Ecology, and Ecosystem

Ecology, and Ecosystem  [pdf]

1.1 ENVIRONMENT 

Environment means anything that surrounds us. It consists of both living (biotic) and non-living  (abiotic) things. Interactions among the biotic and abiotic components shape the habitat and ecosystem  of an organism. 

The environment includes the physical (air, water), chemical (carbon cycle, nitrogen cycle) and  biological (biomolecules, organisms) interactions that affect an organism. 

1.2 ECOLOGY 

Ecology is the study of relationships between living organisms, including humans and their physical  environment. There are five main levels of organization of ecology. 

   Ecological Organization 

Population refers to a group of individuals usually of the same species, occupying a defined area during  a specific time. 

Community refers to all populations of different species that live in the same area and interact with one  another. A community is composed of all of the biotic factors of a site. Communities in most instances  are named after the dominant plant form and can be divided into two types: 

1. Major Community– These are large-sized and relatively independent. They depend only on the  sun’s energy from outside. E.g., Tropical Evergreen Forests. 
2. Minor Community– These are dependent on the neighboring communities. E.g., A mat of  lichen on a cow dung pad. 

Ecosystem is the structural and functional unit of a biosphere. It consists of a community of living  organisms in conjunction with their environment’s non-living components, both interacting and  exchanging materials between them.  

This Red Book is a part of a Supplementary Study Material for ForumIAS Academy Comprehensive Guidance Program ( CGP) 2022 

Biome is the terrestrial part of the biosphere. They are characterized by climate, vegetation, animal life  and general soil type. 

Biome distribution based on Temperature and Precipitation: 

This Red Book is a part of a Supplementary Study Material for ForumIAS Academy Comprehensive Guidance Program ( CGP) 2022 

Biosphere is a part of the earth where life can exist. It comprises of the atmosphere (air), hydrosphere (water) and lithosphere (land).

Pointers for prelims: 1.       Biosphere is absent at extremes of North and South poles, the highest mountains and deepest oceans since existing in hostile conditions there; do not support life. 2.       Occasionally, spores of fungi do exist at great heights beyond 8000 meters, but they are metabolically inactive.

1.3 FUNCTIONS OF ECOSYSTEM

1.3.1 Ecological Succession

 Ecological succession is the process of change in the species structure of an ecological community over time. The time scale can range from decades to even millions of years. Plants and animal species in an area are replaced or changed into another over a period of time. One community replaces another until a stable and mature climax community develops.

The stages leading to the climax community are called seres or successional stages. Succession is characterized by increased productivity, a gradual increase in food webs’ complexity and increased diversity of organisms with increased niche development.

Succession occurs faster in regions existing in the middle of the large continent because seeds of plants belonging to the different seres would reach here much faster.

Stages in succession are:

1. Primary Succession: It takes place over an area where no community has previously existed. Few hardy pioneer species like lichens, mosses and microbes first colonialize the new site.

The pioneers, over a few generations, alter the habitat conditions by their growth and development. These new conditions may be conducive to establishing additional organisms that may subsequently arrive at the site.

1. Secondary Succession: It is the sequential development of biotic communities following the complete or partial destruction of the existing community. A mature or intermediate community may be destroyed by natural events like floods or human interventions like deforestation.

This abandoned land is first invaded by hardy grasses species that can survive in bare, sunbaked soil. Tall grasses and herbaceous plants may soon join these grasses. Eventually, some trees come up in this area, seeds of which may be brought by wind or animals. And over the years, a forest community develops.

The difference between primary and secondary succession is that secondary succession is relatively faster than primary succession as it starts on a well-developed site already formed at the site. Also, secondary succession starts on a well-developed soil already formed at the site.

Types of succession are:

1. Autogenic Succession: When living inhabitants of the community itself bring about succession.
2. Allogenic Succession: When outside forces bring about succession.
3. Autotrophic Succession: Succession in which green plants are much more significant in quantity.
4. Heterotrophic Succession: Succession in which heterotrophs are more significant in quantity.

1.3.2 Energy Flow Through an Ecosystem

Energy flow is unidirectional and decreases from the first trophic level to upwards. This is due to loss in energy in the form of heat at each trophic level.

Trophic level interaction deals with how members of an ecosystem are connected based on nutritional needs.

Basic Concepts 1.     Food Chain: A sequence of organisms that feed on one another form a food chain. It can be a grazing food chain (beginning from green plants at the base) or a detritus food chain (beginning from dead organic matter). Food chains are not found within the population of a species (for e.g., a lion won’t eat a lion). 2.     Food Web: Multiple interlinked food chains make a food web. A food web denotes the numbers of each organism which are eaten by others.

