Ecology: Greek words ‘oikos’ meaning ‘house’, ‘logy’ meaning the ‘science of’. Literally, ecology is the study of the earth as a ‘household’, of plants, human beings, animals and micro-organisms. They all live together as interdependent components.

• German zoologist Ernst Haeckel, who used the term as ‘oekologie’ in 1869, became the first person to use the term ‘ecology’. The study of interactions between life forms (biotic) and the physical environment (abiotic) is the science of ecology.
• Ecology: scientific study of interactions of organisms with their physical environment and with each other.
• Ecological systems: The interactions of a particular group of organisms with abiotic factors within a particular habitat resulting in clearly defined energy flows and material cycles on land, water and air.
• Ecosystem: It is the functional unit of nature, where living organisms interact amongst themselves and also with the surrounding physical environment.
• Ecological adaption: Process in which various plants and animals adapt themselves to varying range of environmental conditions through

Types of Ecosystems:

Ecosystem is too complex and big; It is divided into two basic categories:

1. Terrestrial: Further classified into biomes: Land based plant and animal community that covers a large geographical area. Boundaries of different biomes on land are determined by climate:
   • o Biomes: Can be defined as total assemblage of plant and animal species interacting within specific conditions.: Rainfall temperature, humidity and soil conditions. Some major biomes are: Forest, Grassland, Desert, Tundra Biomes.
2. Aquatic: Can be classified into following aquatic Zones:
   • o Marine: includes oceans, costal, estuaries and coral reefs.
     • Brakish – 5-35 ^o/_oo – Chlika, Pulicat
     • Saline 35-50 ^o/_oo –
     • Brine >50 ^o/_oo – Sambhar
   • o Freshwater: Lake, ponds, streams, marshes (relatively drier than bogs) and bogs.
     • Moving water – Lotic ecosystem
     • Stagnant – Lantic ecosystem (Pond)

Ecotone: Junction between two type of ecosystem: Edge effect – Edge species; For example, Mangrove forests between Terrestrial and Aquatic.

Structure and Function of Ecosystems:

Involves a description of available plant and animal species. Structural point of view all ecosystem consists of biotic and abiotic factors:

1. Abiotic factors: Rainfall, temperature, sunlight, atmospheric humidity, soil conditions, inorganic substances (CO₂, Water, N, Ca, P, K etc.)
2. Biotic Factors:
   • Producers:  include all green plants, which manufacture their own food – photosynthesis.
   • Consumers: (Primary, Secondary and Tertiary)
     • Primary consumers include herbivorous animals:  goats, deer, mice etc.
     • Carnivores: flesh eating mammals: snake, tigers and lions.
     • Top Carnivores: Certain carnivores feed on Carnivores: Hawks and mangooses, man.
     • Scavengers: Vultures and crows.
   • Decomposers: feed on dead organisms:
     • Decomposing agents: Bacteria and various micro-organisms. Turn into substances such as nutrient, organic and inorganic salts essential for soil fertility.

Niche:

Niche is the condition/habitat that species need to flourish; Unique functional role, Place/ fundamental role of a species in an Ecosystem. It is a description of all the biological, physical and chemical factors that a species needs to survive, stay healthy and reproduce. 4 types of Niche: 1.       Habitat Niche: This refers to the specific environment or location where an organism lives. It includes factors like temperature, light, and moisture. For example, a coral reef fish lives in the warm, shallow waters of a coral reef, which provides shelter and food. 2.       Food Niche: This refers to the role an organism plays in the food web, including its diet and feeding behaviors. For example, an owl is a nocturnal predator that hunts small mammals, occupying a specific food niche as a carnivore in its ecosystem. 3.       Reproductive Niche: This encompasses the specific conditions and strategies organisms use for reproduction. It includes mating behavior, gestation, and care of offspring. An example is sea turtles that return to specific beaches to lay their eggs, ensuring species survival in a favorable environment. 4.     Physical & Chemical Niche: This refers to the organism’s interaction with the physical and chemical elements of its environment, like temperature, humidity, and soil composition. For instance, certain bacteria thrive in hot springs due to their ability to withstand extreme temperatures and acidic environments.

