Ecology and Environment

Ecology is the study of the interactions among organisms and between organisms and their physical environment. It comes from Greek: "Oikos" (house) + "Logos" (study). A particular aspect of this is the study of anthropogenic environmental degradation and the socio-political issues it has raised. This unit describes as well as takes a critical view.

Few examples of populations : All the cormorants in a wetland, rats in an abandoned dwelling, teakwood trees in a forest tract, bacteria in a culture plate and lotus plants in a pond.  Population ecology is an important area because it links ecology to population genetics and evolution.

1.0Attributes of Population

• Age pyramid
• Birth rates 
• Death rates
• Sex ratio
• Population density

2.0Population Growth

The size of a population for any species is not a static parameter. It keeps changing with time, depending on :

(i) Food availability

(ii) Predation pressure

(iii) Adverse weather.

Growth Models (i) Exponential growth : For unlimited resources, the population grows in an exponential or geometric fashion or J-shaped curve.

_dN/dt = rN 

r = 'Intrinsic rate of natural increase' 

N_t = N₀ e^rt 

Where 

N_t = Population density at time t 

N₀ = Population density at time zero 

r = Intrinsic rate of natural increase 

e = the base of natural logarithms (2.71828)

(ii) Logistic growth (Verhulst-Pearl Logistic Growth): for limited resources. 

Carrying capacity (K) 

This graph shows 

(a) Lag phase 

(b) Acceleration phase 

(c) Deceleration phase 

(d) Asymptote       

3.0Population Interaction

Predation (+, –) ⇒Catch, kill and eat. ⇒Conduits of energy transfer. ⇒Keep prey population under control e.g. Prickly pear cactus controlled by moths in Australia (1920) e.g. Biological control of pests in agriculture. ⇒ Predators maintain species diversity. e.g. Removal of Pisaster causes extinction of >10 species of invertebrates within a year. ⇒Predators are prudent in nature as they never over exploit their prey population. ⇒ Defense camouflage by frogs and insects. ⇒Prey can be poisonous and distasteful e.g. Monarch butterfly. ⇒Nearly 25 percent of all insects are phytophagous (Feeding on plants) ⇒Plants show morphological defences e.g. Thorns/spines (Cactus, Acacia). ⇒Plants show chemical defences. e.g. Calotropis (cardiac glycosides) ⇒Nicotine, caffeine, quinine, strychnine, opium etc. are produced as defence against grazers & browsers. 

Parasitism (+, –) ⇒Mode of life ensuring free lodging and meals. ⇒Parasites can be host specific and both host and parasite co-evolve. ⇒Adaptations of parasites include – loss of unnecessary sense organs, presence of adhesive organs 'or' suckers to cling on to the host, loss of digestive system and high reproductive capacity. ⇒Life cycles of parasites are often complex involving intermediate hosts or vectors. e.g. Human liver fluke needs snails and fish, malaria parasites need mosquitoes. ⇒Parasites harm the host by reducing survival, growth and reproduction, reduce its population density, and make the host vulnerable to predation by making it physically weak. ⇒Ectoparasite : Feed on external surface of host e.g. Lice on humans, ticks on dogs, Copepods on many marine fish etc. ⇒Endoparasite : Live inside the host body at different sites. Morphology and Anatomy of endo parasites is simple but their reproductive potential is high. ⇒Brood parasitism : Parasitic birds lays egg in nest of host, and host incubate them e.g. Cuckoo & Crow.

Competition (–, –) ⇒Interspecific competition is a potent force in organic evolution. ⇒Totally unrelated species can compete for the same resources e.g. visiting flamingoes and resident fishes compete for zooplanktons in shallow South American lakes. ⇒Competition can occur when resources are not limited as in interference competition. ⇒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. ⇒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. This may be true if resources are limited, but not otherwise.

Amensalism (–, 0) One species is harmed whereas other is unaffected eg. Parthenium, Production of antibiotics

Mutualism (+, +) e.g. Lichens – Fungus and Algae or cyanobacteria. e.g. Mycorrhizae – Fungus and roots of higher plants. e.g. Plant and animals ⇒ Plant get pollination and seed dispersal, animals get fees or rewards (as pollen and nectar and juicy and nutritious fruits.) e.g. Fig and wasp ⇒ Fig gets pollinated and wasps get oviposition site and nutrition for its larvae. e.g. Orchid and Bees/Bumble bees. [Ophrys employs sexual deceit and bee pseudo copulates with flowers, helping in pollination (not a true mutualism)] based as coevolution. e.g. Yucca and Pronuba moths.