A food web consists of many food chains. A food chain only follows just one path as animals find food. E.g., a hawk eats a snake, which has eaten a frog, which has eaten a grasshopper, which in turn has eaten grass. However, a food web consists of many food chains. A food web shows many different paths through which plants and animals are connected. For e.g., a hawk might also eat a mouse, a squirrel or some other animal. The snake may eat a beetle or a caterpillar. And the process continues for all the other animals in the food chain. Picture Credits: www.cadavies.com/food-chains-and-food-webs.html Food Chain v/s Food Web

Terrestrial Food Chain: Grass®Grasshopper®Mouse®Snake®Hawk.

Aquatic Food Chain: Phytoplankton (diatoms, cyanobacteria) ®Crustaceans®Herrings

 Ecological Pyramids: They are pyramidical representation of trophic levels of different organisms based on their ecological position (producer to final consumer). They are classified into three categories:

1. Pyramid of numbers: This shows the total number of individual organisms at each level in an ecosystem’s food chain.
2. Pyramid of numbers-upright: In this pyramid, the number of individuals decreases as one moves from lower to higher trophic level. Grassland and pond ecosystem shows this type of pyramid.

1. Pyramid of numbers-inverted: In this, the number of individuals is increased from lower to higher trophic level. E.g., tree ecosystem.

1. Pyramid of biomass: It is determined by collecting all organisms at each trophic level and measuring their dry weight.
   1. Pyramid of biomass-upright: For the majority of ecosystems on land, the pyramid of biomass shows a large base of primary producers and a smaller trophic level perched on top.

1. Pyramid of biomass-inverted: In contrast, in many aquatic ecosystems, the pyramid of biomass may assume an inverted form. This is because producers are tiny phytoplankton.

1. Pyramid of Energy: An energy pyramid is a model that shows the flow of energy from one trophic level to the next along a food chain. It is always upright with a large energy base at the bottom.

Basic Concepts:1.       Bioaccumulation: It refers to how pollutants enter a food chain. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is eliminated.2.       Biomagnification: It refers to the pollutant’s tendency to concentrate as they move from one trophic level to the next. For biomagnification to occur, pollutants must be long-lived, mobile, soluble in fats, biologically active. For e.g., the concentration of DDT moves up the food chain, from one trophic level to another.

1.3.3 Bio-geo-chemical cycle

Bio-geo-chemical cycle is a pathway by which a chemical substance moves through the biotic and abiotic compartments of the earth. They are of the following types:

1. Nutrient Cycling: It is a concept that describes how nutrients move from the physical environment to the living organisms and subsequently back to the physical environment.

1. Gaseous Cycles: Some of the most important gaseous cycles are water, carbon and nitrogen.

1. Water Cycle: It involves a continuous circulation of water in the Earth-atmosphere system, which is driven by solar energy.

1. Carbon Cycle: It involves a continuous exchange of carbon between the atmosphere and organisms. It is usually a short-term cycle. Respiration, decay and volcanic actions are some factors that add CO₂ to the Carbon Cycle.

1. Nitrogen Cycle: Nitrogen is converted into many chemical forms as it circulates from the atmosphere to the soil to organism and back into the atmosphere.
2. Nitrogen fixation: They are accomplished in three different ways: by microorganisms like bacteria and blue-green algae, by man using industrial process like fertilizer factories and to a limited extent by atmospheric phenomenon like thunder and lighting.

1. Nitrification: Ammonium ions are oxidized to nitrites or nitrates by two specialized bacteria; Nitrosomonas bacteria to promote ammonia transformation into nitrite, which is then further transformed into nitrate by the bacteria Nitrobacter.

• Denitrification: Special denitrifying bacteria pseudomonas convert nitrites/nitrates to elemental nitrogen.

3. Sedimentary Cycles: Phosphorus and sulphur circulate by means of sedimentary cycle.
4. Phosphorus Cycle: The main storage for phosphorus is in the earth’s crust. It occurs in large amounts as a mineral in phosphate rocks and enters the cycle from erosion, weathering and mining activities.

3. Sulphur Cycle: Sulphur is locked in organic (coal, oil and peat) and inorganic deposits (pyrite rocks and Sulphur rocks).

It is released by weathering activities. It also enters the atmosphere from sources like volcanic eruptions, fossil fuel combustion, ocean surface and decomposition.

While the Sulphur cycle is mostly sedimentary, hydrogen sulphide and Sulphur dioxide add a gaseous component to it. This hydrogen sulphide also gets oxidized into Sulphur dioxide which dissolves in rainwater and falls as acid rain.

1.4 TERRESTRIAL AND AQUATIC ECOSYSTEMS

1.4.1 Terrestrial Ecosystem

Terrestrial ecosystems, namely tundra forest, boreal forest, temperate deciduous forest, tropical rain forest, savannah, steppe and desert have been discussed earlier in this booklet.

Important terrestrial ecosystems required from prelims point of view will be discussed in this chapter.

1. Indian Forest Types (based on Champion and Seth classification of forest)

Picture Credits: Wildlife Institute of India

2. Grassland Ecosystem: These are found in regions where rainfall is about 25-75 cm per year. Rainfall is not enough to support a forest, but more than a true desert. Steppe formations are found in western Rajasthan while dry savannah grasslands are found in the central and eastern parts of Rajasthan. Fire is a natural part of the grassland ecosystem which helps control trees, woody shrubs and invasive species and maintain its health and vigor.

