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​​​In Spotlight: Invasive Species


Most of us experience nature and wildlife through its beauty. But regardless of how majestic or photogenic a species may be, its purpose in an ecosystem is far greater than what we can appreciate visually. Based on its traits and the environment it interacts in, each species plays a vital role within the context of their habitat. This inherent intelligence in nature provides the foundation necessary for stability and balance in the web of life. So, does nature’s design allow organisms to seamlessly move between biomes and ecosystems? The answer is both yes and no. Sometimes it is inconsequential when a species moves between ecosystems, and sometimes the impact is so detrimental that we are left with a $1.4 trillion mess to clean up (National Geographic).
 
In this edition, we will highlight the importance of native species within their respective habitats and the negative impact invasive species have on ecosystems. We will explore these concepts using some of nature’s most intriguing storylines. Examples include prey-predation interactions and plot twists in which unpretentious species emerge as heroes, and sometimes the hunter becomes the hunted. Let’s get started by first understanding the difference between a native and an invasive species.

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What is a native species?
A native species is one that has evolved with an ecosystem for hundreds and thousands of years. It has been able to sustain its populations and, over time, may have developed unique dependencies or interdependencies with other organisms within that ecosystem. For example, a bald eagle is native to the North American continent, and a kangaroo is native to Australia.

What is a non-native species?

A non-native species is one that has not naturally evolved in the region in question but was brought to a geographic area by humans, either intentionally or unintentionally.
 
What are invasive species?
An invasive species is a non-native species (including seeds, eggs, spores, or other propagules) whose introduction causes or is likely to cause economic harm, environmental harm, or harm to human health. ​

Why are native species critical to an ecosystem?
Depending on their traits, native species fill a specific ecological niche within an ecosystem, allowing them to function synergistically. To understand this concept, let’s look at the role sea oats, a native perennial grass play on Cumberland Island, a barrier island off the coast of Georgia, USA. 
 
As Dr. Anthony Martin, a professor at the Department of Environmental Sciences at Emory University, explains, “Sea oats are an anchor system for the primary dunes on the shores of Cumberland Island.” Its tall blades trap blowing sand, and its deep root system facilitates the formation of sand dunes. The dunes, in turn, provide vital ecological services on the barrier island; they protect the island from storm surges and provide refuge for several species of ground-nesting birds from high tide. Without the sea oats holding the dunes in place, the storm waves will erode the beaches, and high tide will destroy nesting grounds for the birds. In other words, the sea oats are not only instrumental in safeguarding the ecological landscape of the island, but they also protect the biodiversity that lives in that ecosystem.
While species such as the sea oats become the bedrock of an ecosystem, others step in to regulate it. They add checks and balances and support interdependencies among species to stabilize these ecological communities. We will explore this concept using the prey-predator interaction between two native species in Japan, the Japanese honeybee and its natural predator, the giant hornet. ​

​The National Wildlife Federation estimates that 42% of the biodiversity listed as threatened or endangered is at risk because of invasive species.
​
Japanese honeybees are like most honeybee species: they live in large colonies and have a sophisticated hierarchical social structure consisting of a queen bee, drones, workers, guards, and so on. While the workers spend their day collecting pollen and nectar, the guards stay vigilant to potential attacks by their natural predator, the giant hornet. Having coevolved with their predator, they are acutely aware of how a single misstep can threaten the survival of the entire colony. The giant hornet can kill up to 40 European honeybees in a minute and decimate the entire colony in a matter of hours. So, what do the Japanese bees do to defend themselves? 
 
When the Japanese honeybees notice a giant hornet in the vicinity of their nest, they release a chemical signal called a pheromone that alerts the guards to hide. An unguarded entryway gives the hornet easy access into the nest. Upon entry, it is ambushed by about 500 bees who hold on to it and start flapping their wing muscles vigorously. This starts heating the ball of bees with the hornet at its center. The bees can tolerate temperatures up to 122 F while the hornet can tolerate temperature only up to 115 F. The bees continuously flap their wing muscles till the temperature around the hornet reaches exactly 117 F. At this point, the hornet succumbs to its death, and the bees fly away triumphant. Needless to say, this evolutionary adaptation that the bees have perfected over millennia is extraordinarily creative and a foolproof approach to protecting themselves from extinction. While the obvious benefactors of this strategy are the honeybees themselves, their survival has a much broader impact on the stability of the ecosystem. Pollination services provided by bees help plants complete their life cycle and also ensures food security for wildlife and humans. Without the native Japanese honeybees, a large number of native plants will cease to exist, thus jeopardizing the survival of native wildlife that depends on the flowers, fruits, and berries that these plants produce. 
 
