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

Abstract

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.

A multidimensional study on population size, deadwood relationship and allometric variation of Lucanus cervus through citizen science

“…During our two‐week sampling campaign, we collected a remarkably high number of L. cervus individuals (651), much greater than usually reported in other studies. For instance, the average number of collected individuals among sampling campaigns conducted across 23 sites in seven European countries was 123 (Bardiani et al, 2017; Chiari et al, 2014; Della Rocca et al, 2020; Méndez & Thomaes, 2021). These results may be largely dependent on different sampling methodologies employed across these studies.…”

“…These included observing or collecting remains of predations or living individuals along transects, using baited and aerial traps, and have recently started to rely on citizen science (Bardiani et al, 2017;Chiari et al, 2014;Romiti et al, 2016;Thomaes et al, 2021). The latter allows to obtain large data despite the difficulties related to the fact that the activity peak of the beetle is mostly restricted to a few weeks of June and July and the species is mostly active at dusk (Bardiani et al, 2017;Campanaro & Bardiani, 2012;Campanaro et al, 2011;Chiari et al, 2014;Della Rocca et al, 2020;Rink & Sinsch, 2007;Romiti, Bissattini, et al, 2017;Romiti, De Zan, et al, 2017;Thomaes et al, 2017Thomaes et al, , 2021Tini, Bardiani, Campanaro, Chiari, et al, 2017).…”

The European Stag Beetle (Lucanus cervus) Monitoring Network: International Citizen Science Cooperation Reveals Regional Differences in Phenology and Temperature Response

“…Consequently, a difference in engagement or start-up year between countries should not be a concern for future analysis. Furthermore, innovative techniques allow trend or population estimates to be separately made for each transect (or group of transects) [39][40][41].…”

Biology and conservation of the European stag beetle: recent advances and lessons learned

“…Continuous monitoring and long time series will allow to relate abundance with climatic and land use variables (Thomaes et al ., 2017), thus providing a mechanistic understanding of adult phenology and abundance. Transects and dusk can be combined with other monitoring methods (Della Rocca et al ., 2020).…”

“…A major recent finding has been a reliable monitoring method of adult populations, after a decade of search (Hawes, 2005, 2008; Vrezec & Kapla, 2007; Campanaro et al ., 2011, 2016; Harvey et al ., 2011b; Vrezec et al ., 2011; Chiari et al ., 2014; Bardiani et al ., 2017). CMR have been rarely used to assess population size (Chiari et al ., 2014) and can be now superseded (Della Rocca et al ., 2020). Transects at dusk (Campanaro et al ., 2016) provide now a standardised index of population size.…”