The demography of free-roaming dog populations and applications to disease and population control

Understanding the demography of domestic dog populations is essential for effective disease control, particularly of canine-mediated rabies. Demographic data are also needed to plan effective population management. However, no study has comprehensively evaluated the contribution of demographic processes (i.e. births, deaths and movement) to variations in dog population size or density, or determined the factors that regulate these processes, including human factors. We report the results of a 3-year cohort study of domestic dogs, which is the first to generate detailed data on the temporal variation of these demographic characteristics. The study was undertaken in two communities in each of Bali, Indonesia and Johannesburg, South Africa, in rabies-endemic areas and where the majority of dogs were free-roaming. None of the four communities had been engaged in any dog population management interventions by local authorities or animal welfare organizations. All identified dogs in the four communities were monitored individually throughout the study. We observed either no population growth or a progressive decline in population size during the study period. There was no clear evidence that population size was regulated through environmental resource constraints. Rather, almost all of the identified dogs were owned and fed regularly by their owners, consistent with population size regulated by human demand. Finally, a substantial fraction of the dogs originated from outside the population, entirely through the translocation of dogs by people, rather than from local births. These findings demonstrate that previously reported growth of dog populations is not a general phenomenon and challenge the widely held view that free-roaming dogs are unowned and form closed populations. Synthesis and applications. These observations have broad implications for disease and population control. The accessibility of dogs for vaccination and evaluation through owners and the movement of dogs (some of them infected) by people will determine the viable options for disease control strategies. The impact of human factors on population dynamics will also influence the feasibility of annual vaccination campaigns to control rabies and population control through culling or sterilization. The complex relationship between dogs and people is critically important in the transmission and control of canine-mediated rabies. For effective management, human factors must be considered in the development of disease and population control programmes

A Two-Phase Model for Smoothly Joining Disparate Growth Phases in the Macropodid Thylogale billardierii

Generally, sigmoid curves are used to describe the growth of animals over their lifetime. However, because growth ratesoften differ over an animal’s lifetime a single curve may not accurately capture the growth. Broken-stick models constrainedto pass through a common point have been proposed to describe the different growth phases, but these are oftenunsatisfactory because essentially there are still two functions that describe the lifetime growth. To provide a single,converged model to age animals with disparate growth phases we developed a smoothly joining two-phase nonlinearfunction (SJ2P), tailored to provide a more accurate description of lifetime growth of the macropod, the Tasmanianpademelon Thylogale billardierii. The model consists of the Verhulst logistic function, which describes pouch-phase growth– joining smoothly to the Brody function, which describes post-pouch growth. Results from the model demonstrate thatmale pademelons grew faster and bigger than females. Our approach provides a practical means of ageing wildpademelons for life history studies but given the high variability of the data used to parametrise the second growth phaseof the model, the accuracy of ageing of post-weaned animals is low: accuracy might be improved with collection oflongitudinal growth data. This study provides a unique, first robust method that can be used to characterise growth overthe lifespan of pademelons. The development of this method is relevant to collecting age-specific vital rates fromcommonly used wildlife management practices to provide crucial insights into the demographic behaviour of animalpopulations

Review of the Amphibian Immune Response to Chytridiomycosis, and Future Directions

The fungal skin disease, chytridiomycosis (caused by Batrachochytrium dendrobatidis and B. salamandrivorans), has caused amphibian declines and extinctions globally since its emergence. Characterizing the host immune response to chytridiomycosis has been a focus of study with the aim of disease mitigation. However, many aspects of the innate and adaptive arms of this response are still poorly understood, likely due to the wide range of species' responses to infection. In this paper we provide an overview of expected immunological responses (with inference based on amphibian and mammalian immunology), together with a synthesis of current knowledge about these responses for the amphibian-chytridiomycosis system. We structure our review around four key immune stages: (1) the naïve immunocompetent state, (2) immune defenses that are always present (constitutive defenses), (3) mechanisms for recognition of a pathogen threat and innate immune defenses, and (4) adaptive immune responses. We also evaluate the current hot topics of immunosuppression and immunopathology in chytridiomycosis, and discuss their respective roles in pathogenesis. Our synthesis reveals that susceptibility to chytridiomycosis is likely to be multifactorial. Susceptible amphibians appear to have ineffective constitutive and innate defenses, and a late-stage response characterized by immunopathology and Bd-induced suppression of lymphocyte responses. Overall, we identify substantial gaps in current knowledge, particularly concerning the entire innate immune response (mechanisms of initial pathogen detection and possible immunoevasion by Bd, degree of activation and efficacy of the innate immune response, the unexpected absence of innate leukocyte infiltration, and the cause and role of late-stage immunopathology in pathogenesis). There are also gaps concerning most of the adaptive immune system (the relative importance of B and T cell responses for pathogen clearance, the capacity and extent of immunological memory, and specific mechanisms of pathogen-induced immunosuppression). Improving our capacity for amphibian immunological research will require selection of an appropriate Bd-susceptible model species, the development of taxon-specific affinity reagents and cell lines for functional assays, and the application of a suite of conventional and emerging immunological methods. Despite current knowledge gaps, immunological research remains a promising avenue for amphibian conservation management

