Ontogenetic niche shifts as a driver of seasonal migration

Wimke Fokkema,Han Olff,Theunis Piersma,Thomas K Lameris,Adriaan M Dokter,Barwolt S Ebbinge,Henk P Van Der Jeugd,André M De Roos,Bart A Nolet

doi:10.1007/s00442-020-04682-0

Abstract

Ontogenetic niche shifts have helped to understand population dynamics. Here we show that ontogenetic niche shifts also offer an explanation, complementary to traditional concepts, as to why certain species show seasonal migration. We describe how demographic processes (survival, reproduction and migration) and associated ecological requirements of species may change with ontogenetic stage (juvenile, adult) and across the migratory range (breeding, non-breeding). We apply this concept to widely different species (dark-bellied brent geese (Branta b. bernicla), humpback whales (Megaptera novaeangliae) and migratory Pacific salmon (Oncorhynchus gorbuscha) to check the generality of this hypothesis. Consistent with the idea that ontogenetic niche shifts are an important driver of seasonal migration, we find that growth and survival of juvenile life stages profit most from ecological conditions that are specific to breeding areas. We suggest that matrix population modelling techniques are promising to detect the importance of the ontogenetic niche shifts in maintaining migratory strategies. As a proof of concept, we applied a first analysis to resident, partial migratory and fully migratory populations of barnacle geese (Branta leucopsis). We argue that recognition of the costs and benefits of migration, and how these vary with life stages, is important to understand and conserve migration under global environmental change.

Highlights

Because foraging abilities and vulnerability to predation risk tend to vary with body size, many species change their food and habitat use in the course of their life
Quantifying population dynamics of migrants with ontogenetic niche shifts We suggest that the explicit consideration of ONS in demographic analyses is vital for understanding migratory systems
The above empirical examples show the generality that conditions in the breeding range are beneficial for juveniles rather than for adults, in terms of abiotic conditions as found in humpback whales and salmons, or because of better quality food or higher food availability, for barnacle and brent geese

Summary

Introduction

Because foraging abilities and vulnerability to predation risk tend to vary with body size, many species change their food and habitat use in the course of their life. As a first step and a proof of concept (Fig. 2), we applied a preliminary analysis to detect the most successful current migration strategy and to establish the effect of using multiple habitats on different life stages of the barnacle goose We chose this species since demographic data are available for three subpopulations with different migration strategies and because its ecology shows similarities to that of the brent goose, which we have presented as an example earlier, but lacks the non-migratory and short-distance migrant strategies and is still fully migratory. The population growth rate of the long-distance migrants was much less sensitive to changes in juvenile survival (ajj) than the resident and short-distance migrants (Table S1) This fits our expectation that juveniles benefit most from the conditions in the high-latitudinal breeding range and is in line with the green wave hypothesis, which predicts higher quality food for birds which migrate northwards along with the early spring quality peak of the vegetation (van der Graaf et al 2006; Kolzsch et al 2015). The different populations are all viable, albeit at different rates, suggesting that the long-distance migratory strategy is so because of the advantages of the juveniles in the Arctic

Discussion

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