Important Issues of Environment and Ecology

By Dr. Roman Saini

The Environment

What is Environment?

● According to the Environment Protection Act 1986, “environment" includes water, air and land and the inter-relationship which exists among and between water, air and land, and human beings, other living creatures, plants, microorganisms and property.

● Therefore, it includes both-

○ The biotic components - Human, animals, birds etc.

○ The abiotic components - Water, air, land etc.

Environmental Pollution

● Environmental pollution is defined as the unfavourable alteration of our surroundings wholly as a by-product of man's activities, through direct or indirect effects of changes in the physical, chemical and biological characteristics of the land, air, or water that harmfully affect human life or any desirable living thing.

● Human population explosion, rapid industrialisation, deforestation, unplanned urbanisation, scientific and technological advancement etc. are the major causes of environmental pollution.

Classification of Pollution

● It may be classified as natural and artificial or man-made pollution.

1. Natural Pollution:

● It originates from natural processes or sources such as hydrocarbons in the atmosphere, radiation pollution coming from the sun or radioactive materials found in nature, oxides of carbon, sulphur etc. coming out from volcanic activity.

2. Artificial or Man-made Pollution:

● It originates due to the activities of man such as lead aerosols in the atmosphere coming from automobile exhaust, chlorinated hydrocarbons (DDT, etc.) from excessive use of pesticides, etc.

Types of Pollutants

● Primary Pollutants:

○ These are those which are emitted directly from the source and persist in the form in which they were added to the environ ment.

○ Typical examples of pollutants included in this category are ash, smoke, fumes, dust, nitric oxide, sulphur dioxide, hydrocarbons etc.

● Secondary Pollutants:

○ These are those which are formed from the pri mary pollutants by chemical interaction with some constituent present in the atmosphere.

○ Examples: sulphur trioxide, nitrogen dioxide, alde hydes, ketones, ozone, etc.

Air Pollution

● Air pollution is the presence of materials in the air that are harmful to humans and the environment they live in.

● Air pollutants are mainly of two types:

a. Gaseous pollutants like hydrocarbons, carbon monoxide, carbon dioxide, oxides of sulphur and nitrogen, hydrogen sulphide, ozone, etc.

b. Particulate pollutants like smoke, dust, mist, fume, spray, etc.

Sources of Air Pollution:

● Industrial pollutants like carbon dioxide, sulphur dioxide, carbon monoxide, hydrogen sulphide, nitrous oxide, ozone, chlorine, arsenic, etc.

● Domestic pollutants from fossil fuels burnt by humans.

● Automobile exhaust or vehicular emission.

● Industrial accidents like leakage of methyl isocyanate from the Union Carbide Plant at Bhopal etc.

● Suspended particulate matter (SPM) like fine dust particles and soot emitted by industrial units.

Effects of Air Pollution:

● Carbon monoxide, having an affinity to haemoglobin, replaces oxygen from oxyhaemoglobin when it enters blood and thus increases the concentration of CO2 in blood causing headache, eye irritation, breathing problem and death.

● Ozone, which also causes smog, is toxic to plant growth and harms human and animal health.

● Smog causes reduced visibility, eye irritation and plant damage.

● Carbon dioxide released by the burning of fossil fuels causes global warming.

● SPM like asbestos dust causes lung diseases, lead causes nervous disorder and brain damage.

Photochemical smog:

● Photochemical smog is caused by the action of solar ultraviolet radiation on atmosphere polluted with hydrocarbons and oxides of nitrogen especially from automobile exhaust.

● Smog can occur both during the day and at night but photochemical smog only happens in the presence of sunlight.

● When volatile organic compounds exit from a smokestack or tailpipe after burning of fossil fuel, they combine with hydroxide molecules in the air to form water and complex molecules which in turn combine with the nitrogen oxide that is emitted at the same time.

● The reaction produces nitrogen dioxide.

● Nitrogen dioxide breaks down again into nitrogen oxide in sunlight, but this degradation produces a free oxygen radical.

● The highly reactive radical combines with molecular oxygen in the air to form ozone.

National Air Quality Index

● The index was launched in 2014 as a part of Indian Government’s mission to introduce the culture of cleanliness.

● Institutional and infrastructural measures have been undertaken in order to ensure that the mandate of cleanliness has been fulfilled across the country.

● There are six AQI categories, namely Good, Satisfactory, Moderately polluted, Poor, Very Poor, and Severe.

● The AQI considers eight pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3 and Pb) for which short-term (up to 24-hourly averaging period) National Ambient Air Quality Standards are prescribed.

Water Pollution

● Water, an essential component for our survival and the most important ecological factor present everywhere, has also been extensively polluted over the years.

Sources:● Domestic sewage

● Industrial waste

● Chemical inputs of agriculture

● Elevated temperatures

Causes of Freshwater Pollution: ● Excess of nutrients from sewage and soil erosion causing algal blooms;

● Pathogens from sewage which spread disease.

● Heavy metals and organic compounds that bioaccumulate in aquatic organisms.

Effects of Water Pollution:● Increased water treatment costs

● Spread of epidemics like cholera, jaundice, dysentery, typhoid, etc.

● Metals like mercury, copper, zinc, lead, etc. and their oxides from industrial waste cause nervous disorder.

● Release of dyes, etc. into water sources and their use by humans and animals affect biological processes.

