Breaking the rules is good for survival

Invasive species have been likened to bullies, leaving an ecological path of destruction in their wake.

Now researchers have discovered that these plants break all the rules once they’ve left their native environment, adapting and thriving in a way that contradicts ecological laws.

This sheds light on how to arrest unwanted species and help others adapt to harsh conditions wrought by climate change, according to a paper published in the journal PNAS.

“Species extinction has become an urgent issue with the escalating climate crisis,” says lead author Annabel Smith from the University of Queensland, Australia. 

“But scientists still know surprisingly little about how plants will adapt to the drastic changes we’re witnessing.”

Decades of field research has established certain “rules of ecology” that explain how plants foster genetic diversity, which helps them adapt to environmental changes.

One theory rests on demographics – small populations tend to have little genetic diversity while large populations that have lots of seeds and produce many offspring have higher genetic diversity.

On the other hand, gene flow from dispersal between populations can reduce diversity. However, the relative contributions of these factors are unclear.

To explore this, Smith and colleagues – a global team of nearly 50 ecologists – set up 53 monitoring sites in 21 countries to study the plantain (Plantago lanceolate), a plant that grows in an extensive range of environments including its native European habitat.

They tagged thousands of individual plants, tracked which plants died, which had new seedlings and, by counting flowers and seeds, how much reproduction had occurred.

DNA analysis enabled them to determine how many individual plants were historically introduced into countries outside Europe.

In the plants’ native habitat, the researchers found that the environment determined their degree of genetic diversity, but in new environments they adapted better than most other plants.

“We were a bit shocked to find that the ‘rules of ecology’ didn’t seem to apply to this species,” says Smith. “We didn’t see large populations with many seeds having higher genetic diversity.”

What they did find was that through multiple, ongoing introductions into Australia, New Zealand, North America, Japan and South Africa, the plants developed higher genetic diversity than their relatives back home – regardless of their environment.

“This gave them a greater capacity for adaptation.”

The findings suggest that invasive plants don’t need any particular environment to adapt, which could be time-consuming, but rather frequent movement of seeds and pollen.

“Simply mixing genetic stock from multiple populations is enough to provide an adaptive advantage and this is something that can happen quickly,” Smith says.

For native plants, it means that we can protect existing habitats or regenerate cleared or degraded habitats by facilitating transferral of seeds and pollen – especially areas that have suffered large-scale land clearing or bushfire damage.

“The mixing and movement of seeds has always been important for plants for adapting to new climates, but this is now critical.”

As far as invasive species go, which can cause extinction of native species and cost the government billions of dollars, the news is good – their spread can be curtailed by avoiding repeated introductions, even in areas where they already grow.