biohorizon
30
south of the Sahara), Oriental (tropical Asia and western Indonesia), Australasian (eastern Indonesia, Australia and Polynesia), Nearctic (America north
of the tropics) and Neotropical (tropical and southern America). From pole
to equator the following marine provinces are distinguished: arctic areas-antarctic areas, boreal areas-antiboreal areas, warm temperate areas and tropic
areas, but this division is less marked in pelagic regions than in shelf and littoral regions. Ranges may (have) become discontinuous either by climatic or
geological events (-?plate tectonics) or by a founder population that has settled beyond the previous border. -?invasions.
biohorizon [also datum level (less accurate) 1 isochronous level based on events
that can be correlated over a wide area; in a biostratigraphical sense, biohorizons represent evolutionary events such as the first appearance datum (FAD)
and the last appearance datum (LAD). Care must be taken to distinguish between a "first appearance datum" and "first occurrence", the latter being the
observation of the first appearance within a (local) stratigraphic sequence.
Also confusing is the practice (by oil geologists) of using the term FDA for
the first downhole appearance (as seen from the top of the section, i.e., the
last appearance datum when used in a chronological sense). The (time- or
rockstratigraphic) interval between the first and the last appearance of a
taxon is called its range (or stratigraphic range).
biological clock phenomenum present in organisms with an endogenous periodicity, i.e., the rhythm persists, even when information from the outside world
is lacking. Without synchronizing signals (Zeitgebers) from the outside
world, however, free-running biological clocks, as experiments with activity
rhythms of animals show, get out of phase and run too slowly or too fast.
With the aid of their biological clocks animals can perform, e.g., daily or circadian rhythms (circa = about, dies = day) and yearly cycles in their behavior
and physiology, or even shorter rhythms like tidal periodicity, while, e.g.,
swimming activity of small pelagic animals can show cycles of minutes.
biological cycles (1) a periodically repeating complete set of biological events;
(2)-?biogeochemical cycles.
biological monitoring -?monitoring.
biological oxygen demand (BOD) yields an estimate of the concentrations of organic matter in the water available to microorganisms. The oxygen uptake is
usually calculated by subtracting the oxygen content after 5 days' incubation at 20°C in the dark from the 100 % oxygen content at the start of incubation.
30
south of the Sahara), Oriental (tropical Asia and western Indonesia), Australasian (eastern Indonesia, Australia and Polynesia), Nearctic (America north
of the tropics) and Neotropical (tropical and southern America). From pole
to equator the following marine provinces are distinguished: arctic areas-antarctic areas, boreal areas-antiboreal areas, warm temperate areas and tropic
areas, but this division is less marked in pelagic regions than in shelf and littoral regions. Ranges may (have) become discontinuous either by climatic or
geological events (-?plate tectonics) or by a founder population that has settled beyond the previous border. -?invasions.
biohorizon [also datum level (less accurate) 1 isochronous level based on events
that can be correlated over a wide area; in a biostratigraphical sense, biohorizons represent evolutionary events such as the first appearance datum (FAD)
and the last appearance datum (LAD). Care must be taken to distinguish between a "first appearance datum" and "first occurrence", the latter being the
observation of the first appearance within a (local) stratigraphic sequence.
Also confusing is the practice (by oil geologists) of using the term FDA for
the first downhole appearance (as seen from the top of the section, i.e., the
last appearance datum when used in a chronological sense). The (time- or
rockstratigraphic) interval between the first and the last appearance of a
taxon is called its range (or stratigraphic range).
biological clock phenomenum present in organisms with an endogenous periodicity, i.e., the rhythm persists, even when information from the outside world
is lacking. Without synchronizing signals (Zeitgebers) from the outside
world, however, free-running biological clocks, as experiments with activity
rhythms of animals show, get out of phase and run too slowly or too fast.
With the aid of their biological clocks animals can perform, e.g., daily or circadian rhythms (circa = about, dies = day) and yearly cycles in their behavior
and physiology, or even shorter rhythms like tidal periodicity, while, e.g.,
swimming activity of small pelagic animals can show cycles of minutes.
biological cycles (1) a periodically repeating complete set of biological events;
(2)-?biogeochemical cycles.
biological monitoring -?monitoring.
biological oxygen demand (BOD) yields an estimate of the concentrations of organic matter in the water available to microorganisms. The oxygen uptake is
usually calculated by subtracting the oxygen content after 5 days' incubation at 20°C in the dark from the 100 % oxygen content at the start of incubation.