Scientists assess existing research on invasive species, identify key unknowns, and point toward what’s next in the management of this global crisis.

By: Dylan Meek

The term “invasive species” draws a general consensus when brought up amongst conservationists—namely, that they are a significant threat to biodiversity and ecosystem integrity. But why? To what extent do invasive species impact ecosystems, and what can we do about it?

Postdoctoral researchers Laure Gallien and Marta Carboni have taken on the task of answering these questions. Their work has culminated in the publication “The community ecology of invasive species: where are we and what’s next?” This paper presents a thorough summary of invasive species community ecology. By examining existing publications, the researchers identified potentially helpful areas of research that would further knowledge of invasive species impacts and management.

Although gaps remain in our understandings of invasive species community ecology, on one point we have unwavering certainty: invasive species are, by definition, harmful. Once an invasive species is using limited resources that originally supported a native species, ecological damage and even the risk of native species extinctions is at hand.

Findings to date

Are some species more likely to be invasive than others?

An introduced species becomes invasive when they negatively impact the native species. A successful invasion depends on many variables, such as environmental factors, the time period of introduction, and the resilience of the native biological community. Consistent findings across scientific studies indicate that invasions are nuanced and fall along a spectrum of ecological damage. Some data support the notion that the more similar an introduced species is to a native species, the more likely it is to become invasive, as it will be drawing from the same niche resources.

Are some environments better equipped to resist invasive species than others?

How can native biological communities defend themselves against invasive species? A diverse biological community contains many different types of species. These species occupy a variety of niches, which means they all use different resources. By definition, no two species can occupy the same niche. So the more species there are, the more resources are being used–without overlap.

This also means that fewer resources are available for an invasive species to exploit. Native communities with increased biodiversity are therefore more resistant to invasion.

Is it possible for native and introduced species to coexist?

Coexistence is more likely to occur when an introduced species is very different from the native species. In other words, if the introduced species occupies different space on the food chain, it need not compete with a similar native species; both can thrive on their own accord. In the event of a native species and an introduced species coexisting, the introduced species would be called “non-native.” In order for an introduced species to be deemed invasive, they have to negatively impact the native species.

Areas in Need of Research

Does the likelihood of invasion change with different life stages of a species?

There is a general understanding of the processes that promote a successful invasion of a species, however there is hardly any research exploring variation of these processes during different life stages of the invasive species. For instance, certain species may only be considered a threat if they are introduced to an environment as a juvenile.

Does the likelihood of invasion change in different environments?

Field observations suggest that invasion success increases when the invasion aligns with certain environmental events, such as drastic environmental disturbances. Research that examines the variation in processes that promote invasion in different environmental conditions have produced varied or contradictory results. Therefore, this area of study requires more data, and more in-depth research. Although scientists can agree on some general trends, more conclusive data is required.

How can knowledge about native species relationships be integrated with native/invasive species relationships?

Many scientists have studied the processes that determine coexistence between species in the native environment. But are these the same processes that determine coexistence between native and introduced species? For the most part, these two concepts have been studied separately, and never integrated.

Do invasive species change their behaviors in new environments?

Another potential area for research involves figuring out whether invasive species somehow change their behavior in the non-native environment. If so, does the altered behavior promote or inhibit invasion success? This area of study has not frequently been addressed, so very little is known.

That we don’t currently understand everything about invasive species does not mean that all hope is lost. These unknowns of community ecology are the products of high standards from the scientific community. In any field, the more evidence is available to support a claim, the stronger the argument. A question may remain unanswered indefinitely until more data is collected.

The Future 

Outstanding questions:

• Is there an age that correlates with invasion?
• Are there any instances of mutualism, where both the native and introduced species benefit from the others existence?
• What types of interactions are there between an invasive species and other species on different levels of the food chain (and not just the native species that sustains the most damage from the invasive species).

By clarifying what we already know about invasive species community ecology and identifying areas in need of more research, Gallien and Carboni’s paper confirms that future research will only benefit our understanding of invasive species. This bodes well for the future of invasive species removal, control, and prevention, and promises to propel us forward in the race against extinction.

Featured photo: Desecheo Anole. Credit: Island Conservation
Source: Wiley Online Library