Context-dependent conservation responses to emerging wildlife diseases

Emerging infectious diseases pose an important threat to wildlife. While established protocols exist for combating outbreaks of human and agricultural pathogens, appropriate management actions before, during, and after the invasion of wildlife pathogens have not been developed. We describe stage-specific goals and management actions that minimize disease impacts on wildlife, and the research required to implement them. Before pathogen arrival, reducing the probability of introduction through quarantine and trade restrictions is key because prevention is more cost effective than subsequent responses. On the invasion front, the main goals are limiting pathogen spread and preventing establishment. In locations experiencing an epidemic, management should focus on reducing transmission and disease, and promoting the development of resistance or tolerance. Finally, if pathogen and host populations reach a stable stage, then recovery of host populations in the face of new threats is paramount. Successful management of wildlife disease requires risk-taking, rapid implementation, and an adaptive approach."Funding was provided by the US National Science Foundation (grants EF-0914866, DGE-0741448, DEB-1115069, DEB-1336290) and the National Institutes of Health (grant 1R010AI090159)."https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/14024

Using decision analysis to support proactive management of emerging infectious wildlife diseases

Despite calls for improved responses to emerging infectious diseases in wildlife, management is seldom considered until a disease has been detected in affected populations. Reactive approaches may limit the potential for control and increase total response costs. An alternative, proactive management framework can identify immediate actions that reduce future impacts even before a disease is detected, and plan subsequent actions that are conditional on disease emergence. We identify four main obstacles to developing proactive management strategies for the newly discovered salamander pathogen Batrachochytrium salamandrivorans (Bsal). Given that uncertainty is a hallmark of wildlife disease management and that associated decisions are often complicated by multiple competing objectives, we advocate using decision analysis to create and evaluate trade-offs between proactive (pre-emergence) and reactive (post-emergence) management options. Policy makers and natural resource agency personnel can apply principles from decision analysis to improve strategies for countering emerging infectious diseases

Using decision analysis to support proactive management of emerging infectious wildlife diseases

Despite calls for improved responses to emerging infectious diseases in wildlife, management is seldom considered until a disease has been detected in affected populations. Reactive approaches may limit the potential for control and increase total response costs. An alternative, proactive management framework can identify immediate actions that reduce future impacts even before a disease is detected, and plan subsequent actions that are conditional on disease emergence. We identify four main obstacles to developing proactive management strategies for the newly discovered salamander pathogen Batrachochytrium salamandrivorans (Bsal). Given that uncertainty is a hallmark of wildlife disease management and that associated decisions are often complicated by multiple competing objectives, we advocate using decision analysis to create and evaluate trade-offs between proactive (pre-emergence) and reactive (post-emergence) management options. Policy makers and natural resource agency personnel can apply principles from decision analysis to improve strategies for countering emerging infectious diseases

Null expectations for disease dynamics in shrinking habitat: dilution or amplification?

