Down-sizing of dung beetle assemblages over the last 53 000 years is consistent with a dominant effect of megafauna losses

The ongoing down-sizing of the global mammal communities is assumed to have subsequent effects on mutualistic species communities. Dung beetles co-evolved with large-sized animals since millennia and depend on the megafauna feces of an appropriate size. Mammal community down-sizing as a result of past and ongoing megafauna losses is therefore likely to result in a down-sizing of dung beetle communities. However, empirical evidence for this co-down-sizing is lacking especially on larger spatial scales and over extended periods of time. Here, we show a significant down-sizing of European dung beetle assemblages over the last $\sim$53 000 years by relating Quaternary fossil records with trait information on body size of beetles. This significant down-sizing of dung beetle communities was thereby not linear, but characterized by a weak decrease until the early Holocene but a strong acceleration in the recent pre-history, from 6–7000 years BP onwards. This acceleration of down-sizing coincides with the completion of the Quaternary megafauna extinction and the start of major shifts in human agricultural land-use. In contrast, assemblage mean body size of non-coprophagous scarabids as well as ground beetles – two groups of beetles with no or weak relations to megafauna – was observed to increase towards the present with an acceleration of body size increase coinciding with the onset of late-glacial warming (14 200 years BP). In summary, the observed late-Quaternary down-sizing of European dung beetle communities is consistent with an effect of pre-historic megafauna losses, and not with the coincident general warming. Ongoing down-sizing of mammal communities is therefore likely to result in further down-sizing of dung beetle assemblages, with potential effects on their important role for nutrient cycling and secondary seed dispersal in natural and extensive agro-ecosystems. Future nature management initiatives could halt or even reverse this functional diversity loss via effective protection or restoration of megafauna communities.