Population variability of species can be deduced from citizen science records: a case study using British butterflies

Abundance data are the foundation for many ecological and conservation projects, but are only available for a few taxonomic groups. In contrast, distribution records (georeferenced presence records) are more widely available. Here we examine whether year-to-year changes in numbers of distribution records, collated over a large spatial scale, can provide a measure of species' population variability, and hence act as a metric of abundance changes. We used 33 British butterfly species to test this possibility, using distribution and abundance data (transect counts) from 1976 to 2012. Comparing across species, we found a strong correlation between mean year-to-year changes in total number of distribution records and mean year-to-year changes in abundance (N = 33 species; r2 = 0.66). This suggests that annual distribution data can be used to identify species with low versus high population variability. For individual species, there was considerable variation in the strength of relationships between year-to-year changes in total number of distribution records and abundance. Between-year changes in abundance can be identified from distribution records most accurately for species whose populations are most variable (i.e. have high annual variation in numbers of records). We conclude that year-to-year changes in distribution records can indicate overall population variability within a taxon, and are a reasonable proxy for year-to-year changes in abundance for some types of species. This finding opens up more opportunities to inform ecological and conservation studies about population variability, based on the wealth of citizen science distribution records that are available for other taxa