Host-plant nitrogen preference did not predict faster butterfly gains at higher nitrogen deposition on 3,409 British transects in 1985-2024

We tested whether butterfly species whose larval host plants prefer nitrogen-rich soils increased relative to species of poor-soil hosts at sites with more atmospheric nitrogen deposition. We used 507,113 UK Butterfly Monitoring Scheme site indices of 54 resident taxa on 3,409 transects in England, Wales and Scotland from 1985 to 2024. Host N was the mean British Ellenberg N value of primary host plants. Site deposition was the 1986-2012 mean CBED total N deposition for the 5-km square. Site x year, species x year and site x species fixed effects compared species at the same site in the same year. The host N x deposition x decade term was negative, not positive as predicted: -0.0118 log units per decade per SD x SD with trait, thermal-niche and geography controls (95% CI -0.0253 to +0.0017; 50-km clusters). This excludes a relative gain larger than about 6% over 40 years for host N 8 versus 2 at 10 kg N/ha/yr more deposition. A 10,000-shuffle trait permutation gave one-sided p = 0.97 for the predicted sign. With controls, only 1 of 6 region-period samples was positive (northern England 1985-2004). A community host-N index did not increase at low, mid or high deposition. A positive control (species thermal index x site northing) was detected (+0.104, SE 0.045). An exploratory split into ammonia (NHx) and oxidised N (NOx) gave opposite signs, but these became small with controls and did not replicate across regions and periods. Limitations: modelled 5-km deposition, no land-cover data, literature host lists and recorder-chosen sites.

nitrogen deposition · butterflies · UKBMS · Ellenberg N · eutrophication · host plants · CBED · ammonia · community index · fixed effects · null result · Great Britain