In a warming world, changes in climate may result in species-level responses as well as changes in community structure through knock-on effects on ecological interactions such as predation and herbivory. Yet, the links between these responses at different levels are still inadequately understood. Assessing how microclimatic conditions affect each of them at local scales provides information essential for understanding the consequences of macroclimatic changes projected in the future. 

Focusing on the rapidly changing High Arctic, we examine how a community based on a common resource species (avens, Dryas spp.), a specialist insect herbivore (Sympistis zetterstedtii), and natural enemies of lepidopteran herbivores (parasitoids) varies along a multidimensional microclimatic gradient. We ask (1) how parasitoid community composition varies with local abiotic conditions, (2) how the community-level response of parasitoids is linked to species-specific traits (koino- or idiobiont life cycle strategy and phenology) and (3) whether the effects of varying abiotic conditions extend to interaction outcomes (parasitism rates on the focal herbivore and realized herbivory rates). 

We recorded the local communities of parasitoids, herbivory rates on Dryas flowers and parasitism rates in Sympistis larvae at 20 sites along a mountain slope. For linking community-level responses to microclimatic conditions with parasitoid traits, we used joint species distribution modelling. We then assessed whether the same abiotic variables also affect parasitism and herbivory rates, by applying generalized linear and additive mixed models.

We find that parasitism strategy and phenology explain local variation in parasitoid community structure. Parasitoids with a koinobiont strategy preferred high-elevation sites with higher summer temperatures or sites with earlier snowmelt and lower humidity. Species of earlier phenology occurred with higher incidence at sites with cooler summer temperatures or later snowmelt. Microclimatic effects also extend to parasitism and herbivory, with an increase in the parasitism rates of the main herbivore S. zetterstedtii with higher temperature and lower humidity, and a matching increase in herbivory rates. 

Our results show that microclimatic variation is a strong driver of local community structure, species interactions and interaction outcomes in Arctic ecosystems. In view of ongoing climate change, these results predict that macroclimatic changes will profoundly affect arctic communities. 

This dataset comprises of parasitoids caught during summers 2015 and 2015 at 20 sampling sites distributed at different elevations and snowmelt charasteristics near the Zackenberg research stations in North-East Greenland. All sites were of Dryas heath habitat, characterised by Dryas octopetalaXintegrifolia dominated vegetation. Trapping of parasitoids was done using 10 open sticky traps (5cm by 4.5cm white sticky traps cut out from sticky board: Barrettine Environmental, UK [product no longer available]) and 5 emergence traps (with a half a square metre footprint) placed on Dryas tussocks.  The traps were emptied every six days 4 sites a time in a rolling schedule.

The parasitoids were subsequently picked of off the sticky traps, their whole DNA was extracted and half of their Cytochrome Oxidase I barcode region was amplified using Primers B-F and HCO. See the supplementary information of the publication for more details. The dual tag indexed library of parasitoid samples was sequenced at the FIMM Technology Centre in a HiSeq2500 2x250bp run.

Additionally, each year, roughly 50 larvae of noctuid moth Sympistis zetterstedtii were collected from around each sampling site by hand and also though sticky trapping. The whole DNA of these larvae was sequenced and parasitoid barcode sequences were amplified while suppressing the amplification of lepidopteran sequences using a species specific blocking primer. 

Dryas flower numbers, flowering phenology and flower damage by insect herbivores was recorded during every visit to the sites. These counts were done in 5 square metre monitoring plots per trapping site. 

Microclimate was recorded at trapping sites using Lascar EL-USB-2 tempeerature and air humidity loggers under a small white plastic dome at ~ 10 cm height.

The accompanying file README_ZackenbergParasitoids.txt contains information on all files and columns of data in this dataset as well as additional information on the dataset.