On fitness and partial migration in a large herbivore – migratory moose have higher reproductive performance than residents

Abstract

Partially migratory populations comprise both resident and migratory individuals. These tactics may coexist if their demographic contribution to future generations (i.e. fitness) are equal or vary temporally with environmental conditions, or if individuals switch between being migrant and resident. Alternatively, the choice of movement tactic can be based on individual attributes such as age, competitive ability or personality. In the latter cases, the two tactics are not expected to have similar average fitness. In this study, we examined the effect of movement tactic on reproductive performance and survival of 82 GPS-marked female moose and their offspring in a partial migratory population in central Norway. The results indicated higher growth in the migrating part of the population because migrating females produced more twins than resident females. We found no differences in pregnancy rates or survival of adults or their offspring, indicating a net fitness benefit of being migrant. We found the average shoulder height of residents to be slightly lower than of migrants, but doubt that this affected their migration ability. A more likely explanation is that migratory females are both more fecund and grow bigger because of better conditions in their summer ranges. This may be a temporal phenomenon if the fitness differences between migratory and resident moose vary according to environmental fluctuations.

Novel Type of Chronic Wasting Disease Detected in Moose (Alces alces), Norway

“…Norway is populated by several species of wild cervids with varying degrees of overlapping range. Seasonal migrations are common and distances might exceed 150 km ( 13 – 15 ). However, studies tracking global positioning satellite–collared moose have not documented regular seasonal migrations between Selbu and Lierne municipalities, suggesting that these can be considered different moose subpopulations.…”

Fitness consequences of different migratory strategies in partially migratory populations: A multi‐taxa meta‐analysis

“…Our results suggest the within‐taxonomic group variability in our data is less marked than the between‐group differences; in addition to the stark differences in migratory distance between taxonomic groups, between‐taxa variances in body size, general physiology and life histories may also be driving differences in relative fitness benefits and susceptibility to the effects of climate change. Altitudinal migrants, such as in the ungulate populations which comprised our mammal data, may benefit from climate change‐induced longer vegetation growth periods, resulting in comparatively more forage of higher nutritional value in the higher‐altitude migrant ranges (Rolandsen et al, ). Differences between taxa may also not necessarily be down to direct taxonomic differences; we did not, for instance, distinguish between different models of partial migration, which differ according to which season (breeding or non‐breeding) residents and migrants are allopatric (Chapman et al, ).…”

Migration in geographic and ecological space by a large herbivore

“…In another study, Norwegian female moose had a higher fecundity and grew to a larger body size than resident moose, possibly due to improved foraging conditions on migrant summer ranges (Rolandsen et al. ).…”