Since the surgeon and obstetrician Ignas Semmelweis proposed in 1847 systematic hand hygiene with a calcium hypochlorite solution as a method to prevent puerperal infections, throughout the history of science the proverbial saying ‘ prevention is better than cure ‘ ‘ has been taken as an application principle in many fields.
Currently, the phenomenon of invasive species is one of the main drivers of anthropogenic global change, and the greatest cause of biodiversity loss. Given these facts, the application of this principle in the context of invasive species is particularly necessary, both for ecological and economic reasons. It is proven that the most effective and least expensive way to manage impacts is prevention .
However, and given that many non-native species are deliberately introduced, there are a series of conflicting interests between the economic, aesthetic and cultural services provided by their cultivation and prevention, in such a way that drastic action is often unfeasible. total ban.
Actions against invasive species
In the management of invasive species, different strategies have been proposed depending on the stage of invasion in which they are found. If the invasion has not started, the priority would be prevention . Early detection and, when possible, eradication would be the optimal course of action when the population is already established but still manageable.
If the invasion is too advanced to achieve its eradication, control and containment is chosen. And when none of the above works, everything possible must be done to mitigate the environmental and socioeconomic impacts caused by biological invasions.
In any case, no mitigation, containment, control, or eradication will be necessary if the invasion is successfully prevented before it occurs. For effective prevention, it is necessary first to be able to predict which species may become invasive in a given place.
The three key factors in an invasion
An invasive species is not an invasive species everywhere, or all the time. In general, whether or not a species is invasive depends on three factors.
The first factor is related to the invasiveness of the species , that is, those traits that make it, or not, a species capable of rapidly dispersing, successfully competing and colonizing new territories. A plant like the pampas duster , capable of reproducing successfully both by rhizomes under the ground and by very small seeds that can be carried by the wind for miles, is much more invasive than the mango tree, with large fruits. and that, in Spain, depends on the constant care of the human being.
A second factor has to do with the invasibility of the ecosystem , that is, the susceptibility of being invaded by the new environment. A species adapted to humid climates, it will easily invade an environment such as the banks of the Bilbao estuary, but it will have serious difficulties in the Tabernas desert; and, on the contrary, a plant adapted to arid climates, such as the prickly pear, will be very successful in Almería, but very little in Vizcaya.
Finally, the third factor is the history of the introduction, represented above all by the pressure of the propagules , that is, the number of individuals that are introduced into an ecosystem. A potentially invasive species may never invade a place because it is never introduced or is introduced so anecdotally and punctually that it fails to form a stable reproductive population —what is called “naturalization”. However, if it is massively introduced at a given time, the pressure of the propagules in the environment can cross the invasion threshold and become a problem in a few years.
Something like this happened in the past with the carp in the Spanish rivers; it was first introduced in 1580 , but remained in small isolated populations until the 1950s, when its massive introduction for fishing caused the invasion event. Today it is one of the most abundant invasive species in the Spanish basins.
predicting the invasion
Knowing this type of data, predictive systems can be established that allow knowing if a species that has not yet settled in an ecosystem is potentially invasive or not for that place.
Therefore, among the risk analyzes developed in recent decades, factors that have to do with the traits of the species and the susceptibility of ecosystems are included. Among others, that the species has an invasive behavior in other places, that it is tolerant to the climate, or that it presents impacts on the environment or human activities where it settles.
Thoroughly analyzing large listings is complex; For this reason, simple and rapid risk analyzes are used to prioritize species according to their risk of invasion. This risk analysis is called ” horizon scanning “, and allows a series of lists to be made that group the species according to the factors that favor invasion, remember, the invasiveness of the species —the traits that make it invasive— and the invasibility of the ecosystem —its susceptibility—. With this, the probability of invasion and of causing impacts of each species is obtained.
Regarding the pressure of propagules , and given that most species of invasive animals and plants enter as pets or ornamental plants, a system has recently been proposed that includes a value in the risk analysis that allows approximating the interest of people for a certain species . Species that people are more interested in tend to be more consumed, and that leads to more pressure from propagules, thus favoring invasion.
This novel system allows researchers to establish a more objective order of priority in the lists , so that managers and administrations act, with maximum speed, on those species of greater invasiveness, in the environment with greater invasibility, and present a greater potential propagule pressure.
Bayón, Á. et al. 2019. Horizon scanning to identify invasion risk of ornamental plants marketed in Spain. NeoBiota, 52, 47-86. DOI: 10.3897/neobiota.52.38113
Blackburn, T. M. et al. 2011. A proposed unified framework for biological invasions. Trends in ecology & evolution, 26(7), 333-339. DOI: 10.1016/j.tree.2011.03.023
Clavero, M. 2022. The King’s aquatic desires: 16th‐century fish and crayfish introductions into Spain. Fish and Fisheries, faf.12680. DOI: 10.1111/faf.12680
Pyšek, P. et al. 2010. Invasive Species, Environmental Change and Management, and Health. Annual Review of Environment and Resources, 35(1), 25-55. DOI: 10.1146/annurev-environ-033009-095548
Robertson, P. A. et al. 2020. A proposed unified framework to describe the management of biological invasions. Biological Invasions, 22(9), 2633-2645. DOI: 10.1007/s10530-020-02298-2