Conservation and population biology of the Hong Kong newt (Paramesotriton hongkongensis)

Abstract

The Hong Kong newt (Paramesotriton hongkongensis) is a tropical stream-dwelling salamander threatened by habitat loss and overexploitation throughout its range (<400 km2). Adult newts exhibit distinctive seasonal patterns in habitat use, occupying aquatic habitats for breeding and terrestrial habitats outside of the breeding season. However, knowledge of their terrestrial habitat requirements, demography, and population genetics remains fragmentary. I investigated the ecology of P. hongkongensis, with an emphasis on determining the extent of core terrestrial habitats, examining the significance of biotic and abiotic factors on demography, and quantifying genetic structure and variability of P. hongkongensis populations. Finally, I developed a conservation action plan that summarizes the life history, demography, and threats to the Hong Kong newt, and prescribed recommendations that will enhance its conservation.

I combined radio-telemetry and transect surveys to study habitat use and quantify movement and site-level distribution patterns of P. hongkongensis during its terrestrial phase to delineate core terrestrial habitat for the species. Fifty-two newts radio-tracked during the wet season primarily used forest, maintained small home ranges (mean=0.04 ha), and made short-distance movements (<7 m/day) between cover objects. From transect surveys in which I detected 117 newts, I estimated that the core terrestrial habitat extended 113 m from stream margins.

A seven-year mark-recapture dataset of four P. hongkongensis populations was analyzed to determine changes in abundance and evaluate relationships between forest cover, body size, and rainfall on survival. Annual survival was positively associated with quantity of forest cover within core habitat of all populations, and negatively related to body size, but was not influenced by rainfall. Despite the positive association between forest extent and survival, population sizes increased substantially at two sites including the site with the lowest forest cover, and declined at the fourth site, which had the highest forest cover. Population sizes at the third site remained stable.

Genetic samples of 310 newts from 10 populations located in different drainage basins on the mainland and two nearby islands were genotyped at nine microsatellite loci, with the aim of inferring population genetic structure and quantifying genetic diversity within and gene flow among populations. Analysis of genetic composition revealed five spatially distinct clusters that accorded with major geographical features, such as mountain ridges and marine barriers. One population was anomalous and may represent an introduction. Genetic variability within populations was high and most populations lacked signs of historic genetic bottlenecks.

Habitat protection and forest succession during recent decades may have been responsible for the population growth observed at two sites, and the positive relationship between forest cover and survival rate suggests that protection of forest is important for the persistence of P. hongkongensis. Although most populations occur within protected areas, the Hong Kong newt remains vulnerable to overexploitation throughout its range. The importance of conduit entrapment and road mortality as impacts on populations warrant further investigation. The findings of this study have been integrated into a conservation action plan for P. hongkongensis for consideration and implementation by the Agriculture, Fisheries and Conservation Department of Hong Kong SAR Government.