We are in Utah. It’s the late Tertiary period, two million years ago. Looking across the landscape, we see rolling mountains and valleys. Volcanic eruptions spew debris in the distance. Streams snake through the valleys joining a giant lake that stretches through current day Nevada, Idaho, and Utah. After the extinction of the dinosaurs, mammals diversified. Now camels, mastodons, horses, and ground sloths graze, while saber tooth cats and giant wolves stalk nearby.
Fast-forward 400,000 years. It’s the Pleistocene epoch. The Ice Age is in full swing. Mammoths invade North America from Asia and encounter Utah’s native flora and fauna. Over the next 1.5 million years, species compete and adapt as cycles of glaciation and deglaciation change landscapes and, with that, the requirements for survival.
Then, about 10,000 years ago, after Homo sapiens had arrived, the game changed (Utah Geological Survey). As the Ice Age came to a close, humans proliferated and dominated. By the end of the Pleistocene, there was a net loss of biodiversity as extinction claimed all the species mentioned above (Utah Geologic Survey). The invasion of humans and subsequent loss of species has occurred throughout the world (Boivin et al. 2016).
Barnacles are very common invasive species because they often attach to ship hulls and are transported to new locations. Their larvae then travel in ocean currents extending their reach.
Golden-fronted woodpecker (Melanerpes aurifrons) seen in Tikal, the ancient Maya site in Peten, northern Guatemala in April 2018. The species ranges from the United States down through Nicaragua.
The movement of species into new geographic areas is an expected consequence of changing climates and ecosystems.
A herd of gemsbok (Oryx gazella) is spotted in the distance trekking across the Etosha Salt Pan in Etosha National Park, Namibia.
The Concept of Invasive Species is Erroneous
Invasive species often cause biodiversity loss within a habitat. This statement introduces the topic in countless scientific papers, which often end with a call for management or eradication of said species. This is the prevailing view and bias: human activity has introduced countless invasive species that can threaten the integrity of ecosystems by eliciting changes within native communities. Therefore, we need to mitigate their impacts by focusing on prevention, management, and eradication.
The problem with this assessment is twofold. First, the definition of ‘invasive’ hinges on human involvement. An invasive species is not only non-native with the potential to cause harm, but also humanity must have played a role in its introduction (U.S. Department of Agriculture). Conversely, native species haven’t been introduced by humanity and don’t cause harm.
However, no landscape, seascape, or species has escaped the influence of humankind. Through agriculture, animal and plant domestication, and the destruction and creation of ecosystems, we have affected Earth’s climates and species distributions and extinctions (Boivin et al. 2016). According to those definitions either no species is native, and all are invasive — an absurd idea — or we need to rethink the invasive species concept. The definitions also assume humans are separate from the natural world and therefore, our interference with species’ distributions is unnatural.
Second, this view employs a short time span, creating the illusion that landscapes are, and should be, static. Any change to a habitat would then be obvious and considered detrimental, since we are looking at a single snapshot in history instead of watching the entire movie.
But our planet is in a constant state of physical and evolutionary flux. It’s naive to view the world as if frozen in time. The movement of species into new geographic areas is not only an expected consequence of changing climates and ecosystems within a broad evolutionary timescale, but those species are not inherently detrimental to native communities. Ultimately, it’s not realistic to control species’ movements. We need to reassess our view of invasive species.
