biology notes

ECOLOGY:

Ramdeo Misra-- Father of Ecology in India.

Government of India established the National Committee for Environmental Planning and Coordination (1972) which, in later years, paved the way for the establishment of the Ministry of Environment and Forests (1984).

*Ecology-studies the interactions among organisms and between the organism and its physical (abiotic) environment. Ecology is basically concerned with four levels of biological organisation – organisms, populations, communities and biomes.

*physico-chemical (abiotic) components alone do not characterisethe habitat of an organism completely; the habitat includes biotic components also – pathogens, parasites, predators and competitors – of the organism with which they interacts constantly.

*A few organisms can tolerate and thrive in a wide range of temperatures (they are called eurythermal), but, vast majority of them are restricted to a narrow range of temperatures (such organisms are called stenothermal)

*For aquatic organisms the quality (chemical composition, pH) of water becomes important. The salt concentration (measured as salinity in parts per thousand), is less than 5 per cent in inland waters, 30-35 per cent the sea and > 100 per cent in some hypersaline lagoons. Some organisms are tolerant of a wide range of salinities (euryhaline) but others are restricted to a narrow range (stenohaline). Many freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems, they would face

*many species would have evolved a relatively constant internal (within the body) environment that permits all biochemical reactions, physiological functions to proceed with maximal efficiency. This constancy could be in terms of optimal temperature and osmotic concentration of body fluids. then organism should try to maintain the constancy of its internal environment (a process called

homeostasis) despite varying external

environmental conditions.

*the ‘success’ of mammals is largely due to their ability

to maintain a constant body temperature and thrive whether they live in Antarctica or in the Sahara desert

*Heat loss or heat gain is a function of surface area. Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then they have to expend much energy to generate body heat through metabolism. This is the main reason why very small animals are rarely found in polar regions

*Some snails and fish go into aestivation to avoid summer–related problems-heat and desiccation. Under unfavourable conditions many zooplankton species in lakes and ponds are known to enter diapause, a stage of suspended development.

*Mammals from colder climates generally have shorter ears and limbs to minimise heat loss. (This is called the Allen’s Rule.) In the polar seas aquatic mammals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat.

*altitude sickness--symptoms include nausea, fatigue and heart palpitations. This is because in the low atmospheric pressure of high altitudes, the body does not get enough oxygen. The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding capacity of hemoglobin and by increasing breathing rate.

*An individual may have births and deaths, but a population has birth rates and death rates. In a population these rates refer to per capita births & deaths, respectively.

*Ideally, when resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number, as Darwin observed while developing his theory of natural selection. Then the population grows in an exponential or geometric fashion.

             birth rate-death rate= r.                                            r- intrinsic rate of natural increase and is a very important parameter chosen for assessing impacts of any biotic or abiotic factor on population growth.

*Population size, more technically called population density (designated as N), need not necessarily be measured in numbers only.

*The number of fish caught per trap is good enough measure of its total population density in the lake. We are mostly obliged to estimate population sizes indirectly, without actually counting them or seeing them. The tiger census in our national parks and tiger reserves is often based on pug marks and fecal pellets.

*A plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth

*Some organisms breed only once in their lifetime (Pacific salmon fish, bamboo) while others breed many times during their lifetime (most birds and mammals)

*Assigning a ‘+’ sign for beneficial interaction, ‘-’ sign for detrimental and 0 for neutral interaction…

Species A      Species B       Name of Interaction

+                   +            Mutualism

–                      –             Competition

+                  –               Predation

+                   –                 Parasitism

+                0                 Commensalism

–                 0                  Amensalism

*Biological control methods adopted in agricultural pest control are based on the ability of the predator to regulate prey population. Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species.

*Nearly 25 per cent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants)

*weed Calotropis growing in abandoned fields produces highly poisonous cardiac glycosides and that is why you never see any cattle or goats browsing on this plant. A wide variety of chemical substances extracted from plants (nicotine, caffeine, quinine, strychnine, opium, etc.,) are produced actually as defences against grazers and browsers.

*competition is best defined as a process in which the

fitness of one species (measured in terms of its ‘r’ the intrinsic rate of increase) is significantly lower in the presence of another species.

*in some shallow South American lakes visiting flamingoes and resident fishes compete for their common food, the zooplankton in the lake. Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, apparently due to the greater browsing efficiency of the goats.

*In general, herbivores and plants appear to be more adversely affected by competition than carnivores.

*Gause’s ‘Competitive Exclusion Principle’ states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually

But species facing competition might evolve mechanisms that promote co-existence rather than exclusion. One such mechanism is ‘resource partitioning’. If two species compete for the same resource, they could avoid competition by choosing, for instance, different times for feeding or different foraging patterns.

*The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of its primary host.

*Parasites that feed on the external surface of the host organism are called ectoparasites

*The female mosquito is not considered a parasite.

*endoparasites are those that live inside the host body at different sites (liver, kidney, lungs, red blood cells, etc.).

