Invasive Species: Friends or Foes?

We’ve all heard horror stories about invasive species, but are introduced plants and animals really as bad as the media paints them?

News headlines on invasive species. Image by author. Sources for headlines.

The answer to this question depends on exactly which invasive species we are referring to.

The brown tree snake (Boiga irregularis) is an example of a truly harmful invasive species. 

Brown tree snake. Public domain image. Source.

The brown tree snake arrived on the small Pacific Island of Guam in the late 1940s or early 1950s as a stowaway on military cargo, and has since eaten most of Guam’s birds, lizards, and small mammals. Guam’s fauna never experienced predation by a large snake before, and they are suffering horribly under the reign of the invasive brown tree snake.

In addition to eating Guam’s native species, the brown tree snake causes frequent power outages. How can a snake cause power outages? By climbing pylons and shorting out the power circuits! Climbing pylons is a dangerous hobby as it kills the snake, inconveniences Guam’s citizens, and costs power companies too much money in repairs.

Brown tree snake on top of a fence post. Creative commons image. Source.

The brown tree snake also costs the US military stationed on Guam millions of dollars each year in safety measures to prevent this pesky predator from escaping to another island. So far, this money is well spent as the brown tree snake has not escaped Guam.

The only good thing about the brown tree snake is that it eats Guam’s rats.

But what about another invasive species, garlic mustard (Alliaria petiolata)? I remember when garlic mustard was one of the most hated plants in NYC. Garlic mustard grew in dense monocultures and drove out other plants. Every time I went on a walk I would see huge piles of garlic mustard the parks department ripped out of the soil in an attempt to eradicate this species. Now, I rarely see piles of dead garlic mustard. Instead, I see garlic mustard growing alongside other plants along the park paths. What caused this change?

Garlic mustard. Creative commons image. Source.

 Garlic mustard was deliberately introduced to the United States in 1868 on Long Island for its ability to control erosion and its medicinal properties. While garlic mustard may look innocent and charming with its little white flowers, this plant had serious issues with poisoning its neighbors. 

Sinigrin, the toxic chemical garlic mustard emits, kills nearby plants and mycorrhizal fungi. Mycorrhizal fungi are a type of fungi which colonize the roots of plants and help their plant partners absorb more water and nutrients. Without their mycorrhizal fungi, the lives of plants living near garlic mustard were jeopardized, which allowed garlic mustard to push these plants out. Soon garlic mustard was dominating the forest floor.

Now, garlic mustard has been living in the United States for a long time and it is learning to be a kinder neighbor. U.S. garlic mustard doesn’t emit as much sinigrin as it used to, and the plant can grow next to other species without killing them.

Garlic mustard flowers. Creative commons image. Source.

Why is this?

High levels of sinigrin release, seen when garlic mustard first was colonizing the states, is most beneficial for garlic mustard when the plant is mainly competing with other species. However, when garlic mustard is well established, it mainly competes with itself, which means low levels of sinigrin release are preferable. Low levels of sinigrin emission are currently so favorable for the U.S. garlic mustard population that the genetics of this population changed to make low levels sinigrin release widespread and innate.

Now that garlic mustard has had a chance to settle into its new home, it’s not acting particularly dangerous and invasive anymore, is it?

Purple loosestrife (Lythrum salicaria) and Canadian pondweed (Elodea canadensis) are two other introduced species, like garlic mustard, accused of forming monocultures and driving out native species. After forming dense stands during the first few years of introduction, purple loosestrife and Canadian pondweed populations both declined significantly, like garlic mustard did, and they now live peacefully next to native plants. Non-native species may need a few years to acclimate to their new homes. We may be accusing them of wrongdoing too quickly.

The purple haze in the background of this photo is purple loosestrife.
Photo by PBM. Used with permission.

Admittedly, garlic mustard, purple loosestrife, and Canadian pondweed are not the worst invasive species. These plants don’t hold a candle to the brown tree snake. Are the more wickedly painted invaders, like zebra mussels (Dreissena polymorpha) or tamarisk (Tamarix sp.), ever falsely accused?

News headline on invasive species. Image by author. Sources for headlines.

Yes, non-native species are often blamed for problems we humans caused simply because they are found near where the damage occurred. 

Illustration of a zebra mussel. A public domain image. Source.

Zebra mussels are incriminated for clogging pipes, covering every hard surface underwater, and eliminating endangered freshwater mollusks. The fact is, freshwater mollusks were on the decline long before zebra mussels ever arrived because of habitat degradation and pollution caused by humans. Zebra mussels do compete with these mollusks for food, but it is wrong to blame them for endangering the mollusks. 

Zebra mussels. Creative commons image. Source.

Zebra mussels do cover a large amount of hard surface area underwater, but while doing so, they filter polluted water. As a result of the zebra mussels’ filtering job, the water is clearer, which promotes the growth of aquatic plants. These plants provide cover for fish and invertebrates and help increase their populations. The fish then feed on the zebra mussels and help clear some of the hard surfaces they live on. Zebra mussels also serve as a major food source for waterfowl. 

Yes, zebra mussels may inconvenience water companies by clogging their pipes, but they aren’t the evil species the media makes them out to be.

Zebra mussels on water meter. Public domain image by NOAA. Source.

