Abstract
AbstractPartial migration is common in a large variety of taxa in seasonally variable environments. Understanding the mechanisms underlying migration is important, as migration affects individual fitness. Migratory herbivores benefit from delayed forage maturation and hence higher food quality during migration and at their summer range, termed the forage maturation hypothesis (FMH). The link between diet quality and rumination time allows migrants eating a higher quality diet to spend less time on rumination, and they can thus allocate more time to additional feeding. However, such an argument implicitly assumes that deer are energy maximizers, while studies have reported also time minimization strategies under risk of predation. Male and female distributions are limited by different factors linked to both body size differences and reproductive strategies, but there is no study investigating differences in activity pattern according to the individual migratory patterns for male and female deer. We here unify the FMH with the hypotheses predicting sex‐specific time allocation strategies. To test predictions of sex‐specific activity of resident and migratory red deer (Cervus elaphus), we analyzed activity data of 286 individuals that were fitted with GPS collars from a population in western Norway. While migrants were more active during the migration itself, we found no differences in activity pattern between migrant and resident deer during the main growth season, neither in terms of proportion of daily time active nor in terms of daily mean movement speed, thus rejecting that deer were energy maximizers. Overall, we found that females were more active during the main growth season even after controlling for body size differences. These patterns are consistent with patterns predicted from sexual segregation theory linked to the reproductive strategy hypothesis. Our study highlights how the understanding of migration can be advanced by considering it in the context of different reproductive strategies of males and females.
Highlights
Migration between distinct seasonal ranges is observed in a large variety of taxa including invertebrates, fishes, birds, and mammals (Chapman et al 2011) and is an especially common phenomenon among ungulates living in seasonal environments (Berger 2004, Bolger et al 2008).Individuals tracking better foraging conditions or avoiding predators at a seasonal range may enhance their fitness, and migration is known to have consequences on population structure and dynamics (Fryxell and Sinclair 1988, Mysterud et al 2001, Chapman et al 2011)
Migratory herbivores with summer ranges at higher elevations or latitudes benefit from delayed forage maturation and improved food quality over a prolonged time, what is termed the forage maturation hypothesis (FMH; Fryxell and Sinclair 1988, Hebblewhite et al 2008)
The individual migration status and forage quality measured by Cumulative instantaneous rate of green-up (CIRG) were not included in the topranked models (P2, P4; Table 2); we could reject predictions from the energy maximization strategy (P1, P3)
Summary
Migration between distinct seasonal ranges is observed in a large variety of taxa including invertebrates, fishes, birds, and mammals (Chapman et al 2011) and is an especially common phenomenon among ungulates living in seasonal environments (Berger 2004, Bolger et al 2008).Individuals tracking better foraging conditions or avoiding predators at a seasonal range may enhance their fitness, and migration is known to have consequences on population structure and dynamics (Fryxell and Sinclair 1988, Mysterud et al 2001, Chapman et al 2011). Migratory herbivores with summer ranges at higher elevations or latitudes benefit from delayed forage maturation and improved food quality over a prolonged time, what is termed the forage maturation hypothesis (FMH; Fryxell and Sinclair 1988, Hebblewhite et al 2008). Herbivore migration is according to the FMH driven by selection on a phenological gradient of plant development in order to maximize energy intake (Hebblewhite et al 2008, Bischof et al 2012). Empirical studies of partial migration, where only a fraction of a population is migratory, have shown that migrants benefit from a higher quality diet relative to resident individuals (Nicholson et al 1997, Sakuragi et al 2003, Hebblewhite et al 2008, Sawyer and Kauffman 2011, Bischof et al 2012, Gaidet and Lecomte 2013, Merkle et al 2016)
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