CMU study suggests long-held belief about how rare species survive may not hold in fragmented habitats

Carnegie Mellon researchers report that negative frequency-dependent selection, a process thought to help rare species persist, can fail to maintain diversity when populations are separated; their models and analysis of bird data from Japan's Ryukyu Islands support this conclusion.

Researchers at Carnegie Mellon University's Ray and Stephanie Lane Computational Biology Department report that a classic ecological idea may not apply when habitats are fragmented. The idea, called negative frequency-dependent (NFD) selection, holds that rarer types gain an advantage that helps prevent any one type from dominating. The team used mathematical models and simulations, then compared results to a bird dataset from Japan's Ryukyu Islands. The paper appears in the Proceedings of the National Academy of Sciences. Key findings: - Negative frequency-dependent selection is the hypothesis that rarer species or variants gain a local advantage that helps maintain coexistence. - In mathematical models where populations are separated and do not mix freely, the local advantage associated with rarity can fail to translate across the whole system, and coexistence persisted longer in neutral (equal-treatment) scenarios than under NFD selection. - The result held when additional species were included in the models, indicating a broader pattern in the simulations. - Analysis of bird communities in the Ryukyu Islands showed NFD-like dynamics at individual islands but not consistently across the island cluster, matching model expectations. - The researchers note these findings are relevant to conservation planning (for example, habitat corridors) and to understanding clonal diversity in tumors, as reported in the study. Summary: The study challenges an assumption used to explain how rare species persist by showing that spatial structure and separation can change outcomes predicted by NFD selection. The work suggests that connectivity across landscapes affects whether rarity provides a lasting advantage, and the authors plan further research and tool development to explore how space influences biodiversity and related biological systems.