Function of Ecosystem:

• Flow of Energy: Transfer of energy occurs during process of food-chain from one level to another.
• Nutrient Cycle: See Bio-Chemical Cycles.
• Ecological Succession: Next Page.

Flow of Energy:

See Ecosystem (Biology).

• Food Chain: Organisms of an ecosystem are linked together through a food chain – sequence of eating and being eaten and the resultant transfer of energy from one level to another. For example, Plant – beetle – frog – snake – hawk.
• Food Web: Organisms take more than one type of food: food- chains get interlocked with one another – This interconnecting network of species.
• Generally, two types of food-chains are recognised:
  1. Grazing food-chain: based on autotroph’s energy capture initiated by grazing animals;

• • First level starts with plants as producers and ends with carnivores as consumers as the last level, with the herbivores being at the intermediate level.
  • There is a loss of energy at each level which may be through respiration, excretion or decomposition. The levels involved in a food-chain range between three to five and energy.

1. Detritus food-chain: (Detritus: means waste) involves the decomposition or breaking down of organic wastes and dead matter derived from the grazing food-chain. These are then consumed by other organisms. This chain depends less on the sun for energy.

Types of Biomes:

5 Major types: Forest, desert, grassland, aquatic and altitudinal biomes.

Swamp is woody, Marsh is non-woody.

 

Ecosystem services:

Products of ecosystem: healthy air, water, soil, habitat, wildlife, pollinators, carbon sink, as well as asthetic, cultural and spiritual values.

• Researchers have put an average price tag of US $ 33 trillion a year on these fundamental ecosystem’s services, which are largely taken for granted because they are free. This is nearly twice the value of the global gross national product GNP which is (US $ 18 trillion).
• Out of the total cost of various ecosystem services, the soil formation accounts for about 50%, and contributions of other services like recreation and nutrient cycling, are less than 10% each. The cost of climate regulation and habitat for wildlife are about 6% each.

Ecosystem – Structure and function

• Stratification: Vertical distribution of different species occupying different levels.
  • For example, Trees occupy top vertical strata or layer of a forest, shrubs the 2nd and herbs and grasses occupy bottom layers.
• Components: Case study: pond ecosystem
  • Abiotic components: Water, minerals, sunlight radiance other sources of energy like thermal.
  • Autotrophic: Phytoplankton, some algae and floating, submerged and marginal plants found at edges.
  • Consumers:
    • Heterotrophs: zooplankton, free swimming and bottom dwelling
    • Decomposers: fungi, bacteria and flagellates; Phototrophs (consuming whole of heterotroph directly).
  • System performs all the functions of any ecosystem and biosphere as a whole.
  • Aspects of study:
    • Productivity
    • Decomposition
    • Energy flow
    • Nutrient cycling.

Productivity:

The rate of biomass production.

1. Primary productivity: amount of biomass/organic matter produced over unit area over a time period by plants during photosynthesis. Productivity can be divided into:
   • Gross primary productivity (GPP): Rate of production of organic matter in respiration.
   • Net primary productivity (NPP): Gross primary productivity – respiration losses.

GPP – R = NPP

• Primary productivity varies in different types of ecosystems. It depends on plant species inhabiting a particular area, environmental factors, availability of nutrients and photosynthetic capacity of plants.

2. Secondary productivity: Rate of formation of new organic matter by consumers.

Net primary productivity of the whole biosphere is approx. 170bn tons (dry weight) of organic matter. Of this ocean is only 55bn tones. 70% belongs to land.

