Charles H. Daugherty

Have the harmful effects of introduced rats on islands been exaggerated

Introduced rats are now being eradicated from many islands. Increasingly, these eradications are contested by activists claiming moral, legal, cultural, historic or scientific reasons and poorly documented evidence of effects. We reviewed the global literature on the effects of rats on island flora and fauna. We then used New Zealand as a case study because of its four-decade history of rat eradications and many detailed and innovative studies of how rats affect native species. These include use of exclosures, local manipulations of rat populations, video surveillance, and measurements of responses following eradications. The most intensive studies have been on the Pacific rat (Rattus exulans), a small South-East Asian species spread by Polynesians throughout the Pacific. These and the more recently introduced Norway rat (R. norvegicus) and ship (roof) rat (R. rattus) suppress some forest plants, and are associated with extinctions or declines of flightless invertebrates, ground-dwelling reptiles, land birds, and burrowing seabirds. On islands off France, Norway rats are also implicated in declines of shrews. Globally, ship rats were associated with declines or extinctions of the largest number of indigenous vertebrate species (60), including small mammals such as deer mice and bats. Effects of rats on forest trees and seabird populations are sufficiently pervasive to affect ecosystem structure and function. However, the data are patchy. Deficiencies in our knowledge would be reduced by documenting distribution and abundance of indigenous species before and after eradications. Comprehensive measurements of the responses of indigenous species to rat eradications would enable the development of testable models of rat invasion effects.

Patterns of range contractions and extinctions in the New Zealand herpetofauna following human colonisation

Abstract Evidence from subfossils and from present distributions confirming range contractions and extinctions of New Zealand amphibians and reptiles is consistent with that from New Zealand landbirds, in which 40% of the fauna, including the largest species, has become extinct in the 1000 years since human arrival. The largest extant species of all higher taxa of herpetofauna—leiopelmatid frogs, tuatara, skinks, and geckos—are extinct on the mainland; 41 % of the extant fauna (27 of 65 species) survive largely or entirely on rat‐free offshore islands; and many species are now restricted to a few isolated locations, remnants of once wider distributions, a pattern called “secondary endem‐ism”. Habitat alterations and occasional human predation may have contributed to range contractions, but the primary factor in extinctions is almost certainly introduced mammals, especially rats. At least three lines of evidence support this view: (1) species diversities and population densities are both far higher on rat‐...

Mega-island or micro-continent? New Zealand and its fauna.

The terrestrial New Zealand fauna has developed on an ancient landmass of continental origins that has had an increasingly isolated existence since the late Mesozoic. As a continental remnant, New Zealand harbours survivors of many ancient lineages many of which were once far more widely distributed. But New Zealands fauna also resembles that of an isolated archipelago: many higher taxa are missing; some have undergone extensive radiations in situ; and levels of endemism approach 100% in many groups. Ecologically, the fauna is characterized by frequent niche shifts, gigantism, and extended life histories with low reproductive rates, factors that make many species vulnerable to human disturbance. Data continue to amass supporting the ecophysiological as well as phylogenetic distinctiveness of the fauna. Described taxonomic diversity, even of terrestrial vertebrates, continues to increase.

Taxonomic and conservation review of the New Zealand herpetofauna

Abstract The extant New Zealand herpetofauna is now considered to consist of at least 65 endemic species of terrestrial reptiles and amphibians, an increase of about 64% in the size of the known fauna since 1980. The list includes four species of Leiopelma*, two species of Sphenodon, seven Naultinus, 22 Hoplodactyius, eight Cyclodina, and 22 Leiolopisma, all endemic to New Zealand. Discoveries in the past decade include many cryptic species identified using allozyme data, but also some morphologically well‐differentiated forms not previously known. At least 30 species (46%) are rare, threatened, or endangered, and 26 species (40%) are restricted largely or entirely to offshore islands. All but three species are protected. The New Zealand Department of Conservation has developed a comprehensive scheme for establishing management priority for indigenous species. At present, formal Recovery Plans exist in draft or approved form for at least 11 species, and more are in preparation.

Genetic diversity and differentiation at MHC genes in island populations of tuatara (Sphenodon spp.)

Neutral genetic markers are commonly used to understand the effects of fragmentation and population bottlenecks on genetic variation in threatened species. Although neutral markers are useful for inferring population history, the analysis of functional genes is required to determine the significance of any observed geographical differences in variation. The genes of the major histocompatibility complex (MHC) are well‐known examples of genes of adaptive significance and are particularly relevant to conservation because of their role in pathogen resistance. In this study, we survey diversity at MHC class I loci across a range of tuatara populations. We compare the levels of MHC variation with that observed at neutral microsatellite markers to determine the relative roles of balancing selection, diversifying selection and genetic drift in shaping patterns of MHC variation in isolated populations. In general, levels of MHC variation within tuatara populations are concordant with microsatellite variation. Tuatara populations are highly differentiated at MHC genes, particularly between the northern and Cook Strait regions, and a trend towards diversifying selection across populations was observed. However, overall our results indicate that population bottlenecks and isolation have a larger influence on patterns of MHC variation in tuatara populations than selection.

