Weather explains inter-annual variability, but not the temporal decline, in insect biomass

Abstract

Müller et al. re-analysed published data on temporal variation in insect biomass in Germany between 1989 and 2016, with a focus on modelling the effects of weather conditions on insect biomass. These upgraded analyses, using an external validation dataset, are a nice demonstration of the strong impact of climatic conditions on annual insect biomass. However, Müller et al.'s conclusion that temporal variation in weather conditions explained most of the temporal changes in insect biomass was overstated. We argue that their methodological approach was unsuitable to draw such conclusion, because of omitted variable bias. We re-ran the analyses of Müller et al. but accounting for a remaining temporal trend in insect biomass due to missing drivers. Our results suggest that the main conclusion of Müller et al. was wrong: there is a significant temporal decline in insect biomass that is not explained by weather conditions. Our commentary recalls that not accounting for missing predictors is likely to produce highly biased results, especially when missing predictors are correlated with the available ones, which is likely to be the case for most of the anthropogenic pressures linked to global change. This highlights the difficult challenge of estimating the relative importance of the global change components in driving the observed biodiversity changes.