Decomposition:

Decomposition includes breaking down of complex organic matter into inorganic substances like CO₂, water and nutrients (with the help of decomposers)

Decomposition based on the Nature of Detritus (dead matter)

• If detritus is rich in lignin and chitin, decomposition is slower.
• If it is rich in Nitrogen and water-soluble substances like sugars decomposition would be quicker.
• Detrivores: Organisms that get nutrition from detritus Such as worms; However, these must be distinguished from other decomposers such as bacteria fungi etc.

Important steps include:

• Fragmentation: detritus material into smaller particles.
• Leaching: water soluble inorganic nutrients go down into soil horizon and get precipitated as unavailable salts.
• Catabolism: Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
• Humification: accumulation of dark coloured amorphous substance called humus.

• Highly resistant to microbial action and
• Undergoes decomposition at an extremely slow rate)

• Mineralisation: Humus is further degraded by some microbes and release inorganic nutrients.

Factors affecting Decomposition:

• It requires oxygen.
• It is controlled by chemical composition of detritus
• Climatic factors: Most important are temperature and soil moisture. They regulate the activities of microbes.  High Temperature and moisture enhance its rate.

Energy flow:

Photosynthetic and chemosynthetic bacteria fix sun’s radiant energy to make food from simple inorganic materials. Except deep sea hydro-thermal ecosystem, sun is only source of energy for all ecosystems on earth.

This process is highly inefficient. Only about 50% of solar radiation is photo synthetically active radiation (PAR), i.e. chlorophyll has the ability to absorb the radiation. The following figure shows the particular wavelength that can be absorbed by the chlorophyll. We can see that chlorophyll are unable to absorb yellow and nearby colours.

Further, Plants capture only 2-10% of the PAR and this small amount of energy sustains the entire living world.

 

Categorisation of Species on the basis their trophic level

• Producers (autotrophs or first trophic level): phytoplankton, algae, green plants in the ecosystem. Major producers are herbaceous and woody plants.
• Consumers(heterotrophs): depend (directly or indirectly) on plants for their food needs.
  • Primary consumers (herbivores or second trophic level): Feed on autotrophs. Many Insects, birds and mammals in terrestrial ecosystem; Molluscs in aquatic.
  • Secondary consumers (Carnivores or third trophic level): animals eat other animals.
    • Primary Carnivores: feed on herbivores.
    • Secondary Carnivores: depend on primary carnivores.

Food chain:

Food chains are formed because of interdependency of the animals on the producers or other consumers for food. No energy that is trapped into an organism remains in it for ever.

1. Grazing food chain (GFC): begins with: Grass.
2. Detritus food chain (DFC): begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria.
   • Saprotrophs: [sapro: decompose/degrade] They meet their energy and nutrient requirements by degrading dead organic matter or detritus.
   • They secrete digestive enzymes that breakdown dead and waste materials into simple, inorganic materials which are subsequently absorbed by them.

In terms of Energy flow

• For Aquatic ecosystem, GFC is major conduit for energy flow.
• For Terrestrial ecosystem: A much larger fraction of energy flows through DFC than GFC.

Biological Magnification:

Chemicals (pollutants, pesticides, insecticides) enter water bodies, and then food chain: absorbed by plants, taken up by aquatic and terrestrial animals. These are non-degradable, and get accumulated progressively at each trophic level. As Humans are at the top of food chain, they get accumulated in maximum concentration in our bodies.

 

• Food web: DFC may be connected with GFC at some levels: some of organisms of DFC are prey to GFC animals, and in a natural ecosystem, [animals like cockroaches, crows, etc., are omnivores] These natural interconnections make food web.
• Trophic level: Based on source of nutrition or food, organisms occupy a specific place in the food chain.
• Tertiary consumers (top Carnivore or Fourth trophic level): No one feeds on them.
• Standing crop: Each trophic level has a certain mass of living material at a particular time called as the standing crop; measured as the mass of living organisms (biomass) or the number in unit area. Can be measured in dry mass or fresh mass.

Ecological Pyramids:

Relationships between number, biomass or energy is represented in the form of Pyramids.

