DOI: 10.5061/dryad.8041k
title: Data from: Demographic responses of a site-faithful and territorial predator to its fluctuating prey: long-tailed skuas and arctic lemmings

description: 1. Environmental variability, through interannual variation in food
 availability or climatic variables, is usually detrimental to population
 growth. It can even select for constancy in key life-history traits,
 though some exceptions are known. Changes in the level of environmental
 variability are therefore important to predict population growth or
 life-history evolution. Recently, several cyclic vole and lemming
 populations have shown large dynamical changes, that might affect rodent
 predator demography or life histories. 2. Skuas constitute an important
 case study among rodent predators, because of their strongly saturating
 breeding productivity (they lay only two eggs) and high degree of site
 fidelity, in which they differ from nomadic predators raising large broods
 in good rodent years. This suggests that they cannot capitalize on lemming
 peaks to the same extent as nomadic predators, and might be more
 vulnerable to collapses of rodent cycles. 3. We develop a model for the
 population dynamics of long-tailed skuas feeding on lemmings to assess the
 demographic consequences of such variable and nonstationary prey dynamics,
 based on data collected in NE Greenland. The model shows that populations
 of long-tailed skua sustain well changes in lemming dynamics, including
 temporary collapses (e.g. 10 years). A high floater-to-breeder ratio
 emerges from rigid territorial behaviour and a long life expectancy, which
 buffers the impact of adult abundance's decrease on the population
 reproductive output. 4. The size of the floater compartment is affected by
 changes in both mean and coefficient of variation of lemming densities
 (but not cycle amplitude and periodicity per se). In Greenland, the
 average lemming density is below the threshold density required for
 successful breeding (including during normally cyclic periods). Due to
 Jensen's inequality, skuas therefore benefit from lemming
 variability; a positive effect of environmental variation. 5. Long-tailed
 skua populations are strongly adapted to fluctuating lemming populations,
 an instance of demographic lability in the reproduction rate. They are
 also little affected by poor lemming periods, if there are enough
 floaters, or juveniles disperse to neighbouring populations. The status of
 Greenland skua populations therefore strongly depends upon floater numbers
 and juvenile movements, which are not known. This reveals a need to
 intensify colour-ringing efforts on the long-tailed skua at a circumpolar
 scale.
description: FBarraquand et al. J
 Anim Ecol 2013 Data and CodeContains the field data
 pertaining to skua reproduction and lemming densities from the study sites
 at Karupelv, Traill Island, and Zackenberg (both in Greenland). See cited
 papers by O. Gilg and N.M. Schmidt in Barraquand et al. for a more
 complete description of the data and study sites characteristics. The code
 part of this folder includes all Matlab and Gnuplot scripts that have been
 used to produce the figures in the paper.