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Lecture 26

BIO SCI 94 Lecture Notes - Lecture 26: Compass, Circadian Clock, LightdarkPremium


Department
Biological Sciences
Course Code
BIO SCI 94
Professor
Brad Hughes
Lecture
26

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3/6/19
Where Should I live?
Questions- habitat selection:
Should juvenile leave where they were raised?
How much territory to claim for yourself?
How do habitat density/quality affect fitness?
Proximate/ultimate mechanisms for migration(long distance movement of
population after season change) - relates to questions of habitat selection
Proximate Causes: How Do Animals Navigate?
Three categories of navigation:
Piloting- use of familiar landmarks
Compass orientation- movement in specific direction
True Navigation- locate specific place on Earth
Little understanding about true navigation, piloting/compass orientation well
understood
Piloting
Many species use piloting
Some birds/mammals- offspring memorize route by following parents south in fall
and north in spring
Compass Orientation
Birds/Other organisms- multiple mechanisms for finding compass direction
Some use Sun compass, star compass, magnetic compass
System used depends on weather/other circumstances
Sun difficult to use, position changes throughout day
Most animals- have circadian clock; maintains 24 hour rhythm of chemical
activity
Clock set by light-dark transition of day and night→ tells animals about
time of day→ animals use sun position to find magnetic north
Clear nights- migratory birds use North star to find magnetic north
True Navigation (Map Orientation)
Some species use Earth’s magnetic field→ determine location on globe
Variation in Earth’s magnetic field→ predictable gradient of intensity/angle
Experimenter- manipulate magnetic field artificially→ alter general direction sea
turtles swim in circular pool
Why Do Animals Migrate?
Individuals migrate→ higher reproductive success
Benefit of migration- increase access to food
High cost in time, energy, predation risk
How Should I Communicate?
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Communication- process when signal from one individual changes behavior of
another individual
Communication- social process
Not enough for signal to be sent; signal must be received and acted on
Proximate Causes: How Do Animals Communicate?
Honeybees- highly social, lives in hives, queen bee lays eggs, eggs cared by
workers
Workers also obtain food for themselves and other colony members
Hypothesis- successful food finders communicate location of food to other
individuals
Ultimate leve- communication easily understood, researchers unsure of
proximate mechanism of communication
The Dance Hypothesis
Karl von Frisch- suggested honeybees successful in finding food communicate
location of food
Observed bees display “round dance” and “waggle dance” to workers
Bees follow dance by touching dancing bee
Round dance/waggle dance communicate information about food sources
Communicating Directions and Distances
Round dance- indicate presence of food within 80-100m of hive
Waggle dance- direction/distance to food over 100 from hive
Orientation of waggle dance→ direction of food source
Length of straight waggling run proportional to distance foragers had to fly
to reach food
Dance communicated position of food relative to current position of Sun
Why Do Honeybees Communicate the Way They Do?
Type of signal used by organisms connect with habitat
Each communication type has advantages and disadvantages; communication
system honed by natural selection for maximum benefit and minimum cost
When Is Communication Honest or Deceitful?
Ultimate level- is signal reliable
Some cases- beneficial for individual to convey information accurately
Deceiving Individuals of Another Species
Individuals provide inaccurate/misleading information to members of different
species→ increase fitness
Example:
Hognose snakes play dead when near predator
male /female fireflies flash species specific signal to each other in
courtship
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