The environment is the sum total of all biotic (living) and abiotic (non-living) components. The environment is the aggregate of all those things and set of conditions which directly or indirectly influence not only the life of organisms but also the communities at a particular place. The different components of the environment are interlinked and interdependent. Environment has profound effect on an organism.
The environmental conditions which influence the life and development of plants are grouped into four main classes (ecological factors) which are as follows :
2.1. Climatic factors/Abiotic components :
The short-term properties of the atmosphere (such as temperature) Light, pressure, humidity, precipitation, cloud cover and wind), at a particular place and at a particular time, is called as the weather. Climate is long term distribution of the weather of an area. Although the weather has profound effects on function, growth and survival of plants. It is the climate that determines the general type of vegetation in that particular area. The study of the climatic factor is known as climatology. The chief climatic factors are:
2.1.1. Water: Precipitation (Rainfall) is the main source of soil moisture. The hydrological cycle is the exchange of water between earth surface and atmosphere. The humidity of the air is expressed in terms of relative humidity. It is measured by hygrometer (Psychrometer). Epiphytes and cryptogamic plants grow in those regions where relative humidity is high. The root of epiphytes absorbs water from the environment. The type of vegetation in any region can be determined by the annual rainfall. Amount of water in soil measured by tensiometer.
2.1.2. Light: All important biological functions are carried out by radiation energy of sunlight without this life is not possible except in a few bacteria. Light is measured by luxmeter or photometer. Solar radiation before entering the atmosphere carries energy at a constant rate i.e., 2 cal cm.–2 min.–1 known as the solar constant. On this basis of relative light requirements and the effect of light on the overall vegetative development, plants are classified ecologically into the following categories :
(a) Heliophytes: These plants grow maximum in full sunlight. In these plant internodes are short. The leaves of plants are small and narrow. Cuticle and hair are present on the surface of leaves.
(b) Sciophytes: These plants grow best in lower light intensity. In these plant internodes are long, leaves are large broad and thin, leaf surface is dull.
The plants grow in total darkness are called etiolated (Long thin, weak and yellow in colours).
Albedo value –
The fraction of solar energy that is reflected by the earth surface back into the space called albedo value. Albedo value is 80% for snow area. It is 20-30% for the sand area and 5-10% for the forest. Out of the total sunlight only 1-5% is utilized in photosynthesis.
188.8.131.52. Effect of light -
(a) Photokinesis - Regulation of speed of locomotion due to light is called photokinesis. eg., larvae of mussel crab move faster if light intensity increases.
(b) Photomorphogenesis in plants. Photoperiodism, seed germination, plant movements and distribution of plants.
(c) light also affect the animal distribution in the aquatic ecosystem. Like in lake, pond and oceans.
Plant distribution in aquatic ecosystem and stratification is observed in lake, pond and oceans ecosystem. Light is a limiting factor for plants in deep water. Seasonal and diurnal activities like foraging, reproductive and migratory activities are controlled by light.
(d) Phenology - Timing of seasonal activities of plants in relation to change in environmental condition (Flowering in particular season, leaf abscission etc.)
The different stratification is observed in the lake, pond, oceanic ecosystems due to the distribution of light.
2.1.3. Temperature: Temperature is the degree of hotness or coldness of a substance. Temperature is a result of light. Temperature affects the growth of plants and animal. Due to high-temperature plants suffer solarization and due to low-temperature plants suffer freezing or frost injury. The vertical temperature gradient over the earth's surface is called the lapse rate. And it's value is 6.5ºC per 1000m elevation.
On the basis of temperature the plants are classified as below :
184.108.40.206. Megatherms or Tropical Climate:- Region where high temperature prevails throughout the year (30-40°). The dominant vegetation is a tropical rain forest. The tropical rain forests are the densest forests of the world. They are in South America (on the side of the Amazon river), Middle Africa (on the side of Congo River) and south-east Asia.
220.127.116.11. Mesotherms Climate-subtropical, Climate:- The high and low temperature alternates annually. The tropical deciduous forest is the dominant vegetation type in this region. Deciduous plants are those plants in which leaf fall takes place once in a year. e.g. Ficus religiosa (Sacred tree).
