Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome

Chronic, low intensity herbivory by invertebrates, termed background herbivory, has been understudied in tundra, yet its impacts are likely to increase in a warmer Arctic. The magnitude of these changes is however hard to predict as we know little about the drivers of current levels of invertebrate herbivory in tundra. We assessed the intensity of invertebrate herbivory on a common tundra plant, the dwarf birch (Betula glandulosa-nana complex), and investigated its relationship to latitude and climate across the tundra biome. Leaf damage by defoliating, mining and gall-forming invertebrates was measured in samples collected from 192 sites at 56 locations. Our results indicate that invertebrate herbivory is nearly ubiquitous across the tundra biome but occurs at low intensity. On average, invertebrates damaged 11.2% of the leaves and removed 1.4% of total leaf area. The damage was mainly caused by external leaf feeders, and most damaged leaves were only slightly affected (12% leaf area lost). Foliar damage was consistently positively correlated with mid-summer (July) temperature and, to a lesser extent, precipitation in the year of data collection, irrespective of latitude. Our models predict that, on average, foliar losses to invertebrates on dwarf birch are likely to increase by 6–7% over the current levels with a 1 °C increase in summer temperatures. Our results show that invertebrate herbivory on dwarf birch is small in magnitude but given its prevalence and dependence on climatic variables, background invertebrate herbivory should be included in predictions of climate change impacts on tundra ecosystems. This study is a joint contribution of the Herbivory Network (http://herbivory.biology.ualberta.ca) and the Network for Arthropods of the Tundra (NeAT; https://tundraarthropods.wordpress.com/). Dwarf birch distribution maps were kindly provided by Kyle Joly. Sample collection during 2014 was facilitated by INTERACT (http://www.eu-interact.org/). ICB was supported by a postdoctoral fellowship funded by the Icelandic Research Fund (Rannsóknasjóður, grant nr 152468-051) and AXA Research Fund (15-AXA-PDOC-307); MtB and EK were supported by the Nordic Centre of Excellence TUNDRA, funded by the Norden Top-Level Research Initiative ‘‘Effect Studies and Adaptation to Climate Change’’; EMS and KAB were supported by COAT (Climate-ecological Observatory of the Arctic Tundra); AB was supported by MOBILITY PLUS (1072/MOB/2013/0) and the Polish-American Fulbright Commission; CGB was supported by IUT 20-28, EcolChang e Center of Excellence; BCF and TK were supported by the Academy of Finland (project 256991); MMPDH was supported by The Netherlands Organization for Scientific Research (NWO-ALW, VIDI grant 864.09.014); DSH was supported by the Natural Sciences and Engineering Research Council of Canada; AH was supported by the Research Council of Norway (grant 244557/E50); JL was funded by the German Research Foundation DFG (project WI 2680/8-1); MM-F was supported by a NERC IRF fellowship NE/L011859/1; SN was supported by the Villum foundation’s Young Investigator Programme (VKR023456); JS was supported by Kempestiftelserna and the Research Foundation Flanders (FWO); AS and NS were supported by the grant of RFBR (project 16-44-890108), grant of UB of RAS (project 15-15-4-35) and IEC “Arctic” of Yamal Government Department of Science and Innovation; LES and PAW were supported by the UK Natural Environment Research Council (NERC) grant NE/K000284/1; MVK and VZ were supported by the Academy of Finland (project 276671). Scopus