Enemy Invaders

     It's an early autumn morning, the crisp bite of air warning of winter's onset. A grey squirrel is on the move, scurrying around collecting and hiding nuts and seeds. These will sustain him in the cold months to come, when food is scarce. He will bury up to 3000 nuts this fall, many of which will still be hidden the following spring. These forgotten nuts allow new trees to grow.

    Grey squirrels, native to Eastern North America, help the environment in this way. A species's native range refers to where it occurs naturally and has evolved to live. This means that grey squirrels are supposed to live in Eastern North America.

    However, grey squirrels cannot survive by themselves. The entire ecosystem (all living things in a given area and their interactions with each other and their environment) is interconnected. Grey squirrels rely on native plants like oak, beech, pine, and flowers for food. In turn, the trees benefit from the squirrels dispersing their seeds, and predators like hawks, raccoons, and foxes use grey squirrels as a source of food. This is a simple example, but it helps show that removing any one species could have an unforeseen ripple effect.

    Equally consequential could be adding an additional factor, such as the sudden introduction of a new species. When a species is brought to a new location, it is facing a new environment, with new challenges and opportunities. Often, the challenges will be too great and the species will die off. Another option is that the species could integrate into the existing ecosystem without overpopulating or otherwise causing harm. These foreigners are often called "naturalized species." However, if the newcomer becomes widespread and causes harm to human health, the economy, or the existing ecosystem, it is considered invasive.

     For example, the grey squirrel, while beneficial in Eastern North America, is invasive in Europe. They out-compete native squirrel populations, carry and transmit parapoxvirus to native squirrels, and they strip the bark off native trees. Despite having the name "invasive species" grey squirrels are far from invaders. They were first brought to Europe by people who wanted them as pets or as ornamental animals to roam in the yards of stately homes. The grey squirrel simply found itself in a new land, brought there by people, and did its best to survive.

    Invasive species come in all shapes and forms: emerald ash borers killing ash trees across North America, brought here in shipping vessels from north-eastern Asia and spread by the transport of infected wood; cane toads (right) in Australia outcompeting native species and poisoning native predators that try to consume them, introduced deliberately in the hopes they would control the cane beetles destroying sugar cane crops; zebra mussels, a freshwater mollusk native to seas of Eastern Europe, brought to Canada in ballast water on cargo ships, clogging drain pipes, damaging boats, eating large amounts of plankton, and growing on native mussels, suffocating them; among numerous other examples.

    A common trend among almost all invasive species is the role humans play. We humans have spread from our corner in Africa to the entirety of the globe. Today, we can travel anywhere in the world in just a few hours or days via airplane. We ship products across the world through the global trade system. With us, we bring plants and animals--invasive species waiting to be unleashed. Sometimes on purpose, as pets or ways of controlling other invasive species. Sometimes by accident, since invasive species can hitch a ride in just about anything: food, water, wood, or even clothes.

    But this doesn't have to be the case. We can take measures to stop the spread of invasive species, and to control them once they arrive in an area.

Things you can do to stop the spread of invasive species and help your local ecosystem thrive include:

• Leave firewood, food, and plants at home when you travel. These can harbour invasive species.
• Learn about invasive species in your area and what you can do to help control their population.
• Don't grow invasive species in your garden (many of them are common flowers).
• Plant native species in your garden instead and care for them.
• Wash your boat and boots before boating in a new waterway or hiking on a new trail.

If we all do our part, our ecosystems can thrive.

Have any invasive species affected the place you live? Let me know in the comments!