Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes. They thus enable organisms to best capitalize on environmental resources (e.g. light and food) compared to those that cannot predict such availability. It has therefore been suggested that circadian rhythms put organisms at a selective advantage in evolutionary terms. However, rhythmicity appears to be as important in regulating and coordinating internal metabolic processes, as in coordinating with the environment. This is suggested by the maintenance (heritability) of circadian rhythms in fruit flies after several hundred generations in constant laboratory conditions, as well as in creatures in constant darkness in the wild, and by the experimental elimination of behavioral, but not physiological, circadian rhythms in quail. 

Norwegian researchers at the University of Tromsø have shown that some Arctic animals (ptarmigan, reindeer) show circadian rhythms only in the parts of the year that have daily sunrises and sunsets. In one study of reindeer, animals at 70 degrees North showed circadian rhythms in the autumn, winter and spring, but not in the summer. Reindeer on Svalbard at 78 degrees North showed such rhythms only in autumn and spring. The researchers suspect that other Arctic animals as well may not show circadian rhythms in the constant light of summer and the constant dark of winter.
What are light and food categorized as?
What kind?
Do certain rhythms let living things prepare for things?
What kind?
What do they generally prepare for?
What sort?
Are these changes sporadic?
How are they described?
What is the nationality of scientists at the University?
What university?
What many examples of arctic animals are given?
What is the first one?
And the second one?
Do these animals display circadian rhythms?
In what times of the year?
What season was not mentioned as one in which an animal at 70 degrees North displays rhythms?
How many seasons did the animal on Svalbard at 78 display rhythms?
What is the first one mentioned?
And the second one?
What allows living things to make the best of resources of the environment?
Resources
They thus enable organisms to best capitalize on environmental resources (e.g. light and food)
Environmental
They thus enable organisms to best capitalize on environmental resources (e.g. light and food)
Yes
Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes
Circadian
Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes.
Changes
Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes
Environmental
Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes
No
regular environmental changes.
Regular
regular environmental changes.
Norwegian
Norwegian researchers at the University of Tromsø
University of Tromsø
Norwegian researchers at the University of Tromsø
Two
Arctic animals (ptarmigan, reindeer)
Ptarmigan
Arctic animals (ptarmigan, reindeer)
Reindeer
Arctic animals (ptarmigan, reindeer)
Yes
Norwegian researchers at the University of Tromsø have shown that some Arctic animals (ptarmigan, reindeer) show circadian rhythms only in the parts of the year that have daily sunrises and sunsets
Parts that have daily sunrises and sunsets
Arctic animals (ptarmigan, reindeer) show circadian rhythms only in the parts of the year that have daily sunrises and sunsets.
Summer
 In one study of reindeer, animals at 70 degrees North showed circadian rhythms in the autumn, winter and spring, but not in the summer. 
Two
Reindeer on Svalbard at 78 degrees North showed such rhythms only in autumn and spring
Autumn
 Reindeer on Svalbard at 78 degrees North showed such rhythms only in autumn and spring.
Spring
 Reindeer on Svalbard at 78 degrees North showed such rhythms only in autumn and spring.
Circadian rhythms
Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes. They thus enable organisms to best capitalize on environmental resources 