*Brood parasitism in birds is a fascinating example of parasitism in which the parasitic bird lays its eggs in the nest of its host

*Commensalism: This is the interaction in which one species benefits and the other is neither harmed nor benefited. An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither the mango tree nor the whale derives any apparent benefit. The cattle egret and grazing cattle in close association, the interaction between sea anemone that has stinging tentacles and the clown fish,- examples of commensalism.

*Mutualism: This interaction confers benefits on both the interacting species. Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria. Similarly, the mycorrhizae are associations between fungi and the

roots of higher plants. The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy-yielding carbohydrates.

ECOSYSTEM – terrestrial & aquatic.

Forest, grassland and desert - examples of terrestrial ecosystems; pond, lake, wetland, river and estuary - examples of aquatic ecosystems. Crop fields and an aquarium may also be considered as man-made ecosystems.

*Vertical distribution of different species occupying

different levels is called stratification. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.

*Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by

plants during photosynthesis. It is expressed in terms of weight (g –2) or energy (kcal m–2). The rate of biomass production is called productivity. It is expressed in terms of g–2 yr –1 or (kcal m–2) yr–1.

*Gross primary productivity GPP of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP).

*Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers). Primary productivity depends on the plant species inhabiting a particular area, variety of environmental factors, availability of nutrients and photosynthetic capacity of plants.

*Secondary productivity is defined as the rate of formation of new organic matter by consumers.

* The annual net primary productivity of the whole biosphere is approximately 170 billion tons(dry weight) of organic matter. Of this, despite occupying about 70 percent of the surface, the productivity of the oceans are only 55 billion tons

* decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition. Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecal matter, constitute detritus, which is the raw material for decomposition

* Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation. By the process of leaching, water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts. Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism.

all the above steps in decomposition operate simultaneously on the detritus

* Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralization

* Decomposition is largely an oxygen-requiring process

* In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-soluble substances.

* Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR). Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world.

* ecosystems are not exempt from the Second Law of thermodynamics

* A simple grazing food chain (GFC) is GRASS TO GOAT TO MAN

* The detritus food chain (DFC) begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria. They meet their energy and nutrient requirements by degrading dead organic matter or detritus. These are also known as saprotrophs (sapro: to decompose). Decomposers secrete digestive enzymes that breakdown dead and waste materials into simple, inorganic materials, which are subsequently absorbed by them.

*In an aquatic ecosystem, GFC is the major conduit for energy flow. As against this, in a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC. Detritus food chain may be connected with the grazing food chain at some levels: some of the organisms of DFC are prey to the GFC animals, and in a natural ecosystem, some animals like cockroaches, crows, etc., are omnivores.

These natural interconnection of food chains make it a food web

* The amount of energy decreases at successive trophic levels

*Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area. The biomass of a species is expressed in terms of fresh or dry weight. Measurement of biomass in terms of dry weight is more accurate.

*The number of trophic levels in the grazing food chain is restricted as the transfer of energy follows 10 per cent law – only 10 per cent of the energy is transferred to each trophic level from the lower trophic level. In nature, it is possible to have so many levels – producer, herbivore, primary carnivore, secondary carnivore in the grazing food chain.

*the trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time

*energy at a lower trophic level is always more than at a higher level.

*Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area.

*ecological pyramids does not take into account the same species belonging to two or more trophic levels. It assumes a simple food chain, something that almost never exists in nature; it does not accommodate a food web. Moreover, saprophytes are not given any place in ecological pyramids even though they play a vital role in the ecosystem.

*composition and structure constantly change in response to the changing environmental conditions. This change is orderly and sequential, parallel with the changes in the physical environment. These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community. The gradual and fairly predictable change in the species composition of a given area is called ecological

succession. During succession some species colonise an area and their populations become more numerous, whereas populations of other species decline and even disappear.

*The entire sequence of communities that successively change in a given area are called sere(s). The individual transitional communities are termed seral stages or seral communities.

*succession and evolution would have been parallel processes at that time.

*Succession is hence a process that starts where no living organisms. - primary succession. Ex; newly cooled lava.

  Areas that lost all the living organisms that

existed there.- secondary succession. Ex: abandoned farmlands, burned forests. secondry succession is faster than primary succession

*Hydrarch succession takes place in wetter areas and the

successional series progress from hydric to the mesic conditions. As against this, xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions. Hence, both hydrarch and xerach successions lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric).

*The species that invade a bare area are called pioneer species. *In primary succession on rocks these are usually lichens which are able to secrete acids to dissolve rock, helping in weathering and soil formation. These later pave way to bryophytes,… ultimately a stable climax forest community is formed. The climax community remains stable as long as the environment remains unchanged.

*In secondary succession the species that invade depend on the

condition of the soil, availability of water, the environment as also the seeds or other propagules present

*The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc..present in the soil at any given time, is referred to as the standing state.

*nutrients never lost.

*The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling. Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo: rocks, air, water).  

*Nutrient cycles-two types: (a) gaseous and (b) sedimentary

*reservoir for gaseous type of nutrient cycle (e.g., nitrogen, carbon cycle) exists in the atmosphere and for the sedimentary cycle (e.g., sulphur and phosphorus cycle), the reservoir is located in Earth’s crust.

