Bats shield younger bushes from insect injury, with thrice fewer bugs

Photo Credit: CC0 Public Domain

Bats help forests grow. Without bats to keep their populations in check, insects eating tree saplings become rampant, causing three to nine times more damage than when bats are present. That’s according to a new study from the University of Illinois. The article “Bats reduce insect density and defoliation in temperate forests: a rule-out experiment” is published in Ecology.

“A lot of people associate bats with caves. But as it turns out, the habitat you could really associate with almost every species of bat in North America is forest. And that applies worldwide. Forests are just really important to bats,” says Joy O’Keefe, co-author of the study and an assistant professor and wildlife extension specialist in Illinois’ Department of Natural Resources and Environmental Sciences. “We wanted to ask the question: are bats important for forests? And in this study, we have shown that they are.”

Other researchers have demonstrated the insect control services of bats in crop fields and tropical forest systems, but no one has yet demonstrated their benefits in temperate forests.

“It is particularly important for us to learn how bats affect forests, as bats are declining due to diseases such as white-nose syndrome or collisions with wind turbines. This type of work can reveal the long-term consequences of bat decline,” says Elizabeth Beilke, postdoctoral researcher and lead author of the study.

The research team built giant mesh-enclosed structures in an Indiana forest to exclude the eight bat species that frequent the area, including two federally threatened or endangered species. The mesh openings were large enough to allow insects to move freely, but not flying bats. For three summers, Beilke opened and closed the net sides and tops of the structures every morning and evening to ensure birds had daytime access to the plots. That way she could be sure she was isolating the effects of bats.

Beilke then measured the number of insects on oak and hickory seedlings in the forest undergrowth, as well as the amount of defoliation per seedling. Since she set up just as many box frames without bars, Beilke was able to compare insect densities and defoliation with and without bats.

Overall, the researchers found three times as many insects and five times more defoliation on the seedlings when bats were excluded than in control plots, which allowed bats every night. When analyzed separately, oak trees without bats experienced nine times more defoliation and hickories three times more.

“We know from other research that oaks and hickories are ecologically important because acorns and hickories are food sources for wildlife and the trees serve as hosts for native insects. Bats use both oaks and hickories for roosting, and now we see that they might be using them as a source of prey insects as well. Our data suggest that bats and oaks have a mutually beneficial relationship,” says Beilke.

While insect pressure was intense in plots without bat predation, the seedlings did not succumb to their injuries. But the researchers say a long-term decline in bats could prove deadly for the baby trees.

“We have observed sublethal levels of defoliation, but we know that defoliation makes seedlings more susceptible to death from other factors such as drought or fungal diseases. It would be difficult to trace the fate of these trees over 90 years, but I think a natural next step is to examine the effects of sustained low defoliation on these seedlings,” says Beilke. “To what extent does repeated defoliation reduce their competitiveness and contribute to oak decline at?”

The researchers point out that birds, many of which share the same insect diet as bats, are also declining. While specifically trying to isolate the effects of bats on forest trees, the researchers are confident that insect densities and defoliation rates would have been higher if they had excluded both birds and bats from their study. In fact, similar exclusion studies that focused on birds did not include bats in their study designs, so the mesh pens remained open all night.

“When we initially worked on the proposal for this research, we looked at 37 different bird exclusion studies in agricultural and forestry systems. We found that almost everyone made this mistake. Most of them had not opened their treatment plots or removed them to bats,” says Beilke.

In other words, prior to Beilke’s study, at least some credit was given to the birds for the work that bats did in the shade.

Apparently, both types of winged predators are important to forest health in temperate climates. And according to O’Keefe, that makes these studies even more important to forestry.

“I think it’s important to emphasize the value of doing this kind of experimental work with bats, to really try to find out in a conscious way what their ecosystem services are. While we can probably extrapolate and say that bats are important in other forest species, I wouldn’t discount the value of the same work in other systems, especially if there are questions about specific insect or tree species and how bats affect them Try to figure out like bats use plants,” she says. “And before they’re gone, hopefully.”

More information:
Elizabeth A. Beilke et al., Bats Reduce Insect Density and Defoliation in Temperate Forests: A Rule-Out Experiment, Ecology (2022). DOI: 10.1002/ecy.3903

Provided by the University of Illinois at Urbana-Champaign

Citation: Bats protect young trees from insect damage, with three times fewer bugs (2022, November 1) Retrieved November 9, 2022 from https://phys.org/news/2022-11-young-trees-insect-bugs.html

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