1. Pyramid of Number
2. Pyramid of biomass

• Pyramid of energy

Pyramid of Number and Biomass

In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores.

Exceptions:

1. If you were to count the number of insects feeding on a big tree. [of Number]
2. [Of Biomass] in terms of g/m2

 

Pyramid of Energy

10% law: Only 10% of the energy is transferred to each trophic level from the lower trophic level. Thus, Pyramid of energy is always upright, i.e. Energy at lower trophic level is always more than higher level. Some energy is always lost at each step.

Limitations of Ecological pyramids:

1. Doesn’t consider that a given species may occupy more than one trophic level in the same ecosystem at the same time; For example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.
2. Can’t accommodate food web: It assumes a simple food chain, that almost never exists.
3. Saprophytes (Decomposers) are not given any place in ecological pyramids; Though have a vital role.

Ecological succession:

Composition and structure of all communities (or population) change in response to changing environmental conditions. This change is orderly and sequential, parallel with the changes in the physical environment. Succession and evolution are a parallel process.

• Climax community: near equilibrium with environment.
• Ecological succession: Fairly predictable change in species composition of a given area.

• Sere(s): Entire sequence of communities that successively change in a given area.
• Stages or Seral: Individual transitional communities.
• Primary Succession: When succession starts from scratch. Life occurring in an area which was devoid of life. No living organism ever existed.
  • In case of a new biotic community.
• Secondary succession: Life occurring where, it existed before but somehow lost.
  • Where natural biotic community have been destroyed such as abandoned farm lands, burned or cut forests, flooded land.

Stages of primary succession

1. Pioneer species: Lichens and other small plants that can survive with little soil are the first to colonize the area. These species are called pioneer species because they require minimal resources to survive.
2. Soil formation: As the pioneer species decompose, they create the first layers of soil.
3. Grasses and shrubs: Grasses and shrubs replace the pioneer species, shading them out and altering the soil.
4. Trees: Large trees and more shade-tolerant species replace the grasses and shrubs.
5. Climax community: This is the final stage of primary succession, where the ecosystem is stable and has high species diversity.

• Succession of Plants: Based on nature of habitat – wet or dry; towards mesic habitat (well-balanced moisture content)

• Hydrarch Succession: In Wetter areas and successional series progress from hydric(saturated) to mesic(well-balanced) conditions.
• Xerarch Succession: Takes place in dry areas and series progresses from xeric(dry) to mesic.

Important species Playing role in Succession

• Keystone species: Which has a big effect on its environment relative to its number. For example Corals.
  • The ecosystem depends on them and would be much changed if they were not there.

• Indicator Species: no species will replace it after it gets extinct.

• For example, Great Indian Bustard or Godawan: State bird of Rajasthan.
• Bustard recovery Program:

• Engineer species: Organism that significantly modifies, maintains or destroys a habitat.
  • For example, Corals, Beavers of North America
• Pioneer Species: That invade a bare area. Examples of pioneer species in primary succession:
  • [On Land] Lichens are generally able to secrete acids to dissolve rock and help soil formation by weathering; later pave way for other small plants like bryophytes(mosses), which are able to hold soil. Taken over by bigger plants; Later Climax forest environment. Thus Xerophytic habitat (low water) is changed to mesophytic(medium water).
  • [In Marshy area] Phytoplanktons replaced by free floating angiosperms then by rooted hydrophytes, sedges, grasses and then trees. Climax forest.
• Example Secondary succession; Depends on condition of soil, availability of water, environment and also seeds or other propagates present.

Ecological Balance:

It is a state of dynamic equilibrium within a community of organisms. It occurs in various forms:

• Disturbance in plants: competition where the secondary forest species such as grasses, bamboos or pines overtakes the native species changing the original forest structure is called succession. [Read ecological succession in bio]
• Equilibrium in animals: between predators and prey.
• Plants and Animals: There is a very close relationship between the plant and animal communities within particular habitats. Diversity of life in a particular area can be employed as an indicator of the habitat factor.