Science, statistics and surveys: a herpetological perspective

Bridging the gap between conservation science and conservation practice is a widely acknowledged issue in applied ecology (Hulme 2011). Nowhere is the gap greater than in the area of data collection, analysis and interpretation. Population assessments for conservation are frequently based on traditional practices that use rules of thumb and quasi-quantitative methods. This means that important decisions that have far-reaching conservation, and commercial and financial implications are often based on sketchy population assessments. This is particularly problematic for small-bodied, cryptic animals that have highly seasonal patterns of behaviour tied to prevailing weather conditions. Amphibians and reptiles are a case in point and illustrate many issues that have wider implications for biodiversity assessment. Despite a resurgence of interest in the conservation of these animals over the past two decades (Gibbons et al. 2000), there remain significant challenges in obtaining population data for amphibians and reptiles that are reliable enough to inform conservation decisions. Even in the UK, which has an impoverished herpetofauna that is relatively well studied, surveys are usually based on methods that have changed little over a quarter of a century. For example, great crested newt Triturus cristatus populations can be scored by systems based on simple counts (Table 1). When such counts are carried out as part of a licensed survey to inform recommendations for development impact mitigation, there is a requirement to standardize such counts and record such variables as torch power and water turbidity. However, there remains a multitude of site-specific and survey-specific variables that can affect such counts, particularly in wider surveys where standardization may not be required (Schmidt 2003). Consequently, many population assessments may more reliably reflect species detectability than actual population status. Numerous statistical tools are now available that take account of detectability, and can provide estimates of population size, population density or population presence–absence (Table 2). Despite the fact that some of these tools have been around for many years, their use remains largely confined to academia. But are rigorous, statistically defensible population assessments really helpful when it comes to conservation decision-making? Could their application actually divert resources away from more pressing issues? Exactly what type of evidence is needed for population assessment? In 2011–2012, we held five knowledge exchange workshops in England, Wales and Scotland to explore these issues with professional conservation practitioners. Participants included ecological consultants, planners, local authority ecologists, reserve managers, and government and non-government agency employees. To ensure discussions remained focussed, habitat assessment and spatial modelling were specifically excluded from the workshops, although nearly all participants considered these to be areas that offered good potential to guide future surveys. Participants were asked to brainstorm what types of survey (i.e. presence–absence, population indices, population densities, population estimates) were needed to guide conservation at different scales. They were then asked to assign priorities for improved design and analysis, and identify possible barriers to implementing changes to current practice. This article explores the main themes that emerged from these workshops, particularly with regard to surveys carried out within professional practice.