Inferring the distribution and demography of an invasive species from sighting data: the red fox incursion into Tasmania

Heterogeneous patterns of heterozygosity loss in isolated populations of the threatened eastern barred bandicoot (Perameles gunnii)

Identifying and analysing isolated populations is critical for conservation. Isolation can make populations vulnerable to local extinction due to increased genetic drift and inbreeding, both of which should leave imprints of decreased genome-wide heterozygosity. While decreases in heterozygosity among populations are frequently investigated, fewer studies have analysed how heterozygosity varies among individuals, including whether heterozygosity varies geographically along lines of discrete population structure or with continuous patterns analogous to isolation by distance. Here we explore geographical patterns of differentiation and individual heterozygosity in the threatened eastern barred bandicoot (Perameles gunnii) in Tasmania, Australia, using genomic data from 85 samples collected between 2008 and 2011. Our analyses identified two isolated demes undergoing significant genetic drift, and several areas of fine-scale differentiation across Tasmania. We observed discrete genetic structures across geographical barriers and continuous patterns of isolation by distance, with little evidence of recent or historical migration. Using a recently developed analytical pipeline for estimating autosomal heterozygosity, we found individual heterozygosities varied within demes by up to a factor of two, and demes with low-heterozygosity individuals also still contained those with high heterozygosity. Spatial interpolation of heterozygosity scores clarified these patterns and identified the isolated Tasman Peninsula as a location where low-heterozygosity individuals were more common than elsewhere. Our results provide novel insights into the relationship between isolation-driven genetic structure and local heterozygosity patterns. These may help improve translocation efforts, by identifying populations in need of assistance, and by providing an individualised metric for identifying source animals for translocation.

Aliens on the Road: Surveying Wildlife Roadkill to Assess the Risk of Biological Invasion

Monitoring the presence and distribution of alien species is pivotal to assessing the risk of biological invasion. In our study, we carried out a worldwide review of roadkill data to investigate geographical patterns of biological invasions. We hypothesise that roadkill data from published literature can turn out to be a valuable resource for researchers and wildlife managers, especially when more focused surveys cannot be performed. We retrieved a total of 2314 works published until January 2022. Among those, only 41 (including our original data) fitted our requirements (i.e., including a total list of roadkilled terrestrial vertebrates, with a number of affected individuals for each species) and were included in our analysis. All roadkilled species from retrieved studies were classified as native or introduced (domestic, paleo-introduced, or recently released). We found that a higher number of introduced species would be recorded among roadkill in Mediterranean and Temperate areas with respect to Tropical and Desert biomes. This is definitely in line with the current knowledge on alien species distribution at the global scale, thus confirming that roadkill datasets can be used beyond the study of road impacts, such as for an assessment of different levels of biological invasions among different countries.

Invasive species eradication: How do we declare success?

Deciding whether or not eradication of an invasive species has been successful is one of the main dilemmas facing managers of eradication programmes. When the species is no longer being detected, a decision must be made about when to stop the eradication programme and declare success. In practice, this decision is usually based on ad hoc rules, which may be inefficient. Since surveillance undertaken to confirm species absence is imperfect, any declaration of eradication success must consider the risk and the consequences of being wrong. If surveillance is insufficient, then eradication may be falsely declared (a Type I error), whereas continuation of surveillance when eradication has already occurred wastes resources (a Type II error). We review the various methods that have been developed for quantifying these errors and incorporating them into the decision-making process. We conclude with an overview of future developments likely to improve the practice of determining invasive species eradication success.

Den-Dwelling Carnivores in Central Poland: Long-Term Trends in Abundance and Productivity

The monitoring of medium-sized carnivores is essential because of their role in disease transmission and as predators. We focused on red foxes, badgers, raccoon dogs, and domestic dogs, and considered 9441 ha of field–forest mosaic in Central Poland. We compared current (2011–2018) abundance (i.e., number of natal dens recorded annually) and breeding parameters (assessed with the aid of camera traps) with published past data (1980s–1990s). The red fox population increased after rabies vaccinations were introduced and has increased further in the last few years. The population is now stable, which suggests that other factors, possibly mange, limit the population instead. Contrary to historical data, one-fourth of red fox females now breed outside of forests areas, indicating the high plasticity of the species. The number of natal dens of badgers and recruitment rates have also increased. The mean litter sizes of these two species are positively affected by small rodent availability. The raccoon dog, which is an alien and invasive species, used to be recorded sporadically but now breeds regularly (1.8 breeding cases yearly). Nowadays, free-ranging/feral domestic dogs are not controlled by culling, so they have started to breed in the wild (1.6 cases per year), which is a new occurrence.

