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TIMING RESPONSES Continued…
COMPOUND RHYTHMS
The environment changes most on a shoreline because the cycle of day and night occurs as well as the tidal change.
COMPOUND RHYTHMS
The environment changes most on a shoreline because the cycle of day and night occurs as well as the tidal change.
Eg – Sandhoppers show a rhythm of both daily and tidal components = they emerge at night to forage for food but also only at low tide.
INTERNAL AND EXTERNAL TIMINGInternal / endogenous rhythms
INTERNAL AND EXTERNAL TIMINGInternal / endogenous rhythms
Involve an internal clock – independent of changes in the external environment but set by the environment.
INTERNAL AND EXTERNAL TIMINGInternal / endogenous rhythms
Involve an internal clock – independent of changes in the external environment.
External / exogenous
INTERNAL AND EXTERNAL TIMINGInternal / endogenous rhythms
Involve an internal clock – independent of changes in the external environment.
External / exogenous
Few examples of this – seasonal change in the growth rates of plants = produces variation in the food supply for animals which in turn governs seasonal fluctuations in populations.
EVIDENCE FOR INTERNAL CLOCKSSome plants (Oxalis) show daily sleep movements – even when in constant light.
EVIDENCE FOR INTERNAL CLOCKSSome plants (Oxalis) show daily sleep movements – even when in constant light.
When the period of time does not correspond exactly with the period of the environmental cue = ‘free running’
EXAMPLE…
Bees can be trained to feed at a certain time. In Paris the bees fed between 8pm and 10pm. When transferred to New York, they kept feeding at Paris time SHOWING THAT FEEDING IS NOT DETERMINED BY AN ENVIRONMENTAL RHYTHM.
CIRCADIAN RHYTHMS
Circa – ‘about’ Dian ‘day’
Free-running endogenous rhythms don’t usually coincide with those of the environment – internal clock must be constantly ‘reset’ or entrained by the environment.
CIRCADIAN RHYTHMS
Circa – ‘about’ Dian ‘day’
Free-running endogenous rhythms don’t usually coincide with those of the environment – internal clock must be constantly ‘reset’ or entrained by the environment.
The enviro cue to set the clock is called the zeitgeber (German for time giver) and with circadian = common is sunrise or sunset.
CIRCADIAN RHYTHMS
Circa – ‘about’ Dian ‘day’
Free-running endogenous rhythms don’t usually coincide with those of the environment – internal clock must be constantly ‘reset’ or entrained by the environment.
The enviro cue to set the clock is called the zeitgeber (German for time giver) and with circadian = common is sunrise or sunset.
This entrainment is important – animals can adjust to seasonal change in time of dawn/dusk.
- also allows migratory animals that make considerable east-west movements adjust their clocks.
PHASE SHIFTING
The time of the peaks of an endogenous rhythm are advanced or slowed down.
PHASE SHIFTING
The time of the peaks of an endogenous rhythm are advanced or slowed down.
Often it can be light or temperature (reptiles rely on external heat for warmth), food or social factors.
TIME SENSE THROUGHOUT THE DAY Internal clock can be used to determine the time of day
TIME SENSE THROUGHOUT THE DAY Internal clock can be used to determine the time of day
Eg – bees visit flowers during the periods when there is nectar as if they ‘consulted’ their internal clock to ‘know the best time of day’. A bee can be trained to visit several artificial sources and the bees have no trouble keeping their ‘appointments’ provided the food source is kept to the same timing as their own – 24 hours.
