ECOLOGY

Ecology is the scientific study of the rich and varied interactions between organisms and their abiotic environment. In ecological studies, the environment encompasses both abiotic (such as water, mineral nutrients,light, temperature) and biotic factors (living organism).  

Interactions between organisms and their environment is a two way process in which organisms influence and are influenced by their environment. There are many reasons to care about ecology. Our lives are enriched by the fascinating interactions between the organisms. 

Watching a butterfly visiting a flower and bringing about pollination is worth seeing. Beyond simple curiosity, information from ecological sciences is needed to solve many practical problems. An understanding of ecology allows us to grow food, control pests and diseases and deal with natural disasters such as flood, drought and earthquake.

BRANCHES OF ECOLOGY

Ecology and Evolution

1. Ecology and Evolution

Ecology and evolution are considered sister disciplines of the life sciences.Natural selection, life history, development, adaptation, populations and inheritance are examples of concepts that correlate equally in to ecological and evolutionary theory.

(a) Behavioural Ecology 

This is the study of animal behavior in the natural environment, also known as ethology. Behavioural ecology also deals with ecological and evolutionary changes, because of the interactions among the organisms. 

Adaptation is the central unifying concept in behavioural ecology.The behaviours evolve and become adapted to the ecosystem because they are subject to the forces of natural selection. 

Consider the edible beetles that direct sprays of poisonous chemicals at their attacker. Predator-prey interactions are an introductory concept in behavioral ecology.

(b) Social Ecology 

This is concerned with the relationships between organisms and their environment. Social ecological behaviours are notable in the social insects, slime molds, social spiders and human society. Individuals that belong to a social group have to face competition for food, mates and other limited resources. They face diseases and parasitic infections. 

A special kind of behavior exists between many groups known as altruism (Behavior that harms the individual who performs it but benefits other individuals).Parenting is also altruism, where the children are benefited. Altruism is extreme among some insect societies, such as honeybee and termite colonies.Groups that are predominantly altruists beat groups that are predominantly selfish.

(c) Co-evolution 

Populations of the other species are part of any organism’s environment. The population having prey-predator interactions exert pressure on each other. If prey evolves, the predator counter develops mechanisms to catch the prey. 

This is the basis of co-evolution in populations. There are many examples where interacting organisms evolve together e.g., Lithops (flowering stone) growing in the open area develop stone like pattern and color to hide from herbivores.

(d) Bio-geography 

This is the comparative study of the geographic distribution of organisms and the corresponding evolution of their traits in space and time. Bio-geographical processes that result in the natural splittingof species explain modern distribution of the earth’s biota (flora and fauna).

2. Molecular Ecology

Molecular ecology is a relatively new field where the important relationship between ecology and genetic inheritance is analysed using modern techniques of molecular analysis. 

Molecular ecological research became more feasible with the development of rapid and accessible genetic technologies, such as the polymerase chain reaction (PCR). The DNA of different organisms is compared and their evolutionary relationships are analysed.

3. Human Ecology

Human ecology is the interdisciplinary investigation into the ecology of our species. It is the discipline that inquires into the patterns and process of interaction of humans with their environment. It studies human values, life styles, resource use, waste etc. The human species is not an external disturbance. It is the keystone species within the system.

4. Landscape Ecology

Landscape ecology is a sub discipline of ecology that studies ecological  processes that operate over large areas. A landscape ecologist examines the connections among ecosystem found in a particular region.

THE HIERARCHICAL STRUCTURE OF ECOLOGICAL SYSTEM

The different levels of biological organisation include:

The characteristics of molecules and their organization in a cell up to speciation are discussed in the biology section. This chapter includes interaction at population and the levels above it.

Population Ecology

Population is a group of organisms of the same species that live in the same area at the same time. Certain principles govern the growth and sustainability of populations over time. Ecological interactions start within and between populations.

