Image Credit: Ted, CC BY-SA 2.0, Image Cropped

Invader-pollinator paradox: Invasive goldenrods benefit from large-size pollinators (2021) Moroń, et al., Diversity and Distributions, https://doi.org/10.1111/ddi.13221

The Crux

A plant that invades a new part of the world can’t necessarily bring its regular pollinators along with it. So it stands to reason that plants who successfully invade a new area receives pollination from native pollinators. Seems pretty straightforward, right?

Except that even though this is the case, widespread establishment of invasive plants tends to lead to a loss in abundance of native pollinators. So how do the invasive plants still receive a healthy level of pollination, if they’re wiping out the locals?

It’s called the invader-pollinator paradox, and it’s what today’s authors wanted to investigate. They theorised that larger pollinators probably had a larger distribution range, and could successfully pollinate invasive plants even though their large range sizes meant they didn’t contribute to a small-scale increase in pollinator abundance.

What They Did

Goldenrods are species of the plant genus Solidago, and have invaded large parts of Europe and Asia, often found in huge patches. The researchers set up potted goldenrod plants (potted plants are easy to precisely survey) in 25 goldenrod-infested meadows in southern Poland. These potted plants were observed two to six times for 15-minute intervals over the space of a month, with the species of each visitor noted, as was the seed production of the plants. Average size of the visiting pollinators was then compared to the seed production of each plant, as well as the local coverage of goldenrods in the surrounding meadow.

Did You Know: Self Pollination

Some types of invasive plants don’t even need to bother with local pollinators. Many plants are capable of self-pollination (or selfing), and will turn to this option when pollinators or nearby plants of the same species are in short supply. While this option does have its perks, it also comes at the cost of severely reducing genetic variation within a population. This can make a plant more vulnerable to future disturbances, but it might be worth it in the short-term.

What They Found

As the site’s goldenrod cover increased, the species richness among pollinators decreased markedly, even though the number of visits to each plant didn’t change, confirming the invader-pollinator paradox. Confirming the researchers’ theory, with increasing goldenrod coverage, the body size of pollinators increased, as did plant seed production!

Problems

Obviously confirming a trend for one species doesn’t solve the whole question of the invader-pollinator paradox. However the simplicity of this experiment means it’s easily scaled to more species. There’s also the question of causality. The links between the various trends on display here need a bit more fleshing out in the future.

So What?

This is a really well-designed experiment, not only providing a great example of the paradox in question, but a great theoretical underpinning for why it occures.

More importantly though, it investigates some of the underlying causes for the persistence of some pollinator species over others in the face of invasive species. It’s another link in the food web explained, and can help us predict what will happen not only to smaller native pollinators, but to the species that rely on them.

Dr. Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology and still thinks that botanists are just ecologists who are too lazy to run after animals. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.