addresses invasive species: “By 2020, invasive alien species and pathways are identified and prioritized, priority species are controlled or eradicated and measures are in place to manage pathways to prevent their introduction and establishment.” The authors of the review found that, while most countries have made progress on identifying and prioritizing some of the most prominent and threatening invasive species, “current management practices only target a handful” and “prevention of introduction and establishment lags far behind progress towards the reactive CBD goals.”

Biological invasions are expected to remain high across the globe; however, regions with a high Human Development Index (HDI) face different threats compared to regions with a low HDI. Due to increasing levels of international trade, high-HDI regions will continue to be threatened by introductions via pet and plant imports. Climate change and the coinciding biome shifts and changes in fire frequency are expected to aid in the establishment and perpetuation of invasive species in these regions.

Low-HDI regions have historically been less threatened by invasive species compared to high-HDI regions. As these regions join the global economy, they risk experiencing a much higher level of species introductions. Many of the planet’s biodiversity hotspots are found in low-HDI regions, making these hotspots more vulnerable to invasions as the potential for introductions increases. The authors found that the threat of introductions is at its highest in regions where “high levels of passenger air travel overlap with agriculture conversion.” Low-HDI regions are more limited in their capacity to respond to invasions compared to high-HDI regions and are more vulnerable to food shortages when invasive species disrupt agriculture.

“High risk in low-HDI countries could arise from coincidence between intensifying agriculture sectors and high levels of passenger air travel that is likely to transport arthropod pests. … Low-HDI countries could prioritize screening of passenger baggage for live plants, fruits or vegetables, which could host crop pests and pathogens.” – Early, et al. (2016) – photo credit: wikimedia commons

The authors state: “The intensities and global patterns of introduction and disturbance are changing more rapidly today than at any time during human history.” Introductions are not projected to slow in high-HDI regions, and low-HDI regions will be increasingly threatened as species already well established in high-HDI regions expand their reach. This is grim news, but it also presents an opportunity. Through cooperation and data sharing, our understanding of invasive species can greatly increase, and regions with greater access to resources can share such things with less fortunate regions. This is the hope of the authors as well: “We urge increased exchange of information and skills between regions with a wealth of invasive alien species experts and low-HDI countries that have less expertise.”

For more information about this review, go here. For more information about global trade in the modern era, check out the new podcast Containers.

Learning Lessons from Invaded Forests

In 1946, North American beavers were introduced to the archipelago of Tierra del Fuego at the tip of South America in an attempt to start an industry based on beaver fur. Although this industry has not thrived, beavers have multiplied enormously. By cutting trees and building dams, they have transformed forests into meadows and also fostered the spread of introduced ground cover plants. Now numbering in the tens of thousands in both Chilean and Argentinian parts of the archipelago, beavers are the target of a binational campaign to prevent them from spreading to the mainland of these two nations. — Invasive Species: What Everyone Should Know by Daniel Simberloff

Beavers in South America are just one example of the series of effects a species can have when it is placed in a new environment. Prior to the arrival of beavers, there were no species in the area that were functionally equivalent. Thus, through their felling of trees and damning of streams, the beavers introduced novel disturbances that have, among other things, aided the spread of non-native plant species. Ecologists call this an invasional meltdown, wherein invasion by one organism aids the invasion of another, making restoration that much more difficult.

Complicated interactions like this are explored by David Wardle and Duane Peltzer in a paper published last month in Biological Invasions. Organisms from all walks of life have been introduced to forests around the world, and while many introductions have had no discernable impact, others have had significant effects both above and below ground.

The authors selected forest ecosystems for their investigation because “the imprint of different invaders on long-lived tree species can often be observed directly,” even when the invading organisms are doing their work below ground. Moreover, a greater understanding of “the causes and consequences of invasions is essential for reliably predicting large-scale and long-term changes” in forest ecosystems. Forests do not regenerate quickly, so protecting them from major disturbances is important. Learning how forests respond to invasions can teach us how best to address the situation when it occurs.

