DOI: 10.5061/dryad.jdfn2z3nn
title: Data from: A specialist predator in a food web with cyclic alternative prey: The gyrfalcon-ptarmigan case revisited

description: Population dynamics of specialist predators are tightly linked to their
 main prey and can in simple food webs, lead to complex predator-prey
 interactions (e.g., predator-prey cycles). However, the strength of these
 interactions may be affected by the availability of alternative prey if it
 appears in high numbers and the predator's diet is sufficiently
 flexible. A prominent example of a specialist predator-prey interaction is
 the interaction between gyrfalcon and ptarmigan known from simple food
 webs with few alternative prey. Here we use 23-year long time series from
 a more complex food web in northern Fennoscandia to investigate the
 relative roles of main (ptarmigan) and cyclically fluctuating alternative
 prey (lemmings) in driving gyrfalcon nesting territory occupancy and
 production of young. We find that nesting territory occupancy dynamics are
 dependent on both main and alternative prey, while fledgling production
 within occupied territories is independent of prey abundance dynamics.
 Population density of willow ptarmigan had the expected direct and delayed
 effect on gyrfalcon territory occupancy dynamics, while onehigh-amplitude
 lemming population peak year in the time series boosted colonization of
 nesting territories. This study demonstrates that the population dynamics
 of alternative prey can play an important role also for specialist
 predators. While it might be uplifting that the gyrfalcons being a
 regionally red listed species seem to be able to consume alternative prey,
 both ptarmigan and lemmings are negatively impacted by ongoing climate
 change. Hence, the population status of gyrfalcon should still be a
 conservation concern.
description: # Data from: A specialist predator in a food web with cyclic alternative
 prey: The gyrfalcon-ptarmigan case revisited Dataset DOI:
 [10.5061/dryad.jdfn2z3nn](10.5061/dryad.jdfn2z3nn) ## Description of the
 data and file structure Here we provide data and code to replicate the
 study "A specialist predator in a food web with cyclic alternative
 prey: The gyrfalcon-ptarmigan case revisited". The dataset include a
 23 years of monitoring data on 34 gyrfalcon nesting territories and an
 equally long snap-trapping time series on Norwegian lemming from Finnmark
 in Northern Norway. It also include scripts to run analysis of driver of
 occupancy dynamics of nesting territories and territory productivity.  ###
 Files and variables #### File: 0_jagsmodel.R **Description:** Define the
 näive dynamic occupancy model used to investigate drivers of occupancy
 dynamics in gyrfalcon nesting territorier #### File:
 0_productivity_normalregression.R **Description:** Code to run the
 productivity analysis. #### File: 1_run_jags_model.R **Description:** Code
 to run the dynamic occupancy model using JAGS.  #### File:
 artificial_nest.rda **Description:** Dataset on which nesting territory
 contain at least one artificial nest for use in the occupancy model. Each
 row represent a nesting territory (n=34), and the columns represent the
 years (2000-2020)  ##### Variables * Artificial nests #### File: falk.rda
 **Description:** Nesting territory occupancy dynamics, where each row
 represent a nesting territory (n=34) and a column represent a year
 (2000-2022). NA indicate that the territory has not be checked in that
 given year, 0 indicate that it was checked but determined to not be
 occupied and 1 indicate that it was checked and found to be occupied by a
 territorial couple.  ##### Variables * Nesting territory occupancy ####
 File: lem.rda **Description:** Vector giving standardized (to mean = 0 and
 sd=1) abundance of Norwegian lemming for each year from 2000-2020. #####
 Variables * Abundance of Norwegian lemming #### File: pt.rda
 (Supplementary file) **Description:** Vector giving standardized (to mean
 = 0 and sd = 1) regional ptarmigan densities. The rows represent the years
 from 2000-2021 while the columns represent unique regions in Finnmark,
 Northern Norway.   ##### Variables * Regional ptarmigan densities ####
 File: productivity_data.rda (Supplementary file) **Description:** Data for
 productivity analysis, including covariates. The table contain one row for
 each occupied territory year (n=192) in the dataset.  ##### Variables *
 'loc' : a unique number for each gyrfalcon nesting territory *
 'year': the year * 'chicks': number of chicks produced
 in the given territory in the given year * 'lem_f1': Lemming
 abundance standardized to mean = 0 and sd = 1  * 'pt': Willow
 ptarmigan density in the monitoring cluster closest to the gyrfalcon
 nesting territory in the previous year standardized to mean = 0 and sd =
 1. * 'kr': Presence of artificial nest in the breeding territory
 (0 if not present, 1 if at least one artificial nest is present in the
 territory) * 'perctot1': Total precipitation (measured in mm) in
 the three moths preciding egg-laying (January-March) standardized to mean
 = 0 and sd = 1 * 'perctot2': Total Precipitation (measured in
 mm) in the first month after hatching (May) standardized to mean = 0 and
 sd = 1 * 'snow_depth': Snow depth (measured in cm) in
 April standardized to a mean = 0 and sd = 1 ## Code/software The software
 R is used for this analysis. Packages used to run the scripts are clearly
 shown in the scripts. JAGS is used to run the occupancy model in a
 bayesian framework. JAGS needs to be downloaded and installed, then the
 scripts will access it from the R-interface. ## Access information Other
 publicly accessible locations of the data: * The ptarmigan data is a
 subset of a larger dataset downloaded from GBIF ([Tetraonid line transect
 surveys from Norway: Data from Finnmarkseiendommen
 (FeFo)).](https://www.gbif.org/dataset/c47f13c1-7427-45a0-9f12-237aad351040)