Stefano Canessa

When do we need more data? A primer on calculating the value of information for applied ecologists

Summary Applied ecologists continually advocate further research, under the assumption that obtaining more information will lead to better decisions. Value of information (VoI) analysis can be used to quantify how additional information may improve management outcomes: despite its potential, this method is still underused in environmental decision-making. We provide a primer on how to calculate the VoI and assess whether reducing uncertainty will change a decision. Our aim is to facilitate the application of VoI by managers who are not familiar with decision-analytic principles and notation, by increasing the technical accessibility of the tool. Calculating the VoI requires explicit formulation of management objectives and actions. Uncertainty must be clearly structured and its effects on management outcomes evaluated. We present two measures of the VoI. The expected value of perfect information is a calculation of the expected improvement in management outcomes that would result from access to perfect knowledge. The expected value of sample information calculates the improvement in outcomes expected by collecting a given sample of new data. We guide readers through the calculation of VoI using two case studies: (i) testing for disease when managing a frog species and (ii) learning about demographic rates for the reintroduction of an endangered turtle. We illustrate the use of Bayesian updating to incorporate new information. The VoI depends on our current knowledge, the quality of the information collected and the expected outcomes of the available management actions. Collecting information can require significant investments of resources; VoI analysis assists managers in deciding whether these investments are justified.

Drivers of salamander extirpation mediated by Batrachochytrium salamandrivorans

The recent arrival of Batrachochytrium salamandrivorans in Europe was followed by rapid expansion of its geographical distribution and host range, confirming the unprecedented threat that this chytrid fungus poses to western Palaearctic amphibians. Mitigating this hazard requires a thorough understanding of the pathogen’s disease ecology that is driving the extinction process. Here, we monitored infection, disease and host population dynamics in a Belgian fire salamander (Salamandra salamandra) population for two years immediately after the first signs of infection. We show that arrival of this chytrid is associated with rapid population collapse without any sign of recovery, largely due to lack of increased resistance in the surviving salamanders and a demographic shift that prevents compensation for mortality. The pathogen adopts a dual transmission strategy, with environmentally resistant non-motile spores in addition to the motile spores identified in its sister species B. dendrobatidis. The fungus retains its virulence not only in water and soil, but also in anurans and less susceptible urodelan species that function as infection reservoirs. The combined characteristics of the disease ecology suggest that further expansion of this fungus will behave as a ‘perfect storm’ that is able to rapidly extirpate highly susceptible salamander populations across Europe.

Improving supplementary feeding in species conservation.

Supplementary feeding is often a knee-jerk reaction to population declines, and its application is not critically evaluated, leading to polarized views among managers on its usefulness. Here, we advocate a more strategic approach to supplementary feeding so that the choice to use it is clearly justified over, or in combination with, other management actions and the predicted consequences are then critically assessed following implementation. We propose combining methods from a set of specialist disciplines that will allow critical evaluation of the need, benefit, and risks of food supplementation. Through the use of nutritional ecology, population ecology, and structured decision making, conservation managers can make better choices about what and how to feed by estimating consequences on population recovery across a range of possible actions. This structured approach also informs targeted monitoring and more clearly allows supplementary feeding to be integrated in recovery plans and reduces the risk of inefficient decisions. In New Zealand, managers of the endangered Hihi (Notiomystis cincta) often rely on supplementary feeding to support reintroduced populations. On Kapiti island the reintroduced Hihi population has responded well to food supplementation, but the logistics of providing an increasing demand recently outstretched management capacity. To decide whether and how the feeding regime should be revised, managers used a structured decision making approach informed by population responses to alternative feeding regimes. The decision was made to reduce the spatial distribution of feeders and invest saved time in increasing volume of food delivered into a smaller core area. The approach used allowed a transparent and defendable management decision in regard to supplementary feeding, reflecting the multiple objectives of managers and their priorities. Mejoría de la Alimentación Suplementaria en la Conservación de Especies Resumen La alimentación suplementaria con frecuencia es una reacción instintiva a la declinación de poblaciones y su aplicación no se evalúa críticamente, lo que lleva a opiniones polarizadas sobre su uso entre los manejadores. Aquí abogamos por una estrategia más decisiva para la alimentación suplementaria para que la opción de usarla esté claramente justificada sobre, o en combinación con, otras acciones de manejo y las consecuencias pronosticadas sean entonces evaluadas críticamente después de su implementación. Proponemos combinar métodos de otro conjunto de disciplinas especialistas que permitirán la evaluación crítica de la necesidad, el beneficio y los riesgos de la alimentación suplementaria. Por medio del uso de la ecología nutricional, la ecología de poblaciones y la toma de decisiones estructuradas, quienes manejan la conservación pueden tomar mejores decisiones sobre qué y cómo alimentar al estimar las consecuencias de la recuperación poblacional a través de un rango de acciones posibles. Esta estrategia estructurada también informa al monitoreo enfocado y permite con mayor claridad la integración de la alimentación suplementaria a los planes de recuperación y reduce el riesgo de decisiones ineficientes. En Nueva Zelanda, los manejadores del hihi (Notiomystis cincta) que se encuentra en peligro de extinción, con frecuencia dependen de la alimentación suplementaria para apoyar a las poblaciones reintroducidas. En la isla de Kapiti, la población reintroducida de hihis ha respondido de buena manera a la alimentación suplementaria, pero la logística de proporcionar a una demanda en crecimiento recientemente sobrepasó la capacidad de manejo. Para decidir si el régimen alimentario debería revisarse y cómo hacerlo, los manejadores usaron una estrategia estructurada de toma de decisiones con información sobre las respuestas de la población a regímenes alternativos de alimentación. La decisión se hizo para reducir la distribución espacial de los comederos e invertir el tiempo ahorrado en incrementar el volumen de alimento que se lleva a una zona núcleo más pequeña. La estrategia usada permitió una decisión de manejo transparente y defendible con respecto a la alimentación suplementaria, lo que refleja los objetivos múltiples de los manejadores y sus prioridades.

