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The removal of invasive rodents from a small island off the coast of New South Wales in Australia has triggered a rebound of invertebrate life. Researchers from the University of Sydney and collaborators have documented sharp increases in the abundance of insects and other small animals that underpin the island’s ecosystem.
The study, co-led by NSW Department of Climate Change, Energy, the Environment and Water and PhD candidate Maxim Adams from the Molecular Ecology, Evolution and Phylogenomics (MEEP) laboratory examined how invertebrate communities changed after the island-wide eradication of black rats and house mice in 2019.
The research found total invertebrate abundance increased significantly following the eradication program, particularly among larger-bodied species that are more vulnerable to rodent predation.
Taxonomic orders showing especially strong increases included bush cockroaches and woodlice, while overall invertebrate communities also shifted in composition.
The findings, according to a statement by the University of Sydney, add to a growing body of evidence showing ecological recovery on Lord Howe Island following what was the world’s largest rodent eradication on an inhabited island. Previous research has documented strong recovery among seabirds and native land birds.
This new study is the first to comprehensively examine the response of the island’s invertebrates. It is published in the journal Biological Invasions.
“Invertebrates are easy to overlook, but they are absolutely fundamental to how ecosystems function,” Adams said.
“They pollinate plants, recycle nutrients, break down organic matter and provide food for birds, reptiles and other native animals. Without healthy invertebrate communities, the broader ecosystem can’t fully recover.”
The team collected more than 24,000 invertebrate specimens from 20 forest sites across the island, comparing samples taken before the eradication program in 2016-17 with samples collected in 2023-24.
The strongest increases were observed among larger invertebrates — those more than 13 millimetres long — consistent with the idea that rats and mice had been heavily suppressing these animals through predation for more than a century.
“We found dramatic increases in larger invertebrates, which is exactly what you would expect if invasive rodents had been preying on them,” Adams said.
“That matters because these animals are also an important food source for native predators including geckos and insect-eating birds.”
The researchers say the recovery of invertebrates may already be helping fuel rebounds in native wildlife populations. Earlier monitoring on the island found strong increases in species including the Lord Howe woodhen following rodent eradication.
Nathan Lo, who leads the MEEP laboratory, said the findings demonstrate how deeply invasive rodents can alter island ecosystems.
“Rodents didn’t just affect a few iconic species, they reshaped ecological relationships across the island,” Lo said. “What we’re seeing now is evidence of an ecosystem beginning to reorganise itself after that pressure was removed.”
The researchers caution that ecosystem recovery is complex and ongoing. While total abundance increased, diversity patterns were mixed, with some groups increasing while others declined. Seasonal variation also remained strong.
The study could not completely rule out the influence of other environmental factors between the two sampling periods, including climatic variation and habitat changes. The researchers also note that their sampling focused on ground and lower-tree-dwelling invertebrates rather than canopy or aquatic species.
“This is not a story of ecosystems instantly snapping back to some untouched historical state,” Professor Lo said.
“Recovery after invasive species removal can take years or decades, and ecosystems may settle into entirely new configurations.”
Future research will use genetic analyses to determine which native and introduced species are increasing following the eradication, and whether ecological changes differ between feeding groups or habitats. The team also hopes to investigate longer-term impacts on soil nutrients and decomposition processes, which are heavily influenced by invertebrates.
Adams said the study also highlights the importance of including invertebrates in conservation monitoring programs.
“Invertebrates make up most of the biodiversity in many ecosystems, but they’re often omitted because they’re difficult and time-consuming to study,” he said.
“This work shows that even relatively simple monitoring approaches can reveal ecological changes after conservation interventions.”
The research was conducted by scientists from the University of Sydney, Gadfly Ecological Services, Æstrelata Restorations, the NSW Department of Climate Change, Energy, the Environment and Water, and The Lord Howe Island Board.
