Contrasting consequences of climate change for migratory geese: Predation, density dependence and carryover effects offset benefits of high-arctic warming.

Kate Layton‐Matthews,Maarten J J E Loonen,Brage Bremset Hansen,Vidar Grøtan,Eva Fuglei

doi:10.1111/gcb.14773

Abstract

Climate change is most rapid in the Arctic, posing both benefits and challenges for migratory herbivores. However, population-dynamic responses to climate change are generally difficult to predict, due to concurrent changes in other trophic levels. Migratory species are also exposed to contrasting climate trends and density regimes over the annual cycle. Thus, determining how climate change impacts their population dynamics requires an understanding of how weather directly or indirectly (through trophic interactions and carryover effects) affects reproduction and survival across migratory stages, while accounting for density dependence. Here, we analyse the overall implications of climate change for a local non-hunted population of high-arctic Svalbard barnacle geese, Branta leucopsis, using 28years of individual-based data. By identifying the main drivers of reproductive stages (egg production, hatching and fledging) and age-specific survival rates, we quantify their impact on population growth. Recent climate change in Svalbard enhanced egg production and hatching success through positive effects of advanced spring onset (snow melt) and warmer summers (i.e. earlier vegetation green-up) respectively. Contrastingly, there was a strong temporal decline in fledging probability due to increased local abundance of the Arctic fox, the main predator. While weather during the non-breeding season influenced geese through a positive effect of temperature (UK wintering grounds) on adult survival and a positive carryover effect of rainfall (spring stopover site in Norway) on egg production, these covariates showed no temporal trends. However, density-dependent effects occurred throughout the annual cycle, and the steadily increasing total flyway population size caused negative trends in overwinter survival and carryover effects on egg production. The combination of density-dependent processes and direct and indirect climate change effects across life history stages appeared to stabilize local population size. Our study emphasizes the need for holistic approaches when studying population-dynamic responses to global change in migratory species.

Highlights

The climate is changing most rapidly in the Arctic, as a consequence of Arctic amplification (Arft et al, 1999; Serreze & Barry, 2011)
Reproductive success in Arctic nesting geese is largely determined by weather conditions during the breeding season (Bêty, Gauthier, & Giroux, 2003; Madsen et al, 2007; Prop & de Vries, 1993), but conditions earlier in the annual cycle may affect individuals at later stages via carryover effects
We have demonstrated how rapid climate change in high‐arc‐ tic Svalbard increased barnacle goose egg production and hatch‐ ing success, through positive effects of advanced spring onset and warmer summers, respectively (Figures 2, 3, and 5). These positive effects of climate change on early reproduction were offset by a temporal decline in fledging probability due to increased preda‐ tor abundance, strongly affecting population growth (Figures 5 and 6)

Summary

| INTRODUCTION

The climate is changing most rapidly in the Arctic, as a consequence of Arctic amplification (Arft et al, 1999; Serreze & Barry, 2011). Reproductive success in Arctic nesting geese is largely determined by weather conditions during the breeding season (Bêty, Gauthier, & Giroux, 2003; Madsen et al, 2007; Prop & de Vries, 1993), but conditions earlier in the annual cycle may affect individuals at later stages via carryover effects. Besides the potential issue of mismatch in migratory timing with peak food abundance (Dickey et al, 2008; Kölzsch et al, 2015; Lameris et al, 2017), future climate change will likely disrupt other processes affecting reproduction and survival, for instance through trophic interactions (Ims, Jepsen, Stien, & Yoccoz, 2013). We quantify the contributions of direct and indirect drivers to population growth using a retrospective perturbation analysis and investigate how temporal trends in environmental vari‐ ables influence population growth

| MATERIALS AND METHODS

Findings

| DISCUSSION