The authors begin by introducing the various groups of organisms that invade forests and the potential impacts they can have. This is summarized in the graphic below. One main takeaway is that the effects of introduced species vary dramatically depending on their specific attributes or traits and where they fall within the food chain. If, like the beaver, a novel trait is introduced, “interactions between the various aboveground and belowground components, and ultimately the functioning of the ecosystem” can be significantly altered.

Wardle, D.A., and D.A. Peltzer. Impacts of invasive biota in forest ecosystems in an aboveground-belowground context. Biological Invasions (2017).  doi:10.1007/s10530-017-1372-x

After highlighting some of the impacts that invasive species can have above and below ground, the authors discuss basic tenets of invasion biology as they relate to forest ecosystems. Certain ecosystems are more vulnerable to invasions than others, and it is important to understand why. One hypothesis is that ecosystems with a high level of species diversity are more resistant to invasion than those with low species diversity. This is called biotic resistance.  When it comes to introduced plants, soil properties and other environmental factors come in to play. One species of plant may be highly invasive in one forested ecosystem, but completely unsuccessful in another. The combination of factors that help determine this are worth further exploration.

When it comes to restoring invaded forests, simply eliminating invasive species is not always enough. Because of the ecological impacts they can have above and below ground, “invader legacy effects” may persist. As the authors write, this requires “additional interventions to reduce or remove [an invader’s] legacy.” Care also has to be taken to avoid secondary invasions, because as one invasive species is removed another can take its place.

Nitrogen-fixing plants (which, as the authors explain, “feature disproportionately in invasive floras”) offer a prime example of invader legacy effects. Introducing them to forest ecosystems that lack plants with nitrogen fixing capabilities “leads to substantially greater inputs of nitrogen … and enhanced soil fertility.” Native organisms – decomposer and producer alike – are affected. Simply removing the nitrogen fixing plants does not at once remove the legacy they have left. Examples include Morella faya invasions of forest understories in Hawaii and invasions by Acacia species in South Africa and beyond.

“It has been shown that co-invasion by earthworms enhances the effects that the invasive nitrogen fixing shrub Morella faya has on nitrogen accretion and cycling in a Hawaiian forest, by enhancing burial of nitrogen-rich litter.” – D.A. Wardle and D.A. Peltzer (2017) – photo credit: wikimedia commons

The authors conclude with a list of “unresolved issues” for future research. A common theme among at least a couple of their issues is the need for observing invasive species and invaded environments over a long period. Impacts of invasive species tend to “vary across both time and space,” and it is important to be able to predict “whether impacts are likely to amplify or dampen over time.” In short, “focus should shift from resolving the effects of individual invasive species to a broader consideration of their longer term ecosystem effects.”

This paper does not introduce new findings, but it is a decent overview of invasion biology and is worth reading if you are interested in familiarizing yourself with some of the general concepts and hypotheses. It’s also open access, which is a plus. One thing that is clear after reading this is that despite our growing awareness of the impacts of invasive species, there is still much to be learned, particularly regarding how best to respond to them.

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Eating the Invasives

Happy National Invasive Species Awareness Week! It’s a fine time to get educated about invasive species, and perhaps even play a role in mitigating them. Opportunities for getting involved are myriad and include volunteering with local conservation groups, replacing invasive plants in your yard with non-invasive alternatives, and being mindful when you visit natural areas not to bring along weed seeds and other pests and diseases. Another strategy in the battle against invasive species is to eat them, which is precisely what I plan on doing. If you are interested in doing the same, this revised post (originally published in November 2013) will help get you started.

Invasivore: One Who Consumes Invasive Species

Invasive species are a major ecological concern, and considerable effort is spent controlling them. The ultimate goal  – albeit a lofty one in many cases – is to eradicate them and to prevent future outbreaks. The term “invasive species” describes plants, animals, and microorganisms that have been intentionally or unintentionally introduced into an environment outside of their native range. They are “invasive” because they have established themselves and are causing adverse effects in their non-native habitats. Some introduced species cause no discernible adverse effects and so are not considered invasive. Species that are native to a specific habitat and exhibit adverse effects following a disturbance can also be considered invasive. (White-tailed deer are an example of this in areas where human activity and development have reduced or eliminated their natural predators resulting in considerably larger deer populations than would otherwise be expected.) Defining and describing invasive species is a challenging task, and so it will continue to be a topic of debate among ecologists and conservation biologists for the foreseeable future.

