Monocultural sowing in mesocosms decreases the species richness of weeds and invertebrates and critically reduces the fitness of the endangered European hamster

Summary

Intensive cereal monoculture is currently the main cause of biodiversity decline in Europe. However, it is difficult to disentanglethe effects of intensive monoculture (e.g. pesticide use, mechanical ploughing and reduced protective cover), letalone evaluate how far the reduction of crop diversity affects biodiversity. It remains unclear to which extent the consequentdecrease in food resources affects farmland biodiversity, and particularly vertebrate species. We therefore designed thisstudy in mesocosms to investigate the effects of monoculture crops (organic wheat or corn seeds) and mixed crops (a combinationof organic wheat, corn, sunflower and alfalfa seeds) on (1) the species richness of weeds and invertebrates and (2)the reproductive success of the European hamster (Cricetus cricetus), a critically endangered umbrella species of Europeanfarmlands. We found a negative impact of organic monoculture crops on plant and invertebrate species richness, with valuesrespectively 38% and 28% lower than those obtained for mixed organic crops. The reproductive success of hamsters wasreduced by 82% in monoculture mesocosms. These results highlight that monoculture per se can be detrimental for farmlandbiodiversity (i.e. from plants to vertebrates), even before taking into account the use of pesticide and mechanization. Webelieve that future research should further consider how food reduction in agroecosystems affects farmland wildlife, includingvertebrates. Moreover, we argue that conservation actions must focus on restoring plant diversity on farmland to reversethe observed trend in farmland wildlife decline.