Rhythmicity is found in a multitude of biotic and abiotic factors. The examples of environmental cycles shown in Table 1 document the wide range of frequencies of cycling abiotic factors. Some environmental cycles have well-known effects on organisms - such as the rhythmic change in foraging behavior of intertidal organisms caused by the ebb and flow of the tides. Other cycles, such as the change in the path of the Earth's revolution around the Sun (the orbital eccentricity rhythm), can potentially affect organisms by causing slow weather changes over thousands of years. A few well-known biological rhythms - some of which are and some ofwhich are not controlled by environmental cycles - are listed in Table 2. Biological rhythms involve repetitive processes ranging in frequency from more than once per second, such as the spontaneous firing rate of neurons in the mammalian central nervous system, to less than once every decade, such as the oscillation in the wild population of the Canadian lynx (Lynx canadensis).

Most research on biological rhythms conducted during the past 50 years has dealt with daily/circadian and annual/circannual rhythms and has concentrated on

Table 1 Some environmental cycles on the Earth

Duration of



2 x 10~15s

Oscillation of electromagnetic waves in visible

2 x 10~2s


Voltage oscillation in alternated current (home



Tides (attractive forces of the Sun and the


24 h

Days (Earth's rotation)

30 days

Months (Moon's revolution around the Earth)

365 days

Years (Earth's revolution around the Sun)

10 years

Cycle of sunspots

22 000 years

Precession of the equinoxes

41 000 years

Variation in Earth's obliquity (axial tilt)

96000 years

Variation in Earth's orbital eccentricity

Table 2 Some biological rhythms

Duration of



10~1 s

Spontaneous firing rate of cortical neuron


Human heart rate


Pulsatile secretion of hormones


Tidal and circatidal rhythms

24 h

Daily and circadian rhythms

4 days

Estrous cycle of rat

7 days

Human work-rest week

30 days

Lunar and circalunar rhythms

110 days

Estrous cycle of elephant

12 months

Annual and circannual rhythms

10 years

Oscillation in the wild population of Canadian


basic behavioral, physiological, neural, and molecular processes studied in a small number of species in the laboratory. Few studies have examined interspecies differences in basic processes, and fewer yet have addressed ecological issues in natural environments. Thus, this article will start with a brief review of what has been learned in the laboratory about the basic processes of biological rhythmicity and will then examine what little we know about the behavioral ecology of biological rhythms.

Was this article helpful?

0 0
Project Earth Conservation

Project Earth Conservation

Get All The Support And Guidance You Need To Be A Success At Helping Save The Earth. This Book Is One Of The Most Valuable Resources In The World When It Comes To How To Recycle to Create a Better Future for Our Children.

Get My Free Ebook

Post a comment