The adverse effects of invasive species are also not always straightforward. Typical examples include outcompeting native flora and fauna, disrupting nutrient cycles, shifting the functions of ecosystems, altering fire regimes, and causing genetic pollution. Countless hours of research and observation are required in order to determine the real effects of invaders. The cases are too numerous and the details are too extensive to explore in this post; however, I’m sure I will cover this topic more thoroughly in the future.

There are many approaches to eradicating invasive species, but one fairly unconventional method is to simply eat them. Why not, right? Historically, the voracious appetite of humans has helped drive several species to extinction, so why not employ our stomachs in the removal of introduced species from their non-native habitats? The folks at Invasivore are suggesting just that. By encouraging people to consume invasive species, they are also promoting awareness about them – an awareness they hope “will lead to decreasing the impacts of invasive species by preventing introductions, reducing spread, and encouraging informed management policies.”

“If you can’t beat ’em, eat ’em!” And so they provide recipes in order to encourage people to harvest, prepare, and consume the invasive species in their areas. Some of the invasive plant species they recommend eating are Autumn Olive (Autumn Olive Jam), garlic mustard (Garlic Mustard Ice Cream), Japanese honeysuckle (Honeysuckle Simple Syrup), purslane (Purslane Relish), and Canada goldenrod (Strawberry-Goldenrod Pesto). And that’s just a sampling. One might ask if we are encouraged to eat invasive species and ultimately find them palatable, won’t our demand result in the increased production of these species? The Invasivores have considered this, and that is why their ultimate goal is raising awareness about the deleterious effects of invasive species. In the end, we should expect to see our native habitats restored. Our craving for Burdock Chips on the other hand will have to be satisfied by some other means.

lonicera japonica

Japanese honeysuckle (Lonicera japonica) – photo credit: wikimedia commons

More about eating invasive species:

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What are you doing to celebrate National Invasive Species Awareness Week? Let us know in the comment section below.

Tufty’s Plight, or Saving the U.K.’s Red Squirrel

“There is the great blank area where no red squirrels have returned, and this is where the grey ones first spread and are now permanent inhabitants. Outside it there are plenty of red squirrel populations still, though they have fluctuated, often severely.” — Charles Elton, The Ecology of Invasions by Animals and Plants, 1958

Sciurus vulgaris, or the Eurasian red squirrel, is widespread throughout northern Europe and east into Siberia. It is a small squirrel with a chestnut top and a creamy underside that spends much of its time in the tops of trees. Its tail is large and fluffy, and its ears are adorned with prominent tufts of hair. It enjoys a broad range of foods from seeds, fruits, and leaves to fungi, insects, and birds’ eggs. It is beloved in the United Kingdom, where its survival is being threatened by a North American cousin. This cousin, now established in the U.K. for well over a century, looks to increase its range across Europe, with a growing population in Italy and the potential to spread to neighboring countries.

Eurasian red squirrel (Sciurus vulgaris) - photo credit: wikimedia commons

Eurasian red squirrel (Sciurus vulgaris) – photo credit: wikimedia commons

Sciurus carolinensis, or Eastern gray squirrel, is native to eastern North America but has been introduced to parts of western North America as well as other parts of the world, including the United Kingdom, Italy, South Africa, and Australia. Its fur is typically dark to pale gray with red tones. It prefers mature forests where food and shelter are abundant; however, it is a highly adaptable species and is common in urban areas and disturbed sites. It shares habitat requirements with the red squirrel, but has the advantages of being larger, stronger, and able to digest acorns.