Optimal release strategies for cost-effective reintroductions

Summary Ex situ programmes for endangered species commonly focus on two main objectives: insurance against immediate risk of extinction and reintroduction. Releases influence the size of captive and wild populations and may present managers with a trade-off between the two objectives. This can be further complicated when considering the costs of the captive population and the possible release of different life stages. We approached this decision problem by combining population models and decision-analytic methods, using the reintroduction programme for the southern corroboree frog Pseudophryne corroboree in Australia as an example. We identified the optimal release rates of eggs and subadults which maximized the size of the captive and reintroduced populations while meeting constraints. We explored two scenarios: a long-term programme for a stable age-distributed captive population and a short-term programme with non-stable age distribution and limited budget. We accounted for uncertainty in the estimated vital rates and demographic stochasticity. Assuming a stable age distribution, large proportions of individuals could be released without decreasing the captive population below its initial size. The optimal strategy was sensitive to the post-release survival of both life stages, but subadult releases were generally most cost-effective, producing a large wild population and requiring a cheaper captive population. Egg releases were optimal for high expected juvenile survival, whereas mixed releases of both life stages were never optimal. In the short-term realistic scenario, subadult releases also produced the largest wild population, but they required a large increase in the size and cost of the captive population that exceeded the available budget. Egg releases were cheaper but yielded smaller numbers in the wild, whereas joint releases of both life stages provided more wild individuals, meeting budget constraints without depleting the captive population. Synthesis and applications. Optimal release strategies for endangered species reflect the trade-offs between insurance and reintroduction objectives and depend on the vital rates of the released individuals. Although focusing on a single life stage may have practical advantages, mixed strategies can maximize cost-effectiveness by combining the relative advantages of releasing early and late life stages.

Land abandonment may reduce disturbance and affect the breeding sites of an endangered amphibian in northern Italy

Although human-related disturbance is usually detrimental for biodiversity, in some instances it can simulate natural processes and benefit certain species. Changes in the disturbance regime, both natural and human-driven, can affect species that rely on it. The Apennine yellow-bellied toad Bombina variegata pachypus, an amphibian endemic to peninsular Italy, has declined throughout its range in the last 3 decades. We sought to identify the drivers of the decline in the region of Liguria, at the north-western limit of its distribution. In 2009 and 2010 we surveyed sites where the species occurred until 2005 and related the persistence of breeding activity to the characteristics of sites. Populations had disappeared from 50% of the sites between 2005 and 2009. Current breeding sites have less aquatic and bank vegetation, fewer predators and better insolation. Frequent disturbance events (desiccation and floods) were related to reduced vegetation, which in turn may decrease predator densities and increase insolation. In this region disturbance is provided by natural factors or, in the case of artificial water bodies, by regular maintenance carried out by landowners. The widespread land abandonment in Liguria can disrupt disturbance regimes, interrupting the removal of vegetation, and thus rapidly reduce the suitability of artificial sites. This was confirmed in our study, with most abandoned breeding sites occurring in formerly cultivated areas. Possible short-term conservation actions include creating new ponds, maintaining artificial water bodies and clearing vegetation. However, long-term conservation may be more problematic as the land abandonment process is unlikely to be reversed.