Each population has its own gene pool and range of traits. It also has a characteristic size, density, distribution pattern and age structure.Environmental conditions and species interactions influence thesecharacteristics. Population size is generally an outcome of births, deaths, immigration and emigration. As long as the per capita birth rate remains evenslightly above per capita death rate, a population can grow exponentially.

Resources in short supply put limits on the growth of population. The maximum number of individuals of a population that can be sustained indefinitely by the resources in a given environment is referred as carrying capacity. The number may rise or fall with changes in resource availability.

The size of a low-density population may increase gradually; go through a rapid growth phase, then levels off once the carrying capacity for the population is reached. The limiting factors vary in their relative effects and vary over time, so, population size also changes over time. Limiting factor such as competition for resources, disease and predation are densitydependent.

Density-independent factors, such as weather on the rampage,tend to increase the death rate or decrease the birth rate more or less independently of population density.

Community Ecology

Community is a natural association that consists of all populations of different species that live and interact within an area at the same time. These interactions in turn influence the structure of communities.The many ways in which organisms interact with one another are as following:

Symbiosis 

Any intimate relationship or association between members of two or more species. Symbiosis is the result of co-evolution. Flowering plants and their pollinators have a symbiotic relationship.

Parasitism: 

Interactions in which one organism is harmed, but the other is benefited. A parasite may weaken its host; it rarely kills its host. More than 100 parasites live in or on the human species. When it causes a disease and sometimes the death of host, it is known as pathogen.Crown gall disease, caused by a bacterium, occurs in many plants.

Mutualism: 

Interactions in which both participants are benefited. The interdependent association between nitrogen fixing bacteria of the genus Rhizobium and legume, is an example. Another example is the association between reef building coral animals and microscopic algae.The symbiotic alga is called zooxanthellae. Mycorrhizae is such an association between fungi and roots of 80% plants.

Commensalism: 

Interactions in which one participant benefits but the other is unaffected, e.g., relationship between two insects; silverfish and army ants, relationship between a tropical tree and many epiphytes, smaller plants, such as mosses, orchids and ferns that live attached to the bark of the tree’s branches. The epiphytes anchor itself to the tree to obtain adequate light and water and not for obtaining nutrients from the tree.

 Important Scientific Laws and Theories

Archimedes’ Principle

1. Archimedes’ Principle: It states that a body wholly or partially immersed in a liquid experiences an upward thrust, which is equal to the weight of the liquid displaced by it. Thus, the body appears to lose a part of its weight. This loss in weight is equal to the weight of the liquid  displaced by the body.

 Aufbau Principle

2. Aufbau Principle: It states that, in an unexcited atom, electrons reside in the lowest energy orbitals available to them.

Avogadro’s Law

3. Avogadro’s Law: It states that equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules.

 Brownian Motion

4. Brownian Motion: It is a zigzag, irregular motion exhibited by small solid particles when suspended in a liquid or gas due to irregular bombardment by the liquid or gas molecules.

Bernoulli’s Principle

5. Bernoulli’s Principle: It states that as the speed of a moving fluid,liquid, or gas increases, the pressure within the fluid decreases. The aerodynamic lift on the wing of an aeroplane is also explained in part by this principle.

Boyle’s Law

6. Boyle’s Law: It states that temperature remaining constant, volume of a given mass of a gas varies inversely with the pressure of the gas.

Thus, PV = K (constant), where, P = Pressure and V = Volume.

Charles’s Law

7. Charles’s Law: It states that pressure remaining constant, the volume of a given mass of gas increases or decreases by 1/273 part of its volume at 0 degree celsius for each degree celsius rise or fall of its temperature.

Coulomb’s Law

8. Coulomb’s Law: It states that force of attraction or repulsion between two charges is proportional to the amount of charge on both charges and inversely proportional to the square of the distance between them.

Heisenberg Principle (Uncertainty principle)

9. Heisenberg Principle (Uncertainty principle): It is impossible to accurately determine with accuracy, both the position and the momentum of a particle such as electron simultaneously.