Gray squirrels were first introduced to the U.K. in 1876. Wealthy collectors were enchanted by them and began releasing them on their estates. The first pair made it to Ireland in 1911. Around this time biologists were becoming concerned by how quickly they were spreading as well as the damage they were doing to young trees and the effect they seemed to be having on red squirrel populations. The U.K. Parliament responded in 1937 by banning the possession and introduction of gray squirrels. In an article published in Science in June 2016, Erik Stokstad writes about this “troubling phenomenon: where gray squirrels established colonies, red squirrels sooner or later vanished.” The current population of red squirrels in the U.K. is estimated at around 140,000, while gray squirrels are thought to number more than 2.5 million.

Why red squirrels vanish when grey squirrels are present is not entirely understood. Competition for food is one factor. Grey squirrels seem to have an advantage over red squirrels in mixed deciduous forests, and according to Schuchert, et al. (Biological Invasions, 2014), after colonization by gray squirrels, red squirrels can become restricted to coniferous forests, which are “less favored by grey squirrels.”

But direct competition alone doesn’t explain the plummeting numbers of reds in the presence of grays. Another explanation was identified in 1981 – grey squirrels were spreading a disease. Several years of experimentation confirmed that red squirrels were dying of squirrelpox – a parapoxvirus that gray squirrels carry but show little or no sign of infection. The virus can spread quickly through a population of red squirrels, leaving them lethargic, malnourished, and an easy target for predators. Stokstad writes, “red squirrels are defenseless…as [they] succumb, gray squirrels quickly take over the habitat.

But not all grey squirrels carry the virus, and there are some regions where the virus isn’t a major problem. Habitat loss and fragmentation due to human development also plays a role in the red squirrel’s decline. Add to that, grey squirrels may be more inclined to live among humans, giving them an advantage over the more reclusive reds.

Efforts have been underway for decades now to reduce, and even eliminate, gray squirrels in the U.K. Tens of thousands of grey squirrels have already been trapped and killed, yet they continue to dominate. Schuchert et al. write, “while culling may decrease grey squirrel population size in the short term, their high dispersal abilities makes re-colonization likely.” Funding for culling programs isn’t always available, and protests from animal rights groups like Animal Aide U.K. and Animal Ethics also have an impact. One area that culling has proved successful is Anglesey, an island off the coast of Wales, where the red squirrel population had once been reduced to just 40 individuals. Schuchert et al. analyzed culling data over a 13 year period and determined that trapping and killing efforts “resulted in the sustained and significant reduction of an established grey squirrel population at a regional landscape scale.”

Eastern gray squirrel (Sciurus carolinensis) - photo credit: wikimedia commons

Eastern gray squirrel (Sciurus carolinensis) – photo credit: wikimedia commons

Red squirrels may also be experiencing some relief thanks to another threatened mammal. Martes martes, or the European pine marten, is a member of the weasel family and, as Stokstad writes, “a cat-sized predator [that] was nearly exterminated in the 20th century.” Hunting, both for fur and pest control, and habitat loss reduced pine marten numbers dramatically until it received legal protection in 1988. Since then it has started to rebound, particularly in Scotland and Ireland. Anecdotes suggested that pine marten recovery in these areas was resulting in fewer gray squirrels. A study published in Biodiversity and Conservation in March 2014 confirmed that gray squirrel populations in Ireland were at “unusually low density,” and that the increasing numbers of pine martens played a role in that. Gray squirrels move slower and spend more time on the ground compared to red squirrels, making them easier prey for pine martens.

Efforts are now underway to introduce pine martens to other parts of the U.K. where gray squirrel populations are problematic. However, according to Stokstad, “red squirrel advocates worry that the pine marten could be a false hope, promising a free and uncontroversial solution that could threaten funds for culling.”

Let’s remember that the gray squirrel was deliberately introduced to the United Kingdom by humans, and that human activity is one of the main reasons for the grey squirrel’s explosion and the red squirrel’s retreat. Culling is not likely to ever eliminate gray squirrels completely, yet no one wants to see red squirrels go extinct. Altered landscapes can favor certain species over others, so ensuring that there is plenty of favorable habitat available for the red squirrel is one way to aid its survival. The grays may be there to stay, but let’s hope a compromise can be found so generations to come can benefit from sharing space with the red squirrel (and perhaps the gray squirrel,too).

