Lesson 17: Dispersal and Migration

Question 1

Dispersal

Answer 1

means moving away from previous home

Question 2

natal dispersal

Answer 2

refers to leaving parent’ home

Question 3

breeding dispersal

Answer 3

refers to moving to a new breeding site

Question 4

migration

Answer 4

movement between locations , can be life-stage specific (e.g. migration to a nursery or breeding habitat) or seasonal or both

Question 5

dispersal benefits

Answer 5

1) reduced competition for resources
2.) reduced risk of inbreeding

Question 6

dispersal costs

Answer 6

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

Question 7

competition hypothesis:

Answer 7

dispersal functions to reduce competition for resources
to test: manipulate availability of food

Question 8

natal dispersal in northern goshawks experiment:

Answer 8

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

Question 9

Natal Dispersal in screech owls: avoiding competition??

Answer 9

• 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)

Question 10

evidence in favor of a biological rhythem in screech owl: natal dispersal

Answer 10

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

Question 11

inbreeding hypothesis: (in voles)

Answer 11

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

Question 12

What do you do after a breeding attempt: stay and try again or move someplace else?

Answer 12

site fidelity
breeding dispersal

^^^^ refer to movements within a breeding season or between breeding seasons

Question 13

site fidelity

Answer 13

remaining at or moving to a previous location to breed

Question 14

breeding dispersal

Answer 14

abandoning one breeding site and moving to another breeding site

Question 15

the win-stay lose-shift strategy: breeding dispersal in dragonflies

Answer 15

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

Question 16

dragonfly experiment:

Answer 16

• 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

Question 17

dragonfly experiment: in the control territories

Answer 17

males mated an average of 6.5 times
- 100% of these males returned the next day to the same breeding territory

Question 18

dragonfly experiment: in experimental territories

Answer 18

• 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)

Question 19

public information

Answer 19

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

Question 20

kittiwakes and public information

Answer 20

• 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

Question 21

what is migration

Answer 21

implies that animals travel away from a site and then go through all the trouble to travel all the way back

Question 22

costs to migration

Answer 22

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

Question 23

benefits to migration

Answer 23

1.) cope with challenging resources
2.) to exploit resources in distant places
3.) to avoid competition for those resources

Question 24

migration and changing resources

Answer 24

• 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

Question 25

if animals are migrating to deal with changing resources, then we might expect

Answer 25

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

Question 26

resource variation and migration in neotropical birds

Answer 26

• 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

Question 27

habitat, diet, and migratory status are sometimes correlated

Answer 27

• 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

Question 28

evidence that migration has a genetic component

Answer 28

• 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

Question 29

researchers tested the autumn directional preference of the 2 groups of migrants

Answer 29

• 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

Question 30

evidence that migration can be conditional

Answer 30

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