Invasive Species: How Concerned Should We Be?

The climate crisis and invasive species are often studied as two independent threats to global biodiversity. However, analyzing the relationships and feedback loops between them creates a more complete picture of how Earth’s natural systems are being changed and shaped by anthropogenic forces. — An invasive species is defined as a population of species that have become established, permanent residents, in an environment that is not their native one, causing ecological and economic harm. Species very rarely “invade” by themselves and are usually introduced by humans, often by accident. While it is true that only a small minority – roughly 10% – of introduced (non-native) species survive in a new ecosystem, and only about 10% of those that do establish go on to become truly invasive, the economic toll is staggering. According to the World Economic Forum, the economic costs of invasive species now total at least $423 billion every year, with the alien invaders playing a key role in 60% of recorded plant and animal extinctions. But the impacts of invasive species are more widespread than that. One of the most studied cases of a singular invasive species and its impacts is the brown tree snake (Boiga irregularis) in Guam. It was most likely introduced by military traffic in the 1950s following World War II. By 1968, it was widespread across the island and has since resulted in the extinction of 10 native forest bird species. The impacts of this extinction, in turn, have been significant, affecting native invertebrates and pollinators and leading to a decline in native plant species. From a social perspective, the fear of snake bites must be considered alongside the loss of productivity resulting from multiple power-outages, as snakes interrupt power lines. At the time of writing, the brown tree snake population on the island is declining. This is suspected to be the result of the population of thee snakes on Guam exceeding the carrying capacity (the maximum population size of the species that the environment can sustain indefinitely), meaning the population is not stable. In addition to this, a study published in the Biological Conservation Journal in 2005 suggested that the stress of overcrowding and competition for food resources limits reproductive ability. Even with this developed understanding, it is still unclear whether this will result in the stabilization of the population or if it could create an opportunity for Guam’s naturally existing predator populations to recover, even temporarily. From an economic perspective, Guam’s brown tree snake research and management efforts are costing the nation US$7 million annually. You might also like: 50% of Earth’s Land Surface Remains Relatively Untouched By Humans The Threat to Our Oceans This crisis is not limited to terrestrial biodiversity. While increased global mobility has historically driven the establishment of introduced species on land, the link between the climate crisis and the spread of invasive species is becoming most apparent in aquatic environments. Warming oceans allow marine species to establish migration corridors across water bodies that were previously too cold for them to survive. If a marine ecosystem is vulnerable to a new predator and the majority of its resident species are specialists (adapted to a strict, highly specific environmental niche), the ecological consequences can be catastrophic. For example, recent years have seen a pronounced expansion of invasive, warmth-loving (thermophilic) species into the central and western basins of the Mediterranean Sea. This expansion has been heavily accelerated by human-made shipping channels, most notably the Suez Canal. Future of Invasive Species The uncertainties of the climate crisis leave many questions open regarding the future of invasive species and whether predicted “invasive hotspots” – areas highly vulnerable to colonization – will fully materialize. Conversely, it is also possible that a warmer climate might eradicate certain existing invasive species, particularly in isolated locations where they are unable to migrate to more favorable climates. As climate-driven species migration accelerates, questions have been raised concerning the very classification of an “invasive” species. If a native species naturally shifts its range poleward or to higher altitudes where it was previously absent, should it be considered invasive? The current scientific consensus is that these expanding species are still considered native unless they cause discernible, disruptive damage to their new environment – either by upending seasonal ecosystem patterns or by entirely displacing the pre-existing species that occupy those local ecological niches. This article was originally publsihed on August 27, 2020.