Gay-Lussac’s Law of Combining Volumes

10. Gay-Lussac’s Law of Combining Volumes: Gases react together in volumes which bear simple whole number ratios to one another and also to the volumes of the products, if gaseous—all the volumes being measured under similar conditions of temperature and pressure.

Graham’s Law of Diffusion

11. Graham’s Law of Diffusion: It states that the rates of diffusion of gases are inversely proportional to the square roots of their densities under similar conditions of temperature and pressure.

Physical Quantity |Science in Everyday Life

Physical Quantity

❖❖ It is the physical property of a body, substance, or of a phenomenon, that can be quantified by measurement.

Measurement of a Physical Quantity

❖❖ It is done by assigning a value to a physical quantity by comparing itwith a standard value (calibrated value) of that physical quantity whichis called unit.

❖❖ To know the value (or magnitude) of a physical quantity, we generally measure it in different systems of units.

System Units

❖❖ Physical quantities are measured in four systems of units:

●● CGS (Centimetre, Gram, Second): In this system of units, Length,

Mass, and Time are measured in Centimetre, Gram, and Second,

respectively. CGS system is also called the Metric or French System

of Units.

●● FPS (Foot, Pound, Second): In this system of units, Length, Mass, and

Time are measured in Foot, Pound, and Second. FPS system is also

called British System of Units.

●● MKS (Metre, Kilogram, Second): In this system of units, Length,

Mass, and Time are measured in Metre, Kilogram, and Second.

●● SI system (International System of Units) of units was adopted and

accepted on the basis of a comprehensive consensus. In fact, the

SI system is an extended and modified form of the MKS system.

Fundamental Quantities in SI System

S. No. Fundamental Quantity Fundamental unit Symbol

1. Length Metre m

2. Mass Kilogram kg

3. Time Second s

4. Electric current Ampere A

5. Temperature Kelvin K

Unit of Length

❖❖ The SI unit of length is metre (m). One metre is the distance travelled by

light in vacuum in 1 /299792458 of a second.

Facts to Know!

❖❖ A vector is a quantity that has magnitude as well as direction, e.g., force, position, etc.

❖❖ A scalar quantity has only magnitude and no direction, e.g., temperature,

mass, etc.

Other Units of Length

❖❖ Light year: The distance travelled by light in one year in vacuum.

1 light year = 9.46 × 1015 m

❖❖ Parsec (Parallactic Second): The distance at which an arc of length equals

to one astronomical unit subtends an angle of one second at a point.

Units of Length or Distance

1 Nautical Mile 1.825 km

1 Mile 1.609 km

1 km 1000 m

1 cm 10–2 m

1 mm 10–3 m

1 mm 10–6 m

1 Nano metre 10–9 m

1 Å 10–10 m

1 pico metre 10–12 m

1 Fermi metre 10–15 m

❖❖ Area is related with square of length; some units of area are:

●● 1 acre = 4047 m2

●● 1 hectare = 104 m2

❖❖ Volume is related with cube of length; some units of volume are:

●● 1 cubic centimetre (cm3) = 1 millilitre (mL)

●● 1 Gallon = 3.7 Litre

●● 1 barrel = 159 Litre

Unit of Mass

❖❖ The SI unit of mass is kilogram. One kilogram is defined as the mass of

5.0188 × 1025 atoms of carbon-12.

Other Units of Mass

❖❖ 1 gram = 10–3 kg

❖❖ 1 ounce-oz = 28.35 gram

❖❖ 1 milligram = 10–6 kg

❖❖ 1 atomic mass unit (amu) = 1.66 × 10–27 kg

❖❖ 1 quintal = 100 kg

❖❖ 1 tonne or metric ton = 1000 kg

❖❖ 1 Chandra Sekhar Limit (CSL) = 1.4 times the mass of sun = 2.8 × 1030 kg

Unit of Time

❖❖ The SI unit of time is second. One second is defined as 1/86400 part of a mean solar day.