As biodiversity declines with anthropogenic land-use change, it is increasingly important to understand how changing biodiversity affects infectious disease risk. The dilution effect hypothesis, which points to decreases in biodiversity as critical to an increase in infection risk, has received considerable attention due to the allure of a win–win scenario for conservation and human well-being. Yet some empirical data suggest that the dilution effect is not a generalizable phenomenon. We explore the response of pathogen transmission dynamics to changes in biodiversity that are driven by habitat loss using an allometrically scaled multi-host model. With this model, we show that declining habitat, and thus declining biodiversity, can lead to either increasing or decreasing infectious-disease risk, measured as endemic prevalence. Whether larger habitats, and thus greater biodiversity, lead to a decrease (dilution effect) or increase (amplification effect) in infection prevalence depends upon the pathogen transmission mode and how host competence scales with body size. Dilution effects were detected for most frequency-transmitted pathogens and amplification effects were detected for density-dependent pathogens. Amplification effects were also observed over a particular range of habitat loss in frequency-dependent pathogens when we assumed that host competence was greatest in large-bodied species. By contrast, only amplification effects were observed for density-dependent pathogens; host competency only affected the magnitude of the effect. These models can be used to guide future empirical studies of biodiversity–disease relationships across gradients of habitat loss. The type of transmission, the relationship between host competence and community assembly, the identity of hosts contributing to transmission, and how transmission scales with area are essential factors to consider when elucidating the mechanisms driving disease risk in shrinking habitat. This article is part of the themed issue ‘Conservation, biodiversity and infectious disease: scientific evidence and policy implications'

Going the distance on kangaroos and water: A review and test of artificial water point closures in Australia

Grazing by overabundant herbivores can cause land degradation and reduce biological diversity. Across arid and semi-arid Australia, predator control, pasture improvement, and artificial water points (AWP) have contributed to increased populations of kangaroos and wallaroos (Macropus spp.). Control efforts (e.g. culling, predator reintroduction, fertility control) can be expensive, controversial and/or unsustainable in the long term. Closure of AWP is an alternative. We reviewed closures in Australia and found experimental tests have been few, and results unconvincing for two main reasons. Firstly, no study has tested AWP closures over distances influential to kangaroos. We identified seven AWP closure experiments in Australia. Five did not generate areas beyond 5 km from water and two used a method ineffective for excluding kangaroos. Secondly, post-closure monitoring has frequently been too short to detect changes amongst natural environmental fluctuations. Our own experimental AWP closure did not influence kangaroo populations and reaffirmed that kangaroo densities are dictated by food availability in Australia's water rich rangelands. Larger experiments are needed with systematic AWP closures that generate water remote landscapes, preferably exceeding 10 km from water. Monitoring must span dry, hot periods of below average rainfall when kangaroos are most likely dependent on drinking water

Data from: Impact of cane toads on a community of Australian native frogs, determined by 10 years of automated identification and logging of calling behaviour

Invasive species may have devastating impacts on native biota. Cane toads Rhinella marina continue to invade northern Australia and the consequences for the endemic frogs are unclear. Monitoring frogs in such remote areas is difficult because their activity depends heavily on unpredictable rainfall events. We developed an autonomous acoustic monitoring system which used machine learning techniques to identify up to 22 calling species in real time. Ten of these systems, capable of operating for at least a year without attention, were deployed over a ten-year period along the Roper River valley in the Northern Territory, logging more than 4 million records pre- and post-toad invasion. Within five years of their arrival, cane toads became one of the most prominent members of the anuran community. We detected an overall impact, with six frog species declining in calling activity and one apparently increasing. However, almost all species detected initially were detected at the end of the monitoring period, and again on a follow-up survey after a further ten years. Synthesis and applications. The overall impact of cane toads on endemic frogs has been largely one of rarefaction rather than elimination. Rather than having a devastating impact on the endemic frogs, cane toads have become a component of the amphibian community. Autonomous recording and identification systems such as ours have great potential for long term monitoring of vocalising species in remote and variable environments

Growth dynamics of freshwater crocodiles (Crocodylus johnstoni) in the Lynd River, Queensland

We analysed growth models for a population of Australian freshwater crocodiles (Crocodylus johnstoni). Competing growth models were tested with two data sets: individuals of known-age, and growth interval data from capture-recapture records. A von Bertalanffy function provided the best empirical fit of several growth models. The estimated asymptotic lengths (snout-vent length of males = 125.3 cm; females = 97.4 cm) agreed well with average lengths of the ten largest males and females in the population. Sexual size dimorphism in this species resulted from a combination of smaller mean length at maturity for females and a subsequent decline in female growth rate. Size dimorphism may result from individual trade-offs in age v. length at maturity as a consequence of sexual selection