Transcript Animal responses to the abiotic environment

Animal responses to the
abiotic environment
Biological orientation responses
• Behaviour by which animal positions self
in relation to surroundings
• Taxes
– Movement of whole animal, guided
continuously towards or away from a stimulus
coming from one side. Movement towards is
positive taxis and vice versa. E.gs
• Kinesis
– Nondirectional response to stimulus. A
change in activity rate. Are actually random
movement but will see a pattern.
Homing and Migration
• Complicated form of orientation, animal must be
able to navigate and orientate self.
• Homing
– The ability of the individual to return to a home site
(hive, nest etc)
• Migration
– Regular, annual or seasonal mass movement of
animals from breeding area to another area. In true
migration the individual does a round trip. E.G.s
Survival during migration depends on an animals
ability to navigate.
Migration has reproductive or survival
benefits. The behaviour to migrate is
inherited and maintained by natural
selection.
Triggers for migration: a drop in
temperature, days become shorter, innate
genetic drive, animal has matured enough.
• There are 3 types of orientation important
in navigation for homing and migration:
piloting, compass orientation and true
navigation.
– Piloting: animal moves from one landmark to
another until destination is reached. Short
distances and uses visual cues.
– Compass: animals can detect magnetic field
lines of earth, chemical cues or sound to
detect a compass direction.
– True: determining ones position relative to
other locations. Ability to orientate oneself
towards a goal without landmarks and
regardless of direction. To do this you need a
map sense (ability to be aware of latitude and
longitude) and a sense of timing (an internal
clock that can compensate for movement of
sun or stars).
Advantages of migration
Disadvantages of migration
•Animals remain in
favourable temp.
•Grow larger
•Leave more offspring
•Have a constant supply of
food
•May colonise an new area
•Reduces
predation/parasitism/disease
•Greater genetic mixing
•Better breeding conditions
•May get caught in storm
•May get eaten by predator
•Huge investment in energy
•May die of exhaustion as
use up energy
•May starve
Methods used for migration/homing
• Visual clues
– Animals can learn surroundings e.g. wasps
• Solar navigation: as the sun moves from
east to west it can be used to tell direction
– Honey bees are a good example: they keep
the sun on one ommatidium of their
compound eye during the outward journey
and on the opposite for the return. If it is
cloudy they use polarised light to navigate.
They dance when they return to the hive to
tell others where a food source is. The round
dance points directly to the food source and
tells it is within 50m of hive. The waggle
dance is a figure of eight.
• The vertical dash line is the sun, the angle of this
and the start of the fig. 8 is the angle of the food
in relation to the sun, The number of waggles as
the bee goes along the straight is the distance –
fewer slower waggles mean food is further away.
– Birds: migratory birds fly mainly in the daytime
and use the sun as a compass. They can
compensate for the changing direction of the
sun.
• Magnetic fields: homing pigeons can
follow magnetic lines in earth, also now
think whales and dolphins can.
• Star navigation: night migrating birds use a
stellar compass, orientate to the brightest
northern stars.
• Chemical navigation: following scent trails,
dogs, ants eels and salmon all use this
method
• Sound as sonar: bats and whales,
echolocation used to navigate around
objects and to give direction.
• Ambient pressure: proven in pigeons and
may be in other birds, can be sensitive to
altitude change of 10m. Gives an
accurate idea of height.
• Most animals use more than one method
to navigate and there are many methods
we as yet do not fully understand.
Biological timing responses in
animals
• Biological clocks: an internal clock to
predict the onset of periodic changes in
the environment. They are used for
control of daily body rhythms (sleep, pulse,
blood pressure, temperature, alertness,
sex drive etc), reproduction timing so
animals come on heat, release sperm and
eggs or perform courtship at same time
and to prepare for migration by eating a
lot.
• Review definitions
Sometimes it can be hard to tell if a rhythm
is endogenous or exogenous. It is
endogenous if one of the following criteria
apply: rhythm has a frequency not exactly
the same as the environmental factor,
period of rhythm deviates under lab
conditions, rhythm persists if animal
moved from one part of world to another.
Circadian rhythms in animals
Diurnal = active in day and inactive at night
Nocturnal = vice versa
Crepuscular = active at dawn and dusk
Arrhythmic = no regular pattern.
If animals (including humans) are cut off
from environmental cues that can tell them
time o day they still show a circadian
rhythm (free running).
Human Rhythms
• Sleep-wake: function on day to night and
vary from person to person. Children
need around 12hrs sleep a night,
teenagers 9hrs, adults 7-8 hours and the
elderly often only 6hrs.
• Temperature: rises in day and drops at
night, lowest point around 3am.
• Heart rate works in step with temperature
• Pain: sensitivity varies over a day, more
sensitive to a needle around midday but
more sensitive to cold at night.
• Alcohol metabolisim: broken down most
efficiently from 4pm to 11pm.
• Efficiency of learning: follows the
temperature curve but has a dip at
lunchtime that is not related to eating.
• Kidney excretions: there is a rhythm of
excretion of chemicals and volume.
• Birth and death: you are most likely to be
born or die in the early morning.
• Hormone secretion: varies but most are
secreted at night, get problems with shift
work as hormones get out of synch and
can take 5-10 days to change to match
change in sleep patterns. No sleep means
certain hormones are not secreted at all.
Circa lunar
• Some evidence ovulation cycle of primates
is linked to lunar cycle.
• Many animals spawning behaviour is
governed by the moon
Circatidal
• Grunions are main known example of
single tidal activity. Crabs and other
marine animals have two periods of
activity per tidal cycle.
Circa annual
• Hibernation, slow metabolisim over winter,
in insects known as diapause.
• Aestivation, summer ‘hibernation’
• Migration
• reproduction