Predicted effects of landscape change, sea level rise, and habitat management on the extirpation risk of the Hawaiian common gallinule (Gallinula galeata sandvicensis) on the island of O'ahu.

Charles B Van Rees,J Michael Reed

doi:10.7717/peerj.4990

Abstract

We conducted a spatially explicit, stochastic, individually based population viability analysis for the Hawaiian common gallinule (Gallinula galeata sandvicensis), an endangered subspecies of waterbird endemic to fragmented coastal wetlands in Hawai‘i. This subspecies persists on two islands, with no apparent movement between them. We assessed extirpation risk for birds on O‘ahu, where the resident gallinule population is made up of several fragmented subpopulations. Data on genetic differentiation were used to delineate subpopulations and estimate dispersal rates between them. We used sensitivity analyses to gauge the impact of current uncertainty of vital rate parameters on population projections, to ascertain the relative importance of gallinule vital rates to population persistence, and to compare the efficacy of potential management strategies. We used available sea level rise projections to examine the relative vulnerability of O‘ahu’s gallinule population to habitat loss arising from this threat. Our model predicted persistence of the island’s gallinule population at 160 years (∼40 generations), but with high probabilities of extirpation for small subpopulations. Sensitivity analyses highlighted the importance of juvenile and adult mortality to population persistence in Hawaiian gallinules, justifying current predator control efforts and suggesting the need for additional research on chick and fledgling survival. Subpopulation connectivity from dispersal had little effect on the persistence of the island-wide population, but strong effects on the persistence of smaller subpopulations. Our model also predicted island-wide population persistence under predicted sea level rise scenarios, but with O‘ahu’s largest gallinule populations losing >40% of current carrying capacity.

Highlights

Island taxa are a conservation priority because of their high species endemism and elevated risks of extinction when compared to mainland ecosystems (Alcover, Sans & Palmer, 1998; Duncan & Blackburn, 2007; Kier et al, 2009)
Among climate change threats to island species are lower adaptive capacity to environmental change (Buckley & Jetz, 2010), a reduced dispersal capacity to adjust to changing habitat conditions, a limited elevational or latitudinal gradient for such adjustments and habitat inundation with sea level rise, a qualitatively higher risk for island systems (Mimura et al, 2007)
The Hawaiian common gallinule (‘Alae ‘ula, Gallinula galeata sandvicensis; hereafter Hawaiian gallinule), is among the most threatened of these (USFWS, 2011), with biannual population survey counts below 1,000 individuals (Reed et al, 2011) and a range limited to the islands of O‘ahu and Kaua‘i. We integrated data on vital rates, movement ecology, and climate change projections to generate a stochastic simulation model of the Hawaiian gallinule population on O‘ahu to investigate the potential impacts of management strategies and climate change on their extirpation risk

Summary

Introduction

Island taxa are a conservation priority because of their high species endemism and elevated risks of extinction when compared to mainland ecosystems (Alcover, Sans & Palmer, 1998; Duncan & Blackburn, 2007; Kier et al, 2009). How to cite this article van Rees and Reed (2018), Predicted effects of landscape change, sea level rise, and habitat management on the extirpation risk of the Hawaiian common gallinule (Gallinula galeata sandvicensis) on the island of O‘ahu. Climate change is a rapidly emerging threat to island species in general (Fordham & Brook, 2010) and birds in particular (Şekercioğlu, Primack & Wormworth, 2012). Among climate change threats to island species are lower adaptive capacity to environmental change (Buckley & Jetz, 2010), a reduced dispersal capacity to adjust to changing habitat conditions, a limited elevational or latitudinal gradient for such adjustments (of particular concern for birds, Devictor et al, 2008) and habitat inundation with sea level rise, a qualitatively higher risk for island systems (Mimura et al, 2007). Population increases have been achieved since the 1970s, principally attributed to the establishment of protected wetland refuges, predator control, and habitat management, by state and federal authorities (Reed et al, 2011; Underwood et al, 2013)

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