Unit:Ecology
Chapter- Responses to the environment
Reference: Ecology, Levels of ecological organisation, Environmental factor, Habitat, Niche, Major Abiotic factors, Types of organism-based tolerance, salinity, Growth, Transpiration, Germination, Pigmentation, Daily rhythms in animals Photoperiodism, Light zone in aquatic habitat, Soil, Responses to Abiotic Factors
Learning objectives
- To understand the effect of major abiotic factors on ecosystem
Ecology
Ecology is the study of interaction among organisms and between the organisms and their abiotic or physical environment. The term ecology is given by Ernst Hackle; however, the term was first used by Reiter.
Levels of ecological organisation
The hierarchy in the levels of organisation connected with ecological grouping of organism is called ecological hierarchy or ecological level of organisation.
Ecology has four levels of biological organisation – organisms, populations, communities, and biomes.
Environmental factor– constituents of environment which directly or indirectly influence the form and functioning of organism in any specific way.
Habitat- a specific place or locality delimited by a combination of factors, physical features, and barriers where a community resides. Ex. Plant of saline and non-saline soil. Types-
- Microhabitat- subdivision of habitat having a specific property. Ex. Forest floor, tree canopy, tree trunk, edge of pond.
- Macrohabitat- it comprises several macrohabitats
Niche- specific part of habitat occupied by individual of a species which is circumscribed by its range of tolerance, range of movement, microclimate, type of food and its availability, shelter, type of predator and timing of activity.
Major Abiotic factors-
- Temperature- temperature is the degree of hotness or coldness. Atmospheric temperature of a place depends upon its latitude, altitude, topography, slope, aspect, season, vegetation, and humidity. Temperature gradient over earth’s surface or lapse rate is 6.4-6.5 per 100 latitude or 1000m altitude. Thus, temperature decease while moving from equator to poles. Organism living in several zones-
- Megatherms- lives in tropical zone
- Mesotherm- lives in subtropical zone
- Microtherms- lives in temperate zone
- Hekistotherms – lives in arctic zone.
Organism are divided into following groups depending upon their ability to tolerate variations in surroundings-
- Eurythermal- who can tolerate a wide range of temperature variations. Ex. Mammals, birds, plats of family Asteraceae.
- Stenothermal- who lives within narrow range of temperature due to their requirement of nearly constant temperature throughout the year. Ex. Polar bear, lizards, amphibians.
Another classification based on temperature is-
- Poikilotherm or cold-blooded animals or ectothermic – their body temperature varies with temperature. Ex. Reptiles.
- Homoiotherm or warm-blooded or endothermic- their body temperature remains constant irrespective of environmental temperature change. Ex. Birds and mammals.
Effect of temperature-
- Growth- rate of growth increase with increase in temperature up to an optimum beyond that it begins to decline.
- Metabolism- enzymes helping in metabolism are affected by temperature.
- Reproduction- maturation gonads and formation of gamete are controlled by temperature.
- Sex ratio- daphnia produce only female at normal temperature and produce both male and female at higher temperature.
- Behaviour- snakes locate their prey by detecting their warm- blooded character.
- Morphology- in colder areas size of animal increase.
Thermoregulation and homeostasis- in ectothermic organism the body temperature changes with environment thus they hibernate during cold and aestivate during summer. In endotherm they maintain a constant body temperature despite outer fluctuating temperature by homoeostasis. For that they either retain heat produced by metabolic reaction or develop insulating coat, or by cutaneous circulation or do migration.
Water- water determine vegetation of an area. Types of terrestrial plant based on moisture availability-
- Hygrophytes- plants of wet areas with soft stem of moderate height, large thin leaves with hydathodes for excreting excess water in guttation.
- Mesophytes- plants of moist habitat with luxuriant vegetative growth.
- Xerophytes- plants of dry habitat, that face the problem of more water loss through transpiration than is the water available in soil.
Types of organism based on tolerance to salinity-
- Euryhaline- organism that are tolerant of a wide range of salinities. Ex. Shark
- Stenohaline- animals that are limited to narrow range of salinity.
- Light- effect of light on various process-
- Photosynthesis- it is maximum at equator and tropical areas
Growth- moderate light intensity and red light. UV radiation favour rosette habit in plants. Blue light favours moderate but normal growth. High intensity light reduced growth but increase development of mechanical tissues.
