Migration Flashcards
Describe partial migration
A population of animals that contain both migratory and resident individuals
Which taxa have demonstrated partial migration and which studies show this?
Ungulates (Ball et al., 2001) Amphibians (Grayson and Wilbur, 2009) Fish (Kerr et al., 2009) Invertebrates (Hanson and Hylander, 2009) Long recognised in birds
What are the three partial migration methods recognised in the literature? Study on this
Chapman et al., 2011
Non-breeding partial migration - migrants and residents breed sympatrically but over-winter apart
Breeding partial migration - migrants and residents overwinter together but breed allopatrically
Skipped breeding migration - Individuals migrate to breed but not every year, leading to partial migration
What ecological drivers are there in partial migration?
Body size Prior residency and early arrival Competitive release Predation risk vulnerability Fasting endurance and limited foraging Trophic polymorphism
How does body size drive partial migration?
In many bird species with non-breeding partial migration the larger individuals remain resident
Large size is advantageous and can afford over-wintering costs
Opposite is true e.g. Great bustards (Otis tarda), large individuals migrate during summer months due to low thermal tolerance
Also Salmonids migrate to sea and become larger while resident stream fish remain small with low growth rate
How does prior residency and early arrival affect partial migration?
High phenotypic quality individuals often arrive earliest at mating grounds
Those already occupying territory have competitive advantage in contest over territory
Those that do not leave breeding grounds would have highest breeding success
Driver of partial migration: territory establishing sex more likely to remain resident, within that sex, more dominant/competitively superior individuals less likely to migrate
How does competitive release affect partial migration?
Intraspecific competition for limited food resources = promotes migration amongst subdominants
Costly aggressive contests with larger, dominant individuals
Predicted that dominant/most competitive individuals remain resident all year round and subs migrate
2 studies into competitive release
Mysterud et al., 2011
Red derr (Cervus elaphus)
Proportion of migrants in populations between 38-100%, more common in areas with high density
Grayson & Wilbur, 2009
Red-spotted newts (Notophthalmus viridescens)
Density dependence of newt migration
63% under high density enclosures vs 39% from low density
Newts migrated earlier from high-density enclosures
How does predation risk vulnerability affect partial migration?
Individuals at high risk migrate to escape predation seasonally when growth opportunities are limited
Individuals more likely to migrate will be:
- more conspicuous
- easy to consume
- behaviourally vulnerable (bold)
Individuals trade off predation risk p (cost) and growth potential g (benefit)
p/g in a given habitat increases above a certain threshold then individuals should migrate to increase g or decrease p
Give a study into predation risk vulnerability
Skov et al., 2011
Common bream (Abramis brama)
Bream and main predators, pike, from 2 Danish lakes were PIT tagged in October 2005
Migration of individuals was then monitored
Predation vulnerability index calculated
Calculated pike length-specific gape sizes and bream length-specific body depths
ADD MORE INFO
How does fasting endurance and limited foraging affect partial migration?
Individual physiological differences in survival probability under seasonally low food conditions
Linked to body size drivers
Can reconsider this as “fasting endurance” (i.e. the ability to store energy reserves increases faster with body size than does metabolic rate)
Range of factors that influence seasonal reduction if foraging
Seasonal weather events can limit foraging in tropical birds
Can drive migration in individuals that cannot tolerate reduction in food intake
How does trophic polymorphism affect partial migration?
Variation in food distribution can play important role in partial migration
Varying food items may result in different migratory strategies
e.g. partially migratory roach (Rutilus rutilus)
- individual fish can specialise on different food
- littoral vs pelagic prey
- Svanback et al., 2008
Points on anthropogenic change on partial migration
Mankind causing unprecedented changes to every habitat in the world
Impacts especially migratory animals
Little attention made to how environment change will affect partial migrants
To provide important insights into consequences future work will need to incomporate long term data sets and theoretical modelling
Studies into anthropogenic change in partial migration
Nilsson et al., 2006 Blue tits (Cyanistes caeruleus) Effect of climate change on patterns, used 30 year data sets, contrary to predicted patterns
Hebblewhite & Merril, 2011
Migratory elks (Cervus elaphus)
Humans influence on relative costs and benefits, indirect effect by providing refuge for residents, increased human activity is shifting demographics
Parecke & Gwinner, 2007
Blackbirds (Turdus merula)
Urbanisation found to influence dynamics, individuals reared in common-garden experiments, more sedentary from urban compared to forest populations
What are the ecological consequences of partial migration?
Partial migration may be profoundly important in ecosystem dynamics
Can lead to a significant seasonal flow of nutrients in and out of ecosystem
Studies into ecological consequences in partial migration
Koyama et al., 2005
Salmonids
Transport marine
nutrients upstream
Bromnark et al., 2010
Cyprinid fish
Highly abundent zooplanktonivourous cyprinid fish
Migrating from shallow lakes in winter
Indirect cascading effects of fish predation
What are the evolutionary consequences of partial migration?
Breeding migrations
- allopatric breeding, partial migration can reduce gene flow and act as a reproductive barrier
Non-breeding migrations
- Sympatric breeding, non-random mating might occur
