Sex Ratio Bias and Extinction Risk in an Isolated Population of Tuatara (\u3ci\u3eSphenodon Punctatus\u3c/i\u3e)

Understanding the mechanisms underlying population declines is critical for preventing the extinction of endangered populations. Positive feedbacks can hasten the process of collapse and create an ‘extinction vortex,’ particularly in small, isolated populations. We provide a case study of a male-biased sex ratio creating the conditions for extinction in a natural population of tuatara (Sphenodon punctatus) on North Brother Island in the Cook Strait of New Zealand. We combine data from long term mark-recapture surveys, updated model estimates of hatchling sex ratio, and population viability modeling to measure the impacts of sex ratio skew. Results from the mark-recapture surveys show an increasing decline in the percentage of females in the adult tuatara population. Our monitoring reveals compounding impacts on female fitness through reductions in female body condition, fecundity, and survival as the male-bias in the population has increased. Additionally, we find that current nest temperatures are likely to result in more male than female hatchlings, owing to the pattern of temperature-dependent sex determination in tuatara where males hatch at warmer temperatures. Anthropogenic climate change worsens the situation for this isolated population, as projected temperature increases for New Zealand are expected to further skew the hatchling sex ratio towards males. Population viability models predict that without management intervention or an evolutionary response, the population will ultimately become entirely comprised of males and functionally extinct. Our study demonstrates that sex ratio bias can be an underappreciated threat to population viability, particularly in populations of long-lived organisms that appear numerically stable

Testing a global standard for quantifying species recovery and assessing conservation impact.

Recognizing the imperative to evaluate species recovery and conservation impact, in 2012 the International Union for Conservation of Nature (IUCN) called for development of a "Green List of Species" (now the IUCN Green Status of Species). A draft Green Status framework for assessing species' progress toward recovery, published in 2018, proposed 2 separate but interlinked components: a standardized method (i.e., measurement against benchmarks of species' viability, functionality, and preimpact distribution) to determine current species recovery status (herein species recovery score) and application of that method to estimate past and potential future impacts of conservation based on 4 metrics (conservation legacy, conservation dependence, conservation gain, and recovery potential). We tested the framework with 181 species representing diverse taxa, life histories, biomes, and IUCN Red List categories (extinction risk). Based on the observed distribution of species' recovery scores, we propose the following species recovery categories: fully recovered, slightly depleted, moderately depleted, largely depleted, critically depleted, extinct in the wild, and indeterminate. Fifty-nine percent of tested species were considered largely or critically depleted. Although there was a negative relationship between extinction risk and species recovery score, variation was considerable. Some species in lower risk categories were assessed as farther from recovery than those at higher risk. This emphasizes that species recovery is conceptually different from extinction risk and reinforces the utility of the IUCN Green Status of Species to more fully understand species conservation status. Although extinction risk did not predict conservation legacy, conservation dependence, or conservation gain, it was positively correlated with recovery potential. Only 1.7% of tested species were categorized as zero across all 4 of these conservation impact metrics, indicating that conservation has, or will, play a role in improving or maintaining species status for the vast majority of these species. Based on our results, we devised an updated assessment framework that introduces the option of using a dynamic baseline to assess future impacts of conservation over the short term to avoid misleading results which were generated in a small number of cases, and redefines short term as 10 years to better align with conservation planning. These changes are reflected in the IUCN Green Status of Species Standard

Testing Drones as a Tool for Surveying Lizards

A lack of effective methods for sampling lizards in terrain that is inaccessible to human observers limits our knowledge of their ecology and conservation needs. Drones are increasingly being used in wildlife monitoring, but their potential use for surveying lizards has not been evaluated. We investigated: (1) the detectability of model lizards using a drone relative to a human observer, and (2) the response of four lizard species to an approaching drone in three habitat types. Model lizards placed in potential basking positions within a defined search area were detected by both the drone operator and human observer, but the probability of detection was lower with the drone. Jewelled geckos (Naultinus gemmeus) in shrubland and grand skinks (Oligosoma grande) in rocky habitats showed surprisingly little reaction to the approaching drone, enabling close approaches (means of 59 cm and 107 cm, respectively) and accurate species identification with photos taken by the drone camera. For highly patterned jewelled geckos, identification was also possible to individual level. However, the drone was unsuccessful at detecting two alpine skink species in a near-vertical cliff habitat. Collectively, our results suggest that drones have potential as a tool for detecting small-bodied lizards in habitats inaccessible to human observers

Placement period of artificial retreats affects the number and demographic composition but not the body condition of skinks