Transpiration- stomata open in light and closed in darkness.
Germination- photoblastic seeds are sensitive to light.
Pigmentation- animals develop dark colour in dim light and light colour in bright light. Human when exposed to light develop tanning.
Daily rhythms in animals-
- Diurnal animal- active during daytime
- Nocturnal- active during night
- Vesperal- active at dusk or sunset.
- Auroral- active at dawn.
- Crepuscular- active at dusk and dawn.
Photoperiodism– phenology or timing of seasonal activities like, bird migration, leaf fall and dormancy, hibernation, flowering, hibernation, vegetative growth, and animal breeding, of organism is regulated by photoperiodism.
Light zone in aquatic habitat-
- Littoral zone- shallow coastal zone, light is acle to pass through shallow water and reach bottom, thus have abundant of producers.
- Limnetic zone- open water zone where water is very deep, and the amount of oxygen and light decrease with depth. It has three zones-
Photic zone- upper part of limnetic zone to which light can penetrate with 200m depth, and its upper part is called euphotic zone and lower part is called disphotic zone.
Aphotic/profundal zone- zone of deep water below photic zone and above the bottom to which light does not penetrate.
Benthic zone- bottom zone. In deep lake and seas bottom is also in perpetual darkness but in shallow water light does penetrate.
Note- Below 5000-6000 m in ocean, the area is called Abyssal zone
Soil- The study of soil, an Edaphic factor, is called Pedology. The soil is weathered superficial layer of earth’s crust which is intermixed with the living organisms.The nature or properties of the soil varies from place to place, depending upon climate, weathering and the process of soil development. The plants depend upon soil for nutrients, water supply and anchorage. The holding capacity, pH, percolation properties, topography and mineral composition determine the types of vegetation in the area. A good fertile soil consists of mineral matter (~ 40%) water / soil- solution (~25%), soil air (~25%) and organic matter (~10%). The ‘loam’ is best for the plant growth. The soil also affects seeds -germination, size of plants, depth of the roots system, susceptibility to frost and parasites, and the flowering in the plants. The type of vegetation also determines the type of animals which it supports. In case of aquatic environment, it is the type of sediments that determines the category of the thriving organism.
Responses to Abiotic Factors
Homeostasis- animals maintain their body temperature or osmotic concentration of body fluid to the optimum level and maintain a constant internal environment.
Methods adopted by living organism to cope with stressful conditions-
- Regulators- the organism that maintain constant body temperature and osmotic concentration. Ex. Mammals, birds.
- Conformers- organisms that don not have mechanism to maintain a constant internal body temperature. Their body temperature changes with the surrounding temperature. Ex. Asterias, shrew, humming bird.
- Partial regulators- organism having ability to regulate body function to a limited extent. Ex. Cray fish are oxy-regulators.
- Migration- The animal can move away temporarily from a stressful environment to a more hospitable area and return when the environmental conditions are favourable. Every winter thousands of birds migrate from Siberia (extremely cold) to Keoladeo National Park in Bharatpur (Rajasthan)
- Suspend- During unfavourable conditions the lower plants, fungi, and bacteria, produce thick– walled spores which germinate when the environmental condition is favourable. The seeds and the other vegetative reproductive -structures of higher plants similarly undergo ‘dormancy’ and reduce their metabolic activities when the conditions are unfavourable, and form new plant when the moisture and the temperature conditions are suitable. The animals that cannot migrate, avoid the stressful condition for the time period (escape in time) and undergo either Hibernation (in winter), ex. Bear; or Aestivation (in summer), ex. snail and few fishes. Frog undergoes hibernation in winter and aestivation in summer. When the condition is unfavourable, many species of zooplanktons, in lakes and pond, are known to enter ‘diapause’, i.e., a stage of suspended development.
Summary
- Ecology is the study of interaction among organisms and between the organisms and their abiotic or physical environment
- Maintenance of homeostasis by organism contribute to optimal performance, but only some organism, called regulators are capable of homeostasis in face of changing external environment while other that are unable to do so are called conformers.
- Abiotic factors are those that are non-living, such as rocks, sunlight, temperature, and ocean currents for marine ecosystems.