It is the most important and essential ecological factor influencing almost all the activities of the organism.

It is the intensity aspect of the heat energy. It may be studied under the following heads-

1. Distribution of temperature

2. Changes in temperature

ADVERTISEMENTS:

3 Biological action of temperature

4. Thermal regulation

5. Life zones.

1- Distribution of Temperature

ADVERTISEMENTS:

Temperature extremes range in different environment showing characteristic pattern in freshwater, marine and terrestrial ecosystems. Generally, thermal variations are less in the aquatic environment than in the terrestrial environments. Usually, in water environment, the change from sun to shade produces a minor effect, i.e., less than 0.1°C at a depth of 5m. Diurnal fluctuation is also being about 4°C in the ocean and with increasing depth, amplitude is reduced.

The maximum temperature in marine environments of any size is mostly 36°C in Persian Gulf. However, in tide pools of littoral zone and in shallow bodies of freshwater temperatures may go higher. However temperature of air near land is about 17°C higher in daytime than at night and may be even 80°C higher in desert localities.

In terrestrial environment, the lowest temperature reported is- 70°C (-93.6°F) whereas maximum temperature ranges above 60°C (140°F) in some desert areas. Desert soils have been found to have as much temperature as 80°C when exposed to the noonday sun. The water in hot springs may approach 100°C and even higher temperatures occur sporadically in volcanic areas. Horizontal changes in temperature over globe are in range of 32°C in tropical regions and-12°C for Polar Regions.

2. Changes in Temperature

ADVERTISEMENTS:

(a) Horizontal changes

The changes in temperature from place to place over the surface of the earth vary considerably. Generally in tropical region, average temperature is 32°C and -12°C for Polar Regions. In the sea average temperature run from about 30°C in the tropical region to -1.5°C in Arctic and Antarctic region.

(b) Vertical changes

Vertical changes in the temperature of the air varies widely according to local conditions, but a decrease of about 1°C for every 1.5m of altitude is generally found. In the temperate and tropical regions of the sea a permanent thermal gradient is produced between mixed layer near the surface and deep layer of the bottoms. The depth and extent of the zone of rapid temperature change is known as permanent thermocline layer which is up to 1200 m deep in central Atlantic ocean.

ADVERTISEMENTS:

(c) Thermal stratification

In freshwaters, temperature shows various degrees (gradations) in the different layers being more prominent in perennial lakes. As the temperature approaches 4°C, the density of water increases. Thus deeper lakes, if covered with winter ice for some weeks and not exposed to direct wind action, show annual cycle.

(i) In the winter period, the surface water is cooled to freezing ice which prevents the cooling of waters below it. Below this ice layer, temperature falls to about 2°C and this stratum of water remains below the ice due to lightness.

(ii) With the advent of spring season, the ice melts till temperature reaches to 4°C and thus water has same uniform temperature.

ADVERTISEMENTS:

(iii) During summer, there occurs great rise in temperature causing stratification in water. The upper warmer layers are termed epilimnion have temperature ranges from 21°C to 22°C. These layers lying above to thermocline are windstired and largely homogeneous. The basal or bottom layers show the temperature of about 5°C and are called hypolimnion. It is relatively stagnant water layer. Between these two strata, there is present transition intermediate zone, called thermocline, having temperature from 5°Cto 21°C.

In marine ecosystem, temperature ranges from-3°C to 42°C exhibiting great diversity. In Arctic and Antarctic waters, temperature is extremely lowered reaching to ice freezing point, whereas in temperature and tropical regions, it may reach up to about 42°C. Seasonal changes in vertical temperature structure cause thermal stratification. Winter stagnation occurs when lake is ice-covered and summer stratification is found when surface layers are warmed.

Some deserts may show even higher temperature of about 50°C. Terrestrial ecosystems exhibit seasonal fluctuations in the temperatures and other factors like humidity, water and wind greatly affect it. Usually, diurnal temperature ranges from 30°C to 42°C and nocturnal from 19°C to 12°C.