Other Units of Time

❖❖ 1 picosecond =10–12 s

❖❖ 1 nanosecond = 10–9 s

❖❖ 1 microsecond = 10–6 s

❖❖ 1 hour = 60 minute = 3600 seconds

❖❖ 1 day = 24 hours = 1440 minute = 86400 seconds

❖❖ 1 solar month = 30 or 31 days

❖❖ 1 lunar month = 29.5 days or 4 weeks

❖❖ 1 year = 13 lunar months and 1 day = 12 solar months = 365.25 days

❖❖ 1 leap year = 366 days

Indian Measurement System

1. System in the Ancient Period: 8 Parmanus = 1 Rajahkan (dust particle

from the wheel of a chariot)

8 Rajahkans = 1 Liksha (egg of lice)

8 Likshas = 1 Yookamadhya

8 Yookamadhyas = 1 Yavamadhya

8 Yavamadhyas = 1 Angul

8 Anguls = 1 Dhanurmushti

2. System in the Medieval Period: Gaz was divided into 24 equal parts, and

each part was called Tassuj.

Motion, Force, and Laws of Motion

❖❖ The change of position or the movement of any object from one position to another position with respect to the observer is called Motion. It can be described in terms of the distance moved or displacement.

❖❖ Motion of any body is defined by its position with respect to its observer.

❖❖ Distance is the actual path travelled by the object from its initial point to

final point, and it is a scalar quantity.

❖❖ Displacement is the shortest straight line path between initial and final positions. If the initial and final positions are the same, then the displacement is zero.

❖❖ Distance depends upon path but displacement does not.

❖❖ Distance is greater than or equal to displacement; they are equal only

when in straight line motion, without taking a U-turn.

❖❖ The SI Unit of both distance and displacement is Metre (m).

Uniform and Non-uniform Motions

❖❖ Uniform motion is the motion in which equal distance is covered in equal

time intervals.

❖❖ Non-uniform motion on the other hand is one in which an unequal distance is covered in equal intervals of time.

Speed and Velocity

❖❖ Speed is the distance travelled by an object per unit of time.

Speed = Distance travelled/Time taken

❖❖ Average speed, the ratio of total distance travelled to the total time taken by the body to cover it, is known as the average speed.

Average speed = Total distance travelled/Total time taken

❖❖ Instantaneous Speed is the speed of the object at a particular moment in time.

❖❖ Velocity is the displacement of the body per unit time.

Velocity = Displacement of object/Time taken

❖❖ Average Velocity: the ratio of the total displacement to the total time taken by the body is the average velocity.

Average Velocity = Total Displacement/Total time taken

❖❖ Instantaneous Velocity is the velocity of an object in motion at a particular point in time.

❖❖ Speed is a scalar quantity, and its SI unit is metre/ sec, while on the other hand, velocity is a vector

quantity, and its SI unit is metre/sec.

Acceleration

❖❖ Acceleration is the measure of change of velocity with respect to time. It is also called the rate of change of velocity.

Acceleration = (Final velocity – Initial velocity)/Total time taken

❖❖ SI unit of acceleration is metre/sec2. It is a vector quantity.

❖❖ Acceleration has the same direction as velocity if the velocity increases.

Whereas it has opposite direction as velocity if velocity decreases, and in this case, the acceleration is negative. Negative acceleration is also known as Retardation or De-acceleration.

Uniform and Non-uniform Acceleration

❖❖ When the velocity of a body changes by equal amounts in equal time intervals, the acceleration is said to be uniform.

❖❖ When the velocity of a body changes by unequal amounts in equal time intervals, the acceleration is said to be non-uniform.

❖❖ Velocity has both magnitude and direction while speed has only magnitude and no direction.

Velocity has the same direction as displacement.

❖❖ Average speed is always greater than the average velocity except in the case of straight line motion without a U-turn, where both are equal.

❖❖ When a body returns to its initial position, the average velocity will be zero but the average speed will not be zero.

❖❖ When the direction of motion changes, the velocity also changes.