1. Rapid warming has facilitated an increase in deciduous shrub cover in arctic tundra. Because shrubs create a cooler microclimate during the growing season, shrub cover could modulate the effects of global warming on the phenology and activity of ectotherms, including arthropods. This possibility was explored here using two dominant arthropod groups (flies and wolf spiders) in Alaskan tundra. 2. We monitored arthropods with pitfall traps over five summers at four sites that differed in shrub abundance, and used generalised additive mixed models (GAMMs) to separate the two underlying components of pitfall trap catch: the seasonal trend in arthropod density and the effects of short-term weather variation (air temperature, wind speed, rainfall, solar radiation) on arthropod activity. 3. We found that shrub cover significantly altered the seasonal trend in the abundance of flies by reducing early-season pitfall catch, in line with observed later snowmelt in shrub-dominated plots at these sites. 4. Additionally, shrub cover modulated the effects of many weather variables on arthropod activity: shrub cover shifted wolf spiders' temperature–activity relationship, dampened the positive effect of solar radiation on the activity of arthropods in total, and ameliorated the negative effect of wind on the activity of flies. 5. Thus, these results indicate that shrub encroachment will probably be accompanied by altered arthropod responses to warming and other key weather variables. Because the rate of key ecological processes – herbivory, decomposition, predation – are controlled by activity at the organismal level, these effects on arthropods will have long-term ecosystem-level consequences.
Bibliographical noteFunding Information:
We wish to thank Team Bird 2010–2017, especially Leslie Baker, Heather Bass, Rachel Carmickle, Kathryn Daly and Taryn Flink for field and laboratory assistance. Two anonymous reviewers provided comments that greatly improved the manuscript. Toolik Field Station (Institute of Arctic Biology, University of Alaska Fairbanks) and CH2M Hill provided logistical support. Funding was provided by a collaborative NSF grant from the Office of Polar Programs (ARC 090844 to NTB, ARC 0908602 to LG, and ARC 0909133 to JCW). Meteorological datasets for the Imnavait site were provided by the Institute of Arctic Biology, UAF, based upon work supported by the National Science Foundation under grant no. 1107892. Meteorological datasets for Toolik Field Station were provided by the Toolik Field Station Environmental Data Center, based upon work supported by the National Science Foundation under grants 455541 and 1048361.
- Climate change
- pitfall trap