2. The organisms found in a certain region usually adapt to the surrounding physical factors. A good knowledge of these factors is necessary in the understanding the inter-relationships between organisms and their environment. The factors are:

Temperature
In extreme cold temperature, animals have thick fur coat to shelter them from the cold. Some hibernate or migrate to warmer temperature areas. A lizard which is a ‘cold-blooded’ organism relies on the energy exchange between it and its environment to regulate its body temperature.
The camels have hump/s that store fats and water for survival in the desert. Cactus has spikes and fleshy stem to stamp out moisture loss.

Moisture
Water is essential to survival. The availability of water determines the number and location of plants and animals. Aquatic animals like ducks have webbed feet to move in the water, fish have gills to breathe in water and plants like lotus have waxed leaves to float on water.
Evergreen forests and abundant fauna are found in tropical areas with rainfall throughout the year. However, grasslands are found in areas with low rainfall in winter and heavy in summer. Many animal species are also found in tropical jungle compared to desert land which has few surviving animals.

Climate
Controlled by the average temperature and amount of rainfall has an effect on what can grow and its rate of growth. In areas where there is little water and high temperature (eg desert), few animals and plants can survive. Desert organisms have to adapt themselves to the harsh condition by having special physical features, eg water storing mechanism. The lower the temperature the number of species that can grow in an area decreases. The same can be said if there are extreme highs in temperature and low in rainfall.



Wind
Moving air helps in the migration of flying mammals from colder to warmer region during winter. Strong winds cause soil erosion reducing soil fertility. It can also cause desertification by shifting sand to fertile areas. It increases the rates of evaporation and transpiration in plants. It helps in the dispersal of many seeds, fruits, spores and even some adult animals like winged insects. Hot and dry winds kill the young shoots and damages the buds and fruits.


Light
Without sunlight, photosynthesis could not go on and all life on earth would die and almost all oxygen and nitrogen would disappear from the atmosphere. Carbon dioxide and other greenhouse gases would increase and the temperature of the planet would be too high to sustain life.

Plants grow to great height to reach sunlight for survival. Many animals need light to catch their prey and to detect predators. Nocturnal animals develop special adaption to survive in the dark. Nocturnal behaviour, for example, many seabirds and sea turtles attend breeding sites nocturnally to reduce the risk of predation.

For examples, Catfish are a large group of nocturnal scavengers, living at the bottom of shallow waters. It can “walk” on land. When droughts cause shallow ponds to dry up, the walking catfish is capable of travelling across land during the night to move to deeper ponds. It uses its fins and tail to slither across the ground, or “walk”, in search of new water, surviving on oxygen stored in an air chamber in its gill arch.

Bats are extremely well-equipped for nocturnal activity. They fly and hunt by sending out pulsed emissions of high-frequency sounds that are reflected back to their ears enabling them to work out the position and distance of their surroundings. This allows them to navigate in total darkness. Owls hunt tiny prey such as mice in utter darkness with their extremely well developed hearing and eye-sight. It can detect a mouse 600 metres away.





Soil
It helps in providing water and minerals as well as site for decomposition to the land plants and animals. If the soil is firm and hard, the large animals inhabiting the ecosystem tend to have small hooves or paws. If the soil is wet and spongy, they tend to have broad hooves or paws.

Atmospheric Gases

The gases present in the atmosphere are chiefly oxygen, carbon dioxide and nitrogen which greatly influence the living organisms. Oxygen acts as a limiting factor in the distribution of animals in water. For example, the Black sea lacks the dissolved oxygen so is devoid of animals, and at higher altitudes of mountains, the oxygen content becomes less and so there is a marked decrease in living organisms (plants and animals).

Salt
Too much prevents growth of fresh water organisms and too little prevents growth of salt water organisms. Salt water fish tends to lose water by osmosis due to seawater higher salt concentration than the cytoplasm of animal cells. So it has waterproof closely-fitted scales to prevent moisture loss.
In contrast, fresh water fish cells have higher salt content than the surrounding water. Water will enter these organisms by Osmosis. So fresh water fish have slimy scaly skins to keep water from entering their cells.
The only submerged ocean plants in the current Plant Kingdom are the sea grasses. They provide food and act as habitats for numerous marine animals. They possess remarkable methods of seed dispersal and pollination in a submarine environment of mud, shifting sand and crashing surf. Sea grass salt tolerance is due to their ability to maintain a lower water potential in their cells than the surrounding salt water. They do this by accumulating sodium in the cell vacuoles.
The salt content of the ocean water can be very high and organisms that live in this ecosystem cannot survive in fresh water. Freshwater organisms cannot live in saltwater, because the salt makes fluid leave their bodies.


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