Integrating variability in detection probabilities when designing wildlife surveys: a case study of amphibians from south-eastern Australia

Occupancy-based monitoring programs rely on survey data to infer presence or absence of the target species. However, species may occupy a site and go undetected, leading to erroneous inference of absence (‘false absence’). If detectability is influenced by the time of year or weather conditions, survey protocols can be adjusted to minimize the chance of false absences. In this study, detection probabilities for three amphibian species from south-eastern Australia were modelled using a Bayesian approach. For aural surveys, we compared basic models, which only included effects of survey date, duration and time of day on detection, to models including additional effects of weather. Model selection using deviance information criterion (DIC) suggested that the basic model was the most parsimonious for Crinia signifera, while models including relative humidity and water temperature were most supported for Limnodynastes dumerilii and L. tasmaniensis respectively. When predictive performance was assessed by cross validation, DIC results were largely matched for C. signifera and L. dumerilii, while models of detection for L. tasmaniensis were indistinguishable, AUC scores suggesting inadequate performance. We show how results such as these can be used to design surveys, developing protocols for individual surveys and estimating the number of surveys required under those protocols to achieve a threshold cumulative probability of detection. Conservation managers can use these models to maximize the efficiency of surveys. This will improve the accuracy of occupancy data, and reduce the risk of misdirected conservation actions resulting from false absences.

Salamander chytrid fungus (Batrachochytrium salamandrivorans) in the United States—Developing research, monitoring, and management strategies

The recently (2013) identified pathogenic chytrid fungus, Batrachochytrium salamandrivorans (Bsal), poses a severe threat to the distribution and abundance of salamanders within the United States and Europe. Development of a response strategy for the potential, and likely, invasion of Bsal into the United States is crucial to protect global salamander biodiversity. A formal working group, led by Amphibian Research and Monitoring Initiative (ARMI) scientists from the U.S. Geological Survey (USGS) Patuxent Wildlife Research Center, Fort Collins Science Center, and Forest and Rangeland Ecosystem Science Center, was held at the USGS Powell Center for Analysis and Synthesis in Fort Collins, Colorado, United States from June 23 to June 25, 2015, to identify crucial Bsal research and monitoring needs that could inform conservation and management strategies for salamanders in the United States. Key findings of the workshop included the following: (1) the introduction of Bsal into the United States is highly probable, if not inevitable, thus requiring development of immediate short-term and long-term intervention strategies to prevent Bsal establishment and biodiversity decline; (2) management actions targeted towards pathogen containment may be ineffective in reducing the long-term spread of Bsal throughout the United States; and (3) early detection of Bsal through surveillance at key amphibian import locations, among high-risk wild populations, and through analysis of archived samples is necessary for developing management responses. Top research priorities during the preinvasion stage included the following: (1) deployment of qualified diagnostic methods for Bsal and establishment of standardized laboratory practices, (2) assessment of susceptibility for amphibian hosts (including anurans), and (3) development and evaluation of short- and long-term pathogen intervention and management strategies. Several outcomes were achieved during the workshop, including development of an organizational structure with working groups for a Bsal Task Force, creation of an initial influence diagram to aid in identifying effective management actions in the face of uncertainty, and production of a list of potential management actions and key research uncertainties. Additional products under development include a Bsal Strategic Action plan, an emergency response plan, a monitoring and surveillance program, a standardized diagnostic approach, decision models for natural resource agencies, and a reporting database for salamander mortalities. This workshop was the first international meeting to address the threat of Bsal to salamander populations in the United States, with more than 30 participants from U.S. conservation and resource management agencies (U.S. Fish and Wildlife Service, U.S. Forest Service, U.S. Department of Defense, U.S. National Park Service, and Association of Fish and Wildlife Agencies) and academic research institutions in Australia, the Netherlands, Switzerland, the United Kingdom, and the United States.