The roles the sea oats and the Japanese honeybees play within their habitat shed light on how and why native species are relevant to their ecosystems. 

Note: The European honeybees (native to Europe) were successfully introduced to the United States as commercial crop pollinators. Beekeepers move their colonies to farms across the county to pollinate crops adding an estimated 16 billion dollars to the US economy. Given their success in the United States, they were introduced in Japan to do the same. 

​What do you think happened? 

Unlike the Japanese honeybees, the European honeybees did not coevolve with the hornet over millennia. (The giant hornet can kill up to 40 European bees in a minute and decimate the entire colony in a matter of hours.) And thus, they had no strategies to defend themselves against the relentless attacks of the giant hornet. The hornets destroyed colony after colony, and the European honeybees failed to establish themselves in Japan.

The tragic fate that the European honeybees were confronted with in Japan was indeed unfortunate. But from an environmental standpoint, I have to agree with the conservationist in this podcast, “
Honeybees are good for the farmers but not good for the environment.” (NPR - 2 min listen)

Here is why they are bad for the environment. Unquestionably, the European honeybees have become the reliable workhorses of the US agribusiness. And while their contributions benefit humanity handsomely, they do not provide comparable benefits for the native wildlife that coexist with them. 
The European honeybees sometimes compete with the native bees of North America for finite resources such as nectar and pollen and threaten their survival. 
 
The next segment addresses this idea in depth. ​​​

Why are invasive species harmful to an ecosystem? 
​

Invasive species often outcompete native species for habitat and resources. Further, there are no natural predator that have evolved with the invader, so their populations grow unchecked and disrupt the ecological balance of the region.
The National Wildlife Federation estimates that 42% of the biodiversity listed as threatened or endangered is at risk because of invasive species. While efforts are made to protect imperiled species from threats such as loss of habitat, climate change, and human action, invasive species compound the problem and push these at-risk species further towards extinction. Not only that but invasive species are among the top two threats that all wildlife face.


Depending on their traits, native species fill a specific ecological niche within an ecosystem, allowing them to function synergistically.

How do invasive species move out of their natural habitat and the stages of invasion?
Listed below are the four stages of invasion a species goes through before it can be categorized as an invasive species:
 
Transportation: We live in a world where people and goods can travel between continents and waterways in a matter of hours. The modes of transportation that allows this seamless travel are also what allows alien species to move out of their native range into new habitats. Some species manage to establish themselves, and others do not. 
 
Establishment: When a non-indigenous species starts increasing in numbers in a new habitat and can sustain its populations without the risk of extinction, then it is considered established. Because non-native species start in small numbers known as “founder populations,” they often fail to establish. This is a critical stage that determines if a non- native population will persist or die off. 
 
Spread: Under the right conditions, alien species find a foothold in the new environment and flourish.  The expansion of their range from its native habitat to new territories is referred to as the spread. 
 
Impact: A species is considered invasive when it enters its fourth and final stage. In this stage, it is firmly established in its new habitat and now starts degrading or negatively impacting the ecosystem that it has invaded. 
 
Let’s track the four stages of invasion using the example of one of the most well-known invasive plant species in the Southern United States, the kudzu vine. 
 
Transportation: It was introduced to the United States in 1876 at the Philadelphia Centennial Exposition as an ornamental plant for backyards. 
 
Establishment: Along with being an attractive ornamental, it also gained traction as a remedy for soil erosion. The US government distributed approximately 84 million seedlings to southern landowners between 1930 and 1940. This fast-growing ground cover soon became a favorite among landowners and gardeners alike and found its way into several backyards. 
 
Spread: Kudzu, which is native to Japan and southeast China, successfully expanded its home range from Asia to North America by the 1940s.
 
Impact: Left unchecked kudzu grows aggressively over tree canopies and out-competes native vegetation for resources, such as sunlight and nutrients. By blocking their access to sunlight, it impedes their ability to photosynthesis, which eventually kills native shrubs and trees. 
 
Kudzu is one of the most invasive plant species in the southern United States and imposes a huge economic burden. According to the United States Department of Agriculture (USDA), kudzu costs approximately $100 to $500 million annually in lost productivity of forests. The losses are not limited to just the forestry services but extend to utility services as well. Power companies spend an estimated $1.5 million every year to repair damages caused by the plant. Once the economic and environmental implications of kudzu became apparent, the US government listed kudzu as a “common weed.” Finally, in 1997 it was listed as a “noxious weed.” Curbing the spread of kudzu has since become the focus of government agencies and their partners.  
 
As these organizations continue to collaborate and pool resources to manage the kudzu vine, Georgia residents and soybean farmers noticed a new alien species, the kudzu bug. The insect was first observed in October of 2009 in 9 northeastern counties in Georgia. However, by December of 2011, it had already spread to 117 additional counties in Georgia, eight counties in Alabama, the entire state of South Carolina, 57 counties in North Carolina, and one county in Virginia. 
 
