Key concepts:
* Ecology deals with the interactions among organisms and between the organism and its physical (Abiotic) environment.
* It is basically divided into plant ecology and animal ecology.
* It is concerned with four levels of biological organization – Organisms, populations, communities and biomes.
 

Plant Communities and Ecological Adaptations:
* Adaptation is any change (morphological, physiological, behavioral) in the organism that enables the organism to survive and reproduce in its habitat.
* Eugen Warming classified plant communities into hydrophytes, mesophytes and xerophytes based on the relation of plants to water.
 

Hydrophytes:
* Plants that grow in water or in very wet places are called hydrophytes.
* They may be classified into:

* Free floating hydrophytes: e.g.: Pistia, Lemna, Salvinia
* Rooted hydrophytes with floating leaves: e.g.:Nymphaea, Victoria
* Submerged suspended hydrophytes: e.g.: Hydrilla, Utricularia
* Submerged rooted hydrophytes: e.g.: Vallisnaria
* Amphibious plants: e.g.: Saggitaria, Typha, Limnophila Morphological adaptations of hydrophytes:
* Roots are poorly developed. If present they are fibrous, reduced and poorly branched.
* Root caps are usually absent. In Pistia they are replaced by root pockets.
* Stem is long and slender.
* Leaves may be thin, ribbon like, linear or dissected. Some may have floating leaves with wax coated surfaces.
 

Anatomical adaptations of hydrophytes:
* Cuticle is usually absent. It is limited to upper surface in floating leaves.
* The epidermis is made of thin walled cells that perform absorption and photosynthesis.
* Stomata are usually absent. They are limited to upper epidermis in floating leaves.
* Aerenchyma is well developed and helps in gaseous exchange and buoyancy.

* Mechanical tissues (Sclerenchyma) and xylem and poorly developed.
 

Mesophytes:
* Mesophytes are plants that grow under normal conditions of water. They are most suitable for plant growth and form forests and crops.
 

Xerophytes:
* They grow in habitats deficient in water. They may be classified into:
1. Ephemerals: They are annuals which complete their life cycle within a very short periods. e.g.: Tribulus.
2. Succulents: These xerophytes store water in their parts in the form of mucilage when it is available and swell up. They use this stored water during dry periods. e.g.: Opuntia (Stem succulent), Aloe (leaf succulent) and Asparagus (leaf succulent).
3. Non-succulents: These are perennials which can withstand prolonged period of drought.
e.g.: Casuarina
 

Morphological adaptations in xerophytes:
* Root system is well developed with long, branched roots.
* Root hair and root caps are well developed.

* Stems are stunted, woody, hard and covered with thick bark.
* Hair and waxy coating may be present on stems and leaves.
* Leaves are reduced to scales or spines.
 

Anatomical adaptations in xerophytes:
* Epidermis is multilayered and covered with thick cuticle.
* It may contain silica crystals.
* Stomata are present on lower epidermis and sunken in position.
* Mechanical tissues (Sclerenchyma) are well developed.
* Vascular tissues are also well developed.
 

Plant succession:
* The gradual change in the composition of species in a given area is called ecological succession.
* The sequence of communities that successively change in a given area are called seres.
* If the succession starts where no living organisms ever existed like bare rock it is called primary succession. e.g.: cooled lava, bare rock, newly created reservoir or pond.

* If the succession starts in an area where organisms were existing but somehow lost is called secondary succession. e.g.: abandoned farm lands, burned forests, flooded lands.
* Human intervention can convert seral stages to earlier stages and may encourage some species and discourage others.
* Plant succession may be hydrarch or xerarch succession based on the nature of habitat.
* Hydrarch succession starts in water and xerarch succession takes place in dry areas like bare rock.
* The species that invade a bare area is called a pioneer species. e.g.: Lichens
* Different stages in hydrarch succession are:
   •  Phytoplanktons
   •  Free floating angiosperms
   •  Rooted hydrophytes
   •  Sedges
   •  Grasses
   •  Trees

* The climax community is a forest and the hydric conditions gradually convert to mesic conditions.
* Primary succession is a slow process while secondary succession occurs at a fast rate.
 

Ecological services:
* Ecosystem services or ecological services are life supporting and life enhancing services.
* If they are valued with money our earth cannot provide enough money to buy all of them.
* For the first time Robert Constanza tried to put price tags for these ecological services.
* It is estimated that the ecological services account for 33 trillion US dollars which is twice the value of global gross national product (GNP).
* Ecosystem services may be grouped into:
1. Supporting services: e.g.:  Nutrient cycling, oxygen production, soil formation, crop pollination.
2. Provisioning services: Food, fibre, fuel and water.
3. Regulating services: Climate regulation, water purification by microbes and flood protection by mangroves.
4. Cultural services: Education, recreation and aesthetic value by conservation of biodiversity, creating natural beauty through local gardens.

Ecosystem service – pollination
* The most important pollinator for agricultural purposes is the honey bee.
* Decline in pollinator activity results in loss of crop yield.
* Due to deforestation of chaparral and oak-wood trees in California the wild bee population reduced and there was a decline in agricultural yield.
* Nearly one lakh species of invertebrates and 1035 species of vertebrates act as pollinators.
* According to US Fish and Wildlife Service lists 50 pollinator species are threatened or endangered.
* Causes of decline in pollinators are deforestation and chemical pesticides.
 

Measures to protect pollinators:
* Growing native flowering plants in our surroundings.
* Reducing use of chemical pesticides.
* Building artificial habitats like butterfly gardens, bee boards and bee boxes.
* Protection of pollinators to be on the agenda of agricultural policies.

Ecosystem service – carbon fixation
* Forests accumulate large amounts of carbondioxide in the form of timber and provide oxygen in return.
* Based on the equation of photosynthesis the amount of CO₂ absorbed may be calculated.
* 264 gms of CO₂, 108 gms of water and 677.2 K.cal of solar energy produce 180 gms of glucose and 193 gms of oxygen.
* 180 gms of glucose can be converted into 162 gms of polysaccharide or dry matter.
* Therefore for every one gram of dry matter produced 1.63 gms of CO₂ is fixed.
* If a standard cost per unit CO₂ fixed is multiplied with the total fixed CO₂ the economic value of CO₂ can be obtained.
* Natural ecosystems reduce green house gases and also help to moderate regional and local weather.
* Carbon tax system established by many countries also reduces green house gases.
* Afforestation is an effective measure to prevent global warming.

Ecosystem service – oxygen release:
* Trees and planktons produce oxygen during photosynthesis.
* The amount of oxygen produced by a tree depends on the species of the tree, its age, its health and its surroundings.
* A mature leafy tree produces oxygen enough for 10 people to inhale in a year.
* Submerged macrophytes (larger plants in water) enrich dissolved oxygen in water.
* The plants and planktons are called "the lungs of the world" because they exhale billions of tonnes of oxygen.
* Some microbes like cyanobacteria release oxygen directly while others produce oxygen indirectly.
 

How to protect ecological functions?
* Use products produced with methods to conserve resources.
* Minimize waste by reuse.
* Prevent environmental damage by reducing consumption and wastage.
* Reduce use of chemical pesticides and artificial fertilizers and follow natural pest control methods.

* Use renewable energy resources like solar and wind energy.
* Use public transport like buses instead of cars.
* Cycle and walk to conserve natural resources and enjoy health benefits.
* Develop community garden and tree plantation programmes and protect them.
* Grow native plants in gardens to provide and protect wildlife.
* Ecosystem services should be introduced into new societal and policy discussions.
* Land use planning and local decision-making should be implemented.
* The existing markets should consider values of ecosystem services in all transactions.