Decision‐making for mitigating wildlife diseases: From theory to practice for an emerging fungal pathogen of amphibians

Conservation science can be most effective in its decision‐support role when seeking answers to clearly formulated questions of direct management relevance. Emerging wildlife diseases, a driver of global biodiversity loss, illustrate the challenges of performing this role: in spite of considerable research, successful disease mitigation is uncommon. Decision analysis is increasingly advocated to guide mitigation planning, but its application remains rare. Using an integral projection model, we explored potential mitigation actions for avoiding population declines and the ongoing spatial spread of the fungus Batrachochytrium salamandrivorans (Bsal). This fungus has recently caused severe amphibian declines in north‐western Europe and currently threatens Palearctic salamander diversity. Available evidence suggests that a Bsal outbreak in a fire salamander (Salamandra salamandra) population will lead to its rapid extirpation. Treatments such as antifungals or probiotics would need to effectively interrupt transmission (reduce probability of infection by nearly 90%) in order to reduce the risk of host extirpation and successfully eradicate the pathogen. Improving the survival of infected hosts is most likely to be detrimental as it increases the potential for pathogen transmission and spread. Active removal of a large proportion of the host population has some potential to locally eradicate Bsal and interrupt its spread, depending on the presence of Bsal reservoirs and on the hosts spatial dynamics, which should therefore represent research priorities. Synthesis and applications. Mitigation of Batrachochytrium salamandrivorans epidemics in susceptible host species is highly challenging, requiring effective interruption of transmission and radical removal of host individuals. More generally, our study illustrates the advantages of framing conservation science directly in the management decision context, rather than adapting to it a posteriori.

Multi-scale, direct and indirect effects of the urban stream syndrome on amphibian communities in streams.

Urbanization affects streams by modifying hydrology, increasing pollution and disrupting in-stream and riparian conditions, leading to negative responses by biotic communities. Given the global trend of increasing urbanization, improved understanding of its direct and indirect effects at multiple scales is needed to assist management. The theory of stream ecology suggests that the riverscape and the surrounding landscape are inextricably linked, and watershed-scale processes will also affect in-stream conditions and communities. This is particularly true for species with semi-aquatic life cycles, such as amphibians, which transfer energy between streams and surrounding terrestrial areas. We related measures of urbanization at different scales to frog communities in streams along an urbanization gradient in Melbourne, Australia. We used boosted regression trees to determine the importance of predictors and the shape of species responses. We then used structural equation models to investigate possible indirect effects of watershed imperviousness on in-stream parameters. The proportion of riparian vegetation and road density surrounding the site at the reach scale (500-m radius) had positive and negative effects, respectively, on species richness and on the occurrence of the two most common species in the area ( Crinia signifera and Limnodynastesdumerilii ). Road density and local aquatic vegetation interacted in influencing species richness, suggesting that isolation of a site can prevent colonization, in spite of apparently good local habitat. Attenuated imperviousness at the catchment scale had a negative effect on local aquatic vegetation, indicating possible indirect effects on frog species not revealed by single-level models. Processes at the landscape scale, particularly related to individual ranging distances, can affect frog species directly and indirectly. Catchment imperviousness might not affect adult frogs directly, but by modifying hydrology it can disrupt local vegetation and prove indirectly detrimental. Integrating multiple-scale management actions may help to meet conservation targets for streams in the face of urbanization.

Fragile coexistence of a global chytrid pathogen with amphibian populations is mediated by environment and demography

Unravelling the multiple interacting drivers of host–pathogen coexistence is crucial in understanding how an apparently stable state of endemism may shift towards an epidemic and lead to biodiversity loss. Here, we investigate the apparent coexistence of the global amphibian pathogen Batrachochytrium dendrobatidis (Bd) with Bombina variegata populations in The Netherlands over a 7-year period. We used a multi-season mark–recapture dataset and assessed potential drivers of coexistence (individual condition, environmental mediation and demographic compensation) at the individual and population levels. We show that even in a situation with a clear cost incurred by endemic Bd, population sizes remain largely stable. Current environmental conditions and an over-dispersed pathogen load probably stabilize disease dynamics, but as higher temperatures increase infection probability, changing environmental conditions, for example a climate-change-driven rise in temperature, could unbalance the current fragile host–pathogen equilibrium. Understanding the proximate mechanisms of such environmental mediation and of site-specific differences in infection dynamics can provide vital information for mitigation actions.