Can you predict a successful invasive species before it invades?

Specific characteristics can pre-adapt certain plant species to thrive outside of their native environments, according to Javier Galán Díaz and colleagues. The paper, recently published in the journal ‘NeoBiota‘, offers insights that may significantly enhance management practices and structure predictive models for preventing negative impacts from ‘invasive’ species. 

Not surprisingly, plant species with extensive native ranges and diverse climatic niches were more likely to establish successfully in foreign environments, effectively having had practice at adapting to new locales. But Galán Díaz and colleagues found that invasive species had other advantages.

Successful colonisation requires successful reproduction, which can often mean making new partnerships. Coloniser species displayed longer bloom periods, allowing them to be receptive to visitors at times that didn’t only match pollinator activity in their home ranges. They also had faster growth rates and remarkable resource acquisition compared to their counterpart native species in southern Spain. Species that transitioned from being merely colonisers to becoming invasive also displayed greater reproductive height and nitrogen use efficiency. 

The researchers built their findings on a comprehensive dataset, drawing occurrence data from the Global Biodiversity Information Facility (GBIF) and trait data from previous research. They applied this approach to 149 native species from southern Spain to better understand the invasion process. They compared frequency,

Spain is home to many herbaceous species that are naturalised in other Mediterranean-climate regions of the world (Casado et al. 2018). The origin of these introductions can be tracked down to the arrival of the first Europeans settlers into these territories where species were introduced deliberately (i.e. crops, ornamental plants) or accidentally (i.e. weeds introduced with livestock, fodder, wool or cereals) (Barry et al. 2006; Martín‐Forés 2017). These species (henceforth coloniser species) co-existed long-term with anthropogenic activities in their native range (Schlaepfer et al. 2010; MacDougall et al. 2018) and benefitted from an initial high propagule pressure. These coloniser species brought novel traits into the recipient communities, such as annual life cycles and efficient resource-use strategies, highly beneficial in a context of farming, intense herbivory, long drought periods and high soil disturbance (Seabloom et al. 2003; Funk and Vitousek 2007; HilleRisLambers et al. 2010; Molinari and D’Antonio 2014). Therefore, Spain communities constitute good candidates to apply the source-area approach.

Galán Díaz and colleagues found that in Southern Spain, species that invade new ecosystems – colonisers – are more common than those that do not. These colonisers also display greater diversity and richness in the conditions they can live in. Interestingly, these trends hold when examining Mediterranean habitats elsewhere. In these regions, species that have become established, or “naturalised”, are more common than non-colonisers. Both types of colonisers – invasive and naturalised – exhibit similar levels of climatic richness, but invasive species show a greater level of climatic diversity.

The botanists noticed some critical differences between coloniser and non-coloniser species regarding specific characteristics. These include leaf-to-root ratio, bloom period length, and the number of mechanisms for seed dispersal. For instance, the colonisers had larger leaves for their root length by around 17.6%. They also bloomed around a month longer than their non-coloniser counterparts and had more ways to scatter their seeds.

Grasses were particularly successful invaders. These rely more heavily on wind for pollination. More than half of these invaders can self-pollinate, which gives them an edge over the mere 15% of non-colonisers who can do the same. Evidently, being able to spread your seeds around more boosts a species’ colonising potential.

Using a kind of statistical analysis called ‘random forest modelling’, Galán Díaz and colleagues were able to predict whether a species is a non-coloniser or coloniser with an accuracy of over 73%. Variables, including climatic niche richness and the number of seed-dispersal mechanisms, were crucial to these predictions. However, including invasion stages reduced the model’s accuracy to just under 59%.

Galán Díaz and his team offer an in-depth understanding of the characteristics that make certain plant species more likely to survive and even thrive outside their natural habitats. They conclude: “The knowledge derived from such studies may allow us to improve prediction models, identifying key species to monitor; this could, therefore, prevent potential harmful impacts from coloniser species in invaded communities and reduce the investment necessary to target eradication measures.”

READ THE ARTICLE
Galán Díaz, J., de la Riva, E.G., Martín-Forés, I. and Vilà, M. (2023) “Which features at home make a plant prone to become invasive?,” NeoBiota, 86, pp. 1–20. Available at: https://doi.org/10.3897/neobiota.86.104039.