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