Commensalism (+, 0) One species benefits and other is neither harmed nor benefitted e.g. Epiphytic orchid on mango branch. Barnacles on the back of a whale. Cattle egret and grazing cattle. Sea anemone and clown fish.

4.0Ecosystem

An ecosystem is a functional unit of nature where living organisms interact with each other and with their physical environment (soil, air, water, etc.) to form a system. It involves:

• Biotic components (living things) 
• Abiotic components (non-living things)

5.0Functional Components of the Ecosystem

Productivity

• A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. 
• 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 (gm–2 ) or energy (kcal m–2 ). The rate of biomass production is called productivity. It is expressed in terms of gm–2 yr –1 or (kcal m–2 ) yr –1 to compare the productivity of different ecosystems. 
• It can be divided into gross primary productivity (GPP) and net primary productivity (NPP). 
• Gross primary productivity 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). 

GPP – R = NPP

• Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores and decomposers). 
• Secondary productivity is defined as the rate of formation of new organic matter by consumers.

Decomposition

• Catabolism - Bacteria and fungal enzymes degrade detritus into simpler inorganic substances.
• Humification - Accumulation of a dark coloured amorphous substance called Humus. Humus  
• Leaching - Water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
• Fragmentation - Break down of detritus into smaller particles by detritivores.(e.g. Earthworm)
• Mineralisation - Humus is further degraded by some microbes and release of inorganic nutrients occurs.

Factors Affecting Decomposition

• Chemical composition of detritus
• Aeration/O₂
• Temperature
• Soil Moisture

Food Chain /Energy Flow

• GFC (Grazing food chain) - Grass → Goat → Man
• Major Conduit for energy flow in an aquatic ecosystem
• DFC (Detritus food chain) - Detritus →Bacteria/Fungi
• Major Conduit for energy flow in a terrestrial ecosystem

Ecological Pyramids

• The base of a pyramid is broad and it narrows towards the apex. 
• One gets a similar shape, whether you express the food or energy relationship between organisms at different trophic levels.
• This relationship is expressed in terms of number, biomass or energy. 
• The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer. 
• The three types of ecological pyramids that are usually studied are 
• (a) pyramid of number
• (b) pyramid of biomass 
• (c) pyramid of energy.

Limitations of Ecological Pyramids

• It 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. 
• Saprophytes are not given any place. 

6.0Biodiversity and Conservation

• Biodiversity is the term popularised by the sociobiologist Edward Wilson to describe the combined diversity at all the levels of biological organisation.
• Genetic diversity - A single species might show high diversity at the genetic level over its distributional range. The genetic variation shown by the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces. 
• Species diversity: The diversity at the species level, for example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats. 
• Ecological diversity: At the ecosystem level, India, for instance, with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows has a greater ecosystem diversity than a Scandinavian country like Norway.

Biodiversity Conservation 

• Insitu (on site conservation) [When we conserve and protect the whole ecosystem, its biodiversity at all levels is protected – like we save the entire forest to save the tiger] 
• A. Biodiversity Hotspots 
• Very high levels of species richness, high degree of endemism, accelerated habitat loss
• Biodiversity hotspots in the world are 34 
• Three of these hotspots - Western Ghat and Sri Lanka, Indo-Burma and Himalaya - cover our country's exceptionally high biodiversity regions. 
• Although all the biodiversity hotspots together cover less than 2 per cent of the earth's land area, the number of species they collectively harbour is extremely high and strict protection of these hotspots could reduce the ongoing mass extinctions by almost 30 per cent. 
• B. Biosphere reserves – 14 
• C. National parks – 90 
• D. Wildlife sanctuaries – 448 
• E. Sacred groves 
• India has also a history of religions and cultural traditions that emphasised protection of nature. 
• Such sacred groves are found in Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan, Western Ghat regions of Karnataka and Maharashtra and the Sarguja, Chanda and Bastar areas of Madhya Pradesh. 
• In Meghalaya, the sacred groves are the last refuges for a large number of rare and threatened plants. Exsitu (off site 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] 
• A. Zoological parks 
• B. Botanical gardens 
• C. Wildlife safari parks 
• D. Cryopreservation techniques 
• E. Seed banks.