Tufty Fluffytail, a character developed to help teach kids road safety in the U.K., saves Willy Weasel from getting run over (again).

Red Squirrel Conservation Groups:

The Nippleworts of Camassia Natural Area

This is a guest post. Words and illustration by Mesquite Cervino.

At the end of a residential neighborhood that is barely off the 205 in the hills of West Linn, Oregon is a small, 26 acre preserve called the Camassia Natural Area. The defining features of the landscape were caused by the Missoula Floods (aka the Spokane or Bretz floods) at the end of the last ice age (12 to 19 thousand years ago) which swept away the already established soil and in their place deposited glacial erratics from other far-away places, some even coming all the way from Canada. The flood reached eastern Oregon and the Willamette via the Columbia River Gorge and created the green and rocky plateau that is now Camassia.

While the reserve is named after a widespread plant in the park, which is a common camas (Camassia quamash) that blooms in April and early May, the park has over 300 different species overall. However, one species in particular has kicked in the door and far overstayed its welcome in the park, becoming a highly invasive weed in the area. This plant is known as Lapsana communis or nipplewort. It is an annual dicot that is native to Europe and Asia, but is considered invasive in Canada and the United States. In the U.S., the weed is most common west of the Cascades in the Pacific Northwest. It is in the Asteraceae family (aka the aster, daisy, or sunflower family), and like dandelions or common groundsel, nipplewort is part of the weedy side of the family.

nicole illustration_cropped

The name itself has an interesting history that originated around 350 years ago when an Englishman by the name of John Parkinson named the plant after he heard that it was useful for topical treatment of ulcers for women on certain areas of their bodies. It was also an herbal treatment for nursing mothers, and was used to aid cows and goats that were having trouble being milked. Another source of the name is said to have come from the shape of the basal lobes and their resembling features. Because nipplewort is edible, its leaves can be cooked like spinach or served raw in only the most hipster of salads.

In terms of its anatomy, nipplewort is about one to three and a half inches in height, has alternate, ovular, lobed, rich green leaves, and composite yellow flowers with about 13 petals similar in resemblance to a dandelion. They flower from June to September and are pollinated by various insects. Seed set occurs in July to October. The plant then spreads through reseeding, and one plant can produce 400 to 1,000 seeds that put out shoots in fall and spring.

Consult a fellow botanist to find out more about Lapsana communis, especially if you are curious to know if it has invaded your territory. If it has, consider entertaining dinner guests with this unusual plant.

Additional Resources:

What Shall We Do About Invasive Species?

I think about invasive species a lot. This blog doesn’t really reflect that though. I have been avoiding a deep dive into the subject mainly because there is so much to say about it and I don’t really want this to become “the invasive species blog.” Admittedly, I’m also trying to avoid controversy. Some people have very strong opinions about invasive species, and I don’t always agree. But then an article entitled Taking the long view on the ecological effects of plant invasions appeared in the June 2015 issue of American Journal of Botany. Intrigued by the idea of “taking the long view,” I read the article and decided that now is as good a time as any to start exploring this topic in greater depth.

However, before getting into the article, we should define our terms. “Invasive species” is often used inappropriately to refer to any species that is found outside of its historic native range (i.e. the area in which it evolved to its present form). More appropriate terms for such species are “introduced,” “alien,” “exotic,” “non-native,” and “nonindigenous.” The legal definition of an invasive species (according to the US government) is “an alien species that does or is likely to cause economic or environmental harm or harm to human health.” Even though this definition specifically refers to “alien species,” it is possible for native species to behave invasively.

These terms refer not just to plants but to all living organisms. The term “noxious weed,” on the other hand, is specific to plants. A noxious weed is a plant species that has been designated by a Federal, State, or county government as “injurious to public health, agriculture, recreation, wildlife, or property.” A “weed” is simply a plant that, from a human perspective, is growing in the wrong place, and any plant at any point could be determined to be a weed if a human says so. (I’ll have more to say about human arrogance later in the post.)

