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What is a nonnative, or invasive species you ask? From the National Park Service, "Invasive species are plants or animals that are not from a certain area, and have different characteristics than native organisms. This explains what nonnative, or invasive, plants are, and helps us understand what the nonnative plants are on our campus. Knowing this, we can make other conclusions about the plants on our campus.
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Native Plants, Non-native Plants, and Invasive Species - Devils Postpile National Monument (U.S. National Park Service)

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National Parks and other protected areas are samples of the world's natural and unique variety of life. The value of diverse landscape and wildlife in our National Parks is integral and necessary to the enjoyment and health of the park and its visitation.

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Plants on Mountain View High School's campus are all nonnative. Some may wonder, why are these plants nonnative? How do these plants survive in a place they're not originally from? The University of Arizona explains a reason for the thriving of these nonnative plants, "because organisms have evolved where there is huge variation in the environment over a long time or over a large space, so those who cannot take advantage of this variation probably won't do very well."
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Max Li, a University of Arizona doctoral student in the Department of Ecology and Evolutionary Biology, is studying mechanisms that determine how competing desert plants can coexist with each other and what factors can cause the destruction of this stable coexistence.

His research could help inform policies to curb the spread of invasive species.

"I have been lucky enough to get three dry years in a row," said Li, expressing a sentiment probably shared by few in Southern Arizona. But if you're a field ecologist studying how desert species adapt, persist and compete with each other in dry environments, then the lack of rain in recent years means the perfect conditions for a field experiment.

"My question is: Why do some exotic species become invasive and why are some able to coexist naturally with native plants?" Li said.

"In theory, we can explain coexistence in terms of environmental fluctuation. Using a mathematical derivation we have several ideas of distinctive mechanisms that can promote coexistence."

According to his adviser Peter Chesson's theory, Li said, where competing species can stably coexist and where they drive each other to extinction is determined by three coexistence mechanisms that affect how the species relate to each other across space and time under changing environments.

"Environmental fluctuation is prevalent in nature," Li said. "Therefore it is critical to consider how organisms respond to this fluctuation to achieve a dynamic balance."

"It's like in the stock market. If you always buy at the highest price and sell at the lowest price then you don't have stability, you lose money. But if you know how to make gain at the right price and try to diminish your loss in a bearish market, you can make a profit," Li said.

"So that's exactly what organisms do because organisms have evolved where there is huge variation in the environment over a long time or over a large space, so those who cannot take advantage of this variation probably won't do very well."

Li is focusing on two of the coexistence mechanisms that are theorized to be the most effective, termed "storage effect," which refers to the fact that gain in population growth under good conditions can be stored even when species experience bad conditions, and "fitness-density covariance," which refers to how well species can build up population in their favorable habitat.

For the first time, Li's experiments are testing these mechanisms in the field, surveying a number of native desert plants and one invasive species, the Sahara mustard.

"The strength of the mechanisms are measured in fitness, so we measure parameters that indicate the fitness of plants," Li explained. "For example, we can measure the number of seeds that the plant will produce or the mass of the plant."

Li has divided his study site into segments that represent different scales of an ecological community, from neighborhoods of just a few plants living closely together and competing directly with one another for resources like nutrients and water, to habitats, including sand dunes and a sand flat.

"The sand dunes have very unstable soil because in a dune the sand shifts all the time. There are very few large perennial plants living there just because the soil is so dynamic," Li said. Whereas in the sand flat, he said, "the soil is still sandy but it's much more stable and there are large shrubs."

In theory, the population variation among plant species at the smaller scales, such as among neighborhoods or between the habitats, can contribute to the stability of the overall system, Li said.

"The theory predicts that population fluctuations due to environmental variation at lower scales, such as neighborhoods of plants, can give rise to these mechanisms to promote coexistence at higher scales, such as across a landscape," he said.

"There are huge implications for conservation. We can encourage the conditions that promote coexistence and try to prevent these conditions from disappearing."

Understanding the ecological process that could give native species an edge over invasive species could help people to better implement practices to curb the invasion of non-native plants like buffelgrass, a dense-growing non-native that is out-competing native plants in many areas of the Sonoran Desert.

Li's preliminary results show that environmental variation between the dune and sand flat habitat is promoting the coexistence between Sahara mustard and native plants.

"Encouraging habitat diversity is very important in terms of prevention of massive invasion by alien plant species," Li said.

Practices like urbanization, road development and cultivating monoculture crops homogenize the environment over the landscape, making it easier for invasive plants to have an advantage over the native plant species.

"Environmental fluctuation promotes coexistence because no species can do equally well under all conditions," Li said. "Changing environment in time and space provides temporal or spatial niches for different species to reduce direct competition with each other."