Monitoring is important in conservation management, essential for assessing population trends, making decisions and allocating resources. Artificial retreats can offer a reliable, low impact and efficient method for monitoring cryptic herpetofauna. Methods for monitoring artificial retreats vary between different conservation management programmes in New Zealand, however, and a deeper understanding of the consequences of these variations would encourage greater standardisation and enable more reliable comparisons to be made across temporal and spatial scales. We investigate how placement period of artificial retreats affects population size indices and the body condition of common skinks (Oligosoma polychroma) in a grassland in Fiordland, New Zealand. We made 3987 skink sightings during 8250 visual checks and captured 638 skinks in 1200 physical searches of 400 artificial retreats during the summer of 2010/11. We observed more skinks under artificial retreats with a placement period of 2 years (permanent retreats) than under adjacent retreats in place for <2 months (temporary retreats). Placement period influenced the demographic composition of skinks occupying the artificial retreats, with a greater proportion of subadults and juveniles seen beneath temporary retreats and a greater proportion of adults occupying permanent retreats. Physical condition of the skinks occupying the retreats was not related to placement period. Our findings suggest that permanent placement of retreats is unlikely to increase survival or reproductive rates by increasing the body condition of individuals occupying retreats, but may result in competitive exclusion of juveniles and subadults by resident adults. We recommend temporary placement of retreats for assessing monitoring trends in skink populations in environments with moderate to high population densities, and permanent placement in areas of low population densities, due to the potential detection advantage. Our results emphasise the need for placement period to be considered when interpreting results from monitoring programmes using artificial retreats

Evaluation of counting methods for monitoring populations of a cryptic alpine passerine, the rock wren (Passeriformes, Acanthisittidae, Xenicus gilviventris).

Developing and validating methods to determine trends in populations of threatened species is essential for evaluating the effectiveness of conservation interventions. For cryptic species inhabiting remote environments, this can be particularly challenging. Rock wrens, Xenicus gilviventris, are small passerines endemic to the alpine zone of southern New Zealand. They are highly vulnerable to predation by introduced mammalian predators. Establishing a robust, cost-effective monitoring tool to evaluate population trends in rock wrens is a priority for conservation of both the species and, more broadly, as part of a suite of indicators for evaluating effectiveness of management in New Zealand's alpine ecosystems. We assessed the relative accuracy and precision of three population estimation techniques (mark-resight, distance sampling and simple counts on line transects) for two populations of rock wrens in the Southern Alps over six breeding seasons (2012-2018). The performance of these population estimators was compared to known rock wren population size derived from simultaneous territory mapping. Indices of abundance derived from counts on transects were correlated with territory mapping at both study areas, and performed better than either mark-resight methods or distance sampling. Simple counts on standardised line transects are a highly cost-effective method of monitoring birds because they do not require banding a population. As such, we recommend that line transect counts using the design outlined in this paper be adopted as a standard method for long-term monitoring of rock wren populations. Although species-specific testing is required to validate use of low-cost population indices, our results may have utility for the monitoring of other cryptic passerines in relatively open habitats

Sex Ratio Bias and Extinction Risk in an Isolated Population of Tuatara (<i>Sphenodon punctatus</i>)

<div><p>Understanding the mechanisms underlying population declines is critical for preventing the extinction of endangered populations. Positive feedbacks can hasten the process of collapse and create an ‘extinction vortex,’ particularly in small, isolated populations. We provide a case study of a male-biased sex ratio creating the conditions for extinction in a natural population of tuatara (<i>Sphenodon punctatus</i>) on North Brother Island in the Cook Strait of New Zealand. We combine data from long term mark-recapture surveys, updated model estimates of hatchling sex ratio, and population viability modeling to measure the impacts of sex ratio skew. Results from the mark-recapture surveys show an increasing decline in the percentage of females in the adult tuatara population. Our monitoring reveals compounding impacts on female fitness through reductions in female body condition, fecundity, and survival as the male-bias in the population has increased. Additionally, we find that current nest temperatures are likely to result in more male than female hatchlings, owing to the pattern of temperature-dependent sex determination in tuatara where males hatch at warmer temperatures. Anthropogenic climate change worsens the situation for this isolated population, as projected temperature increases for New Zealand are expected to further skew the hatchling sex ratio towards males. Population viability models predict that without management intervention or an evolutionary response, the population will ultimately become entirely comprised of males and functionally extinct. Our study demonstrates that sex ratio bias can be an underappreciated threat to population viability, particularly in populations of long-lived organisms that appear numerically stable.</p></div

Balancing phylogenetic diversity and species numbers in conservation prioritization, using a case study of threatened species in New Zealand

Funding for managing threatened species is currently insufficient to assist recovery of all species, so management projects must be prioritized. In attempts to maximize phylogenetic diversity conserved, prioritization protocols for threatened species are increasingly weighting species using metrics that incorporate their evolutionary distinctiveness. In a case study using 700 of the most threatened species in New Zealand, we examined trade-offs between emphasis on species’ evolutionary distinctiveness weights, and the numbers of species prioritized, as well as costs and probabilities of success for recovery projects. Increasing emphasis on species’ evolutionary distinctiveness weights in the prioritization protocol led to greater per-species costs and higher risk of project failure. In a realistic, limited-budget scenario, this resulted in fewer species prioritized, which imposed limits on the total phylogenetic diversity that could be conserved. However, by systematically varying the emphasis on evolutionary distinctiveness weight in the prioritization protocol we were able to minimize trade-offs, and obtain species groups that were near-optimal for both species numbers and phylogenetic diversity conserved. Phylogenetic diversity may not equate perfectly with functional diversity or evolutionary potential, and conservation agencies may be reluctant to sacrifice species numbers. Thus, we recommend prioritizing species groups that achieve an effective balance between maximizing phylogenetic diversity and number of species conserved