The fact that an invasive species had spread so quickly and was threatening crop production was troubling, but what worried researchers, even more, was when they traced the maternal lineage of the expanded populations, the gene sequencing analysis pointed to a single female. In other words, every generation between 2009 - 2011 was traced back to one female! This incident underscores the devastating impact one invasive bug can have on livelihoods and the regional economy if left unchecked.   
 
Faced with the new challenge of pest control, researchers at the University of Georgia (UGA) spent the next few years studying its origin and ecology. It turns out the bug, like the kudzu vine, is native to Japan. Hence, it’s natural predator, a parasitoid wasp called Paratelonomus saccharaliis, while not found in North America, was found in Japan. Shortly after the link between the three became evident, permits were filed in 2012 with USDA to release the wasp in the southeastern United States as a safe biological control. 
 
Brace yourself! It’s hard to believe what happened next.
 
In the time the USDA was reviewing the case, the wasp somehow found its way to the US from Japan. It was found both in Georgia and Alabama in the year 2013. With plenty of kudzu bug eggs for wasps to feed and develop on, the new natural predator quickly established itself. By 2015, researchers found the parasitoid wasps in every soybean farm in southern Georgia. The timing of the appearance of the wasp was so uncanny that some researchers suspected that the wasp had accidentally escaped from the quarantine facility where the original lab colony was housed. However, genetic testing confirmed that the strain in quarantine was different from the one found in the wild, affirming it was not an accidental release.
 
The positive outcome of the wasp’s establishment in the US is that kudzu bug populations are down to manageable numbers. The wasp now provides natural pest control against kudzu bug infestations both in the soybean farms as well as in urban gardens.

I asked Dr. Michael Toews, Assistant Dean of the University of Georgia Tifton Campus, if there had been any negative implications for the ecosystem due to the presence of this wasp? Dr. Toews said," The wasp is a kudzu bug specialist that has co-evolved with the bug in Japan and there have been no non-target issues." So for now all is good and we can rest easy. 

Did you know?​​
Invasive species are not just harmful to flora and fauna, but they also strain natural resources such as water. The Nature Conservancy estimates that close to 55 billion liters of water is lost annually to invasive plants in Cape Town, South Africa. That is equivalent to one-sixth of the water needs of the city of 4 million residents. In 2018 Cape Town was on the verge of becoming the first major city to run out of water.
  Learn more 

What are the effects of invasion?
Highlighted below are the implications of invasion. 
 
Interaction: Invasive species displace native species and become prominent in the ecosystem allowing interactions between alien and native species that were previously impossible. A good example would be the unexpected dietary shift made by the urban beaver populations of Atlanta towards an invasive plant species, the Chinese privet. Native to China, the Chinese privet has outcompeted indigenous vegetation and has become abundant in the region. While this invasive plant has never been part of the beaver’s diet, its abundance has prompted the beavers to use this non-indigenous plant as a food source.
 
Ecological changes: The presence or interaction of the invasive species within an ecosystem alters the ecological landscape. Let’s find out how? 
 
We discussed earlier the merits of the sea oat, a native perennial grass found on Cumberland Island. Interestingly, Cumberland Island is also home to the feral horse, an invasive species that grazes on the sea oats. As Dr. Martin explains, “When feral horses eat the sea oats down to a nub or pull them out from the roots or stomp on them, then they [sea oats] are unable to hold the dunes, as well as they, did before. This results in the erosion of the dunes. And the dunes with a lower height are less of a barrier to storm waves, which then is going to transport sand further inland. The loss of the dunes is also going to affect the ground-nesting birds that live in that habitat.”
 
Extinction: When an invasive species is well established in the new environment, it outcompetes native species for habitat and resources. This, in turn, threatens the survival of native species and makes them vulnerable to extinction. 
 
We discussed earlier the fate of the European honeybees when introduced in Japan. Now let’s consider for a second if the giant hornet were to get accidentally established in Europe. The most likely outcome is that the European honeybee colonies would crash, and the species would be at risk of extinction. This hypothetical example can undoubtedly become a reality should the giant hornet get established in Europe. 

Evolution: Finally, the introduction of an invasive species in an ecosystem can set in motion evolutionary changes in a native species which can be highly detrimental to the species and or its habitat.
 
This mishap is well documented in a population of the Edith’s checkerspot butterfly in an isolated meadow in Nevada. The butterfly historically has relied on the maiden blue-eyed Mary as its host plant for its caterpillar. However, change in land use practices by humans introduced an invasive plant into the landscape, and the butterfly adapted to it. This evolutionary preference for an invasive plant subsequently led to the butterfly’s extinction. ​


​"Ecosystems are closely interconnected and one disturbance can cause many unforeseen circumstances." 

