Migratory elk (photo: Holger Spaedkte, University of Alberta)
Partial migration, where populations of animals are composed of both migratory and resident individuals, is widespread in nature, and taxonomically diverse. Last year CAnMove hosted a two day symposium into the ecology and evolution of partial migration, and from this workshop we compiled a number of original research articles to create a special thematic issue of Oikos focussing upon this fascinating phenomenon. The papers in the thematic highlight the breadth of work carried out in this field of migration biology, and showcase exciting new research into various aspects of partial migration.
To begin with we present a review of the current literature, and discuss what is known about the ecology and evolution of partial migration and what the future may hold (Chapman et al. 2011). Next, Francisco Pulido presents a revised threshold model of migration, which aims to understand the proximate basis of individual migratory tendency. Pulido revises the current threshold model to include environmental effects (Pulido 2011). Following this, CAnMove’s Anna Nilsson and coauthors (2011) investigate the physiological adaptations of migration in the partially migratory blue tit, showing that residents have a higher basal metabolic rate than migrants in this species. Next, Francesca Cagnacci and coauthors (2011) analyse data on roe deer migration from 5 different countries to understand the environmental correlates of partial migration. They also importantly highlight that partial migration is on a continuum between full residency and full migration.
Partially migratory manakins (photo: Alice Boyle, University of Western Ontario)
The next series of papers investigate the ecological drivers of partial migration. Alice Boyle presents a community-level test of the ‘limited foraging opportunity’ hypothesis, and finds support across a range of Neotropical bird species for the importance of this mechanism (Boyle 2011). Atle Mysterud and co-authors (2011) show that a range of ecological factors are important in shaping patterns of red deer partial migration, and also show evidence for negative density-dependent migration in this species. Next, Hanna Kokko theoretically models the role of intraspecific competition in facultative partial migration, illustrating how important the strength of the prior residency effect is in predicting which individuals migrate (Kokko 2011). The following paper focuses upon the consequences of partial migration. Jakob Brodersen of CAnMove presents a long term data analysis of partially migratory roach, a freshwater fish, and the effects of this migration on an ecosystem level (Brodersen et al. 2011).
The next series of papers look at how anthropogenic influences can affect patterns of partial migration. Cort Griswold presents a theoretical population model of partial migration which is applied to scenarios of environmental change (Griswold et al. 2011). Mark Hebblewhite shifts from theory to empirical data, and using demographic data analysis shows how human impacts can affect migrants and residents differently by altering the costs and benefits of migration vs. residency in ungulates (Hebblewhite & Merrill 2011).
Partially migratory crabs, which migrate to breed but sometimes forgo breeding (and therefore migration): Photo: Allison Shaw, Princeton University
The final paper broadens the classic definition of partial migration to include animals that migrate to breed, but sometimes forgo breeding (Shaw & Levin 2011). Allison Shaw presents what may be the first theoretical investigation of this kind of partial migration.
All in all, I think we have something for everyone! A diverse and interesting issue for a diverse and interesting subject. We are really pleased that the thematic is out in time for Christmas, and thanks again to all the CAnMovians that helped out with the workshop or the thematic production! God Jul!