Download - Animal Orientation
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Animal Orientation
Kineses Taxes
Migration Homing
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Orientation movements
1. Simple responses to immediate surroundings = kineses and taxes and have an immediate benefit e.g. a slater moving into a damper place.
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2. Complex movements over long distances to a pre-determined location which is out of direct sensory contact e.g. migration
and homing which are internally initiated.
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Environmental StimuliA slater retreating to a daytime crevice
could be responding to the dampness, darkness or coolness.
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Choice chambers are often used to identify which stimuli influence their behaviour.
This is a fair test where all factors are kept the same except for the one factor being
investigated.
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For a humidity investigation water is placed in one chamber and a drying
agent such as silica gel is placed in the other chamber.
Left for 20 minutes, the number in each chamber is statistically analysed.
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Simple orientation mechanisms
Taxis = movement of an organism towards or away from a stimulus.
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Positive = towards
Negative = away
Negative phototaxis = movement away from light e.g. earthworms
Positive phototaxis = movement towards the light e.g. many swimming algae
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The direction of the light source is indicated by white
rectangles.
Phototaxis, Dictyostelium giganteum
(A Cellular Slime Mold )
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Positive chemotaxis = movement towards a chemical source e.g. mosquitoes towards people along CO2 gradient
When a capillary tube filled with glucose is placed in a medium
containing E. coli, the bacteria alter their locomotion so that they
congregate near the opening of the tube.
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Positive rheotaxis = movement against a current e.g. salmon
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What does an animal do when it has a specific need, such as food, a higher humidity environment, or shelter from the sun, but it has no information about the location of the needed resource? It may engage in an undirected search, or kinesis.
Kinesis = random movement due to the presence of a stimulus. The rate of activity is determined by the intensity of the stimulus – not the direction
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stim
ulus
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stim
ulus
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This simple diagram illustrates the basics of an undirected search. The animal, travelling from left to right in the diagram, moves in a more or less straight line through unsuitable habitat. When it begins to perceive better conditions (the blue area) two things can change--its rate of speed and the angle of its turns. By turning sharper angles and slowing down, it stays in the vicinity of the improved conditions. Simple changes in movement pattern, in response to better environmental conditions, amount to habitat selection. Conversely, if an animal finds itself in poor conditions, rapid, straightline movements will increase its likelihood of finding better conditions.
http://www.animalbehavioronline.com/kineses.html
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Two types:Orthokinesis = stimulus intensity
determines speed of movemente.g. slater’s rate of movement is inversely
proportional to the humidityKlinokinesis = stimulus intensity
determines rate of turning eg lice turn more often in 35° than in 30°.
Human skin temp is about 35°.lice more likely to return to, and stay
longer in, 35°.Orthokinesis and klinokinesis movies
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Migration
= an active, regularly repeated movement in a particular direction by a population of animals
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Excludes passive dispersal (carried by the wind).
Usually to a feeding and/or breeding area.
Usually a two-way trip.
Usually have regular timing.
Often over long distances.
Often at a definite life-cycle stage
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Examples
Salmon – feed at sea and migrate up rivers to spawn. Swim up same river in which they hatched – find natal stream by its
unique chemical properties.
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Eels and whitebait swim downstream to spawn. Young swim upriver to feed and mature.
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Zooplankton twice-daily migrate 1000m vertically to feed at night and gain protection of depths during the day
http://www.wellesley.edu/Biology/Faculty/Mmoore/research_zooplankton.html
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Vertical MigrationMany freshwater and marine zooplankton perform daily excursions (i.e.,
vertical migrations) up and down in the water column, with changing levels of light triggering these daily migrations. For example, the classic pattern consists of zooplankton residing deep in the water column during
the day when light levels are high. They ascend at dusk to the surface waters where they graze on phytoplankton at night. Then, at dawn, they
descend and the daily cycle of vertical migration begins again. This behaviour most likely evolved as an anti predator strategy. The major predator of zooplankton is planktivorous fish (e.g., perch, alewives, or mackerel in the ocean). Most planktivorous fish are visual feeders and require a certain light intensity for efficient feeding. So zooplankton
avoid becoming dinner for fish by remaining in deep dark waters during the day, and ascending into dark, food-rich waters at night.
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When to migrate?
Need to know time – usually daylength measured by an internal clock
Wilson’s Plover
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Homing
= the ability of an animal to find its way home over unfamiliar territory.
