Comparison of Two Sampling Methods to Estimate the Abundance of Lucanus cervus with Application of n-Mixture Models

• Published in: Forests 2020-10, Vol.11 (10), p.1085
• Main Authors: Della Rocca, Francesca, Milanesi, Pietro, Magna, Francesca, Mola, Livio, Bezzicheri, Tea, Deiaco, Claudio, Bracco, Francesco
• Format: Article
• Language: English
• Subjects: Abundance; Bayesian analyses; Bayesian analysis; Biodiversity; Capture-recapture studies; Confidence intervals; Conservation; Conservation status; detection probability; diurnal tree trunk surveys; Endangered & extinct species; Error correction; Estimates; Evaluation; Geographical distribution; Habitats; Insects; Lucanus cervus; Mathematical models; Methods; Monitoring; non-invasive sampling; Operators; Polls & surveys; Population; Population density; Population number; Population statistics; Probabilistic models; Probability; Sampling; Sampling methods; Sampling techniques; Statistical analysis; Trees; Wildlife conservation
• ISSN: 1999-4907; 1999-4907
• DOI: 10.3390/f11101085

Monitoring programs should be based on the measurement of two main pillars for evaluating the conservation status of a species: population size and geographical distribution. To date, the only way reported in the literature to obtain detailed information on L. cervus population size is to use the capture-mark-recapture method. This is an expensive and time-consuming technique that implies physical capture and handling of individuals, which could affect their survival. Therefore, in this study we tested and compared two non-invasive sampling approaches, namely evening walk transects and diurnal tree trunk surveys, to derive accurate abundance estimates by means of N-mixture models in a Bayesian framework. In our study, both methods showed relatively high detection probability (≥56%). However, tree surveys performed better than walk transects (≈80%), especially with the progression of the sampling season. Tree surveys proved to be more effective than walk transects in providing data for an accurate population density estimate (much smaller 95% Bayesian Confidence Intervals). In light of a cost and benefit assessment, the tree survey is undoubtedly more convenient, as well as more effective, as it is more time consuming but less expensive than a walk transect (one operator for 2–3 h vs. two operators for 30 min each). Moreover, it needs fewer expert operators because of the greater proximity to the species, increasing the probability of correctly identifying it, i.e., reducing type I error (false positive or overestimation of counts). For the first time, we applied N-mixture models for estimating population abundance of L. cervus. Overcoming all the limits imposed by the use of the capture-mark-recapture method, in this study we performed a further step forward in the planning of monitoring aimed at the conservation of L. cervus and the evaluation of its demographic trend.