All life has a common biochemical basis. All life activities such as growth, development, reproduction etc. depend on enzyme mediated bio-chemical reactions. There is a certain range of environmental conditions in which most of these complex reactions occur at their maximum ease and efficiency.
This does not mean that all organisms require similar set of conditions for their optimum growth. However, it does suggest that within this optimal range a large number and type of organisms are likely to occur, grow and multiply. In habitats which do not provide these optimum conditions, organisms shall have to adopt themselves to the prevailing adverse conditions. The process of natural selection shall automatically exclude delicate forms restricting the number of species to only those which are able to exist under the adverse set of conditions.
The enormous diversity of life forms in the biosphere has evolved essentially through a process of trial and error during the course of organic evolution. Those changes in characters of a living organism which confer some advantage to the species are retained. Disadvantageous changes cause elimination of the organism or its entire population.
Harsh conditions of environment quickly force the enfeabled and weaker sections of natural population to extinction, without giving them much chance of struggle, adoptation and evolution to a life form better adjusted to its surroundings. Regions of world with mild, warm and humid climates have developed a bewildering diversity of living organisms as most of the changes in the living stock are perpetuted and allowed to evolve into a new life form.
ADVERTISEMENTS:
Warm tropical regions between the tropic of Cancer and Capricorn on either side of equator have since long provided the most suitable habitat for living organisms. The temperatures vary between 25° to 35°C a range in which most of metabolic activity within a living organism occurs with maximum ease and efficiency.
The rainfall is ample often more than 80 per year and the most remarkable feature of the tropical climate is its stability. Seasonal changes in temperature are usually less than the total variations between the day and night temperatures – a change which is hardly noticeable.
There are only slight changes in humidity and photoperiods over the different seasons. In Singapore, a tropical city, the mean January temperature (30.5°C) differs from the July temperature (31.9°C) by 1.4°C only whereas the daily fluctuation in the day and night temperature is about 10°C (from 25°C in the night to 35°C in the day). As we move towards the poles – the subtropical, temperate and Polar Regions on both sides of equator, climatic conditions gradually become harsh and severe.
Temperatures drop and there is a gradual reduction in the mean annual precipitation. The climate is marked with strong seasonal fluctuations. There are drastic variations in temperatures, humidity, and rainfall and photo periods between different seasons. In Dawson city, Alaska, the mean temperature in January (-26°C) differs by about 47°C from the mean Jul) temperature (21°C).
ADVERTISEMENTS:
The changes in climatic conditions are reflected in the distribution of living organisms and lit pattern of biodiversity on our planet. The number of species present per unit area declines as we move from mild tropics to the severe tundras and taigas. Polar Regions have no trees. Coniferous forests of Northern Canada, Alaska, Northern parts of Europe and Russia possess less than 111 species of trees.
The temperate forests of the United States have 20-35 species of trees whereas the tropical forests of Panama have over 110 species of trees in a relatively small area. In almost even plant and animal groups a similar trend prevails.
Canada has 22 species of snakes whereas 126 species of snakes are found in USA. From Mexico about 295 species of snakes are recorded. Peter S. Aston of Harvard University has reported around 700 tree species from 10 selected one hectare of plots in Kalimanthan, Indonesia. This almost equals the total number of tree species of the entire North America.