Genetic diversity and taxonomy: a reassessment of species designation in tuatara (Sphenodon: Reptilia)

The identification of species boundaries for allopatric populations is important for setting conservation priorities and can affect conservation management decisions. Tuatara (Sphenodon) are the only living members of the reptile order Sphenodontia and are restricted to islands around New Zealand that are free of introduced mammals. We present new data of microsatellite DNA diversity and substantially increased mtDNA sequence for all 26 sampled tuatara populations. We also re-evaluate existing allozyme data for those populations, and together use them to examine the taxonomic status of those populations. Although one could interpret the data to indicate different taxonomic designations, we conclude that, contrary to current taxonomy, Sphenodon is best described as a single species that contains distinctive and important geographic variants. We also examine amounts of genetic variation within populations and discuss the implications of these findings for the conservation management of this iconic taxon.

Four new species and one new subspecies of skinks, genus Leiolopisma (Reptilia: Lacertilia: Scincidae) from New Zealand

Abstract Four new species and one new subspecies of New Zealand skinks, genus Leiolopisma, identified on the basis of allozyme and morphological variation, are described: L. inconspicuum n. sp., L. maccanni n. comb., L. microlepis n. sp., L. notosaurus n. sp., and L. nigriplantare polychroma n. ssp. A morphological key for identifying these species is provided, and the practical difficulties of identifying morphologically cryptic species are discussed.

Influence of major histocompatibility complex genotype on mating success in a free-ranging reptile population

Major histocompatibility complex (MHC) genes are highly polymorphic components of the vertebrate immune system, which play a key role in pathogen resistance. MHC genes may also function as odour-related cues for mate choice, thus ensuring optimal MHC diversity in offspring. MHC-associated mate choice has been demonstrated in some fish, bird and mammal species but it is not known whether this is a general vertebrate phenomenon. We investigated whether MHC-associated mate choice occurs in a wild population of tuatara (Sphenodon punctatus), a territorial and sexually dimorphic reptile. We found weak evidence for MHC-disassortative mating, based on amino acid genotypic distance between pairs, when mated pairs were directly compared with potential pairs in close spatial proximity. No significant association was found between male mating success, number of MHC sequences, microsatellite heterozygosity or MHC lineage. The major determinant of mating success in tuatara was male body size, which was not related to MHC lineage or microsatellite heterozygosity. Our results suggest that male competitive ability is the primary driver of mating success in tuatara. However, MHC-associated preferences also appear to play a role, possibly as a kin avoidance mechanism during territory formation.

Genetic variation in island populations of tuatara (Sphenodon spp) inferred from microsatellite markers

Tuatara (Sphenodon spp) populations are restricted to 35 offshore islands in the Hauraki Gulf, Bay of Plenty and Cook Strait of New Zealand. Low levels of genetic variation have previously been revealed by allozyme and mtDNA analyses. In this new study, we show that six polymorphic microsatellite loci display high levels of genetic variation in 14 populations across the geographic range of tuatara. These populations are characterised by disjunct allele frequency spectra with high numbers of private alleles. High FST (0.26) values indicate marked population structure and assignment tests allocate 96% of all individuals to their source populations. These genetic data confirm that islands support genetically distinct populations. Principal component analysis and allelic sequence data supplied information about genetic relationships between populations. Low numbers of rare alleles and low allelic richness identified populations with reduced genetic diversity. Little Barrier Island has very low numbers of old tuatara which have retained some relictual diversity. North Brother Island’s tuatara population is inbred with fixed alleles at 5 of the 6 loci.

Invertebrate and lizard abundance is greater on seabird-inhabited islands than on seabird-free islands in the Marlborough Sounds,New Zealand

Abstract Addition of nutrients to an ecosystem may increase abundances of organisms at different trophic levels. Seabirds add nutrients to the islands on which they live. Our aim was to determine whether plants, invertebrates, and lizards are utilizing nutrients provided by seabirds and whether the addition of nutrients was correlated with an increase in arthropod and reptile abundance. A higher index of abundance was found for invertebrates and lizards on islands with seabirds than on islands without seabirds in the Marlborough Sounds, New Zealand. Seabird-derived nutrients were identified in the tissues of plants, invertebrates, and lizards on seabird-inhabited islands. Nutrient addition was found to increase abundance of animals from different trophic levels, but the patterns shown were not those expected from classical, top-down, theories of food web regulation.