Data from: A specialist predator in a food web with cyclic alternative prey: The gyrfalcon-ptarmigan case revisited
Data files
Feb 16, 2026 version files 9.28 KB
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0_jagsmodel.R
1.55 KB
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0_productivity_normalregression.R
474 B
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1_run_jags_model.R
2.37 KB
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artificial_nest.rda
227 B
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falk.rda
415 B
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lem.rda
172 B
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README.md
4.07 KB
Abstract
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.
Dataset DOI: 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)).