Remedies of Water Pollution:

● Input control- pollutants should be prevented from being generated in the first place.

● Output control - it attempts to control the pollutant and/or its effect that has been produced.

● Developing of proper sewage system can reduce incoming point source of pollution.

● Extensive afforestation can help in minimizing non-point sources of pollution.

● Strict enforcement of pollution control laws.

● Discharge of drinking water after primary and secondary treatment of water using chlorinator unit.

Eutrophication

● Eutrophication is a kind of nutrient pollution where nutrients like nitrogen and phosphorus are present in excessive quantities in the water.

● Eutrophication occurs naturally, but it occurs very slowly.

● Rapid eutrophication is caused due to discharges of sewage treatment plants and septic tanks into the nearby water bodies, fertilizer runoff from agricultural fields etc.

● Due to the presence of excessive chemicals, there is an explosive growth of algae on the surface of the water body.

● The algal bloom can be seen as a dense layer on the water surface.

● This layer is usually foul smelling and it reduces the clarity as well as the quality of water.

● The dense blooms limit light penetration, reducing growth and causing die-offs of plants in littoral zones.

● When the algae die, microorganisms act upon the dead matter.

● To perform the decomposition, the microorganism needs oxygen.

● Gradually, the eutrophic water body becomes hypoxic i.e. amount of dissolved oxygen becomes low and sometimes the oxygen depletes completely (anoxic state).

● The aquatic organisms start dying.

River Pollution in India

● Untreated municipal sewage is considered to be the major source of pollution of rivers, besides industrial and other non-point sources of pollution.

● The sources of pollution can be classified broadly into two categories, viz.

a. Point sources – These are organized sources of pollution where the pollution load can be measured.

E.g. surface drains carrying municipal sewage or industrial effluents, sewage pumping stations and sewerage systems, trade effluents from industries, etc.

b. Non-point sources – These are non-measurable sources of pollution such as runoff from agricultural fields carrying chemicals and fertilizers, run-off from solid waste dumps and areas used for open defecation, dumping of un-burnt/half-burnt dead bodies and animal carcasses, dhobi ghats, cattle wallowing, etc.

● Water being a State subject, it is the responsibility of the State Government/concerned local bodies to set up proper facilities for collection, transportation and treatment of sewage being generated and ensure that untreated sewage does not fall into the rivers thereby polluting them.

Steps to be taken for control of pollution of rivers include:

● Untreated sewage shall not be disposed into the river or at any other recipient system.

● Local/urban body to set up Sewage Treatment Plants (STPs) of adequate capacity and provide sewerage system to cover the entire local/urban areas and to ensure complete treatment of sewage generated.

● In case of disposal of effluents on land or river or any water body, the treated effluent should meet the designated standards.

● There is a need to reduce the water footprint, including water conservation in the agriculture, industrial and other sectors.

● Need to ensure minimum/adequate flow in the rivers throughout the year, especially in the lean flow season.

National Lake Conservation Plan (NLCP)● For conservation and management of polluted and degraded lakes in urban

and semi-urban areas of India, the Ministry of Water Resources, River Development and Ganga Rejuvenation is implementing the Centrally Sponsored Scheme of National Lake Conservation Plan (NLCP) on 70:30 funding pattern.

● The Plan includes core components of interception, diversion and treatment of wastewaters before their entry into the lake, catchment area treatment, shoreline protection, in-lake treatment etc.

● Non core activities include lakefront eco-development and public participation.

Soil Pollution

Causes:

● Solid and liquid wastes by paper and pulp mills, oil refineries, power plants, etc.

● Use of pesticides, herbicides, fertilizers, etc.

● Domestic waste.

● Soil erosion due to deforestation,

● Wrong farming practices,

● Shifting cultivation,

● High velocity of winds, water flow etc.

Noise Pollution

● Noise is an unpleasant sound or sound without value.

● The Environment (Protection) Act, 1986, recognized noise pollution as an offence.

● The intensity level of sound is measured in decibel (dB) scale.

● It is considered that noise levels below 80 dB (A) do not produce any ill effects.

● However, higher levels often cause impairment of hearing.

● Exposure to noise levels exceeding 75 dB (A) for more than eight hours daily can impair hearing.

● Other effects are stress, hypertension, fatigue, sleep disturbances, speech interference, irritability.

Measures for Noise Pollution:

● Industrial noise can be controlled by using sound absorbing materials.

● Workers should be provided with ear muffs and protectors.

● The working hours should be so adjusted that they are not exposed to high level of noise and Audiometric tests must be done annually.

Radiation Pollution

● Radiation pollution is mainly due to naturally occurring radiations and man-made radiations.

● Exposure to high level of radiations can destroy living tissues.

● Radiations are known to cause cancer, genetic damage, and mutations.

Light Pollution

● Artificial lighting at night is contributing to an alarming increase in light pollution, both in amount and in brightness.

● Some regions have shown a steady increase in light pollution aligned with economic development.

● But more developed nations that were thought to be "going dark" by switching to energy-saving LEDs showed no apparent decline in their rates of light pollution.

Environment Impact Assessment (EIA)

● United Nations Environment Programme defines EIA as a tool used to identify the environmental, social and economic impacts of a project prior to decision-making.