"In invasion biology there are some species that can continue to evolve and adapt to new conditions. These are the most dangerous species, because they are so good at adapting to new conditions."

Invasive species that do extremely well usually have significant genetic diversity created by multiple reintroductions of the species by humans, Li noted.

"If humans continue to bring non-native plants to the same destination and let individuals from different original populations mingle and increase their genetic diversity then all of a sudden they have a strong capacity to adapt to local conditions to become a super weed."

Preventing the introduction of non-native plants to the landscape is likely an easier solution to stop the spread of invasive plants than trying to eradicate an invasion after the weed has become established, Li added.

Meanwhile, understanding the ecological factors that give some plants an advantage over others can help inform environmental policies to curb invasions and give the desert back to the native plants.

"This is the first time in the field that anyone has tried to quantify a mathematically sound coexistence mechanism across multiple scales," Li said. "Hopefully it will bring some good insight into both science and management."

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Invasion in the Desert: Why Some Plant Species are Survivors

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Max Li, a University of Arizona doctoral student in the Department of Ecology and Evolutionary Biology, is studying mechanisms that determine how competing desert plants can coexist with each other and what factors can cause the destruction of this stable coexistence. His research could help inform policies to curb the spread of invasive species.

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Another reason why these nonnative plants are able to survive in the desert they're not from is because they have adapted to the conditions here. To survive, desert plants have adapted to the extremes of heat and aridity by using both physical and behavioral mechanisms, much like desert animals. DesertUSA explains this concept, "Plants that have adapted by altering their physical structure are called xerophytes. Xerophytes, such as cacti, usually have special means of storing and conserving water. They often have few or no leaves, which reduces transpiration." This explains how plants, including the plants on MVT's campus can survive in a nonnative area to their species because of the ways they adapt to their new environment.

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Desert plants have adapted to the extremes of heat and aridity by using both physical and behavioral mechanisms, much like desert animals.

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This video describes the ways different platns can survive in the desert. This is maybe why nonnative plants on the campus of Mountain View High School can thrive, because they have the techniques to stay alive in the desert.

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On the campus of Mountain View High School, there are many oleanders. These plants are not native to Arizona, but rather the Mediterranean area. Although this plant may not be from here, it has the necessary means to survive. From BioWeb it shares, "Nerium oleander is considered to be very drought resistant.  This is because in times of less water it will often slow its growth and stop flowering.  It also has mechanisms, such as a waxy cuticle on its leaves, to help prevent water loss." This explains how this oleander plant can survive through drought. Because of this adaption capacity, it can survive in the desert. This nonnative species is indeed able to thrive because of its capacity to withstand little rain. Including the oleander, all the plants on MVT's campus are able to thrive in the desert conditions because of their different adaptation strategies. Therefore, the nonnative aspect of these plant species aren't as important as their capacity to adapt.
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From the High Desert Coop. website, it explains nonnative species and their positive effects on ecosystems, "Thousands of plant species have been brought to North America in the past three centuries. Most are well-behaved, rarely penetrating natural areas." This shows that the species of plants on the Mountain View High School campus do benefit the area, and do not harm it like some plant species do. These plants can also survive because of the similar adaptations to specific areas they may have come from.
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Desert Ecosystem Analysis and Restoration

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Nonnative species - also called alien, introduced, exotic, intrusive or invasive species - are a direct threat to many desert species, both plants and animals.

In the next century, the greatest threat to our native plants and the wildlife species that depend upon them may well come from other plants. Thousands of plant species have been brought to North America in the past three centuries. Most are well-behaved, rarely penetrating natural areas. Several hundred, however, have no natural controls here, and are able to out-compete and gradually displace our native plants, even deep in forests and undisturbed ecosystems.

Some of these plants were brought here intentionally, for their medicinal, ornamental, or food value. Others hid in soil, crop seed, or ballast. Most came from other continents, but a few have spread from other parts of the US. In each region, different species are better adapted and therefore pose a greater threat.

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Nonnative species - also called alien, introduced, exotic, intrusive or invasive species - are a direct threat to many desert species, both plants and animals. In the next century, the greatest threat to our native plants and the wildlife species that depend upon them may well come from other plants.

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This graph is helpful because it shows the types of plants of the campus of Mountain View High School. All of these plants are nonnative. That being said, all of these plants can survive in the desert even when they're not originally from Arizona! This graph is interesting to understand, and to realize how many plants actually can survive in a place they're not from.

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Nonnative Species Aren't Always Unwanted

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Nonnative Species Aren't Always Unwanted

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Writer from the New York Times, Erica Goode, writes, "Invasive species are bad news, or so goes the conventional wisdom, encouraged by persistent warnings from biologists about the dangers of foreign animals and plants moving into new territories.

