We often talk about the differences between native and non-native species.
On the surface, it seems pretty simple: a native species occurs in an area naturally, while a non-native species was introduced, typically through human movement or trade.
But… what does it mean for a species to occur ‘naturally’? Does it mean that this species has been here for 100 years? 500 years? Or since the beginning of time?
Horsetail is a native species in BC (Photo credit: gwhetham, iNaturalist)
For example, horsetail is a native species in BC, and its existence dates back to at least 300 million years. During the late Devonian (~416 – 359 million years ago) and Carboniferous periods (~359 – 299 million years ago), large horsetail trees, called Calamites, grew 18 m tall, creating a dense, forested landscape. As the climate changed, these plants shrunk to appear as they do today. But not all native species are this ancient… right?
In reality, the line between native and non-native species can get blurry.
Defining ‘native species’
Some people believe the way a species arrives to a new area affects whether it is considered native or non-native.
One common suggestion for defining native and non-native species is to use the year 1500 as the cut-off. Species that were present in an area before the 1500s are considered native, while species arriving after the 1500s are considered non-native. While it may seem arbitrary, the 1500s mark the beginning of settler trade and exploration in North America, along with an increase in mass human movement globally. This has led to a lot of accidental and deliberate movement of species.
Scotch broom is an invasive species that originated from Scotland.
Scotch broom is a notable species that arrived in North America because of settlers. It was brought over from Scotland in the 1850’s as a garden ornamental and planted on Vancouver island by Captain Walter Grant. Amazingly, story has it that Captain Grant only brought over 3 Scotch broom seeds and since then, the plant has managed to spread rapidly across BC.
But.. what if species were moved around before the 1500s?
Another suggestion is to use the last ice age as the cut-off for distinguishing native and non-native species. This demarcation takes into account any movement that would have occurred in the last several thousand years and also considers that species naturally spread, especially in response to climate changes and geographic barriers. Under this definition, a species could still be considered non-native even if it arrived through natural processes, such as post-glacial movement.
What are ‘naturalized’ species?
Some non-native species don’t have negative impacts and can integrate into the new environment. These species are called naturalized – they have established self-sustaining populations and have ecological interactions with local species.
Honey bees are considered naturalized in North America (Photo credit: Joseph Berger, Bugwood.org)
A good example is the honey bee (Apis mellifera), which is originally from Africa, Europe and Asia. It arrived in North America about 500 years ago, and although it’s non-native, it has become an important part of our ecosystems, especially for its role in pollination. It does not cause harm and instead contributes valuable ecological services.
Why does it matter?
While there is no clear consensus on how we should define a native species, recognizing when and where a species originated from can help us better understand the intricate connections between flora and fauna that make up our ecosystems. Whether a species is native, non-native, or naturalized, recognizing its role can help us in preserving biodiversity and maintaining ecological balance.
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