● It aims to predict environmental impacts at an early stage in the project planning and design, find ways and means to reduce adverse impacts, shape projects to suit the local environment and present the predictions and options to decision-makers.

● By using EIA both environmental and economic benefits can be achieved, such as reduced cost and time of project implementation and design avoided treatment/clean-up costs and impacts of laws and regulations.

EIA in India

● To facilitate the collection of environmental data and preparation of management plans, guidelines have been evolved and circulated to the concerned Central and State Government Departments.

● EIA has now been made mandatory under the Environmental (Protection) Act, 1986 for 29 categories of developmental activities involving investments of Rs.50 crores and above.

Environmental Appraisal Committees

● With a view to ensure multidisciplinary input required for environmental appraisal of development projects, Expert Committees have been constituted for the following sectors:

1. Mining Projects

2. Industrial Projects

3. Thermal Power Projects

4. River Valley, Multipurpose, Irrigation and H.E. Projects

5. Infrastructure Development and Miscellaneous Projects

6. Nuclear Power Projects

Climate Change

Evidence of Climate Change

Rise in global temperature:

● Earth’s average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century which has been chiefly driven by anthropogenic activities that release greenhouse gases into the atmosphere.

● Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001.

● 2016 was the warmest year on record, and 8 of the 12 months of 2016- January through September, with the exception of June — were the warmest on record for those respective months.

Warming of the oceans:

● The increase in surface temperature of Earth has resulted in the oceans absorbing a significant amount of this increased heat.

● The top 700 meters (about 2,300 feet) of the ocean has shown warming of 0.302 degrees Fahrenheit since 1969.

Melting of ice-sheets on Greenland and Antarctica:

● The Greenland and Antarctic ice sheets have decreased in mass.

● Data from NASA's Gravity Recovery and Climate Experiment showed that Greenland lost 150 to 250 cubic kilometres (36 to 60 cubic miles) of ice per year between 2002 and 2006, while Antarctica lost about 152 cubic kilometres (36 cubic miles) of ice between 2002 and 2005.

Retreating of glaciers:

● Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.

Decrease in snow cover in the Northern Hemisphere and melting of Arctic sea ice:

● Data collected from satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades.

● Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades.

Increase in ocean acidity:

● Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 per cent.

● The chief reason for this is an increase in carbon dioxide emissions post industrialization era.

● Carbon dioxide dissolves rapidly in waters and is absorbed significantly by the oceans. The dissolved carbon dioxide reacts with water to form carbonic acid.

● The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tons per year.

● The corals have been bearing the brunt of increased ocean acidity.

● Coral bleaching is the result of more acid in the ocean.

Causes of global warming● According to most climate scientists the chief cause of the current global

warming trend is the increase in the "greenhouse effect".

● While greenhouse effect occurs naturally and is the reason behind habitable conditions on Earth, anthropogenic activities have led to an expansion in the greenhouse effect by adding greenhouse gases to the atmosphere.

● Gases that remain semi-permanently in the atmosphere and do not respond physically or chemically to changes in temperature are described as "forcing" climate change.

● Gases, such as water vapour, which respond physically or chemically to changes in temperature are seen as "feedbacks."

Agents for Greenhouse effectWater vapour:● It is the most abundant greenhouse gas, but it acts as a feedback to the

climate. ● Water vapour increases as the Earth's atmosphere warms, but so does the

possibility of clouds and precipitation, making these some of the most important feedback mechanisms to the greenhouse effect.

Nitrous oxide:● It is produced by soil cultivation practices like commercial and organic

fertilizers, fossil fuel combustion, nitric acid production, and biomass burning.

Carbon dioxide (CO2):

● It is released through natural processes such as respiration and volcano eruptions and through human activities such as deforestation, land use conversion, and burning fossil fuels.

● Humans have increased atmospheric CO2 concentration by more than a third since the Industrial Revolution began.

Methane:

● It is a hydrocarbon gas that is produced through decomposition of wastes in landfills, agriculture, and especially rice cultivation, ruminant digestion and manure management associated with domestic livestock.

● On a molecule-for-molecule basis, methane is a far more active greenhouse gas than carbon dioxide, but also one which is much less abundant in the atmosphere.

Chlorofluorocarbons (CFCs):

● They are synthetic compounds entirely of industrial origin used in a number of applications.

● They are a major source of destruction to the ozone layer and also act as greenhouse gases.

● They are now largely regulated in production and released to the atmosphere by international agreement.

Effects of Climate Change

● The Intergovernmental Panel on Climate Change (IPCC), stated that- “the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time.”

● It forecasts a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century.

● According to the IPCC, the extent of climate change effects on individual regions will vary and will depend on the mitigation or adaptation ability of different societal and environmental systems.

Future Effects

● The IPCC predicts that increases in global mean temperature of less than 1 to 3 degrees Celsius above 1990 levels will produce beneficial impacts in some regions and harmful ones in others.

● Net annual costs will increase over time as global temperatures increase.

● It is predicted that global climate change will continue over this century and beyond.

● The magnitude of climate change depends primarily on the emission of greenhouse gases.

● In the countries that experienced frost periods during winters like the US, the length of the frost-free season and the corresponding growing season has been increasing.

● More droughts and heat waves are predicted as the temperature continues to rise.

● Global sea level has risen by about 8 inches since 1880. It is projected to rise another 1 to 4 feet by 2100 due to the addition of water from melting land ice and the expansion of seawater as it warms.

