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Smaller islands offer crucial refuge for endangered mammals in Wallacea, Indonesia

A new study in the Proceedings of the National Academy of Sciences reveals that smaller islands within the Wallacea biodiversity hotspot are crucial refuges for endangered vertebrates, providing higher-quality habitats and supporting populations. These findings challenge conventional conservation approaches and emphasize the importance of prioritizing habitat management on these smaller landmasses.

The research, led by scientists from Queen Mary University of London and the Ludwig Maximilian University Munich, investigated the genetic health of anoa and babirusa populations across islands of varying sizes in Wallacea.

Wallacea, an archipelago in Indonesia, is renowned for its exceptional biodiversity and high rates of endemism. However, it is also a region experiencing rapid development, leading to significant habitat degradation on larger islands like Sulawesi. While small island populations have historically been considered more vulnerable to extinction over geological timescales, this study uncovers a surprising advantage.

Using genomic data from 113 individuals sampled across multiple islands, the team discovered that animals on smaller, less disturbed islands had lower overall genetic diversity but also carried significantly fewer harmful mutations. In contrast, populations on the larger island of Sulawesi, where habitat loss and human activity are more intense, showed high levels of inbreeding and more damaging genetic variation.

"What the genomic data of the anoa and babirusa uncovered is that small islands have huge potential to act as refugia for many other species living there with similar evolutionary history. Of course, as long as their habitat remains intact. They are still vulnerable as they do not have many mating choices or even space to live in already," says Dr. Sabhrina Gita Aninta, who co-led the study.

"Thus, small islands should not be placed on the back burner of national development programs. Monitoring their present and future genetic diversity is crucial to ensure they are still on track to long-term existence.

"This study was a true testament to remote collaboration, largely conducted during the pandemic," continues Dr. Aninta. "It was incredibly rewarding to build upon decades of foundational work from earlier studies, connecting with senior researchers who were thrilled to see their data, some dating back to the 2000s, yield new insights with modern genomic technologies."

"Large vertebrate populations on small islands are often seen as at risk," says Professor Laurent Frantz from Queen Mary University of London and LMU Munich. "But protecting small islands is often easier—in fact, our study shows they can serve as great refuges for endangered species."

"Habitat quality on the smaller islands was higher than on the larger island of Sulawesi, and these areas were generally well protected. In the Togean Islands, for instance, much of the land is encompassed within a large national park. For the long-term preservation of these species on the small islands, it is important to ensure continued protection of these habitats alongside population monitoring," says Dr. Rosie Drinkwater, a postdoctoral researcher from Queen Mary University of London and LMU Munich.

The study cautions against the widespread use of genetic rescue in island ecosystems without careful consideration of local evolutionary history. Instead, the authors argue for a greater focus on protecting the high-quality habitats of small islands, which may serve as natural genetic sanctuaries in the Anthropocene.