Extending the natural range of a declining species: genetic evidence for native great crested newt (Triturus cristatus) populations in the Scottish Highlands

Reliability of environmental DNA surveys to detect pond occupancy by newts at a national scale

The distribution assessment and monitoring of species is key to reliable environmental impact assessments and conservation interventions. Considerable effort is directed towards survey and monitoring of great crested newts (Triturus cristatus) in England. Surveys are increasingly undertaken using indirect methodologies, such as environmental DNA (eDNA). We used a large data set to estimate national pond occupancy rate, as well as false negative and false positive error rates, for commercial eDNA protocols. Additionally, we explored a range of habitat, landscape and climatic variables as predictors of pond occupancy. In England, 20% of ponds were estimated to be occupied by great crested newts. Pond sample collection error rates were estimated as 5.2% false negative and 1.5% false positive. Laboratory error indicated a negligible false negative rate when 12 qPCR replicates were used. Laboratory false positive error was estimated at 2% per qPCR replicate and is therefore exaggerated by high levels of laboratory replication. Including simple habitat suitability variables into the model revealed the importance of fish, plants and shading as predictors of newt presence. However, variables traditionally considered as important for newt presence may need more precise and consistent measurement if they are to be employed as reliable predictors in modelling exercises.

Testing the validity of a commonly-used habitat suitability index at the edge of a species’ range: great crested newt Triturus cristatus in Scotland

Habitat Suitability Indices (HSI) are widely used in conservation and in pre-development surveying. We tested a commonly-used HSI to assess its effectiveness at predicting the presence of a European protected species, the great crested newt Triturus cristatus, at the edge of its range. This HSI is used to understand species’ conservation needs, and in assessing the need for, and designing, mitigation. Given the cost of surveying to developers, it is essential that they can have confidence in the index used in targeting work and in Environmental Impact Assessments. We found that nine of the ten factors which make up the HSI are robust in the region, even in a disjunct population believed to have been isolated for around 3000 years. However, we propose modification of the geographic factor, based upon an improved knowledge of the species’ distribution since the HSI was originally devised.