Fig. 2
Phenology advances and voltinism drive abundance trends in multivoltine species. Advancing phenology correlates with increasing abundance at species- and population-level for multivoltine species (n = 39), but not univoltine species (n = 91). Lines depict model-predicted relationships between phenology and abundance trends, from generalised linear mixed-effects models. a, b Points show changes in phenology and abundance over the study period (1995–2014) at species-level for univoltine and multivoltine species, respectively. Point colour indicates taxonomic group (butterflies: filled, moths: open). Lines show significant (P < 0.05) relationships. c, d Points show changes in phenology and abundance over the study period at the population level. Grey lines show relationships calculated independently for each species; lines are solid if the relationship is significantly different to zero (P < 0.05), or otherwise are dotted. Solid black lines indicate the overall relationship across species, and are plotted only if significant (P < 0.05). Among univoltine species (c), 3/91 (3.3%) show a significant positive relationship, and 3/91 (3.3%) a significant negative relationship, between phenology and abundance change; the average relationship across species is not significant (Table 2). Among multivoltine species (d), 8/39 (20.5%) show a significant positive relationship between phenology and abundance change, and none show a significant negative relationship; the average relationship across species is also significantly positive (Table 2)