● Increase flooding in regions, especially coasts can be experienced in the next several decades when storm surges and high tides combine with sea level rise and land subsidence.

● Sea level rise will continue past 2100, the reason being that oceans take a very long time to respond to warmer conditions at the Earth’s surface.

● Ocean waters will, therefore, continue to warm and sea level will continue to rise for many centuries at rates equal to or higher than those of the current century.

● The Arctic Ocean is expected to become ice free in summer before 2050.

Solving the Climate Change Problem

● The response to climate change revolves around two possible approaches:

a. Mitigation that involves reducing and stabilizing the levels of heat-trapping greenhouse gases in the atmosphere.

b. Adaptation that involves adapting to the climate change that is already taking place.

Mitigation:

● The 2014 report on Mitigation of Climate Change from the IPCC stated that mitigation efforts should-

“Stabilize greenhouse gas levels in a timeframe sufficient to allow ecosystems to adapt naturally to climate change, ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner”.

● The aim of mitigation is to reduce the flow of greenhouse gases into the atmosphere.

● This can be achieved either by reducing the source of GHG, like relying less on fossil fuels and turning to renewable energy sources, or by increasing the carbon sinks like forests.

● The goal of mitigation is to avoid significant human interference with the climate system that will allow the climate system to stabilize itself over the course of time.

Adaptation:

● Examples of adaptation measures include:

○ Using scarce water resources more efficiently;

○ Adapting building codes to future climate conditions and extreme weather events;

○ Building flood defences and raising the levels of dykes;

○ Developing drought-tolerant crops and choosing tree species and forestry practices less vulnerable to storms and fires; and

○ Setting aside land corridors to help species migrate.

The Intergovernmental Panel on Climate Change (IPCC)

● IPCC is the leading international body for the assessment of climate change.

● It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988.

● It was established to provide a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts.

● The IPCC reviews and assesses the most recent scientific, technical and socio-economic information produced worldwide relevant to the understanding of climate change.

● It does not conduct any research or monitor climate related data or parameters.

● IPCC activities prepare comprehensive Assessment Reports about the state of scientific, technical and socio-economic knowledge on climate change, its causes, potential impacts and response strategies.

● It also produces Special Reports, which are an assessment on a specific issue and Methodology Reports meant to provide practical guidelines for the preparation of greenhouse gas inventories.

The Ecology

What is Ecology?● Ecology may be defined as the scientific study of the relationship of

living organisms with each other and with their environment.

● It has been derived from the Greek oikos meaning "house" or "dwelling", and logos meaning "discourse“.

● The term ecology was first coined in 1869 by the German biologist Ernst Haeckel.

Hierarchy Under Ecology

1. Organism-

● The basic unit of study.

2. Population-

● A group of organisms consisting of a number of same species that live in an area and interact with each other.

3. Community-

● A group of organisms consisting of a number of different populations that live in a defined area and interact with each other.

4. Ecosystem- ● Communities of organisms and their physical environment, interacting

as an ecological unit.5. Biome-

● The world's major communities classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment.

● A biome is different from an ecosystem as an ecosystem is the interaction of living and non-living things in an environment.

● A biome is a specific geographic area notable for the species living there.

● A biome can be made up of many ecosystems.

6. Biosphere-

● The biosphere is made up of the parts of Earth where life exists.

● The biosphere extends from the deepest root systems of trees to the dark environment of ocean trenches, to lush rainforests and high mountaintops.

● The solid surface layer of the Earth is the lithosphere.

● The atmosphere is the layer of air that stretches above the lithosphere.

● The Earth’s water—on the surface, in the ground, and in the air—makes up the hydrosphere.

● Since life exists on the ground, in the air, and in the water, the biosphere overlaps all these spheres.

Biosphere Reserve

● Biosphere reserves are areas comprising terrestrial, marine and coastal ecosystems.

● Each reserve promotes conservation of biodiversity with its sustainable use.

● Biosphere reserves have three interrelated zones that aim to fulfil three complementary and mutually reinforcing functions:

a. the core area,

b. the buffer zone and

c. the transition area.

● The core area comprises a strictly protected ecosystem that contributes to the conservation of landscapes, ecosystems, species and genetic variation.

● The buffer zone surrounding the core areas which can be used for scientific research, monitoring, training and education.

● The transition area where human activity is allowed and socio-culturally and ecologically sustainable economic and human development is carried out.

Habitat and NicheHabitat:

● It is an area or a zone where an organism lives.

● A habitat may support many species where the individuals have similar environmental requirements.

● The structural components of habitat are- food, shelter, space/shelter and water.

Niche:

● It refers to the functional characteristics of a species in its habitat and is unique for that species.

Organism’s Adaptation

● Organismal ecology studies interaction of an organism with the biotic and abiotic components of the environment.

● It also involves the adaptations that an organism develops in response to the environment.

● An adaptation is the appearance or behaviour or structure or mode of life of an organism that allows it to survive in a particular environment.

● The adaptations studied pertain to the organism’s behaviour, physiology and morphology, in response to environmental challenges.

Physiological Adaptation-

● Cold-blooded animals like reptiles are not found in low temperature regions like the Arctic region.

● This is because they cannot regulate the body temperature like warm-blooded animals like mammals.

