Research: partial migration
Under what conditions should individuals of migratory species skip migration and how frequently?
In many migratory species, only some individuals migrate each year (termed 'partial migration'). Most theoretical work on partial migration focuses on species where individuals migrate between breeding and wintering grounds. In these species, the decision to migrate or stay resident is based on tradeoffs between survival and competition. However, partial migration is also common in species where individuals migrate between feeding and breeding grounds. In these species, migration is tied to reproduction, so the decision to migrate or stay is based on tradeoffs between current and future reproduction. We developed the first set of models based on this second type of partial migration. We find that partial migration is expected to occur more frequently as the mortality cost of migration increases, and when there is a fecundity benefit to storing energy over several years before reproducing. Stochastic environments can also favor partial migration. (Shaw & Levin 2011)
Three forms of partial migration (adapted from Fig. 1 in Shaw & Levin 2011).
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These same models can also be used to understand breeding frequency in any species with 'intermittent breeding' where individuals wait several years between breeding attempts (Shaw & Levin 2013).
We also show that for a species of land crab with partial migration, global climate change (based on projections) will likely reduce the frequency at which individuals migrate, which could have quite a negative impact for this species (Shaw & Kelly 2013).
We have also demonstrated several infection-related drivers of partial migration. First, if individuals recover from infection while migrating, this can favor partial migration, for species that are long-lived with relatively low rates of infection (Shaw & Binning 2016). Second, infection from a parasite with density-dependent transmission can favor partial migration as this effectively splits the population, reducing density and thus infection risk for all individuals (Shaw et al. 2019). Third, differential migration benefits based on infection status can lead to partial migration where only a subset of the population migrates, based on infection status (Naven Narayanan et al 2020, Balstad et al. 2021).
Relevant papers
Balstad LJ, Binning SA, Craft ME, Zuk M, Shaw AK (2021) "Parasite intensity and the evolution of migratory behavior." Ecology 102(2): e03229.
Naven Narayanan, Binning SA, Shaw AK (2020) "Infection state can affect host migratory decisions." Oikos 129:1493-1503.
Shaw AK, Binning SA (2020) "Recovery from infection is more likely to favor the evolution of migration than social escape from infection." Journal of Animal Ecology 89(6): 1448-1457.
Shaw AK, Craft ME, Zuk M, Binning SA (2019) "Host migration strategy is shaped by forms of parasite transmission and infection cost." Journal of Animal Ecology 88(10) 1601-1602
Shaw AK, Binning S (2016) "Migratory recovery from infection as a selective pressure for the evolution of migration." American Naturalist 187(4): 491-501.
Shaw AK, Kelly KA (2013) "Linking El Niño, local rainfall, and migration timing in a tropical migratory species." Global Change Biology 19: 3283-3290.
Shaw AK, Levin SA (2013) "The evolution of intermittent breeding." Journal of Mathematical Biology 66(4-5): 685-703.
Shaw AK, Levin SA (2011) "To breed or not to breed: a model of partial migration." Oikos 120(12): 1871-1879.
Naven Narayanan, Binning SA, Shaw AK (2020) "Infection state can affect host migratory decisions." Oikos 129:1493-1503.
Shaw AK, Binning SA (2020) "Recovery from infection is more likely to favor the evolution of migration than social escape from infection." Journal of Animal Ecology 89(6): 1448-1457.
Shaw AK, Craft ME, Zuk M, Binning SA (2019) "Host migration strategy is shaped by forms of parasite transmission and infection cost." Journal of Animal Ecology 88(10) 1601-1602
Shaw AK, Binning S (2016) "Migratory recovery from infection as a selective pressure for the evolution of migration." American Naturalist 187(4): 491-501.
Shaw AK, Kelly KA (2013) "Linking El Niño, local rainfall, and migration timing in a tropical migratory species." Global Change Biology 19: 3283-3290.
Shaw AK, Levin SA (2013) "The evolution of intermittent breeding." Journal of Mathematical Biology 66(4-5): 685-703.
Shaw AK, Levin SA (2011) "To breed or not to breed: a model of partial migration." Oikos 120(12): 1871-1879.