A BRIEF DISCUSSION OF THE PREVIOUS CLASS (5:05 PM)

INTERACTION BETWEEN LIFE FORMS (5:10 PM)

• Positive interaction
• Positive interaction between life forms of different species involves benefits for both or one can be benefitted and the other is not affected
• Positive interactions are usually for food, transport, or shelter
• Mutualism
• Mutualism is always interspecies, both derive benefits
• Mutualism can take the form of:
• 1. Obligate mutualism
• Both life forms depend on each other completely for survival and they cannot leave separately
• Lichen, where fungi surround algae, is an example of obligate mutualism
• Fungi supply water and minerals to the algae, whereas algae manufacture food using these inputs along with the use of sunlight
• Since fungi surround algae, the algae are also benefitting because of defensive protection like from blowing wind, swift-moving water
• 2. Facultative mutualism
• Both life forms leave in close association but do not depend on each other for survival and can leave separately
• For example, in the association between honey bees and plants, the bees get nectar from flowering plants and they transfer pollen grains across the plants and therefore plant benefits due to pollination
• But the bees and plants can leave separately because other agencies can help the plants in pollination like wind and the bees may also get the supply of their nectar just from one or two plants without providing the cross-pollination service
• Commensalism
• One species benefits and the other is unaffected
• There is no direct physical exchange between the species
• An example is lianas and trees
• Lianas are woody wines that grow from the ground but need mechanical support from the trees to stand
• Similarly, epiphytes are plant that grows frow from the branches of trees, but not from the ground.
• They do not get nutrition from the trees but from the water flowing down from the trunk and  branches of the trees
• The tree is not affected, but the epiphyte gets shelter and mechanical support
• Inquilinism is commensalism for housing e.g. lianas and epiphytes getting support from trees
• An example of Phoresy Inquilinism is insects moving on the backs of animals like mites over beetles and snakes
• Negative interaction  (5:53 PM)
• Amensalism
• In an amensalism association, one is harmed and the other remains unaffected
• A common example of amensalism is a group of animals marching over croplands or grasslands, destroying the grass and crops and also killing insects in the soil
• There are two types of amensalism:
• 1. Antibiosis
• One is adversely affected or killed while the other remains unaffected
• For example, microorganisms releasing toxins in the water kill the fish while they themselves remain unaffected
• The walnut tree releases toxins called "juglans" in the soil, which kill small plants and weeds in its neighborhood
• 2. Competition
• Competition amensalism is always interspecies for a resource in short supply like food, water, or territory
• Intra-species competition is not amensalism as it is considered interference competition
• In two species that are competing for a resource, the stronger one could remain unaffected and the lesser strong one is adversely affected
• For example, weed growing on the farm consumes soil nutrients affecting the standing crops
• Predation
• Predation is the most common negative interaction which is interspecies and which is usually for food but secondarily and rarely for shelter
• In predator-prey relation, the reduction of the prey species is considered to be good for biodiversity, because the reduction of prey population improves the resources supply to other life forms, hence it can multiply other life forms of other species
• Parasitism
• Parasitism is a negative interaction common in micro-organisms where they are benefited while the other organism is adversely affected
• It is of two types:
• 1. Ectoparasitism- here the parasites (benefiting organism) leave outside the body of the host
• 2. Endoparasitism - here parasites leave inside the body of the host

HOMEOSTASIS  (6:19 PM)

• It refers to the effort by the life forms to maintain a constant internal process or structure
• The different mechanisms of homeostasis are:
• 1. Thermoregulation
• This is to maintain a constant body temperature
• It takes the form of:
• a) Hypothermia or hypo-thermal regulation
• In this, the life forms decrease the body temperature in winter to below normal to conserve heat
• b) Hyperthermia
• In this, the body temperature is raised above normal by the life form in summer to release excess heat
• 2. Osmoregulation
• In this, the cells try to maintain a proper balance between salt and water to maintain the normal body temperature
• 3. Suspension
• It involves the suspension of metabolic activity by organisms till harsh environmental condition exists
• Hibernation
• The life form goes into a long period of inactivity to avoid the cold conditions of the winter
• This is very commonly shown by snakes, bats, bears, etc.
• Aestivation
• This is a state of inactivity of the life form to deal with hot weather conditions in summer
• This is usually shown by fish and snails
• Diapause
• The life forms suspend developmental activity and growth completely to avoid harsh environmental conditions including weather conditions
• The most common species showing diapause belongs to the insect groups
• 4. Migration
• This is resorted by life forms to deal with harsh environmental conditions and sometimes also for food and breeding purposes
• For example, the Siberian Crane and Amur Falcon, fly out of Siberian winters towards warmer regions in the tropics both for food and to beat the winters
• Amur Falcon is the world's longest migratory raptor bird
• Amur falcons come into Southeast Asia and also towards Northeast India in Nagaland
• Similarly, the Arctic Tern migrates to Antarctica when it is winter in the northern hemisphere and migrates back to the Arctic when there is winter in the southern hemisphere
• 5. Adaptation
• Adaptation is the long-term developmental response, by which a life form develops morphological characteristics to deal with changes in habitats
• This is part of a long period of evolutionary development and such developmental structure becomes inheritable i.e. passed on to their offspring

SPECIES (7:25 PM)

• Habitat and Range
• Habitat refers to the nature of the earth's surface which a species has made its home and leaves there
• The nature of the earth's surface implies the physical character of the surface in the region like desert, grassland, type of forest, etc.
• The range is the location of habitat on the earth's surface in terms of geographic location
• For example, if a reptile leaves in a desert, the habitat of the reptile is the desert, but the range of the reptile is a reference to where the desert is located like Thar desert or some other deserts
• Niche
• It is also called an Ecological Niche.
• It is a part of the habitat, a short micro-habitat that provides the resources for the survival of the species.
• Niche is the functional role the species played in that habitat.
• Many species occupy the same habitat but they perform different functions
• Endemic Species
• Endemic species are confined to a particular range
• The reasons for endemism are:
• 1. It has developed a specialized niche in the region
• For example, it may eat a particular plant that is only found in that region
• 2. It has a long period of habitation in that region and therefore becomes highly adapted to that region
• 3. It has had its evolutionary process in the region
• Native Species
• They are also found in a particular range like the endemic species
• They have come to leave here because of natural processes and there is no role for human interference or influence for the species to be present there
• However, native species are also found in the area surrounding the range unlike the endemic species which are only found in the range

Topics for the next class: Productivity of ecosystem, biogeochemical species, biodiversity