● Animals in higher elevations produce more red-blood cells to carry more oxygen as there is lower oxygen concentration in the air.

Morphological Adaptations-

● Presence of thick fur in animals found in colder regions.

● In cacti, the leaves are reduced to spines to reduce transpiration and the stem is green and thick to perform photosynthesis and store water respectively.

Behavioral Adaptations-

● Certain animals like brown and black bears undergo hibernation in response to extremely cold climates.

● Some birds migrate from their original habitat to another place to escape harsher climates.

● E.g. Siberian Cranes, Greater Flamingo and Demoiselle Crane are originally from Siberia but migrate to India during the winter months.

● Olive Ridley sea turtles migrate in huge numbers from the beginning of November, every year, for mating and nesting along the coast of Odisha.

The Population

Population-

● Population refers to a group of individuals belonging to the same species and living in the same geographic area at a given time.

Population density -

● The number of individuals of a species per unit area or volume.

● Natality rate, Mortality rate and Dispersal affect population density.

Natality rate -

● The rate at which new individuals are born and added to a population under given environmental conditions is called natality rate.

Mortality -

● Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time.

Dispersal -

● This includes emigration and immigration.

● Emigration is the movement of individuals of a population out of a region on a permanent basis whereas immigration refers to the movement of individuals into a new area.

Patterns of Dispersion-

● The way in which individuals are spaced in a population.

Population Growth Models-

● The rates at which populations grow is calculated that reflects the reproduction biology of the respective species.

Carrying Capacity-

● The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities are available in the environment.

The Ecological Community

Community-

● An ecological community is a group of actually or potentially interacting species living in the same location.

● They share the environment and form a network of influence that each species has on the other.

● Species diversity contributes to a healthy ecosystem where each species performs a function.

● Disappearance of a species has disturbing consequences on the ecosystem.

● Species richness and species evenness are studied under species diversity.

● Species richness refers to the number of species per unit of area.

● Species richness measures are typically separated into measures of α (alpha), β (beta), and γ (gamma) diversity.

Species Diversity

● α diversity is measured at the local scale and consists of a count of species within a relatively homogeneous area.

● β diversity provides information about how diversity changes along environmental gradients.

● γ diversity is a measure of diversity across habitats or community types within a landscape or region.

● Species evenness refers to how close in numbers each species in an environment is.

● Therefore, the number of species in an area indicate its richness whereas the relative abundance of species indicate its evenness.

● Keystone species maintain the structure and integrity of the ecological community. They have a disproportionate effect on its environment relative to its biomass.

● A keystone species exert a top-down influence on lower trophic levels and prevent species at lower trophic levels from dominating over critical resources, such as competition for space or key producer food sources.

● Sea otters are keystone predators that keep the population of sea urchins controlled. Sea urchins feed on kelp and macroalgae.

● When the population of sea urchins is controlled, there is adequate kelp available for species other than sea urchins as well, and the ecosystem remains balanced.

Keystone Species

● In Ecology, stratification refers to the stratification of a community that refers to the vertical layers of the vegetation.

● E.g. in moist tropical rain forests these distinct strata or layers of vegetation can be found:

○ Ground layer of mosses and liverworts associated with dead leaves and other substances rich in organic matter

○ Herb or grass layer

○ Short shrub layer

Stratification

○ Tall shrub layer

○ Layer of understorey of short trees

○ Layer of canopy of lower tress

○ Emergent tree layer formed by tall trees

● It is a progressive change in which plant and animal species in an area that make up a community are replaced by other species over a period of time.

● The change is triggered by the activities of the species and the physical environment.

● Therefore, ecological succession involves activities of the biotic as well as the abiotic components.

● Usually, two types of Ecological succession are discussed- a. Primary Succession b. Secondary Succession

Ecological Succession

1. Primary Succession- ● It takes place on bare or unoccupied areas where no community lived earlier.

● These areas can be like bare rocks outcrop, newly formed deltas and sand dunes, emerging volcano islands and lava flows glacial moraines etc.

● In primary succession, the area is first weathered by physical forces so that soil formation is initiated.

● The area is first inhabited by pioneer species- algae, mosses, and lichens.

● They further the soil forming process and provide the organic matter in the soil once they die.

● Bacteria and fungi help in decomposition of dead pioneer species.

● The pioneer community, after some time, gets replaced by another community with different species combination.

● Each transitional (temporary) community that is formed and replaced during succession is called a stage in succession or a seral community or sere.

● The terminal (final) stage of succession forms the community which is called as a climax community.

● A climax community is stable, mature, more complex and long lasting.

● Primary succession takes a long time as the area has to be altered to support the growth of living communities.

2. Secondary Succession-

● It takes place in an area that was previously occupied by living communities but the community was wiped out after a destructive event like a fire.

● The area is re-colonized by living communities.

● Secondary succession is faster than primary succession as the area was already colonized before. Therefore the soil there has nutrients in it.

● Therefore, the area might not need pioneer species, although in some cases, pioneer species can be the first to inhabit the area.

● The interaction that occurs among different individuals of the same species is called 'intra-specific' interaction while the interaction among individuals of different species in a community is termed as 'inter-specific' interaction.

● The types of interspecific interactions are divided into –

a. Negative interactions

b. Neutral interactions

c. Positive interactions

Biotic Interaction

● In this association, at least one of the species is harmed by the other.

