DOI: 10.5061/dryad.9p8cz8www
title: Data from: Predator density outweighs experimental warming effects on short-term carbon and nitrogen loss from arctic shrub litter

description: Rapid climate change in the Arctic is altering biological communities and
 their subsequent effects on ecosystem functioning. For example,
 warming-induced shrub expansion accelerates biogeochemical cycles in part
 by increasing high-quality litter inputs. Likewise, warming may enable
 higher densities of wolf spiders, which are dominant invertebrate
 predators whose activities indirectly alter plant litter decomposition
 rates. Although shrubs and wolf spiders are responding to climate change
 simultaneously, it is unclear how more shrub litter and more spiders
 together will influence elemental cycling in Arctic ecosystems. To test
 how warming could influence these processes, we used a fully factorial
 mesocosm experiment to quantify effects of wolf spiders on litter
 decomposition of an expanding species of dwarf deciduous shrub (Betula
 nana) under ambient and warmed conditions. We found higher densities of
 wolf spiders were consistently associated with more litter mass loss and
 more C and N release, regardless of warming treatment, indicating biotic
 interactions may be a stronger driver of short-term B. nana litter
 decomposition than warming when wolf spiders are present. Our findings
 suggest the combined effects of warming-induced shifts in plant and
 arthropod communities may further accelerate C and N cycling, which could
 cause positive feedbacks on Arctic shrub expansion.
description: # Data from: Predator density outweighs experimental warming effects on
 short-term carbon and nitrogen loss from arctic shrub litter Dataset DOI:
 [10.5061/dryad.9p8cz8www](https://doi.org/10.5061/dryad.9p8cz8www) This
 dataset was produced from a field mesocosm experiment near Toolik Field
 Station (68°38′N and 149°43′W, elevation 760 m) on the North Slope of
 Alaska during June-July 2012. We investigated the effects of wolf spider
 densities and experimental warming (using open-topped chambers) on mass, C
 and N loss from litter of Betula nana, which is an expansive shrub in the
 Arctic. Five blocks were distributed in a homogenous area of moist acidic
 tundra, with each block containing a plot for each of the six experimental
 treatments, which were all possible combinations of the temperature
 treatment (ambient/high) and the spider density treatment
 (low/control/high). We deployed three replicate litter bags at evenly
 spaced locations within each plot. Each row in the dataset represents an
 individual litter bag. Mesocosms were assigned one of three wolf spider
 density treatments: low density, control density, and high density.
 Control densities simulated natural wolf spider densities (approximately
 1.1 spider per m2) based on field surveys conducted in an area adjacent to
 our experimental plots. For low density plots, we removed all wolf spiders
 prior to the start of the experiment and maintained the treatment by
 periodically removing stray wolf spiders that had entered the plots
 throughout the course of the experiment. High density treatments received
 enough wolf spiders to double the density of control plots at the
 beginning of the experiment and subsequently received additional wolf
 spiders throughout the summer if densities declined. We used visual
 surveys at the end of the field season to confirm that plot-level wolf
 spider densities varied according to their pre-assigned treatments (ANOVA:
 F2,27 = 21.85, P = &lt; 0.0001), with average densities in high-density
 plots being 3.3 ± 0.47 wolf spiders, control plots 1.8 ± 0.20 wolf
 spiders, and low-density (removal) plots with 0.3 ± 0.213 wolf spiders
 each. In the year of our experiment, the wolf spider community in this
 habitat type around Toolik Lake was dominated by a single species
 (&gt;95%), Pardosa lapponica. Half of the mesocosms were experimentally
 warmed using ITEX open-topped warming chambers (OTCs), which are a common
 experimental method for passive warming in tundra ecosystems. This
 approach typically increases mean daytime air temperature by 1–2 °C and
 surface temperature by 1.27 °C. OTCs were positioned over the mesocosm
 plots during the summers of 2011 and 2012 immediately after snow melt. In
 both years, the experimental warming treatment was in place from
 approximately mid-June to early August. ## Description of the data and
 file structure The dataset contains one csv file:
 Sagi_BetulaLitterData_Oikos.csv **Variables** block: the spatial block in
 which the plot was located, within which the litter bag was deployed.
 plot: the plot within which the litter bag was deployed. year: this
 particular dataset is only from 2012. location: in this dataset there are
 only litter bags that were deployed on the soil surface. weeks incubation:
 6 for all litter bags in this dataset. wolf spider density treatment:
 low/control/high temperature treatment: ambient/high average soil
 moisture: we measured soil moisture at each litter bag location at the
 beginning, middle, and end of the field season using a HydroSense portable
 soil moisture probe. The average of these measurements is reported for
 each litter bag. litter percent moisture [%]: At the end of experiment, we
 estimated litter moisture content by weighing, drying at 60 °C for 72
 hours and reweighing. percent N remaining [%]: Initial and final N content
 was measured using an elemental analyser feeding a continuous flow mass
 spectrometer system. percent C remaining [%]: Initial and final C content
 was measured using an elemental analyser feeding a continuous flow mass
 spectrometer system. The % C and N contained within each sample were
 converted to mass based on the pre- or post-decomposition (initial and
 final respectively) sample weight and then % of C, N, and total mass
 remaining were calculated as follows: % 𝑟𝑒𝑚𝑎𝑖𝑛𝑖𝑛𝑔 = ([%𝑤/𝑤]𝑓 ∗ [𝑚𝑎𝑠𝑠]𝑓) /
 ([%𝑤/𝑤]𝑖 ∗ [𝑚𝑎𝑠𝑠]𝑖) ∗ 100 where %𝑤/𝑤 represent mass percent of the element
 in a sample, whereas 𝑓 and 𝑖 represent final and initial values.
 PercentMassRemaining [%]: Percent mass remaining was calculated as: (final
 dry litter mass / initial litter mass) * 100 ## Code/software Any software
 that can open csv files