The effectiveness of citizen surveillance for detecting exotic vertebrates

Citizen observations of the natural world are increasing in detail, growing in volume and increasingly being shared on web-based platforms for the purpose of sharing information and/or the crowd-sourcing of species identification. From a biosecurity perspective, such citizen data streams are important as they are responsible for the majority of post-border reports and most detections of exotic pest species of concern. The sharing of sightings amongst what are effectively communities of practice is a key driver of having the sighting of an exotic pest species recognized and reported. Whilst it is clear that the eyes, ears, cameras, and microphones of citizens are a major component of biosecurity surveillance, it is unclear what level of surveillance this provides in the prospective sense. As an example, what confidence does citizen science provide about “proof of absence” for exotic pests of concern? The taxonomy of surveillance used within the field of biosecurity would classify such citizen activities as contributing to “general surveillance,” for which non-detections are typically not recorded and methods of quantitative analysis are still under development. We argue that while not recorded, there is considerable information about citizens activities that routinely underpins peoples mental inference about the level of surveillance provided by citizen activities. Furthermore, we show that it is possible to make such inference from general surveillance transparent by describing and characterizing the activities that potentially generate sightings in a way that is amenable to quantitative analysis. In the context of evaluating surveillance provided by citizens for incursions of exotic vertebrates, we provide examples of citizen observations providing early warning and hence preventing the establishment of species from a range of animal groups. Historically, analysis of the power of general surveillance has been restricted to being conceptual, based on qualitative arguments. We provide this, but also provide a quantitative model framework and provide examples of how different forms of general surveillance data may be analyzed, particularly in supporting inference of eradication/extinction.

The Australian Roadkill Reporting Project-Applying Integrated Professional Research and Citizen Science to Monitor and Mitigate Roadkill in Australia

Simple Summary

Australia has no database of national roadkill. The current research project fills that knowledge gap by developing a roadkill reporting application that enables professional and citizen scientists to record photographs of roadkill with location, time and date. This embodies the concept of ‘One Welfare’ as it affects humans, animals and the environment. Uploaded to a website, these data can identify roadkill hotspots, tabulate species of animals killed and potentially be used for ecological studies of roadkill numbers, species distribution, population trends, animal behaviour and disease. Initial results indicate that mammal roadkill mostly occurs at night and that of birds and reptiles during daytime. Mammals make up three-quarters of the roadkill recorded and this includes endangered species. Two examples of roadkill hotspots are shown in Queensland and Tasmania. These will enable further research to suggest how roadkill mitigation measures may be optimally employed.

Abstract

Australia has no national roadkill monitoring scheme. To address this gap in knowledge, a roadkill reporting application (app) was developed to allow members of the public to join professional researchers in gathering Australian data. The app is used to photograph roadkill and simultaneously records the GPS location, time and date. These data are uploaded immediately to a website for data management. To illustrate the capacity to facilitate cost-effective mitigation measures the article focuses on two roadkill hotspots—in Queensland and Tasmania. In total, 1609 reports were gathered in the first three months of the project. They include data on mammals (n = 1203, 75%), birds (n = 125, 7.8%), reptiles (n = 79, 4.9%), amphibians (n = 4, 0.025%), unidentified (n = 189, 11.8%) and unserviceable ones (n = 9). A significant finding is variance in the distribution of mammals and birds at different times of day. These findings reflect diurnal variation in the activity levels of different species and underline the need for data on a targeted species to be collected at appropriate times of day. By continuing to facilitate roadkill monitoring, it is anticipated that the data generated by the app will directly increase knowledge of roadkill numbers and hotspots. Indirectly, it will provide value-added information on animal behaviour, disease and population dynamics as well as for species distribution mapping.

The value of monitoring wildlife roadkill

The number of wildlife-vehicle collisions has an obvious value in estimating the direct effects of roads on wildlife, i.e. mortality due to vehicle collisions. Given the nature of the data—species identification and location—there is, however, much wider ecological knowledge that can be gained by monitoring wildlife roadkill. Here, we review the added value and opportunities provided by these data, through a series of case studies where such data have been instrumental in contributing to the advancement of knowledge in species distributions, population dynamics, and animal behaviour, as well as informing us about health of the species and of the environment. We propose that consistently, systematically, and extensively monitoring roadkill facilitates five critical areas of ecological study: (1) monitoring of roadkill numbers, (2) monitoring of population trends, (3) mapping of native and invasive species distributions, (4) animal behaviour, and (5) monitoring of contaminants and disease. The collection of such data also offers a valuable opportunity for members of the public to be directly involved in scientific data collection and research (citizen science). Through continuing to monitor wildlife roadkill, we can expand our knowledge across a wide range of ecological research areas, as well as facilitating investigations that aim to reduce both the direct and indirect effects of roads on wildlife populations.

A new method for modelling biological invasions from early spread data accounting for anthropogenic dispersal

Biological invasions are one of the major causes of biodiversity loss worldwide. In spite of human aided (anthropogenic) dispersal being the key element in the spread of invasive species, no framework published so far accounts for its peculiar characteristics, such as very rapid dispersal and independence from the existing species distribution. We present a new method for modelling biological invasions using historical spatio-temporal records. This method first discriminates between data points of anthropogenic origin and those originating from natural dispersal, then estimates the natural dispersal kernel. We use the expectation-maximisation algorithm for the first step; we then use Ripley’s K-function as a spatial similarity metric to estimate the dispersal kernel. This is done accounting for habitat suitability and providing estimates of the inference precision. Tests on simulated data show good accuracy and precision for this method, even in the presence of challenging, but realistic, limitations of data in the invasion time series, such as gaps in the survey times and low number of records. We also provide a real case application of our method using the case of Litoria frogs in New Zealand. This method is widely applicable across the field of biological invasions, epidemics and climate change induced range shifts and provides a valuable contribution to the management of such issues. Functions to implement this methodology are made available as the R package Biolinv (https://cran.r-project.org/package=Biolinv).

