Comparison of adult census size and effective population size support the need for continued protection of two Solomon Island endemics

ABSTRACT

Because a population’s ability to respond to rapid change is dictated by standing genetic variation, we can better predict a population’s long-term viability by estimating and then comparing adult census size (N) and effective population size (N_e). However, most studies only measure N or N_e, which can be misleading. Using a combination of field and genomic sequence data, we here estimate and compare N and N_e in two range-restricted endemics of the Solomon Islands. Two Zosterops White-eye species inhabit the small island of Kolombangara, with a high elevation species endemic to the island (Z. murphyi) and a low elevation species endemic to the Solomon Islands (Z. kulambangrae). Field observations reveal large values of N for both species with Z. kulambangrae numbering at 114,781 ± 32,233 adults, and Z. murphyi numbering at 64,412 ± 15,324 adults. In contrast, genomic analyses reveal that N_e was much lower than N, with Z. kulambangrae estimated at 694.5 and Z. murphyi at 796.1 individuals. Further, positive Tajima’s D values for both species suggest that they have experienced a demographic contraction, providing a mechanism for low values of N_e. Comparison of N and N_e suggests that Z. kulambangrae and Z. murphyi are not at immediate threat of extinction but may be at genetic risk. Our results provide important baseline data for long-term monitoring of these island endemics, and argue for measuring both population size estimates to better gauge long-term population viability.

KEYWORDS:

• Zosterops
• conservation genetics
• effective population size
• census population size

Acknowledgements

We thank the Uy lab, William Searcy, and Darren Irwin for helpful comments on this manuscript. Jino Ghemu, many Kolombangara field rangers, and Wesley Sparagon helped with fieldwork. The Villages of the Iriri Corridor, David Boseto and Ecological Solutions Solomon Islands, the Solomon Islands Ministry of Environment, and KIBCA aided in logistics and permitting. We also thank the UW Biotechnology Center and the University of Rochester’s Center for Integrated Research Computing. SAC was supported by grants from the American Ornithological Society, the American Philosophical Society, the Society for Integrative and Comparative Biology, and the UM Kushlan, Evoy, and Savage Funds. BCW was supported by a NSF GRFP (11-44155) and the AMNH Chapman Fund. LP was supported by NIH grant GM133412 to NC. JACU was supported by UM’s Aresty Chair in Tropical Ecology.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

The GBS and field observation data that support the findings of this study are openly available in Dryad https://doi.org/10.5061/dryad.q573n5tht.

Supplemental data

Supplemental data for this article can be accessed here.