The change in ground beetle similarity was uncertain at eight UK sites between 1994–2003 and 2004–2013

We tested whether ground beetle catch composition became more similar across eight fixed UK Environmental Change Network sites. We compared 1994–2003 with 2004–2013. The sample had three fixed trap lines per site, 123 complete site-years and 129 named species. We set catch indices to common seasonal effort and gave lines and observed years equal weight. Mean Bray–Curtis dissimilarity fell from 0.79695 to 0.77686. The change was −0.02009, with a 95% interval of −0.10432 to +0.06976 from joint site and year-block draws. The direction was also uncertain with Hellinger distance, other quality filters, more complete year coverage and source genus groups. Five-year selections gave a mean change of −0.01911. Pooled raw catches gave a larger decrease, which remained after samples were set to 500 individual catches. A later check with shared calendar years within each site pair gave −0.01454. Local composition changed, but these data did not establish a common increase in similarity across sites. Pitfall catches depend on animal movement as well as animal numbers. The sites are not a random UK sample, and their calendar coverage differs. The package contains original open data, provenance, figures, all results, code, and instructions for offline reproduction. An independent daily-calendar rebuild matched all 6,293 annual species-index cells to numerical precision.

ground beetles · biodiversity · biotic homogenization · species composition · pitfall traps · Environmental Change Network · sampling effort · null result