As I have been reading about many species adapting their activity patterns in order to avoid humans (i.e., becoming more crepuscular or even wholly nocturnal), I began wonder if this could affect some functions in organisms that – without humans on the landscape – would exhibit a mixed activity rhythm (i.e., species that are not strictly nocturnal or crepuscular and that might not even have adapted to an entirely nocturnal activity, e.g., through acquiring night vision).
So far I have not come across studies discussing the effects of sunlight on different animal species (except ectotherms) but everybody knows that humans acquire vitamin D through exposure to sunlight and that the amount of light can also affect our mental health.
I wonder if animals that have been ‘forced out of the sunshine’ by humans, equally, suffer physical and/or mental health consequences:
- through inability to acquire some essential compounds;
- through inability to apply full vision resulting in traumas;
- through reduced ability to engage in visual social interactions;
- through altered thermoregulation;
- through effects on psyche that might arise out of the perpetual darkness etc.
Of course, unlike humans, animals also stay outdoors during the daytime even if they are not active (probably resting in a sheltered place).
Thus, at least some of the effects, might be mitigated because exposure still occurs although its intensity might be changed (e.g., due to hiding in denser vegetation).
Lack of sunlight might affect burrowing animals (if they, too, adapt their diel activity pattern to human disturbance) and aspects of animal life that involve the interaction between sunlight and mobility (e.g., social contact).
In fact, I wonder if in some species the reduction of daylight activity might have resulted in changes of diet composition through, e.g., replacing daylight prey (for example, insects active during daylight) with more nocturnal, crepuscular prey.
If the local species assembly is altogether forced into nocturnal, crepuscular activity, the niche separation might become more difficult to achieve, as well, because the overall ‘night-time animal density’ is higher. Everybody has to get along during the more peaceful hours.
Competition and resource pressure might become greater and conflicts might become more frequent also due to lower ability to ensure temporary activity segregation.
This could even result in evolution of ecotypes where populations of the same species take different directions in development and application of their inherent traits depending on their diel activity pattern.
Notes by Ieva 