Ecological factors.pptx

Ecology and Ecological factors

1. Prepared by –Anil Panchal For- B.Sc. 2 nd year Paper- I

2. Plant classification Plants can be classified based on the requirement of light: (a) Heliophytes grow best in full sun­light. (b) Sciophytes grow best at lower light intensity. In comparison to the sciophytes , helio­phytes show thicker stems, more frequent branching, smaller chloroplasts, roots longer, high respiration rate, low water content, higher concentration of salts and sugar, high osmotic pressure etc.

3. Eco- phyiological responses of temperature - Temperature is an ecological factor. It affects the rate of many physiological processes in plants. 1. Transpiration: Rise in temperature increases transpiration rate. High temperature influences the saturation deficit of the atmosphere. It decreases the humidity of air. Thus more water is transpired. High rate of transpiration also increases the rate for absorption of water from the soil. 2. Photosynthesis: Photosynthesis occurs over a wide range of temperature. In some desert plants photosynthesis continues even at 80°C. Most of the algae require lower temperature range for photosynthesis than the higher plants. The optimum temperature for photosynthesis for most of the plants is 25 to 35°C. Photosynthesis stops at 40°C in temperate plants and at 50°C in tropical plants 3. Respiration: The rate of respiration increases with the rise of temperature. It is maximum at optimum temperature. But it decreases rapidly above optimal temperature.

4. 4. General distribution of plants: Temperature and moisture determine the general distribution of vegetation. 5. Germination of seed: Temperature also affects the germination of seed. Every seed has optimal temperature. Seed cannot grow below or above this temperature. 6. Spreading of diseases: Temperature and humidity affects the spreading of plant diseases. Low temperature along with high humidity favours the attack of rust. damping off, seedling blight, foot rot and root rot. 7. Changes in the temperature in the natural environment of plants affect both their functioning and their growth. Maintenance of a relatively stable internal environment is just as important for plant metabolism as it is for animals. 8. Leaf fall in Summer. Eucalypts are evergreen trees that drop some of their leaves during the dry season in hot climates to reduce the surface area exposed to absorb heat. This also reduces the risk of losing too much water by transpiration. 9. Temperature is one factor that controls developmental changes in a plant’s life cycle, from germination through to flowering and seed dispersal.

5. Functions of Temperature: 1. Effect on metabolism: As tempe­rature regulates the activity of enzymes, it regulates the metabolic processes of orga­nisms. It affects the rate of transpiration, photosynthesis and seed germination in plants. 2. Effect on reproduction: (a) Plants: Temperature affects flowe­ring in plants. It also plays an important role in the phenology (study of periodic phenom­ena) of plants. (b) Animals: The maturation of gonads and liberation of gametes take place at a particular temperature that varies from species to species. Breeding also is affected in some due to temperature. The number of eggs laid by blowfly increases with increa­sing temperature up to 32.5°C and thereafter decreases. 3. Effect on growth and development: (a) Plants: Extremes of high and low temperature have adverse effect on the growth of plants. Low temperatures bring about diseases like desiccation, chilling and freezing injury. Extremely high temperature causes stunting and death of plants — called heat injury . (b) Animals: Growth and development of animals are affected by temperature. Corals do not flourish when the temperature of water drops below 21°C. In blow-fly, the incubation period of eggs decreases with increasing temperature .

6. 4. Effect on crossing over: Temperature is seen to affect the crossing over and somatic expression of genes in animals. If the larva or pupa are kept at low or high tempe­rature it affects the development of wings, eyes etc. 5. Effect on sex-ratio: In rotifers and daphnids , temperature affects sex ratio. Under normal temperature, daphnids lay parthenogenetic eggs that develop into females, while with the increase in tempe­rature they give fertilised eggs that develop into either males or females . 6. Effect on colouration: Some species of mammals, birds and insects present in warm humid climates, bear darker pigment than the races of species who resides in cool and dry climate. In Hyla (tree frog) and Phrynosoma (horned toad), low temperature induces darkening of pigments. 7. Effect on morphology: The absolute size of an organism is affected by temperature. Mammals and birds attain larger body sizes in cold regions than in warmer areas . Whereas, poikilotherms are smaller in cold regions.

7. Topographic Factors: The factors concerned with physical geography of the earth are known as topographic factors. These factors influence vegetation which causes variation in climate of a geographic region, ultimately give rise to a characteristic microclimate.

8. The different topographic factors are: 1. Altitude of the place: As the altitude above the sea level increases, there happens a decrease of temperature. Besides, the values of pressure, humidity, wind velocity etc. also changes. All these factors together give a definite pattern of vegetational zone. 2. Steepness and Exposure of the slope: The slope of mountain affects the nature of vegetation. In northern hemisphere, south facing slopes receives more solar radiation than the north facing slope. This may be due to the fact that the steep southern slope receives the solar radiation almost at right angles during the mid-day whereas the northern slopes receive only oblique rays during morning and evening hours. This difference in solar radiation brings about a change in vegetation in the two sides of the slope. In addition to this, the steepness of slope accelerates the downward movement of surface water. The downward movement of water over the slope causes soil erosion and as a result, the vegetation disappears from that area. 3. Direction of mountain chains: The direction of mountain chains considerably influences the rainfall in an area. If the moun­tain chains lie in the path of wind full of water vapour, then there is heavy rainfall on the wind striking side on the mountain chain.

9. Precipitation or rain falling on the earth’s surface returns back to the atmosphere by two ways: 1. Some water is directly evapo­rated from the soil, from open waters of ponds, lakes, oceans etc. and from the surfaces of objects (wet from recent rain). 2. Some water returns back via transpiration (process by which the leaves of plants evapo­rate water taken up from the soil by their roots). The combination of the above two ways is referred to as evapotranspiration

10. Functions of Rainfall 1. Formation of biomes: The annual amount of rainfall evenly distributed in tem­perate latitudes determines the climax biotic communities. 2. Type of vegetation: The annual rainfall determines the type of vegetation. For example, heavy rainfall throughout the year in tropical regions results in evergreen forest. Countries having heavy rainfall in winter and less rainfall in summer results in the formation of sclerophyllous forest—made of shrubs with leathery, thick evergreen leaves. Conversely, areas with heavy rainfall during summer and less in winter results in the formation of grassland. 3. Type of animals: With the change of vegetation due to rain, the animal life also differs in different geographic regions. 4. Flooding and reactions by animals: Flooding by rainwater results in dam buil­ding by beavers. Beaver’s dam contains felled trees, mud, stones and sticks. Terrestrial vegetation in that area dies and aquatic suc­cession begins. Finally the beavers leave, the dam deteriorates and breaks and the valley becomes a dry land again, but with an altered soil consisting of the old lake bed.

11. 5. Effects on metabolism: Rainfall brings along with it a cooling effect which regulates the activity of various animals. 6. Effect on reproduction: Rainfall is one of the physical factors that regulate the maturation and liberation of gonads. For example, the croaking of the male frog can be heard at the time of rainfall which attracts the female for mating . 7. Effect on growth: In case of certain plants, the advent of rainfall witnesses the appearance of shoot and new leaves and branches.