Red deer structure the ground-dwelling beetle community in boreal forest

Abstract

Changes in large herbivore distribution and abundance can have effects that potentially cascade throughout the trophic structure of an ecosystem. Little is known about these indirect trophic effects of ungulate herbivory, so the aim of this study was to investigate the role of red deer (Cervus elaphus) in determining the distribution and diversity of ground-dwelling beetles. We collected > 9000 beetles belonging to 149 species in a Western Norway boreal forest by pitfall trapping inside and outside red-deer exclosures placed along a gradient in herbivory intensity. Our study showed that red deer herbivory had a significant effect on structuring ground beetle communities in this boreal ecosystem. Key findings were that: (1) out of 17 beetle species represented by more than 100 specimens, four species benefited from red deer herbivory and associated impacts, while two were detrimentally affected; 2) red deer herbivory did not affect beetle abundance or alpha diversity, but increased local variation in beetle community structure (higher beta diversity); and 3) red deer browsing is important for the composition of the ground-beetle fauna. Herbivory improved the explanation of variation in beetle species composition on the forest floor by 40%. Given that herbivory is an indirect but central predictor of ground-dwelling beetle communities, it should be included in future studies or monitoring programs of red listed or keystone ground-dwelling beetles.