Detecting rare carnivores using scats: Implications for monitoring a fox incursion into Tasmania

The ability to detect the incursion of an invasive species or destroy the last individuals during an eradication program are some of the most difficult aspects of invasive species management. The presence of foxes in Tasmania is a contentious issue with recent structured monitoring efforts, involving collection of carnivore scats and testing for fox DNA, failing to detect any evidence of foxes. Understanding the likelihood that monitoring efforts would detect fox presence, given at least one is present, is therefore critical for understanding the role of scat monitoring for informing the response to an incursion. We undertook trials to estimate the probability of fox scat detection through monitoring by scat‐detector dogs and person searches and used this information to critically evaluate the power of scat monitoring efforts for detecting foxes in the Tasmanian landscape. The probability of detecting a single scat present in a 1‐km² survey unit was highest for scat‐detector dogs searches (0.053) compared with person searches (x¯≅0.015) for each 10 km of search effort. Simulation of the power of recent scat monitoring efforts undertaken in Tasmania from 2011 to 2015 suggested that single foxes would have to be present in at least 20 different locations or fox breeding groups present in at least six different locations, in order to be detected with a high level of confidence (>0.80). We have shown that highly structured detection trials can provide managers with the quantitative tools needed to make judgments about the power of large‐scale scat monitoring programs. Results suggest that a fox population, if present in Tasmania, could remain undetected by a large‐scale, structured scat monitoring program. Therefore, it is likely that other forms of surveillance, in conjunction with scat monitoring, will be necessary to demonstrate that foxes are absent from Tasmania with high confidence.

Making inference from wildlife collision data: inferring predator absence from prey strikes

Wildlife collision data are ubiquitous, though challenging for making ecological inference due to typically irreducible uncertainty relating to the sampling process. We illustrate a new approach that is useful for generating inference from predator data arising from wildlife collisions. By simply conditioning on a second prey species sampled via the same collision process, and by using a biologically realistic numerical response functions, we can produce a coherent numerical response relationship between predator and prey. This relationship can then be used to make inference on the population size of the predator species, including the probability of extinction. The statistical conditioning enables us to account for unmeasured variation in factors influencing the runway strike incidence for individual airports and to enable valid comparisons. A practical application of the approach for testing hypotheses about the distribution and abundance of a predator species is illustrated using the hypothesized red fox incursion into Tasmania, Australia. We estimate that conditional on the numerical response between fox and lagomorph runway strikes on mainland Australia, the predictive probability of observing no runway strikes of foxes in Tasmania after observing 15 lagomorph strikes is 0.001. We conclude there is enough evidence to safely reject the null hypothesis that there is a widespread red fox population in Tasmania at a population density consistent with prey availability. The method is novel and has potential wider application.

Assessment of non-target risks from sodium fluoroacetate (1080), para-aminopropiophenone (PAPP) and sodium cyanide (NaCN) for fox-incursion response in Tasmania

Context Access to effective toxicants and delivery systems that target red foxes (Vulpes vulpes) are likely to be required as part of a management strategy in the event of future red fox incursions into Tasmania. Potential toxicants include sodium fluoroacetate (1080), para-aminopropiophenone (PAPP) and sodium cyanide (NaCN). Aims To assess the risk of three toxicants (1080, PAPP and NaCN) to non-target native Tasmanian mammals and birds and domestic dogs and cats. Methods We identified native Tasmanian mammal and bird species that may potentially consume fox baits, by reviewing the ecological traits of native species and by monitoring 180 buried bait stations with video cameras. We also assess the potential risk to non-target species of dying from a single standard dose of each of the three toxicants. Key results Seven native mammal and 20 native bird species have the potential to consume fox bait. All vertebrates would be susceptible to a single dose of NaCN. Consumption of a single fox bait containing 3 mg 1080 may be lethal to five native mammals, three native birds, and the domestic cat (Felis catus) and dog (Canis familiaris). Consumption of a single fox bait containing 226 mg PAPP may be lethal to the spotted-tailed quoll (Dasyurus maculatus) and the domestic cat and dog. Delivery of toxicants via a mechanical ejector would reduce non-target exposure to toxicants. Conclusions It appears that PAPP would provide a useful alternative to 1080 for use in lethal fox control in Tasmania, either in the event of an incursion or in the eradication of an established population. NaCN is not suitable for broadscale use in Tasmania because of the high susceptibility of all vertebrates to this toxicant. Nevertheless, NaCN would be useful in highly restricted areas in the event of an incursion where carcass recovery is important. The use of a mechanical ejector to target delivery of toxicants to red foxes would reduce non-target risks. Implications Our results clarify theoretical non-target risks from any future fox-poisoning programs in Tasmania and highlight the need for further research on the susceptibility of native species to PAPP as a potential alternative to 1080.