Tamarisk has a similar story. This small tree is blamed for being a water hog and for destroying native bird habitat. Actually, humans were the ones using all the water. Tamarisk use about the same amount of water as native plants. In addition, tamarisk provides habitat for native birds. This plant isn’t quite as bad as the headlines make it seem.

Tamarisk flowers. Creative commons image. Source.

The whole idea that introduced species must be harmful is a xenophobic attitude. Once a non-native species takes root, it is next to impossible to eradicate. Introduced species are not going away anytime soon either, as international trade and travel just make it easier for species to globe trot. It’s time to accept the innocent immigrants species and the benefits they can offer our ecosystem.

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The Brain on Coffee

I recently became a coffee drinker, and as I drank my coffee one morning, enjoying how much more awake and alert I felt with every sip, I began to wonder: why does coffee help me wake up and focus? What is caffeine doing to my brain?

Photo by History Underfoot, Used with permission.

Energized by my morning brew, I jumped right into research. Soon I learned many new words (neuroscience papers are superfluously verbose) and why coffee helps most of us feel more human on even the least promising morning.

A drawing of the brain.
A public domain image. Source.

The invigorating effect of coffee can be traced to the caffeine present in the beans. We all know that caffeine is a central nervous system stimulant. But how does it get into our nervous system in the first place? Caffeine can easily cross the blood brain barrier, a screening system which prevents most chemicals from entering the brain, to interact with our neurons. 

Stained neurons.
A creative commons image. Source.

What does that mean?

Before I explain exactly how caffeine interacts with our neurons let’s back up a little and briefly review how our brain works. Our brains are made of neurons which respond to stimulus by sending and receiving neurotransmitters. Neurotransmitters are chemical messages which either trigger neurons to release more neurotransmitters—or stop neurons from releasing more neurotransmitters. The complex patterns of releasing and withholding neurotransmitters are what allow us to move our muscles, to make decisions, and form memories.

A creative commons image. Source.

One end of a neuron—the end which receives neurotransmitters—is made of many branched extensions called dendrites. The dendrites are covered in receptors which interact neurotransmitters. Different types of receptors respond to different neurotransmitters. 

Now, let’s get back to the coffee. Caffeine mainly affects two types of receptors known as the A1 and A2A receptors. These receptors normally receive adenosine, a neurotransmitter which helps us sleep and relax. Caffeine blocks the A1 and A2A receptors and prevents them from receiving adenosine. With less adenosine interacting with our neurons we automatically feel more alert and awake. 

Drawing of neurons.
A public domain image. Source.

Caffeine,  in preventing adenosine from doing its job, has a few side effects like increasing anxiety. People who are prone to anxiety and panic attacks—and first-time coffee drinkers—are more likely to feel nervous after a cup.

Luckily for us regular coffee drinkers, most people’s brains habituate to caffeine very easily, and the caffeine jitters become less pronounced the more frequently one drinks coffee. After my first cup of coffee, I felt a little on edge, but now that I’ve been enjoying coffee daily for about two weeks, I don’t feel nervous after my morning mug.

Vintage coffee can.
A creative commons image. Source.

Caffeine promotes alertness, which is great during the day, but not as pleasant at bedtime. Even if one does manage to fall asleep after drinking coffee in the afternoon, caffeine reduces the amount of deep sleep per night and increases the amount of light sleep. The rapid eye movement (REM) sleep, or dreaming sleep, remains the same regardless of coffee consumption. First-time coffee drinkers are more likely to experience sleep disruption as increased caffeine tolerance reduces the drug’s influence on sleep.

Another thing I learned is exactly how quickly one becomes accustomed to caffeine depends largely on genetics. Some people’s livers metabolize coffee slowly, and since caffeine would remain in their bodies longer, it may have a stronger effect on them. In general, people of Asian and African descent tend to metabolize caffeine more slowly than those of European descent. 

Author's own image.

I have not gotten my DNA sequenced yet, but I’m guessing that my liver metabolizes caffeine fairly quickly because I quickly became habituated to caffeine and my ancestors were European.

Coffee has a few other side effects like excessive urine production, increase in systolic blood pressure, and dilation of the airways. I’ve read that drinking too much coffee can raise the blood pressure to dangerous levels in people with hypertension. (Always do your own research.)

Author's own image.

For people without hypertension or caffeine-induced anxiety, lifelong coffee drinking is suspected to delay the onset of cognitive decline, Parkinson’s disease, and diabetes. One recent study found that drinking coffee reduced the risk of brain tumors in Japanese populations. The benefits of coffee drinking tend to be more pronounced in women.

Unfortunately, these health benefits only apply to lifelong coffee drinkers. Starting to drink coffee as an older adult can possibly increase cognitive decline. People with Parkinson’s disease and diabetes who began to drink coffee after they were afflicted reported no change in their symptoms.

Even if coffee can’t change the symptoms of Parkinson’s or diabetes, it can improve one’s mood. Coffee paired with bread and blue light is one of the top mood improvers! I know next time I’m feeling down try this coffee, bread, and blue light strategy. (Where do I find blue lights?)

Coffee and bread, my breakfast this morning! Author's own image.

Happy coffee drinking to my fellow coffee lovers!

Inspired to learn more about coffee? Check out my post on my other blog, Totally Baroque, about 17th century men and women who couldn’t pass a day without the “drink which drove away drowsiness" here.

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