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Citizen-science data shows long-term decline of snakes in southwestern Europe

Abstract

It is difficult to obtain evidence of population trends for some animals due to their elusive behaviour and/or low density, hindering the acquisition of quantitative data to measure population size that would allow an evaluation of their vulnerability. This is the case for top predators such as snakes. This study explores the usefulness of citizen-science datasets, gathered between 1980 and 2018, in two large regions of southwestern Europe (Spain and the area of Languedoc-Roussillon in southern France) to estimate long-term snake population trends. We used the TRIM (Trends and Indices for Monitoring data) program to analyse trends in 14 snake species during the chronosequence, and modelled the response of each species (the slope of the trend) with a generalized linear mixed model (GLMM) in order to identify the functional traits that explain population trends. Overall, the results showed a general decline of snake fauna in both regions. The GLMM detected that this decline is attenuated in Eurosiberian species compared to Mediterranean species, as well as in species that dwell in forested habitats. The open Mediterranean landscapes in both study regions have been anthropically transformed, and the pressure on their biota has accelerated over recent decades due to habitat loss and degradation. This degradation is affecting Mediterranean organisms such as snakes. The framework we developed allows citizen-science data to be used as a tool to detect population trends and to apply IUCN criterion A (Population size reduction) to species with a high level of imperfect detection or that are suspected to be inaccurately ranked in the assessment of their vulnerability.

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Fig. 1

(Modified from http://www.eea.europa.eu/ last access 05/09/2020). Pictures of the 14 snake species included in the study (details in Table S1): Coronella austriaca (1), Coronella girondica (2), Hemorrhois hippocrepis (3), Hierophis viridiflavus (4), Macroprotodon brevis (5), Natrix maura (6), Natrix astreptophora (7), Zamenis longissimus (8), Zamenis scalaris (9), Malpolon monspessulanus (10), Vipera aspis (11), Vipera berus (12), Vipera latastei (13), Vipera seoanei (14)

Fig. 2
Fig. 3

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Data availability on request.

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Acknowledgements

We would like to thank all the herpetologists who input their observations in the French and Spanish databases over the years. Those from the Languedoc-Roussillon region are acknowledged in Geniez and Cheylan (2012), pp. 10–17. We are also grateful to Albert Montori and Dani Villero from the Spanish Herpetological Society, and Elise Bradbury, who edited the manuscript. This study was partially funded by the Direction régionale de l’environnement, de l’aménagement et du logement de l’Occitanie (DREAL).

Funding

This study was partially funded by the Occitanie Regional Directorate for the Environment, Development and Housing (DREAL).

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Xavier Santos: data curation, formal analysis, supervision, writing original draft. Juan M. Pleguezuelos: data curation, methodology, writing original draft. Brahim Chergui: formal analysis, software. Philippe Geniez: data curation, writing original draft. Marc Cheylan: data curation, conceptualization, writing original draft.

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Correspondence to Xavier Santos.

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Communicated by Indraneil Das.

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Santos, X., Pleguezuelos, J.M., Chergui, B. et al. Citizen-science data shows long-term decline of snakes in southwestern Europe. Biodivers Conserv 31, 1609–1625 (2022). https://doi.org/10.1007/s10531-022-02415-8

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Keywords

  • Citizen science
  • Long-term decline
  • Population trend
  • Snake conservation
  • Southern France
  • Spain