Can we successfully monitor a population density decline of elusive invertebrates? A statistical power analysis on Lucanus cervus

Abstract

Monitoring global biodiversity is essential for understanding and countering its current loss. However, monitoring of many species is hindered by their difficult detection due to crepuscular activity, hidden phases of the life cycle, short activity period and low population density. Few statistical power analyses of declining trends have been published for terrestrial invertebrates. Consequently, no knowledge exists of the success rate of monitoring elusive invertebrates. Here data from monitoring transects of the European stag beetle, Lucanus cervus, is used to investigate whether the population trend of this elusive species can be adequately monitored. Data from studies in UK, Switzerland and Germany were compiled to parameterize a simulation model explaining the stag beetle abundance as a function of temperature and seasonality. A Monte-Carlo simulation was used to evaluate the effort needed to detect a population abundance decline of 1%/year over a period of 12 years. To reveal such a decline, at least 240 1-hour transect walks on 40 to 100 transects need to be implemented in weekly intervals during warm evenings. It is concluded that monitoring of stag beetles is feasible and the effort is not greater than that which has been found for other invertebrates. Based on this example, it is assumed that many other elusive species with similar life history traits can be monitored with moderate efforts. As saproxylic invertebrates account for a large share of the forest biodiversity, although many are elusive, it is proposed that at least some flagship species are included in monitoring programmes.

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

“…Monitoring is providing useful information about distribution (Zapponi et al ., 2017) and in a few cases several snapshots are available for comparison (Percy et al ., 2000; Smith, 2003, 2011). Although abundance trends are scarce and time series are still too short to allow assessment of trends, tools are being developed to infer decline (Thomaes et al ., 2017).…”

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

“…Secondly, international comparison of national datasets is often not possible due to differences in monitoring protocols, or is limited to comparing metadata [16,17]. Thirdly, trend analysis can be demanding in terms of the number of monitoring sites and volunteers involved [18][19][20]. These may often not be met for rare species or small regions or countries (e.g., [20]), and data at large spatial scale is needed [21].…”

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

“…[13]. All these methods are suitable for non-experts, and are relatively inexpensive and non-invasive, but they mostly make it possible to obtain presence/absence data or raw estimates of relative population densities [17].…”

“…However, the only way provided by the guidelines, and generally reported in the literature, for obtaining detailed information on L. cervus population size is to use the capture-mark-recapture method [13,19]. Other quantitative methods for estimating population size, such as the use of distance sampling, could in some cases be too inaccurate, or not realistic for flying insects [17]. On the other hand, estimating population size of endangered species by the capture-mark-recapture method is not recommendable because it not only requires expensive and time-consuming field work, but necessarily implies physical capture and handling of individuals, which could affect their survival [20].…”