Scientists Find Close Relatives Drive Island Plants Extinct

A new study published in Biological Conservation shows that invasive plant species are more likely to drive island plants extinct if they are closely related. Robin Pouteau and colleagues from France, Germany, and China analyzed over 1400 pairs of native and invasive plant species. They found native island plants threatened by phylogenetically similar invasive relatives have a significantly higher risk of extinction.

The ecologists found that native island plants are more at risk of extinction when threatened by closely related invasive plant species, likely due to similar traits and competition for resources. The relationship between phylogenetic distance and extinction risk was strongest on remote oceanic islands like Hawaii. More isolated islands tend to have lower native plant diversity and weaker competitive abilities. Phylogenetic relatedness could help predict the impacts of potential new invaders, especially on islands. It should be considered along with other factors in risk assessments.

This study provides new insights into the extinction crisis affecting island floras. Islands are hotspots of endemic biodiversity but are also highly vulnerable to invasive species. Over 85% of recorded plant extinctions due to invasive species have occurred on islands.

The researchers analyzed phylogenetic relationships between 1407 pairs of native and invasive plant species globally. Extinction risk data came from the IUCN Red List of Threatened Species. They also looked at population trends and geography.

The analysis showed phylogenetic distance is negatively related to extinction risk, but only on oceanic islands. Closely related invaders appear to pose a greater threat to native island species through resource competition. However, phylogenetic distance showed no significant relationship on continents or continental shelf islands.

This research could help guide conservation efforts by revealing a key predictor of impact. Preventing high-risk invaders from establishing could mitigate biodiversity declines on vulnerable islands. Prioritizing the management of invasive species already present based on phylogenetic relationships to native plants may also limit future extinctions. Pouteau and colleagues conclude:

This study is the first to document that native species co-occurring with close alien relatives are more likely to be threatened with global extinction, especially on oceanic islands. Since phylogenetic relatedness is associated with increased extinction risk in native species, this simple attribute could theoretically help predict potential impacts of alien species in conjunction with other attributes. This calls for integrating phylogenetic relatedness or at least for considering the presence of congeneric or confamilial native species in invasive species risk assessments. This could help to predict potential impacts of newly introduced alien species and to prioritize management efforts of already naturalized alien species.

Pouteau et al. 2023.

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Pouteau, R., van Kleunen, M. and Strasberg, D. (2023) “Closely related aliens lead to greater extinction risk,” Biological Conservation, 284(110148), p. 110148. Available at: https://doi.org/10.1016/j.biocon.2023.110148.