● Types of negative interaction are:

Amensalism: ● This is a negative association between two species in which one species is

harmed or restricted by the other species that itself is not adversely affected or harmed by the presence of the other species.

● Examples- antibiosis in which one organism secretes a chemical that kills the other organism, while the one that secreted the chemical is unharmed.

● For example, penicillin is an antibiotic secreted by the fungus Penicillium which destroys many forms of bacteria.

1.Negative Interaction

Predation:

● In this type of interaction, predator actively hunts for a prey.

● The predator captures, kills and eats an animal of another species called the prey.

● Example- In the wild, lions and tigers hunt for preys like deer.

Parasitism:

● In this, one species that is called a parasite is benefitted at the expense of the other species called the host.

● The parasite can live within the host or outside it.

● Parasite derives all the nutrients from the host and in this process harms the host.

● A parasite living inside the host is called endoparasite whereas the parasite living outside the host (on the surface of the host) is called ectoparasite.

● Example of endoparasite- Tapeworm lives inside human intestines and sucks the nutrients from the intestine.

● Malarial parasite Plasmodium completes its life cycle in human cells.

● Example of exoparasite- Flea, lice, leech.

● In this, the two species that interact but do not affect each other.

● It describes interactions where the health of one species has absolutely no effect whatsoever on that of the other.

● Example- Rabbit and deer interact with each other without harming each other.

2. Neutral Interaction

Commensalism:● In this relationship, one of the species benefits while the other is neither

harmed nor benefited.

● Example – Epiphytes like orchids grow on the trees and derive moisture and nutrients from the air, rain, water or from debris accumulating around it.

● Suckerfish (Remora) attaches itself to a big fish like shark and feeds on the leftovers of the food of the shark.

● Apart from food, it also achieves free locomotion.

3. Positive Interaction

Mutualism:● In mutualism, both the individual’s benefit.

● Symbiotic association is mutualism.

● Examples- Lichens are a symbiotic association between fungi and alga.

The Ecosystem

● The term ‘ecosystem’ was coined by A.G. Tansley in 1935.

● An ecosystem is a functional unit of nature that encompasses a complex interaction between the living components called biotic components and non-living components called abiotic components.

● They perform the following crucial functions:

○ Energy flow through food chain

○ Nutrient cycling through biogeochemical cycles

○ Ecological succession or ecosystem development

○ Homeostasis (or cybernetic) or feedback control mechanisms

Terrestrial ecosystem:

● Ecosystems found on land e.g. forest, grasslands, deserts, tundra, etc.

Aquatic ecosystem:

● Plant and animal communities found in water bodies.

● These can be further classified into two sub-groups:

1. Freshwater ecosystems, such as rivers, lakes and ponds, etc.

2. Marine ecosystems, such as oceans, estuary, etc.

Natural Ecosystem

● Humans have modified the natural ecosystems to their benefit and consumption. Such ecosystems are man-made ecosystems.

● For example, forest land is converted to agricultural land for economic prosperity and increasing food availability for human population.

● This conversion brings down the species diversity and needs human intervention, for example, irrigation and use of fertilizers, insecticides, pesticides etc. for the crops to grow.

● This is an agro-ecosystem which is a human-made ecosystem.

Man-made Ecosystem

Characteristics of a man-made ecosystem:

1. Highly simplified

2. Low species diversity

3. Huge dependence on humans

4. Since species diversity is low, food chains are smaller

5. Soil erosion is common.

6. Unstable without constant human intervention and support

Biotic components:

● Producers, i.e. autotrophs which perform photosynthesis or chemosynthesis to gain energy.

● Most of the green plants are producers as they perform photosynthesis for conversion of solar energy to chemical energy in the presence of carbon dioxide and water.

● Consumers, i.e. heterotrophs that depend upon producers or other consumers for food.

● Example, herbivores that eat plants, carnivores that eat other animals, omnivores that eat both plants and animals.

Components of Ecosystem

● Decomposers or detritivores: e.g. fungi and bacteria, break down chemicals from producers and consumers (usually dead) into a simpler form which can be reused.

Abiotic components:

● These include physical conditions and non-living resources that affect the biotic components.

● Examples of abiotic factors are temperature, light intensity, moisture and water levels, air currents, carbon dioxide levels and the pH of water and soil, minerals present in the soil.

● Food chain represents the flow of energy in a linear sequence from one organism at one trophic level to another organism at another trophic level.

● Each step in the food chain is called a trophic level.

● An example is:

Grasses → Grasshopper → Frog → Snake → Hawk

● Here, the grass is an autotroph that converts solar energy to chemical energy and stores it in form of carbohydrates.

● Grass represents the first trophic level. Grasshopper is a herbivore, a consumer that feeds on grass.

Food Chain

● The frog is a carnivore that feeds on a grasshopper. The Frog is the food of a snake.

● The hawk is the fifth trophic level and the last organism in this food chain.

● Another example is:

Diatoms (Phytoplankton)→ crustaceans → small fish → larger fish like salmon → Shark or a Seal

● During each trophic level, between 80% and 90% of an organism's energy, or biomass is lost as heat energy.

● Therefore, the transfer of energy from one trophic level to another is inefficient and thus the length of the food chain become limited to 4-6 trophic levels.

