By Haley Depner
This is the first article in a four part series. The first article focuses on introducing the concept of invasive species. The remaining articles will look at case studies of invasive species in Maine.
Every year damage from invasive species costs the United States billions of dollars more than damage from all other natural disasters in the U.S. combined.
According to the Washington State Invasive Species Council, invasive species in the US impact nearly half of the species listed as threatened or endangered by the US Endangered Species Act.
But what is an invasive species and how do they cause problems? In order to fully understand the answer, we first need to have a little background in ecology.
Ecosystems are never static. The ranges where species inhabit have been altered, spread, and eliminated since the beginning of competitive life on Earth.
Natural disasters and shifting climate have always had influence on where lifeforms can spread and thrive. Natural disasters have the potential to wipe out local populations as well as sweep species into new territories that they had yet to colonize.
Fluctuating climate causes some lifeforms to migrate to more desirable ranges (if accessible) while prompting other species to shift the timing of their breeding or growing seasons.
When an organism is taken away from or a new organism is added to an ecosystem, the change may be felt throughout the system. Such changes could signal the end to some populations in a community and the introduction and proliferation of others. Whenever a population joins or leaves a community or shifts its life cycle according to a change in climate, there is potential for the ecosystem to be significantly altered.
The Pennsylvania State New Kingston University sums up the reasons for this nicely in an entry in their Virtual Nature Trail:
“A consequence of living is the sometimes subtle and sometimes overt alteration of one’s own environment. The original environment may have been optimal for the first species of plant or animal, but the newly altered environment is often optimal for some other species of plant or animal. Under the changed conditions of the environment, the previously dominant species may fail and another species may become ascendant.”
With that being said, it is not surprising when humans bring exotic species from far away places into new communities that the effects of the introduction may be felt throughout the ecosystem. Anthropogenic introduction of species occurs in a variety of ways and for an assortment of purposes. Domesticated and game species are brought to new ecosystems by people who rely on them as resources. Some species are brought in as a form of biological control for serving anthropogenic activities such as agriculture. Other species that are brought in are merely for decorative purposes, kept as pets, or are unintentionally introduced by hitchhiking their way into new ecosystems. All of these situations have the potential for the non-native species to find their way into the foreign ecosystem.
Non-native species can compete with, prey upon, and infect native species with parasites and/or diseases of which they have no immunity to. Executive Order 13112 defines a native species as “with respect to a particular ecosystem, a species that, other than as a result of an introduction, historically occurred or currently occurs in that ecosystem.”
A non-native or alien species, on the other hand, is defined by the order as “with respect to a particular ecosystem, any species, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem.”
If a non-native species has a significant ecological impact it is dubbed “invasive.” An invasive species, as defined by the Executive Order, is “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.”
The amount of impact inflicted by the non-native species on its new habitat depends on many factors. A good example of this is Oryctolagus cuniculus, a species of rabbit that, according to Flavia Schepmans of Columbia University, writing for the Invasive Species Summary Project , has spread from its original range in Europe to every continent except Asia and Antarctica, thanks to the aid of humans.
The spreading of this species began about a thousand years ago when Romans brought the mammal with them to Italy for food. According to researchers at the World Rabbit Science Association, today introduced populations of O. cuniculus in Italy are relied upon as a keystone species.
While the introduction of O. cuniculus worked out fine in Italy and select other regions, the same cannot be said for other environments that the rabbits have spread to. As Schepmans wrote:
“in Australia (and many small islands where it has been introduced), the rabbit, virtually unchecked by local predators, decimates plants, affects soil composition, and changes entire ecosystems. In Australia, the rabbit competes for food and shelter with native animals such as the wombat, the bilby, the burrowing bettong and the bandicoot, and therefore has contributed to the decline of these native species.”
Schepmans explains that this species has become particularly problematic in Australia largely due to its fitness and the lack of predators:
“The European rabbit is a highly adaptable animal. It is not a picky eater and breeds very fast. In Australia, the rabbit was particularly successful at spreading like wildfire because its natural predators from back home, the weasel and fox, were not originally present Down Under. The dingo and Tasmanian wolf, Australia’s native carnivores (and potential rabbit consumers), were themselves being kept in check by local sheep and cattle ranchers, so they were not effective at keeping the rabbit populations down. The rabbits’ spread was also aided by early hunters whose interest lay in having the animals spread so they could hunt more of them.”
The contrast between the outcomes of the introduction of O. cuniculus in different settings demonstrates that it is not just what species but where it is released that determines the amount of impact on local ecosystems. The same species exists as a thriving nonnative keystone species in Italy, while having detrimental effects in Australia.
According to the National Oceanic and Atmospheric Administration (NOAA), there are already approximately 50,000 exotic species known to be in the United States. Of these, the US Geological Survey reports that there are currently over 6,500 species that are considered invasive.
During their 2012 fiscal year, the Department of the Interior spent over $2 billion on the prevention and control of invasive species in the United States. This funded activities that help slow the spread and impact of invasive species in the United States through prevention, early detection and rapid response, control and management, research, habitat restoration, education and public awareness, and leadership and international cooperation.
This is a small investment compared to the almost $138 billion estimated by the NOAA to be lost every year due to the impacts of invasive species in the U.S.
Maine residents and companies lose millions every year because of invasive species. These species affect Maine residents by negatively impacting agricultural productivity, the productivity of fisheries, forest and other habitat growth and stability, decrease property values, and disfigure favored tourism and recreational destinations. This damage is caused by dozens of species of plants, invertebrates, fish, microorganisms, and fungus that have found their way into the state.
The age-old adage “an ounce of prevention is worth a pound of cure” may be cliché but is a truism nonetheless. The best way to fight invasive species is to not let them become established in the first place. This means taking measures to prevent introduction, such as keeping firewood within 30 miles of where it was collected, making sure boats are clean of any plants or animals before entering new waters, thoroughly inspecting vehicles for insect eggs when traveling out of state and selecting species for cultivation and biological control that are native to the area or support the ecosystem (for example, apples are not native to North America but are relied upon by many species as a food source). These measures do more to reduce damage caused by invasives than trying to rebalance ecosystems after the damage has occurred.
This is not to say that attempts to heal ecosystems affected by invasive species are not important. Clearing away invasive species and reintroducing native species can help an ecosystem reestablish its balance. Actions such as removing invasive plant species from your garden and replacing them with native plants help to reverse the damage.
According to Sarah Ogden, Program Coordinator at the Maine Wildlife Park in Grey, species are more likely to become invasive if, in the foreign habitat, they have no natural predators (or in the case of plants, have nothing consuming their plant matter), have a quick reproduction rate, and/or are a generalist species (species that are highly adaptable and capable of thriving in a variety of habitats).
This article is the first in a four part series on invasive species in Maine. Three more articles in this series will be published in this paper throughout the spring semester. These articles will look at case studies of three invasive species in Maine that students can easily play a role in their control and eradication. Each article will introduce a species, give its profile, discuss its history as to how it was introduced, explore the impacts it has on Maine’s ecosystems and the Maine economy and provide information as to how that species is spread and how it can be controlled.
The topic for the next article is the potentially invasive red-eared slider turtle (Trachemys scripta elegans) and will be coming out in the next few weeks. The two remaining articles will focus on wood-boring beetles and invasive plants you may find in your garden.