Lesson 17: Dispersal and Migration Flashcards
Dispersal
means moving away from previous home
natal dispersal
refers to leaving parent’ home
breeding dispersal
refers to moving to a new breeding site
migration
movement between locations , can be life-stage specific (e.g. migration to a nursery or breeding habitat) or seasonal or both
dispersal benefits
1) reduced competition for resources
2.) reduced risk of inbreeding
dispersal costs
1.) energy needed for travel
2.) risks associated with traveling in unfamiliar area (don’t know where predators lurk, where to hide from predators, etc)
3.) risk of not finding appropriate new home with appropriate food and shelter, etc
competition hypothesis:
dispersal functions to reduce competition for resources
to test: manipulate availability of food
natal dispersal in northern goshawks experiment:
METHODS
- food supplemented treatment: platform with several dead quail
- control: platform only
- tracked movement of birds with radio transmitters
RESULTS
- control birds dispersed father than food-supplemented birds so hypothesis supported
Natal Dispersal in screech owls: avoiding competition??
- owls disperse away from parent’s territory largely because the territories cannot support multiple families (competition)
- SO question arises: do they disperse because they, the young owls simply possess the behavior to disperse? Or, do their competitors chase them away? That is, do their parents eject them from the territory? (proximate question)
evidence in favor of a biological rhythem in screech owl: natal dispersal
expt. 1: IN THE FIELD
- fit with radio transmitters
- found that travel distance increases daily after fledging and peaks on Day 50 after which dispersal occurs
expt: IN THE LAB
- raised in isolation
- fitted with pedometers
- peak activity occurred at about 50 days and then fell back to normal (measured hops)
^^^ suggests innate activity level
inbreeding hypothesis: (in voles)
dispersal minimizes the likelihood of inbreeding (ultimate question)
prediction: juveniles living near their siblings should exhibit greater dispersal behavior than juveniles living near non-kin
METHODS
- experimental plots of tall, dense grass, each surrounded by plowed ground
- voles live in the dense grass - are only found in short grass when traveling
TREATMENTS:
- sibling treatment - 2 males and 2 females; all siblings
- control: 2 males and 2 females, not siblings
- captured and identified all individuals in mown ground
RESULTS
- more males than females were captured in short-grass areas (if they were in these areas then they were traveling—- so dispersing)
So males more likely to disperse – when only one sex disperses, it suggests inbreeding avoidance
- sibling voles dispersed earlier and more often than non-sibling voles
SOOOO — relatedness matters!!!!
— inbreeding avoidance influences the dispersal behavior of meadow voles
What do you do after a breeding attempt: stay and try again or move someplace else?
site fidelity
breeding dispersal
^^^^ refer to movements within a breeding season or between breeding seasons
site fidelity
remaining at or moving to a previous location to breed
breeding dispersal
abandoning one breeding site and moving to another breeding site
the win-stay lose-shift strategy: breeding dispersal in dragonflies
in this study, researchers looked to see if prior breeding success had a role in the decision to stay (site fidelity) or leave (breeding dispersal)
key info: male dragonflies are territorial. females pick a male based in part on whether the territory has a decent spot for the female to lay her eggs
dragonfly experiment:
- researchers set up territories with equal resources
- each had a perch for the male to rest on and an oviposition stick for the female to lay eggs on above water
- when a female entered the site, the male would bein to court, the researcher would then lower the oviposition stick under the water
- with no place to lay eggs the female would leave and the male would have zero mating success
dragonfly experiment: in the control territories
males mated an average of 6.5 times
- 100% of these males returned the next day to the same breeding territory
dragonfly experiment: in experimental territories
- males mated 0 times
- only 50% of these males stayed
- so 50% showed breeding dispersal
SO
yes, prior breeding success had a role in the decision to stay (site fidelity) or leave (breeding dispersal)
public information
information obtained from the activity or performance of others about the quality of an environmental parameter or resource
– assess the breeding site not only on their own success but also on the success of others
kittiwakes and public information
- kittiwakes are a kind of seagull. They nest in colonies on sea-cliffs
- in this experiment, researchers give different public information, but the same personal information
- so if the behavior of the birds varies it will be due to the manipulation of the public information
METHODS
- divided colony into “patches
- uniquely marked a ‘focal’ bird in each patch so they could keel track of it
Personal INFO:
- nest failure (researchers swiped the eggs of all focal birds)
Public INFO:
- the nesting success of neighbors was varied (in half the cases, researchers swiped the neighbors’ eggs)
Results:
- if the neighbors were successful at raising young, then about 70% of the focal birds returned to the same breeding sites the next year
- BUT if the neighbors were NOT successful, less than 50% of the focal birds returned to the same breeding sites the next year
- because the only difference between the 2 groups was the public information about the neighbor’s nesting success, we conclude that public information affects kittikwake breeding dispersal
what is migration
implies that animals travel away from a site and then go through all the trouble to travel all the way back
costs to migration
1.) energy needed to fuel the journey
2.) the risks of traveling through unfamiliar area
3.) risk of failing to find suitable area at the end of the trip
benefits to migration
1.) cope with challenging resources
2.) to exploit resources in distant places
3.) to avoid competition for those resources
migration and changing resources
- in the serengeti, wildebeest and zebra migrate hundreds of kilometers in a circut from tanzania to kenya and back
- they appear to track available biomass of grass and its quality
if animals are migrating to deal with changing resources, then we might expect
that species with stable resources would be unlikely. to migrate and those with varying resources would be more likely to migrate
- to study this - researchers took advantage of data on large group of species in which different species vary in resource use and behavior
resource variation and migration in neotropical birds
- in tropical areas of the new world (the neotropics) there are over 300 species in the bird family Tyrannidae
- some are frugivores (fruit-eaters) and others are inscetivroes
- some are found in forests while others are found in more open habitats
- some are migratory and others are not
habitat, diet, and migratory status are sometimes correlated
- insectivorous species from non-forest habitats were most likely to be migratory than those from forest habitats
- no relationship between habitat type and migration in frugivorous speceies
– results may reflect resource variation
- fruit resources seasonally stable in both habitats
- insect populations highly variable in nonforest habitats (between wet and dry seasons) but not in the forest
so – variable food source correlates with likelihoof of migratory behavior
evidence that migration has a genetic component
- the eurasian blackcap is a small bird that summers in germany
- historically, the blackcaps migrated southwest from Germany into southern Spain during the fall migration
- in the 1960’s things changed, some blackcaps started spending the winter in Britian
- british bird lovers were leaving out enough bird seed so that the blackcaps could survive the cold
- advantage of going to britian is that it is closer to germany than southern spain
researchers tested the autumn directional preference of the 2 groups of migrants
- tested when showing migratory restlessness
- orientation measured using an emlen funnel
- also tested orientation of the offspring to see if directional preference was heritable
EVIDENCE
- the results show that offspring show the same behavior as parents— even before they have traveled –
- this behavior is thus likely to be innate since the bird had no experience migrating and were tested in absence of parents
evidence that migration can be conditional
aquatic and terrestrial phenotypes of individual newts
key info: red spotted newts exhibit partial migration
- some migrate from pond to terrestrial habitat in winter and back in spring
- others don’t and are called sedentary
- if they migrate, then they switch from aquatic to terrestrial phenotype
- if sedentary, then they always have an aquatic phenotype
