Traits determining invasion success in woody plants — the case of Proteaceae

A major aim of invasion ecology is to identify the characteristics that make invasive species successful, and this understanding is essential for the prevention of future invasions. In a paper published in the journal PLoSONE, C·I·B student, Desika Moodley, and colleagues Sjirk Geerts, David Richardson and John Wilson, looked at the characteristics of plants in the protea family, many of which are endemic to, and emblematic of, South Africa. This fascinating plant family has many taxa that have been widely distributed and grown by humans around the world, but few species are known to have become invasive.

The researchers categorised all members of the protea family globally as introduced, introduced, naturalized or invasive and then used statistical analyses to determine the factors that are important for determining their invasion status. They found that, as with many other plant groups, species that were widespread (i.e. with large native ranges) were more likely to be introduced, to naturalize, and to become invasive. Interestingly, species that had a naturally high resistance to Phytophthora, a root rot fungus, were more likely to become naturalised or invade successfully; on the other hand, species that were highly resistant to this pathogen posed a low invasion risk. This finding underlines the importance of diseases in the invasion process.

Flowers of a naturalized Hakea victoriae

Desika Moodley examining the flowers of a naturalized Hakea victoriae planted in the Western Cape, South Africa. This species was introduced for the cut flower industry, but its foliage was found to be undesirable as an ornamental, and the population was abandoned.

The research team also found that the purpose for which a species is planted influences its likelihood of invasion. For example, plants used as barriers or windbreaks are typically planted on the edges of farms and are more likely to spread into neighbouring natural vegetation. In addition, the plantís exposure to fire may result in increased opportunity to invade, as many of the plants in the protea family only release seeds in response to fires. Therefore, species that are usually planted in gardens are unlikely to invade because they are protected from fires.

This study highlights how invasion ecology can go a long way to providing accurate predictive risk assessments by understanding: 1) which traits are correlated with introduction, naturalization and invasion success; 2) what the mechanisms behind such correlations are; and 3) under which conditions invasions are favoured.

Read the paper:

Moodley D, Geerts S, Richardson DM & Wilson JRU (2013) Different traits determine introduction, naturalization and invasion success in woody plants: Proteaceae as a test case. PLoS ONE 8(9): e75078. doi:10.1371/journal.pone.0075078.

For more information contact, Desika Moodley.

Variables associated with Proteaceae invasions

Some of the most influential variables associated with Proteaceae invasions. These factors should be taken into consideration before allowing the introduction of new species: A) large native range size; B) small seed mass; C) species used as barrier plants adjacent to natural vegetation; and D) species that are tall in stature.