Global changes in insect biodiversity – trends, causes, solutions

Roel van Klink

Insects are the most diverse group of animals on earth, and are responsible for important ecosystem services and disservices. Over the past two decades, reports of declines of insect populations, diversity and biomass have made headlines, but the magnitude, prevalence, and the causes of the problem remained unclear for a long time. To shed light on these questions, we compiled a database of 176 long-term insect monitoring studies from around the world.

In this talk, I will first focus on the global changes in insect numbers and biomass. Despite large geographical variation, insect abundance is, on average, declining in the terrestrial realm, but freshwater insects are on the rise, according to our analysis. One clear driver that emerged was that urbanization is strongly associated with a decline in insect numbers. We attribute the increases of freshwater insects to improvements in water quality and climate change in the temperate zone.

More recently we showed that not only biomass and abundance are declining, but also local species numbers. The declines are mostly attributable to disproportionate declines of the formerly most abundant species, whereas the rarer species have either remained stable, or were replaced by other rare species. I will finish with some ideas on how insect biodiversity can be better protected.