Species' traits explain differences in Red list status and long-term population trends in longhorn beetles

Some species are more likely to go extinct than others and this is partially due to species' traits. Therefore, it is important to establish links between traits and extinction risks. Different aspects of a species' biology also relates to different sources of threat, such as fragmented populations or low population growth rate. In a comparative study of Swedish longhorn beetles (Coleoptera: Cerambycidae), we related species' traits to two aspects of extinction risk - population decline and small/fragmented populations - measured by long-term population trends and IUCN Red list classifications. Trait relationships were analysed with generalized linear models and multi-model inference. We found that extinction risk generally increased with longer generation times, corresponding to slower life histories. Adult activity period was also related to both metrics of extinction risk, but in different ways. We also found that extinction risk increased with larval host plant specialization, but only for Red list classification. Large body size was related to increased Red list classification in species overwintering as adults, and overwintering stage also structured the effects of several other traits. Our results show that both intrinsic demographic traits and ecological traits affect extinction risks, and also suggest that risks are shaped by multiple mechanisms. Therefore, researchers should carefully choose their metric of extinction risk for comparative studies, as the Red list classification may best capture current risk, whereas population trends can be used more proactively but may reflect historical relationships between traits and extinction risk.