Moth communities at 37 Finnish traps showed no clear spatial homogenization between 1993–2002 and 2010–2019

We tested whether moth communities at fixed Finnish light traps became more alike. We used open National Moth Monitoring records and compared the same 531 trap pairs in 1993–2002 and 2010–2019. The panel had 37 traps in 35 sites. Each pair had at least three shared survey years in each period. We used a fixed seasonal window and standardized species lists to 300 caught individuals. Mean species-list dissimilarity changed from 0.6483 to 0.6547. The change was +0.0063, with a joint 95% resampling interval of −0.0046 to +0.0199. Relative-count dissimilarity changed by −0.0015, with an interval of −0.0226 to +0.0201. A negative change means that communities became more alike. Mean local richness at 300 individuals rose from 87.3 to 91.9 species. Coverage, catch-size and shared-year checks gave small positive species-list changes. The records give no clear evidence of spatial homogenization in this panel. They do not prove no change. The locations are not a random sample of Finland and do not cover the far north. Trap methods, detection and missing surveys limit inference. We provide the source archive, code, data, figures and all results.

moths · Finland · biodiversity · spatial homogenization · species composition · rarefaction · paired surveys · null result · reproducible research