*Environmental factors, e.g., soil, moisture, pH, temperature etc., regulate the rate of release of nutrients into the atmosphere.

*4 × 10^13 kg of carbon is fixed in the biosphere through photosynthesis annually

*The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates. When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants. Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed  by phosphate-solubilising bacteria releasing phosphorus.

*Energy flow is unidirectional.

*The biotic community is dynamic

BIODIVERSITY

*Biodiversity is the term popularized by the sociobiologist Edward Wilson

*More than 70 per cent of all the species recorded are animals, while plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) comprise no more than 22 per cent of the total. Among animals, insects are the most species-rich taxonomic group, making up more than 70 per cent of the total

*india’s share of the global species diversity is an impressive 8.1 per cent. One of 12 mega diversity countries

*species diversity decreases as we move away from the equator towards the poles

*tropics (latitudinal range of 23.5° N to 23.5° S) harbour more species than temperate or polar areas

*temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years.

*the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola.

*increased diversity contributed to higher productivity

*rivet popper hypothesis used by ecologist Paul Ehrlich

*amphibians appear to be more vulnerable to extinction

*‘bioprospecting’ (exploring molecular, genetic and species-level diversity for products of economic importance

*When we conserve and protect the whole ecosystem, its biodiversity at all levels is protected - we save the entire forest to save the tiger. This approach is called in situ (on site) conservation

*Ex situ Conservation– In this approach, threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care. Zoological parks,botanical gardens and wildlife safari parks, in vitro fertilisation, tissue culture propagation and cryopreservation of gametes.

*Convention on Biological Diversity (‘The Earth Summit’) held in Rio de Janeiro in 1992, called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilisation of its benefits.

*the World Summit on Sustainable Development held in 2002 in Johannesburg

ENVIRONMENTAL ISSUES

*Environment (Protection) Act, 1986 to protect and improve the quality of our environment (air, water and soil

*According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health. These fine particulates can be inhaled deep into the lungs and can cause breathing and respiratory symptoms, irritation, inflammations and damage to the lungs and premature deaths

*Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing emission of poisonous gases. As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively. Motor vehicles equipped with catalytic converter should use unleaded petrol because lead in the petrol inactivates the catalyst.

*CNG burns most efficiently, unlike petrol or diesel, in the automobiles and very little of it is left unburnt. Moreover, CNG is cheaper than petrol or diesel, cannot be siphoned off by thieves and adulterated like petrol or diesel.

*Euro II norms, for example, stipulates that sulphur be controlled at 350 parts-per-million (ppm) in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42 per cent of the concerned fuel. The goal, according to the roadmap, is to reduce sulphur to 50 ppm in petrol and diesel.

*the Air (Prevention and Control of Pollution) Act came into force in 1981, but was amended in 1987 to include noise as an air pollutant

*Water (Prevention and Control of Pollution) Act, 1974 to safeguard our water resources

*Micro-organisms involved in biodegradation of organic matter in the receiving water body consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. This causes mortality of fish and other aquatic creatures.

*hyacinth (Eichhornia crassipes), the world’s most problematic aquatic weed- ‘Terror of Bengal’

*Biomagnification refers to increase in concentration of the toxicant at successive trophic levels. This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted, and is thus passed on to the next higher trophic level. This phenomenon is well-known for mercury and DDT.

*High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations.

*Eutrophication is the natural aging of a lake by biological enrichment of its water. natural aging of a lake may span thousands of years. However, pollutants from man’s activities like effluents from the industries and homes can radically accelerate the aging process. This phenomenon has been called Cultural or Accelerated Eutrophication. The prime contaminants are nitrates and phosphates, which act as plant nutrients.

*Thermal wastewater eliminates or reduces the number of organisms sensitive to high temperature, and may enhance the growth Of plants and fish in extremely cold areas but, only after causing damage to the indigenous flora and fauna.

*dry composting toilets- human excreta can be recycled into a resource (as natural fertilizer), which reduces the need for chemical fertilizers. There are working ‘EcoSan’ toilets in many areas of Kerala and Sri Lanka.

*Polyblend, a fine powder of recycled modified plastic. This mixture is mixed with the bitumen that is used to lay roads.

*Integrated organic farming is a cyclical, zero-waste procedure, where waste products from one process are cycled in as nutrients for other processes. This allows the maximum utilisation of resource and increases the efficiency of production.

*The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).

*In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called snow-blindness cataract, etc. Such exposure may permanently damage the cornea.

*the Montreal Protocol, was signed at Montreal (Canada) in 1987 (effective in 1989) to control the emission of ozone depleting substances.

*National Forest Policy (1988) of India has recommended 33 per cent forest cover for the plains and 67 per cent for the hills.

Biofortification – breeding crops with higher levels of vitamins and minerals, or higher protein and healthier fats – is the most practical means to improve public health.

*This capacity to generate a whole plant from any cell/explant is called totipotency