 ~​Dr. Michael Toews 

Assistant Dean, University of Georgia Tifton Campus
The timeline played out in this order – cattle ranchers moved into the meadows and brought with them an invasive plant. The habitat alterations impacted the maiden blue-eyed Mary, and it became sparse. Responding to the changes in the unavailability of its host plant, over time, the butterflies evolved a preference for the invasive. A few years later, the cattle ranchers moved out, the native vegetation was restored, and the invasive plant disappeared. But because the butterfly had transitioned entirely to the invasive as its host plant, it could not readapt to the maiden blue-eyed Mary quickly enough, and all the butterflies in that meadow died. 
For several years there were no Edith’s checkerspot butterflies in that area. Then neighboring populations slowly moved back into the meadow and recolonized. Since the new community of butterflies had not undergone an evolutionary change, they continued to prefer the original host plant, the maiden blue-eyed Mary, and thrived. 
 
Nature
The Tale of the Edith's Checkerspot: Butterflies Caught In An Evolutionary Trap. Watch short video

What can you do to help?
 
  1. Do your research before buying plants for your garden to make sure they are not invasive. Choose native plants over exotic or hybrids. Exotics and hybrids, by default, are not necessarily invasive but have the potential to become invasive.
  2. Do not release pets such as turtles, fish, snakes, or other animals into the wild if you are unable to care for them. Contact the US Fish and Wildlife Service or the Department of Natural Resources to ask for assistance. As a result of people releasing Burmese pythons in Florida, the species has become abundant in the Everglades and is competing with native wildlife for habitat and resources.
  3. Do not transport seeds, fruits, or vegetables across international borders.
 
Additional resources


  1. National Geographic : Invasive species 101 Watch Short video
  2. Nature Conservancy: Learn more or watch a short video about how you can help keep invasive species from altering or destroying wild spaces.
  3. Ocean Conservancy: Find out how you can keep our waterways safe and clear of alien invaders. 3 easy ways to stop invasive species
  4. National Wildlife Federation: Combatting Invasive Species 
  5. US Fish and Wildlife Service offers helpful resources on the following topics:  
    1. Prevent Spread of Invasive Plants
    2. Information on Pets and Aquariums
    3. Find a list of native plants and nurseries
    4. Volunteer On a National Wildlife Refuge and General Information. 
  6. Tracking the Golden Isles. The Natural and Human Histories of the Georgia Coast: Dr. Anthony Martin’s new book covers many fascinating topics, including the impact invasive animals have on the Georgia coast and how they negatively affect the native species. Coming soon! You can buy his book at the following sites - University of Georgia Press, Amazon or Barnes and Nobles.

It costs an estimated $1.4 trillion to the global economy to manage invasive species.
~National Geographic
The United States spends approximately $120 billion annually to manage invasive species.
~Nature Conservancy

Who to Support: Please find listed below organizations that are working to protect our land and waterways from invasive species. Follow their links to learn more about their work and the species they protect. ​Please consider supporting their cause by making a donation, signing petitions, volunteering, learning about their work and educating others. 
  • Nature Conservancy
  • Ocean Conservancy
  • National Wildlife Federation
  • US Fish and Wildlife Service

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  • Home
  • My Story
  • Current Issue
  • Past Issues
    • Anniversary Edition (5 year)
    • Bald Eagle >
      • Photo Gallery - Bald Eagle (Fall 2017)
    • Climate Change
    • Common Sense Advocacy
    • Conversations on Conservation I
    • Conversations on Conservation II
    • Conversations on Conservation - Part III
    • Conversations on Conservation: Part IV
    • Conversations on Conservations: Part V
    • Conversations on Conservation: Part VI
    • Coral Reef >
      • Photo Gallery: Coral Reef (Spring 2016)
    • Ecology, Economics and Evolution
    • Elephant
    • Flying Fox
    • Gopher Tortoise, Eastern Indigo Snake and Gopher Frog >
      • Photo Gallery: Gopher Tortoise (Spring 2019)
    • Honeybee >
      • A Day in the Life of a Honey Bee
      • Nature at Work
      • Colony Collapse Disorder
      • Photo Gallery: Honeybee (Winter 2014)
    • Invasive Species
    • Lion
    • Monarch Butterfly
    • Native Orchids >
      • Photo Gallery - Orchids (Winter 2017)
    • Pitcher Plant Moth, Happy-Face Spider & Ogre-Faced Spider
    • Tiger >
      • Photo Gallery: Tiger ( Fall 2015)
    • Water
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