Common beetles had an earlier mean May–October catch date across seven UK sites in 2004–2013 than in 1994–2003

We tested whether a change in the mean seasonal catch date of ground beetles came from changes within species or changes in species catch shares. We used open UK Environmental Change Network data. The main set has 20 fixed transects, 327 complete transect-years and 39 common species at seven sites. We corrected monthly catches for valid trap-days and compared 1994–2003 with 2004–2013. The mean May–October catch date was 5.86 days earlier, with equal weights for sites. A shared two-year block bootstrap gave a 95% interval of 0.54 to 9.25 days earlier. An exact symmetric decomposition assigned 5.70 days to changes within species and 0.16 days to changes in species shares. The share component had an interval across zero. The site effects had both signs. Their separate t interval also crossed zero. All nine sensitivity checks gave earlier point estimates, but several intervals crossed zero. All identified species gave a 4.94-day advance, with an interval across zero. Selected seasonal curves show that a mean-date change can come from a change in spring and autumn catch shares while the peak month stays the same. The result describes seasonal catches in this selected network. It does not establish earlier emergence, climate causation or a UK-wide change. The package preserves source data, provenance, code, figures, all checks and an independent calculation from source records.

Carabidae · seasonal timing · pitfall traps · Environmental Change Network · species catch shares · reproducible analysis