Different currencies for calculating resource phenology result in opposite inferences about trophic mismatches

Shifts in phenology are among the key responses of organisms to climate change. When rates of phenological change differ between interacting species they may result in phenological asynchrony. Studies have found conflicting patterns concerning the direction and magnitude of changes in synchrony, which have been attributed to biological factors. A hitherto overlooked additional explanation is differences in the currency used to quantify resource phenology, such as abundance and biomass. Studying an insectivorous bird, Sanderling, and its prey, we show that the median date of cumulative arthropod biomass occurred, on average, 6.9 days after the median date of cumulative arthropod abundance. In some years this difference could be as large as 21 days. For 23 years, hatch dates of Sanderlings became less synchronized with the median date of arthropod abundance, but more synchronized with the median date of arthropod biomass. The currency-specific trends can be explained by our finding that m..., To evaluate how our choice of currency for prey phenology will affect our perception of a phenological mismatch, we introduce a model system: the breeding phenology of an arctic shorebird, Sanderling (Calidris alba), and the phenology of their arthropod prey. We derive measures of arthropod phenology in terms of abundance and biomass (with the latter inferred using allometric length-biomass regressions). For this purpose, we analyzed 23 years of arthropod and bird data collected at Zackenberg. In addition, we use a simple simulation to assess how rates of phenological change are affected by the choice of currency for prey phenology. Since 1996 arthropod communities have been sampled throughout the snow-free season at Zackenberg, northeast Greenland (74°28' N, 20°34' W). To calculate annual seasonal trends in arthropod biomass at Zackenberg we first calculated the average number of specimens caught per taxonomic group per day per trap. This we did for each day of the time window during w..., This Dryad repository contains five R-scripts (i.e. script 0, I, II, II, and IV). Script 0 is automatically sourced in the other scripts and does not need to be run manually. Script IV is a standalone script that does not require input files. In contrast, scripts I, II, and III rely on six data files as input. Five of these input files (i.e. I, III, IV, V, and VI) are provided in this Dryad repository. One input file (II) is not provided in this Dryad repository due to conflicting licenses. This file can be downloaded for free from the Greenland Ecosystem Monitoring webpage at the following permanent location https://data.g-e-m.dk/datasets?doi=10.17897/V285-Z265. When downloading this file, the date range needs to be specified as 1996-06-03 to 2020-08-26. All six input files need to be placed in the same working directory as the R-scripts. In addition to these six input files, scripts I, II, and III also require input files that are generated as output in the other R-scripts. It is ther..., # Different currencies for calculating resource phenology result in opposite inferences about trophic mismatches

This online supplementary information contains five R-scripts and five data files.

## DESCRIPTION OF THE DATA AND FILE STRUCTURE

### R-SCRIPTS

* (0): Versluijs2022_Script_0-AuxilliaryFunctions.R
A script containing auxiliary functions that are automatically sourced in Script 1 and Script 5. This script does not need to be run manually.
* (I): Versluijs2022_Script_1-ArthropodDataZAC_DataPreparation.R
Script with data preparation steps for the arthropod dataset from Zackenberg containing pitfall data collected from 1996 to 2020. This adjusted data file is required as an input file for scripts II and III.
* (II): Versluijs2022_Script_2-ArthropodDataZAC_AddBiomass_NumbersvsBiomass.R
To study whether the timing of the yearly arthropod peak at ZAC differs when depicted by arthropod numbers versus arthropod biomass, we first need to add estimates of biomass to ...