EPOW - Ecology Picture of the Week

Explanation:  Farewell to 2003, and welcome to the New Year (on most human calendars)!  As we exit the old year, we are reminded of the many organisms that stir in the twilight zone between day and night ... that evening (or early morning) period of time of crepuscular activity.  

It is a twilight time ... in which many nocturnal (nighttime) animals, including many carnivores, first stir on the hunt for food, mates, or other needs ... and in which many diurnal (daytime) animals, such as American robins, linger into dusk to extol territorial songs or final activities before the ink of night closes in.  Yet, there seem to be few if any organisms that are obligately crepuscular, that is, that are active only during dawn or dusk.  

On a broader time scale, so many organisms on this planet are variously adapted to hierarchical temporal cycles ...  daily (or diel) rhythms of night and day; monthly lunar cycles; seasonal changes in temperature, precipitation, and food availability; and even multi-year life cycles attuned to changes we only dimly understand.  Some animals, such as the bobcat, may switch from crepuscular or nocturnal hunting during summer, to diurnal hunting during winter, to take advantage of higher daytime temperatures and better prey availability.  In the ocean, some zooplankton undergo daily vertical migrations in the water column in response to light intensity.  

So as we enter a new year, we can ponder how so much life has evolved to the daily spin of our wondrous planet, the swirls of storms and ocean currents, our globe's axial tilt creating the seasons, and the long annual treks around our star ... and marvel at the astounding richness of biological diversity that has arisen on this small and humble sphere.

Happy New Year from EPOW!