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Résumé :
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Method for the monitoring of Lestes macrostigma (Eversmann, 1836) populations: a trade-off between level of information and effort invested (Odonata: Lestidae). Lestes macrostigma (Eversmann, 1836) is threatened at the French and European Union scales, and as such should be included in the Habitats Directive. This species is integrated into the French National Action Plan for dragonflies and implementing its national monitoring is a priority action. We present here a method offering trade-off between gathered information and invested effort. This method focuses on the autochthony of the studied population and aims to estimate the total number of imagos emerging from a breeding site. To do so, the site is surveyed along a walk determined by the operator and imagos are counted over a width of 3 m, distinguishing the tenerals which are used as a proxy for evidence of autochthony. This count is then extrapolated to the site scale considering the area of habitat favourable to the species oviposition and emergence, and finally over the season in order to assess the minimal size of the autochthonous population. This size is expressed in classes on an exponential scale: 0 – no individual; 99 – tens of individuals; 999 – hundreds of individuals; 9999 – thousands of individuals, etc. To allow analysis at different scales, we argue that this specific monitoring should be mutualised with a general dragonfly monitoring scheme, such as the French “Steli”, at least at one of the monitored stations.
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