18.104.22.168. Microtherms: The low temperature (10-20°C) condition prevail throughout the year. The vegetation is mixed coniferous forests type (Teiga).
22.214.171.124. Hekistotherms: The vegetation growing in the very low temperature (0-10°C) conditions. The dominant vegetation is Alpine vegetation (Tundra). The plants growing at very low temperature are called cryophytes or psychrophytes.
Animals use a variety of techniques to survive in cold temperatures. Some organisms change their behaviour, curling up into a ball to reduce the exposed surface area. Others, such as penguins, may huddle together to conserve heat.
There is a linear relationship between temperature and development. The absolute length of time is not important; rather, a combination of time and temperature, called degree-days, determines development. Thus, 100 days × 4 degrees above the threshold = 400 degree-days, and 50 days × 8 degrees = 400 degree-days also.
126.96.36.199. Effect of Temperature on the animal :
Temperature affects the absolute size of an animal and its body parts.
1. Bergman rule - Birds and mammals attain greater body size in cold region and lesser in the warm region. Some ecologist defines Bergmann’s rule as the tendency for the average body mass of animal populations within a species to increase with latitude.
2. Allen's rule -Allen’s rule states that among closely related endothermic (warm-blooded) vertebrates, those living in colder environments tend to have shorter appendages than those living in warmer environments. A classic example is the ear size of hares and foxes. The tail, ears, limbs, eyes and snout of mammals are smaller in the colder region and larger in a warm region. The greater the surface area, the greater the heat loss.
3. Jorden's rule - Fishes in cold water posses more vertebrae than those living in warm water.
4. Gloger rule - Warm-blooded animals in a hot and humid area (tropical region) are darker in colour (heavily pigmented) than cold area.
5. Rensch's rule - Birds in the cold region have narrow wings and in the warm region have broader wings.
2.1.4. Wind: High wind velocity causes soil erosion, breakage and uprooting of trees. The pollutants are dispersed through the air.
The plants which are grown in strong wind areas, have small and rolled leaves so that they can not be damaged by the wind easily. Small leaves do resistance to wind. Wherever the wind is not strong, the leaves are long in plants. Wind affects the humidity also. Near equator absolute humidity is maximum and it decreases towards the poles. Strong winds do not occur in humidity. So temperature, rainfall, humidity and wind are the major factors concerned with the control of climate.
2.2. Topographic or Geographic factor :
Topographic factors are concerned with the physical geography of the earth in an area. The chief topographic factors are as follows: Microclimate refers to local combinations of factors such as wind, the rate of evaporation, humidity, temperature which differ from regional climate.
2.2.1. Altitude: In simple words, Altitude means height or depth. In other words, altitude is a distance measurement in the vertical (up) direction from a datum (any point of the earth) to an object. It is commonly used by the mean of the height above sea level of a location. The height of mountain chains with the increase in altitude, climate changes like a decrease in temperature, increase in humidity, increase in precipitation and increase in wind velocity.
Earth’s vegetation can be divided into different zones based on altitude :
(a) Up to 1800 feet: Tropical rain forest are found in this altitude. Tropical moist deciduous with 1000-1500 mm rainfall is found. Tropical moist evergreen with 2500 mm rainfall is found.
(b) 1800-3800 feet: Grassland or desert, savanna.
(c) 3800-7800 feet: Deciduous forest. Oak is common.
(d) 7800-12000 feet: Coniferous forest (Temperate evergreen forests) e.g., Pinus, Abies, Picea. 12000 feet is regarded as a tree or timberline. Above this height of plants decreases.
(e) 12000-14000 feet: Alpine vegetation (tundras) Rhododendron, Betulla. Cushion-shaped dwarf shrubby vegetation.
(f) 140000 upward: Snow line.
Generally, the vegetation that develops on the base of the mountain to the top is Tropical Temperate, Taiga and Tundra. Species diversity generally increases as one proceeds from high altitude to low altitude and from high latitude to low latitude.
2.3. Biotic components: Biotic factor means the effect of the living organism upon other living organisms.