A revised system for interpreting great crested newt habitat suitability indices

Buxton, Andrew and Griffiths, Richard (2022) A revised system for interpreting great crested newt habitat suitability indices. The Herpetological Journal, 33. pp. 114-119. ISSN 0268-0130

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A widely used system for assessing habitat for the great crested newt, uses five categories ranging from ‘poor’ to ‘excellent’ based on thresholds for the habitat suitability index. However, how these categories relate to pond occupancy, at an England wide scale, is unknown. Equally, the habitat suitability index system has so far only been validated using traditional direct observation methods rather than environmental DNA protocols that are becoming commonplace. Without further validation on a national scale, misleading decisions may be made concerning the likely presence or likely absence of great crested newts. Using environmental DNA data collected from over 5300 ponds distributed across much of England, we show that the existing scoring system underestimates pond occupancy in the lower categories and overestimates pond occupancy in the higher categories, while the median habitat suitability index value was found just within the “good” category. We found that the median habitat suitability index for occupied ponds was 0.7, confirming this value as a target to aim for when creating or restoring ponds for great crested newts. We suggest a revised system based on the median occupied pond habitat suitability index score, whereby the two extreme “poor” and “excellent” categories each contain just 10% of occupied ponds; the “below average” and “good” categories each contain 20% of all occupied ponds, and the “average” category contains the central 40% of occupied ponds. Although regional variation in estimated pond occupancy rates using this system may need to be accounted for when interpreting habitat suitability index scores, the revised scoring system is generally robust across England. Both the existing and revised habitat suitability index scoring systems are no substitute for surveys, and caution is needed when interpreting absence of newts based on habitat suitability data only.

Item Type: Article
Additional Information: Open Access Policy: The Herpetological Journal supports "green" open access, as outlined by the Research Councils UK, to facilitate deposition of articles e.g. at institutional repositories. The Herpetological Journal also offers the option of "gold" open access for individual articles (free of charge for members of the British Herpetological Society, and at an article processing charge of £97 for non-members). https://www.thebhs.org/policies/the-herpetological-journal-instructions-to-authors
Keywords: Habitat Suitability Index, Triturus cristatus, HSI, UK Regions, environmental DNA
Divisions: Real Estate and Land Management
Depositing User: Dr Andrew Buxton
Date Deposited: 12 May 2022 17:35
Last Modified: 08 Jun 2022 08:51
URI: https://rau.repository.guildhe.ac.uk/id/eprint/16528

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