The trophic levels identified in the food chain are:

1. Autotrophs:

● They are the producers of food for all other organisms of the ecosystem.

● They are largely green plants and convert inorganic material in the presence of solar energy by the process of photosynthesis into the chemical energy (food).

● The total rate at which the radiant energy is stored by the process of photosynthesis in the green plants is called Gross Primary Productivity (GPP).

Trophic Levels in the Food Chain

● This is also known as total photosynthesis or total assimilation.

● From the gross primary productivity, a part is utilized by the plants for its own metabolism.

● The remaining amount is stored by the plant as Net Primary Production (NPP) which is available to consumers.

2. Herbivores:

● The animals which eat the plants directly are called primary consumers or herbivores.

● E.g. insects, birds, rodents and ruminants.

3. Carnivores:

● They are secondary consumers if they feed on herbivores and tertiary consumers if they use carnivores as their food. e.g. frog, dog, cat and tiger.

● Sometimes quaternary consumers can also be found.

● Organisms at the top of a food chain are called apex consumers.

4. Omnivores:

● Animals that eat both plant and animals e.g. pig, bear and men

5. Decomposers:

● They take care of the dead remains of organisms at each trophic level and help in recycling of the nutrients e.g. bacteria and fungi.

1. Grazing Food chain:

● It starts from the autotrophs on which the primary consumers feed.

● The energy usually comes from the sun as photosynthesis by green plants requires it.

2. Detritus Food chain:

● It starts from the dead organic matter like fallen leaves, plant parts or dead animal bodies on which the detritivores organisms called saprophytes like protozoans, bacteria, fungi feed.

Types of Food Chain

● It is the gradual buildup of toxic chemicals or heavy metals inside an organism’s body over time.

● Bioaccumulation is seen in food chains.

● The pesticides or insecticides sprayed on plants comprises toxins.

● These plants are consumed by primary consumers, which are eaten by secondary consumers, and the secondary consumers are eaten by higher level consumers.

● At each trophic level, the consumer consumes more quantity e.g. a secondary consumer may feed on two primary consumers and the tertiary consumer may feed on 4-5 secondary consumers.

Bioaccumulation

● Thus, the amount of toxin accumulated increases at each trophic level and is the maximum at the apex level

● Harmless substances are usually excreted but the toxins deposit in the tissues.

● Especially fat tissues of organisms and the concentration of toxin becomes most concentrated in the body tissues of the animals at the top of the food chain.

● In the 1940s and 1950s, a pesticide called DDT (dichloro-diphenyl-trichloroethane) was widely used to kill insects that spread diseases.

● DDT bioaccumulates in an ecosystem and causes damage to the environment.

● It was the cause of decline in the population of bald eagles, which are the apex predators.

● DDT caused the eggs of the eagles to have extremely thin shells and the eggs broke before they could hatch.

Biomagnification-

● Increase in concentration of a substance/toxin in a food chain across trophic level and not in an organism is called Bio-amplification or biomagnification.

● Ecological pyramids are the graphic representations of trophic levels in an ecosystem.

Pyramid of number:

● This represents the number of organisms at each trophic level.

● For example, in a grassland, the number of grasses is more than the number of herbivores that feed on them and the number of herbivores is more than the number of carnivores.

● In some instances the pyramid of number may be inverted, i.e herbivores are more than primary producers as many caterpillars and insects can feed on a single tree.

Ecological Pyramid

Pyramid of biomass:

● This represents the total standing crop biomass at each trophic level.

● Standing crop biomass is the amount of living matter at any given time. It is expressed as gm per unit area or kilocal per unit area.

● In most of the terrestrial ecosystems, the pyramid of biomass is upright.

● However, in the case of aquatic ecosystems the pyramid of biomass may be inverted e.g. in a pond phytoplankton are the main producers.

● They have very short life cycles and a rapid turnover rate (i.e. they are rapidly replaced by new plants).

● Therefore, their total biomass at any given time is less than the biomass of herbivores supported by them.

Pyramid of energy:

● This pyramid represents the total amount of energy at each trophic level.

● Energy is expressed in terms of rate such as kcal per unit area per unit time or cal per unit area per unit time.

● Energy pyramids are always upright.

● The matter on Earth comprises the elements that are necessary for the structure and chemical processes of life.

● These elements are cycled continuously through the atmosphere, hydrosphere, biosphere, and lithosphere, on time scales ranging from a few days to millions of years.

● The biogeochemical cycles comprise biological, geological, and chemical processes.

● The major biogeochemical cycles are carbon cycle, nitrogen cycle and hydrological cycle (water cycle).

Biogeochemical Cycles

● The carbon cycle involves two sub-cycles which differ in the time scales.

● The first sub-cycle is fast and occurs at the biological level.

● An estimated 1,000 to 100,000 million metric tons of carbon move through the biological pathway each year.

● The second sub-cycle is geochemical and takes an enormous amount of time as the geological processes take a lot of time, sometimes which extends upto millions of years.

The Carbon Cycle

The global carbon cycle consists of the following steps:

Photosynthesis:

● Green plants in the presence of sunlight utilize CO2 in the process of photosynthesis and convert the inorganic carbon into organic matter (food) and release oxygen.

● A part of the food made through photosynthesis is used by plants for their own metabolism and the rest is stored as their biomass which is available to various herbivores, heterotrophs, including human beings and microorganisms as food.

