What the researchers found
Across the islands studied, non-native animals now make up 44 percent of seed-dispersing communities, while 23 percent of original frugivores have been lost to extinction. This turnover has reduced the presence of native large-gaped flying dispersers such as pigeons, doves, and bats and increased the presence of non-native terrestrial omnivores such as pigs and rats.
The shift limits the ability of island plants with large seeds to spread successfully. The researchers reported an average 7.9-millimeter decrease in the maximum gape size of effective seed dispersers, which narrows which seeds can be swallowed whole and transported. Over time, this could mean fewer native plants are able to regenerate.
Global lessons with local relevance
Islands provide an early-warning system for what could happen elsewhere, according to Rogers.
“Islands are small, and changes happen faster,” she said. “They can give us a glimpse of what might be ahead for mainland forests, including here in Virginia, where bird populations are in decline and seed dispersal is also shifting.”
The findings also complicate how conservationists think about introduced species. While some non-native species can take on parts of the role once held by extinct animals, many others disrupt seed dispersal instead of supporting it. Understanding which species help and which harm is important for developing better management strategies.
Virginia Tech’s impact
By contributing Mariana Islands data, Rogers ensured that the Pacific’s most extreme case of seed disperser loss was included in the global analysis. Her work reflects the college’s strength in connecting local ecological research to international collaborations.
“Bringing together data from 120 islands helps us see the bigger picture,” Rogers said. “It shows that changes in seed dispersal are happening worldwide, and that we need to understand them if we want to protect forests into the future.”
Rogers said the study’s findings will be integrated into her courses at Virginia Tech, giving students a real-time look at how large international collaborations come together. By working through global datasets, students can see how ecological questions are answered at different scales, from individual islands to worldwide patterns.
She also said the research offers lessons in critical thinking about conservation.
“This is a chance for students to see how science informs management decisions,” Haldre said. “We can talk about why extinctions matter, but also why species introductions change ecosystems in ways we might not expect.”