Conservation organizations bill alien species as the foremost threat to native wildlife. Cities rip out exotic trees and shrubs in favor of indigenous varieties. And governments spend millions on efforts to head off or eradicate biological invaders." After she explains the danger of nonnative species, she tells of the positive effects these species have on the environment, "But a growing number of scientists are challenging this view, arguing that not all invasive species are destructive; some, they contend, are even beneficial. The assumption that what hails from elsewhere is inherently bad, these researchers say, rests more on xenophobia than on science." This proves that not all nonnative species are bad, and that's why the nonnative plants on the MVT campus are in fact beneficial to the environment, and do not harm the ecosystem.
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In Spain, nonnative crayfish serve as prey for migratory wetland birds. Credit Credit Rafa Huertas/Reuters

Invasive species are bad news, or so goes the conventional wisdom, encouraged by persistent warnings from biologists about the dangers of foreign animals and plants moving into new territories.

Conservation organizations bill alien species as the foremost threat to native wildlife. Cities rip out exotic trees and shrubs in favor of indigenous varieties. And governments spend millions on efforts to head off or eradicate biological invaders.

"I think the dominant paradigm in the field is still a 'when in doubt, kill them' sort of attitude," said Dov Sax, an associate professor of ecology and evolutionary biology at Brown University.

But a growing number of scientists are challenging this view, arguing that not all invasive species are destructive; some, they contend, are even beneficial. The assumption that what hails from elsewhere is inherently bad, these researchers say, rests more on xenophobia than on science.

"It's almost a religious kind of belief, that things were put where they are by God and that that's where they damn well ought to stay," said Ken Thompson, an ecologist and retired senior lecturer at the University of Sheffield in England, who wrote the 2014 book "Where Do Camels Belong: Why Invasive Species Aren't All Bad."

"We're actually moving plants and animals around the world all the time," he said. "We have been for centuries."

Dr. Thompson and other scientists have called for a more nuanced approach to evaluating whether the presence of a species is harmful or beneficial. Eradicating most invasive species is virtually impossible in an era of globalization, they note. And as climate change pushes more species out of their home ranges and into new areas, the number of so-called invaders is likely to multiply exponentially.

Yet the notion that a species should not be judged on its origins is highly controversial, as Mark Davis, a biology professor at Macalester College in Minnesota, discovered when he and 18 other researchers submitted an article in 2011 saying just that in the journal Nature.

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Asian carp are taking over many rivers in the Midwest. Credit Travis Heying/Wichita Eagle, via Getty Images

The response was immediate - and signed by 141 scientists, many of them specialists in the field known as invasion biology. Their approach, they said, was already sufficiently "nuanced," thank you very much.

"Most conservation biologists and ecologists do not oppose nonnative species per se," wrote Daniel Simberloff, a professor of environmental science at the University of Tennessee, who led the group that wrote the rebuttal. He added that Dr. Davis and his colleagues had vastly played down the severe harm that alien species caused.

But in the five years since that contentious exchange, the idea that invasive species should be assumed guilty until proven innocent has begun to wane, the shift prompted in part, Dr. Davis speculated, by concerns over the use of chemical pesticides and the disruption of landscapes caused by many eradication efforts.

Some alien species are undeniably harmful, a fact that neither Dr. Davis nor others who share his view dispute. The fungus that causes chestnut blight, for example, decimated thousands of trees and changed the American landscape in the early 1900s. The Zika virus is invading new regions, carried by infected mosquitoes that some say are being driven northward by warmer temperatures. The vampirelike lamprey, sneaking into the Great Lakes in the 19th century, gradually champed its way through the fish population.

Islands and mountaintops are especially vulnerable to damage from invaders because their native species often evolved in isolation and lack natural defenses against predators or immunity to exotic diseases. The brown tree snake, accidentally transported to Guam, has virtually eliminated the bird population there.

But, Dr. Davis noted, "all species have negative impacts on something," and the danger, he said, is often exaggerated.

A study published Feb. 17 in the journal Biology Letters, for example, concluded that alien species "are the second most common threat associated with species that have gone completely extinct" since 1500 A.D.

But the study, Dr. Davis and other experts said, relies on subjective judgments about extinction and does not distinguish between island species - which are far more vulnerable - and land or ocean species.

In some instances, nonnatives offer clear benefits. In California, for example, monarch butterflies prefer to spend their winters in the branches of the eucalyptus, an exotic tree transplanted to the state more than 150 years ago and viewed by some as an invasive fire hazard. In Spain, non-native crayfish serve as prey for migratory wetland birds, including some endangered species.