Respiration:

● Respiration is carried out by all living organisms.

● It is a metabolic process where food is oxidized to liberate energy, CO2 and water.

● The energy released from respiration is used for carrying out life processes by living organism (plants, animals, decomposers etc.).

● Thus CO2 is released into the atmosphere through this process.

Decomposition:

● All the food assimilated by animals or synthesized by the plant is not metabolized by them completely.

● A major part is retained by them as their own biomass which becomes available to decomposers on their death.

● The dead organic matter is decomposed by microorganisms and CO2 is released into the atmosphere by decomposers.

Combustion:

● Burning of biomass releases carbon dioxide into the atmosphere.

● It may take up to millions of years.

● Carbon may be stored for long periods of time in the atmosphere, bodies of liquid water—mostly oceans— ocean sediment, soil, rocks, fossil fuels, and Earth’s interior.

● Oceans play a very important role in the geological carbon cycle. CO2 readily dissolves in water, hence oceans can store a great amount of carbon dioxide.

● The dissolved CO2 combines with water molecules to form carbonic acid, which is unstable and dissociates into carbonate ions.

Geological Carbon Cycle

● The carbonate ions react with calcium ions to form calcium carbonate.

● Calcium carbonate is the chief inorganic material that forms the shells of marine organisms.

● Once the organisms are dead, the calcium carbonate remains settled on the ocean floor as sediment.

● Over the course of time, the sediment is converted to carbonate rocks like limestone.

● However, the exchange of carbon in this form with the atmosphere is very slow.

● Carbon is stored in the interior of the Earth in the form of carbonate rocks, such as limestone, dolomites, and chalk.

● Also, fossil fuels are a carbon reservoir that forms over the course of millions of years.

● When humans burn them, carbon is released into the atmosphere as carbon dioxide.

● Carbon is released from the Earth’s interior into the atmosphere during volcanic eruptions as well.

● Carbon is in the form of carbon dioxide.

The main steps in the nitrogen cycle are:

Nitrogen fixation:

● This process involves the conversion of gaseous nitrogen into Ammonia, a form in which it can be used by plants.

● Atmospheric nitrogen can be fixed by the following three methods:

1. Atmospheric fixation: Lightning, combustion and volcanic activity help in the fixation of nitrogen.

The Nitrogen Cycle

2. Industrial fixation: At high temperature (400oC) and high pressure (200 atm.), molecular nitrogen is broken into atomic nitrogen which then combines with hydrogen to form ammonia.

3. Bacterial fixation: There are two types of bacteria-

A. Symbiotic bacteria e.g. Rhizobium in the root nodules of leguminous plants.

B. Free living or symbiotic e.g. Nostoc, Azotobacter, cyanobacteria can combine atmospheric or dissolved nitrogen with hydrogen to form ammonia.

Nitrification:

● It is a process by which ammonia is converted into nitrates or nitrites by Nitrosomonas and Nitrococcus bacteria respectively.

● Another soil bacteria Nitrobacter can convert nitrate into nitrite.

Assimilation:

● In this process, nitrogen fixed by plants is converted into organic molecules such as proteins, DNA, RNA etc.

Ammonification :

● Living organisms produce nitrogenous waste products such as urea and uric acid.

● These waste products, as well as dead remains of organisms are converted back into inorganic ammonia by the bacteria called Ammonifying bacteria.

Denitrification:

● Conversion of nitrates back into gaseous nitrogen is called denitrification.

● Denitrifying bacteria live deep in soil near the water table as they like to live in the oxygen free medium.

● Denitrification is reverse of nitrogen fixation.

The Water Cycle● Most of the water on the Earth does not cycle very rapidly.

● The residence time of water refers to the average time that an individual water molecule spends in each of Earth’s major water reservoirs.

● Water in oceans, underground, and in the form of ice tends to cycle very slowly.

● The driving forces for water cycle are solar radiation and gravity.

● Evaporation and precipitation are two main processes involved in the water cycle. These two processes alternate with each other

● Water from oceans, lakes, ponds, rivers and streams evaporates by sun’s heat energy.

● Plants also transpire huge amounts of water.

● Water remains in the vapour state in air and forms clouds.

● Clouds meet with the cold air in the mountainous regions above the forests and condense to form precipitation (e.g.rain) which comes down due to gravity.

● When precipitation reaches the Earth's surface, it has a few options: it may re-evaporate, flow over the surface as runoff, or percolate i.e. sink down into the ground.

● Water usually flows as runoff when the soil is saturated with water, during a heavy downpour, or when the surface can't absorb much water.

● Water in the upper levels of the soil is absorbed by plant roots.

Homeostasis

● Homeostasis is the capacity of the ecosystems to maintain a dynamic equilibrium.

● Ecosystems self-regulate using negative feedback mechanism that makes them relatively stable.

● Interactions between predators and prey are widely cited as a classic example of how consumer/ resource dynamics can result in negative feedback that stabilizes the system.

● In a simple predator-prey system - initial increases in prey populations result in increased resource availability for their predator.

● Because consuming prey results in increased reproduction and survival in the predator population.

● In this way, increases in the prey population initially provide an impetus for the predator population to increase.

● As predator abundance increases, the demand for prey also increases and the increase in death rate for the prey causes declines in prey populations.

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