Rush skeletonweed (Chondrilla juncea) - labeled a noxious weed in Idaho

Rush skeletonweed (Chondrilla juncea) – labeled a noxious weed in Idaho

The authors of the AJB article (S. Luke Flory and Carla M. D’Antonio) begin by clarifying that “most introduced species are not problematic.” Those that are, however, can “cause significant ecological and economic damage.” This damage is well documented, and it is the reason why billions of dollars are spent every year in the battle against invasive species. But there is a dearth in our research: “less is known about how ecological effects of invasions change over time.” The effects of invasive species could “increase, decrease, or be maintained over decades,” and “multiple community and ecosystem factors” will determine this. For this reason, the authors are calling for “concentrated efforts to quantify the ecological effects of plant invasions over time and the mechanisms that underlie shifting dynamics and impacts.” Armed with this kind of information, managers can better direct their efforts towards invasive species determined to be “the most problematic.”

The authors go on to briefly explain with examples why an invasive species population may decline or be maintained over time, highlighting selected research that demonstrates these phenomena. Research must continue with the aim of improving our understanding of the long term effects of plant invasions. The authors acknowledge that this “will require carefully designed experiments,” “patient and persistent research efforts,” and significant amounts of money. However, they are convinced that through a widespread collaborative effort it can be done. They encourage researchers to deposit data obtained from their research in open source online repositories so that future meta-analyses can be conducted. The information available in these online repositories can be used to develop management plans and help predict “future problematic invasions.”

Considering the amount of time and resources currently spent on confronting invasive species, the approach proposed by the authors of this article is quite reasonable. It seems absurd to continue to battle a problematic species that will ultimately be brought down to more manageable levels by natural causes. It also seems absurd to battle against a species that is essentially here to stay.

Field bindweed (Convulvulus arvensis) - labeled a noxious weed in Idaho

Field bindweed (Convulvulus arvensis) – labeled a noxious weed in Idaho

And that brings me to the point in which I make enemies. Take a look at the terms defined earlier. When we talk about introduced species, we are referring to introductions by humans, whether purposeful or accidental. An “alien” species introduced to a new location by wind, water, or animal (other than human) would be considered a natural introduction, right? If that species becomes established in its new location, it would simply be expanding its range. If a human brought it there, again whether purposefully or accidentally, it would be considered an exotic indefinitely.

Humans have been moving species around since long before we became the humans we are today in the same way that a migratory bird might move a species from one continent to another. At what point during our evolution did our act of moving species around become such a terrible thing?

I will concede that our species has become an incredibly widespread species, able to move about the planet in ways that no other species can. We also have technological advances that no other species comes close to matching. In the time that our species has become truly cosmopolitan, the amount of species introductions that we have participated in has increased exponentially. Leaving ecological destruction in our wake is kind of our modus operandi. I don’t want to make excuses for that, but I also don’t see it unfolding any other way. Give any other species the opportunities we had, and they probably would have proceeded in the same manner. Just consider any of the most notorious invasive species today – “opportunist” is their middle name.

More and more, as we are able to see what we have done, we are making efforts to “fix it.” But how de we rewind time? And if we could, when do we rewind back to? And how do we not “ruin it” again? The earth does not have a set baseline or a condition that it is supposed to be in at any given time. The earth just is. It is operating in a state of randomness, just like everything else in the universe. Any idea of how the earth must look at any given time is purely philosophical – conceived of by humans. I’m not saying that we shouldn’t try to repair the damage, but we should acknowledge that the repairs we’re trying to make are largely for the perpetuation of our own species. Yeah, we’ve developed a soft spot for other species along the way (thankfully), but ultimately we’re just trying to maintain. The earth, on the other hand, would be fine without us.

So, what shall we do about invasive species? I’m not entirely sure. The only thing I’m certain of is that I will continue to ruminate on them and potentially bore you with more blog posts in the future. Until next time…

Puncturevine (Tribulus terrestris) - labeled a noxious weed in Idaho

Puncturevine (Tribulus terrestris) – labeled a noxious weed in Idaho