Not necessarily distinct from migration i.e. salmon might be homing on natal stream
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Examples
Albatrosses wander thousands of kilometres of Southern Oceans and return every two years to NZ to breed.
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Limpets return to the same spot on a rock before low tide.
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Ecological significance of migration
Migration costs energy and runs risk of getting lost
Advantages include longer feeding time, safer breeding area, reduce intra-specific competition, kill parasites
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How animals find their way
Some learn by moving with older ones.
But, a shining cuckoo can fly 4000km from NZ to Solomon Islands without ever meeting its own sp. behaviour must be innate
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An animal must have:a sense of direction (some form of
compass)a sense of location (understand
where it is starting from)
"Well according to the Global Positioning System we are exactly in the middle of
nowhere."
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Animal compasses
To find out if an animal uses a particular cue it is eliminated by blocking off the
sense used to detect it i.e. light – cover eyes/use mirrors
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Many migratory birds have a sun compassMust allow for the apparent movement of
sun during the day – i.e. needs to know ‘the time of day’
Sun compasses
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Seasons
Summer sun
Winter sun
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Birds have a highly developed sun compass.
At the time of migration, a caged bird tends to orientate itself in the direction of
migration.
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When mirrors changed the direction of the light, birds orientated themselves relative
to the reflected sun’s rays.
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10am
Direction of
migration
90°
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3pm
Direction of
migration
180°
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10am
Direction of migration
90°
mirror
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When their internal clock was delayed, the birds orientated themselves relative to their
perceived time – not to the actual time.
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Actual time 3pm
Direction of
migration
90°
‘Bird time’ 10am
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- the Sun is not always visible
So many birds and insects can see UV light which passes through clouds.
Bees, fish and whales can even detect polarised light
Disadvantage of a solar compass
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Migration movements on an overcast day.
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Star compasses
Birds caged in a planetarium showed a strong tendency to move in the direction of their normal migration.
When the planetarium sky was rotated 180° the birds direction also reversed.
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The key feature is the Celestial Poles.
No internal clock needed because the direction of the Celestial Pole does not
change
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Moon compass
Sandhoppers move towards the sea using the moon’s position and an internal clock
to compensate for moon’s apparent movement
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Using earth’s magnetic fieldMany animals can sense Earth’s magnetic
field.
On an overcast day the homing ability of pigeons with magnets on their heads was impaired yet those with brass rods were
unaffected
A chain of magnetic particles is visible inside this bacterium. This simple compass keeps
the microscopic organisms always swimming north.
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On sunny days bar magnets made no difference.
So solar compass normally takes priority.
The influence of magnetism on pigeon homing. Pigeons were released with either a
magnet or a brass bar of the same weight on their back. On sunny days, the pigeons used the sun as a
compass and homed accurately with or without
a magnet. However, on cloudy days, the magnets disorientated the birds. Each dot represents the
birds vanishing direction. (Modified from Keeton,
1971)
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On sunny days bar magnets made no difference.
So solar compass normally takes priority.
The influence of magnetism on pigeon homing. Pigeons were released with either a
magnet or a brass bar of the same weight on their back. On sunny days, the pigeons used the sun as a
compass and homed accurately with or without
a magnet. However, on cloudy days, the magnets disorientated the birds. Each dot represents the
birds vanishing direction. (Modified from Keeton,
1971)
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A primary compass
one compass = greater accuracy.
Sun and star compasses used when possible with magnetic when it is cloudy.
Pigeons with magnets navigated better on sunny days than pigeons without on cloudy days
Sun very important as a compass
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But birds unable to see the sun as they develop could not navigate by sunlight but could on cloudy days
magnetic compasses are inborn while using the sun and stars is learned.
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Besides compasses some animals use environmental cues such as chemical
characteristics (salmon) and infra-sound of surf or wind
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Experience
Plays an important part.
Migrating birds caught and shifted.
Experienced birds corrected error. Juvenile birds continue in displaced direction
some birds seem to have an innate sense of direction but the ‘map’ needed for navigation has to be learned.
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http://bio.research.ucsc.edu/~barrylab/classes/animal_behavior/DISPERSE.HTM
http://www.monarchlab.umn.edu/Research/Mig/Migback3.html
http://www.life.umd.edu/classroom/biol106h/L23/L23_migr.html