Heavy grazing in grasslands leads to a reduction of the mulch cover of the soil. Microclimate becomes dry and is readily invaded by xerophytes. Due to the absence of humus cover, the mineral soil surface is heavily trampled. It reduces the infiltration of water into the soil and accelerates run-off, resulting in soil erosion.

3. Desert Ecosystem: Animals are physiologically and behaviorally adapted to desert conditions: they are fast runners, nocturnal in habit, have long legs to keep the body away from the hot ground and conserve water by excreting concentrated urine.

Thar desert is an example of Indian desert. It is home to the Great Indian Bustard, Flamingoes and Asiatic Wild Ass. Asiatic Wild Ass, also known as ghudkhur in local Gujrati language, is a sub-species of the onager native of South Asia. The animal has no predators in that area, but its existence is threatened due to the destruction of habitats. It is currently listed as Near Threatened by IUCN.

Cold Desert of India is found in Leh, Ladakh and Kargil of Kashmir and Spiti valley of Himachal Pradesh and some parts of Uttarakhand and Sikkim. The soil of this region is sandy to sandy loam, while the pH type is neutral to slightly alkaline. Tibetan Wild Ass (Kiang) and Snow Leopard are important fauna found here.

1.4.2 Aquatic Ecosystem

Ecosystems consisting of water as the main habitat are known as aquatic ecosystems.

1. Aquatic organisms are classified based on their zone of occurrence and their ability to cross these zones.
2. Neuston: They live at the air-water interface. E.g., beetles, back-swimmers
3. Periphytons: These organisms remain attached to the stems and leaves of rooted plants.
4. Plankton: This group includes microscopic plants like algae and animals like crustaceans and protozoans (zooplankton). Their locomotory powers are primarily controlled by ocean currents.
5. Nekton: This group contains animals that are swimmers.
6. Benthos: These organisms are found at the bottom of the water mass.

Factors like sunlight and oxygen are the most important limiting factors of the aquatic ecosystem. Other factors include dissolved oxygen, transparency and temperature.

2. Wetland Ecosystem: Wetlands are areas of marsh or peatland with water that is static or flowing, fresh, brackish or saline, including areas of marine water, the depth of which at low tide does not exceed 6 m. Wetlands are ecotones between terrestrial and aquatic ecosystems.

Wetlands occupy 18.4% of the country’s area, of which 70% is under paddy cultivation. They are usually rich in nutrients and have an abundant growth of aquatic macrophytes. Wetlands support high densities and diverse fauna.

3. Lake Ecology: A body of standing water, generally large enough in area and depth, irrespective of its hydrology, ecology and other characteristics, is generally known as lake. Ageing of lake occurs as it accumulates mineral and organic matter and gradually gets filled up. Lakes are less productive than the estuary ecosystem but are more than oceans.

4. Estuarine ecosystem: An estuary is a place where a river or stream opens into the sea. They are the most productive water bodies in the world.

4. Mangroves: Evergreen forests that grow in sheltered low-lying coasts, estuaries, mudflats, tidal creek backwaters, marshes and lagoons of the tropical and subtropical regions. They are salt-tolerant or halophytes and are adapted to harsh ecological conditions. E.g., Sonneratia and Avicennia.

Some characteristics of mangroves are:

1. Require high solar radiation.
2. Produces pneumatophores (blind roots/aerial roots) to overcome respiration problems in anaerobic soil conditions or adventitious roots (roots emerging from main trunk of the tree).
3. Exhibit viviparity mode of reproduction (seeds germinate in the tree itself before falling to the ground).
4. Some secrete excess salts through their leaves.

Mangrove Profile

6. Coral Reefs: Corals are marine invertebrates. They typically live in compact colonies of many identical individual polyps. Corals are in a symbiotic relationship with ‘zooxanthellae’ microscopic algae which live on coral. Zooxanthellae assists the coral in nutrient production while the coral polyp in return provides zooxanthellae with a protected environment to live within. A coral reef is made of a thin layer of Calcium Carbonate.

Corals are of two types– hard corals and soft corals. Only hard corals build reefs. Most of the world’s corals are found in tropical shallow waters less than 50 meters deep. Scientists estimate that more than 25,000 described species from thirty-two of the world’s thirty-three animal phyla live in reef habitats-four times the number of animal phyla found in tropical rain forests. Australia accounts for around 17% and Indonesia around 16% of the world’s corals.

They are highly productive and are also referred to as the ‘Tropical Rainforests of the Oceans’. They are classified into fringing reefs, patch reefs, barrier reefs and atolls.

Coral reefs have been included in Schedule I of the Wildlife Protection Act, 1972, thus offering it maximum protection. Also, they have been classified as CRZ-I A under the Coastal Regulation Zone (CRZ) notification, 2011.

Coral Reef distribution in India