1. Biological Rhythms Repeated rhythms in animals which control the body or behaviour and synchronise the organism with the environment

2. Biological Clocks
The existence of rhythms means that animals must have a way of keeping track of time
They have an internal clock which lets them predict and prepare for changes to come
Synchronising mating , migration, etc
Horseshoe crabs mating
They would not be very successful if one turned up on the beach to mate and no-one else was there!

3. Biological Clocks Cont…
Biological clocks are used for:
Control of the daily rhythms of the body
Reproduction timing
Preparing for migration by eating of plenty of food
Preparing for winter by storing of food, increasing thickness of coat and hibernating
Navigating by the sun or stars

4. Biological Timing responses to the abiotic world
All organisms respond to various cues
The responses can be:
Annual cycles – yearly changes of the season
Daily – night and day
Lunar – monthly, often related to the moon
Tidal – related to the ebb and flow of the tides
It is to an individual’s advantage to synchronise its activities to these rhythms.
They are reliable!!

5. There are 2 words to describe where the rhythms come from
Outside the body
Exogenous - A rhythm that is control by the external, environmental stimuli detected by the organisms.
We hear the school bell and move to a different lesson
Inside the body
Endogenous – A rhythm that is controlled by an internal biological clock.

6. How do animals tell the time?
Biological clock is an internal timing system which continues without external time clues, and controls the time of activities of plants and animals
Period of the rhythm the time it takes to complete one cycle of activity
Our biological clocks are constantly corrected by cues in the environment.
They are called zeitgebers ( German for time keepers)
Our most powerful zeitgeber is light. We are programmed to be awake in the day and asleep at night.

7. Jet lag
jet lag is when our biological clock gets out of synch. When we move to a different time zone.

8. Biologists use actograms to record an animals biorhythm
An actogram
They are often double, triple or quadruple plotted so you can see a repeating pattern. (This means repeated side by side)
The dark bars represent the animal being active

9. In the top section zeitgebers ( time cues ) keep the rhythms synchronised at the same time each day.
When the zeitgebers are absent the rhythm still continues because it is endogenous( comes from inside the animal) but it starts to wander off the time by being a bit later each day

10. Circa-(about)
Eg. whelks that come up to feed when the tide is in and hide under rocks when the tide is out and still continue this behaviour when you keep then in a bucket and the is no tide can be said to be circa- tidal
Circadian means circa- daily. It is a rhythm that continues to occur every day without any environmental cues to keep it going.
Circa is a word to describe a biorhythm that is endogenous and free running. This means it continues even when there are no external cues in the environment because it originates inside of the organism.
Often the rhythm wanders off slightly which is why it is circa or approximately

11. Definitions.
Circa – because each of the rhythms is not exactly the time length stated, eg daily is not 24 hours, their names start with circa (which means ‘about’) this can only be used if the rhythm is free running. ( see later for its definition)
Photoperiod – the responses of plants and animals to the lengths of day and night

12. Definitions cont….
Free running period this is the time when the biorhythm is running without any clues from the environment, so it ‘runs free’
Entrainment this is the resetting of the bio clock forcing it to take up the period of the environment. It requires regular zeitgebers
Zeitgeber – the environmental agent that resets the biological clock regularly to keep the biorhythm in time with the environment eg light.

13. Definitions
Phase shift- this is the period of adjustment to a new biorhythm. Eg. When you travel to a different time zone you get jet lag but over a few days your biological clock adjusts to the new time. Look at slide 15 the bottom bit is a phase shift.

14. Circadian Rhythms Animals are active at different times of the day
Diurnal – active during the day, inactive at night
Nocturnal – active at night, inactive during the day
Crepuscular – active at dawn and dusk
Arrhythmic – no regular pattern – tend to be found were changes in the microclimate are negligible

15. Examples of circadian rhythms see page 34 in biozone book
Periods of activity
Periods of sleep
Physiological processes
Endocrine system rhythms
Temperature changes
Heart rate rhythms
Pain rhythms
Alcohol metabolism rhythms
Times of births and deaths, etc

16. Circamonthly Rhythms
Some animals synchronise their behaviour with the phases of the moon
Changes associated with tidal patterns are also considered circamonthly (lunar)
The spawning behaviour of some marine worms is synchronised by the moon so that the egg and sperm are released at the same time
Grunion fish also work on this method of spawning, using the tides

17. Circannual Rhythms
These result from the rotation of the earth around the sun
Also a factor is seasonal changes caused by the tilt of the earth and the seasons produced as it rotates around the sun
Examples of circannual rhythms are:
Migration to and from breeding sites
Hibernation
Reproduction cycles
Aestivation

18. Circannual Rhythms cont….
Hibernation - This is the way some animals survive over winter by slowing their metabolic rate
Aestivation – this is a form of hibernation over summer when the weather gets too dry or temperature gets too hot
Reproduction – the method by which most animals reproduce when conditions are most favourable, ie spring