Biodiversity Drops In Areas Dominated By Non-Native Plants

Some species can adapt to change but others are slightly less resilient. Some insects, it seems, are among the latter category and as non-native plants invade global herbivore communities, insect diversity is beginning to decline. According to a University of Delaware (UD) study, that partly because humans make decisions on which plants to grow in their gardens. 

To test this theory, researchers planted various native and non-native tree species within a controlled garden. Some were fairly similar to one another, while others were non-native. After observing species living among these plants over a three-year period, researchers found that the distantly related trees housed fewer diverse herbivores, and – when moving from one non-native tree species to another – the same was true of insects.

"You get this compounding effect where you have a lower diversity of herbivores per tree, but then you also are getting more similar species as you move between trees species and among sites, so you end up with even less diverse communities than you would expect," Karin Burghardt, a UD alumna and one of the researchers of the study, said in a news release. "There is this group of species of non-natives that do not have any close native relatives at all. These non-natives support more generalized and redundant herbivore communities than the native plants that they're potentially replacing on landscapes."

This habitat change is especially devastating for young herbivores, which act as a good indicator of how plants are supporting the local ecosystem.

"The relationship between the adult and food is far weaker than the relationship between immatures and food, so when you find adults on the non-natives, it doesn't mean that much. When you find immatures, that's what you should be measuring," Doug Tallamy, a professor of entomology in the UD's College of Agriculture and Natural Resources, said in the release. "Those are the plants that are creating those immatures and so we do get significant differences between the immatures that are using native plants versus the immatures using non-natives."

Native plants generally support herbivore communities better on a per tree basis in comparison to the non-native counterparts, the researchers noted. Overall, this study sheds light on how homeowners may be affecting local insects in deciding which plants to grow.

"If you think about it, you're driving around the suburban environment, and every time a new development goes in, you have a lot of decision making happening as to what plant species are going to be planted around those properties," Burghardt explained in a statement. "If we do all that landscaping with non-native plants, are we limiting the wildlife and conservation support system that could be available within that given plot of land? What the gardens we constructed for the study are trying to replicate are landscaping decisions that people might make if they wanted to support native insect communities that in turn support much of the diversity around us."

The study was recently published in Ecology Letters. 

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