And some notorious invaders can have positive effects. Western states have spent a fortune trying to eradicate the tamarisk tree, which many experts believe hogs more than its share of water and damages the habitat of native species.

But Julian D. Olden, an associate professor in the School of Aquatic and Fishery Sciences at the University of Washington, said tamarisks had been found to provide shelter for birds like the southwestern willow flycatcher. Some studies have also concluded that the tree's water use is not significantly different from that of other tree species.

The antipathy to foreign plants and wildlife is relatively recent. While the distinction between native and non-native species dates to the 18th century, the term "invasion" was first used in a 1958 book - " The Ecology of Invasions by Animals and Plants," by Charles Elton - that drew on the militaristic vocabulary of the post-World War II era.

But the moniker did not achieve its full derogatory weight until the 1990s and early 2000s, when academic interest in the subject peaked and the number of papers on the subject generated by invasion biologists grew proportionately.

To biologists like Dr. Simberloff, taking action to head off alien species early on makes sense, allowing governments to address threats before invaders take firm hold. Non-native species are far more likely to do harm than native plants and animals, he argued, adding that the debate was "a phony controversy."

Whether a species is viewed as native, however, often depends on when you arrived on the scene. Much of what Americans eat was originally imported: The horse, an icon of the American West, for example, was reintroduced by the Spanish thousands of years after the original North American horse became extinct. Several states list the honeybee as their state insect. But like many other state fish, insects and flowers, the bees are in fact immigrants.

In at least one case, a species that was long extinct in its native range was treated as an interloper when it finally returned home.

Beavers were common in Britain until they were hunted to extinction centuries ago. But when a group of the toothy dam builders took up residence along the River Tay in western Scotland several years ago, local farmers and fishermen greeted the animals with hostility, saying they posed a threat to farmland and salmon runs and were potential carriers of disease.

Scottish Land and Estates, an organization representing landowners, insisted that the beavers' centuries of absence from Britain nullified their resident status, the Independent reported in 2010.

"It's just silly," Dr. Thompson said, of the reaction to the Tay beavers. "I don't think we would have ended up in this ridiculous situation if we hadn't been so bombarded by propaganda about invasive species."

Often, he and others say, "invasion" is just another word for "change." And the only thing that is certain is that more change is to come. Already, the flora and fauna of countries around the world are more homogeneous than they once were, as globalization has, accidentally or intentionally, moved exotic species from one place to another.

"From birds to plants to fish to mammals, there's strong evidence that things are becoming more similar," Dr. Olden said, likening the phenomenon to "the popping up of big-box retailers and the loss of mom-and-pop shops."

As more species migrate, new quandaries are likely to arise. And as the human population increases, driving more animals and plants toward extinction, a species' second home may be the only one it has.

In a paper published last month in the journal Conservation Biology, two scientists in California, Michael P. Marchetti and Tag Engstrom, describe the "paradox" of species that are under threat in their native range but are viewed as invasive in other places they have settled.

They include the Monterey pine, endangered in California and Mexico but treated as a pest in Australia and New Zealand, and the Barbary sheep, endangered in Morocco and other countries but running rampant in the Canary Islands and elsewhere.

"This is a challenge," Dr. Olden said. "If we identify a plant or animal that might not be able to respond to climate change, do we roll the dice and intentionally move that species northward, or up in elevation?"

"We're playing a little bit of ecological roulette here," he added.

Correction:

A picture caption on Tuesday with an article about invasive species misstated the time period when the fungus that causes chestnut blight killed off many trees in the United States, including the one shown. As the article correctly noted, it was in the early 1900s, not the early 19th century.

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Invasive species are bad news, or so goes the conventional wisdom, encouraged by persistent warnings from biologists about the dangers of foreign animals and plants moving into new territories. Conservation organizations bill alien species as the foremost threat to native wildlife. Cities rip out exotic trees and shrubs in favor of indigenous varieties.

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Nonnative Species Examples Around the World

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Nonnative Species Examples Around the World

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This video shares an example of a nonnative species of plants that is thriving in Korea, unlike its indigenous plants. This could be due to drought resistant adaptations for the invasive species of plant. This is a reason for why the campus at Mountain View High School is covered in nonnative species, they can thrive where they can adapt.

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1.)https://www.nps.gov/depo/learn/nature/invasives.htm
2.)https://uanews.arizona.edu/story/invasion-in-the-desert-why-some-plant-species-are-survivors
3.)https://www.desertusa.com/du_plantsurv.html
4.)http://bioweb.uwlax.edu/bio203/s2013/mcgrath_jaco/adaptation.htm
5.) https://highdeserteco.org/non-native-species/
6.)https://www.nytimes.com/2016/03/01/science/invasive-species.html