Actograms

What is an actogram? Acto = activity Actograms are visual representations of an animals activity (activity record). An animals activity on an actogram is said to be ‘free-running’ – the length of time an organism’s biological clock runs for in the absence of environmental cues. If an animals behaviour continues independently of its external environment, it proves the behaviour is endogenous (has an internal origin). These rhythms are controlled by an internal pacemaker (oscillator).

Free-running, endogenous rhythms aren’t synchronised with the environment, which means the internal clock must be re-set, or entrained. Under normal conditions, an animal’s daily cycle is synchronised with environmental rhythms and it’s internal clock is ‘re-set’ each day (entrainment). The clock-setting external cue (light, temperature, pheromones) that is used to synchronise the internal clock with the environment is a zeitgeber.

Actograms show activity rhythms in an animal species usually looking at one varying environmental factor (eg light). When the start of the period of the rhythm is changed so that it is earlier or later, it is called a phase shift. A phase shift occurs when an organism is entrained to a new regime of environmental cues.

To do Complete pages 41-43 in BZ Read through the ‘Animal timing behaviour’ worksheet to ensure your understanding of words in bold. Work through ‘Assessment activities’ and then check your answers. Look at the actograms and ensure you can read and understand them.

Make sure you can do the following Describe, using supplied actograms, an animal’s free-running period. Explain how zeitbebers entrain an endogenous rhythm to exogenous cues. Discuss the adaptive advantage(s) of using a zeitgeber to entrain a free-running period to environmental cycles.