By Alisha John

BREAKING:Planet Earth is under attack by alien species from out-of-place. They may be lurking in your backyard right now. These invasive species take many forms – from plants to fish to mammals. But one thing is certain: they threaten the delicate balance of our native ecosystems.

Invasive species threaten native ecosystems and wildlife

As defined by Executive Order 13112 signed by President Clinton in 1999, an invasive species is an alien species which causes harm or is likely to cause harm to the environment, economy, or human health. The term alien species applies to any species not native to the ecosystem or environment under consideration. While some alien species can coexist with native plants and animals, others can upset the natural balance in an ecosystem, and thus are labeled as invasive species. The characteristics of an environment susceptible to invasion are somewhat unclear; however, man-made environments (farmland, urban landscapes) and environments with stress induced by degradation and/or climate change seem to be particularly at risk.

Invasive species cause harm to a natural ecosystem in many ways. They may out-compete native species for food and other resources. Some invasive species grow and reproduce quickly, allowing them to spread rapidly across an environment. Others don’t have natural predators in their new environment, leading to ballooning population sizes without much constraint. Some invasive species may eat native species, disrupting the native species’ ability to survive. Others still may carry or cause diseases native plants or animals have no defenses against. Any of these factors can lead to a decrease in biological diversity, or biodiversity, drastically altering an ecosystem and changing important relationships between native plants and animals (including humans).

Invasive species are often transplanted by human activity

In today’s global society, invasive species are often spread by human activity. Sometimes we transport species knowingly. For instance, the European red fox was introduced to Australia in the late 1800s for sport hunting, and has since become an invasive species in the region. With a lack of natural predators in Australia, red foxes have contributed to the decline in many species of birds, small rodents, and reptiles, including threatened species. Additionally, red foxes deplete livestock, preying on lambs, goats, and poultry.

In other cases, despite our best intentions, we create an invasive species problem while trying to solve another problem. In 1935, the cane toad was introduced to Australia in an attempt to control a destructive beetle population that was decimating sugar cane crops. However, the toads reproduced like wildfire, spread disease, produce a toxin native species aren’t adapted to, and ultimately reduced biodiversity in the region.The cane toad is still a problematic species in Australia today. Another well known example involves the Asian carp in the United States. These fish were introduced to help filter pond water in southern United States fish farms in the 1970s. Flooding allowed them to escape from their intended role and establish wild populations in the Mississippi River in the 1980s. Since that time, they have used our interconnected waterways to spread, and are on the cusp of invading the Great Lakes. In the Great Lakes, an Asian carp invasion could have a variety of impacts, from perturbing native ecosystems to disrupting the profitable fishery and recreational boating industries. Furthermore, Asian carp often leap out of the water when startled by boat motors, leading to injuries when they collide with boaters.

Red fox (Left – Image credit) Cane toad (Right – Image credit)

Some invasive species are hitchhikers

Other times humans transport species unknowingly, as is the case for Zebra mussels in the Great Lakes. Zebra mussels arrived via ship ballast water in the late 1980s. Since that time their populations have skyrocketed due to their ability to out-compete native species for food and habitat. Zebra mussels feed by filtering nutrients from water at an astonishing rate of up to one liter of water per day per mussel. This may sound like a good thing for the health and cleanliness of lakes, rivers, and streams, but the sheer number of Zebra mussels leads to their filtering being too effective. The increase of water clarity, along with Zebra mussel waste acting as fertilizer, contributes to algal blooms harboring bacteria that can harm animals and humans. Zebra mussels have also caused inconveniences to humans by clogging water intake and discharge pipes, a costly problem to correct.

If you live around Michigan, you have likely heard of an invasive species introduced unknowingly: the Emerald Ash Borer. This species arrived in North America from Asia in the 1990s, likely in wooden shipping materials. Since 2002,the Emerald Ash Borer has spread to other parts of the United States and Canada, partially through the transport of firewood. Without measures to control Emerald Ash Borer populations, infected Ash trees lose up to 50% of their canopy within 2 years and die within 3–4 years of infestation.In fact, since the 2002 infestation over 99% of mature ash trees in southeastern Michigan have died. Native Ash trees help ease the impact of heavy storms on drainage systems, improve air quality, and decrease energy consumption by offering shade to homes and businesses. The economic cost of Ash tree loss from the Emerald Ash Borer will cost communities not only in replanting costs, but also in the loss of the benefits long standing trees provide. Researchers are searching for tolerant and resistant trees, which may help in reforestation efforts, but the impact of the Emerald Ash Borer is irrefutable.

Zebra mussels      4878926306_d16da208ca_o

Zebra mussels (Left – Image credit)          Emerald Ash Borer (Right –Image credit)

You can take action to help slow the spread of invasive species

These examples point toward one conclusion. Invasive species threaten our ecosystems and livelihoods. Approximately 42% of threatened or endangered species are at risk primarily due to invasive species. The decrease in biodiversity that can result from invasive species also has implications for human health. Once established, it can be very difficult, time-consuming, and expensive to eradicate an invasive species. However, there are some simple things we can all do to help slow the spread of invasive species. You can plant native species of plants in and around your community while taking efforts to remove non-native species that may become invasive. Clean your outdoor clothing, equipment (including boats and tires), and pets thoroughly to dislodge hitchhikers before transporting them to another location. If you’re camping, buy firewood near your campsite and leave any leftovers. Lastly, you can learn to identify invasive species in your area and report sighting to the appropriate authorities. Do your part to help stop these attacks from out-of-place!

About the author

alishaAlisha is a PhD student in Molecular, Cellular, & Developmental Biology at the University of Michigan. A member of the Wittkopp Lab, Alisha studies how changes in gene expression contribute to different phenotypes seen in nature; more specifically, she is trying to figure out how two fruit fly species became very different in terms of coloration. Alisha is a Michigan native and earned her B.S. in Chemical Engineering from Wayne State University in Detroit before making the jump into Biology. When she isn’t busy staring lovingly at Drosophila, you can find Alisha baking delicious desserts, being an amateur foodie, and/or spending time with friends & family. Follow her on Twitter (@AlishaJohn) and on LinkedIn.

Read all posts by Alisha here.

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