A. Temperature

The most ecologically relevant environmental factor. Average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from plains to the mountain tops.

• Thermal Effects: It affects the kinetics of enzymes and through it the metabolic activity and other physiological functions of the organism.
• Eurythermal: Organisms that can tolerate and thrive in a wide range of temperatures (few organisms).
• Stenothermal: Organisms restricted to a narrow range of temperatures (vast majority).

B. Water

Life on earth originated in water and is unsustainable without water. For aquatic organisms the quality (chemical composition, pH) of water becomes important.

• Salinity: Salt concentration (measured as salinity in parts per thousand).
  • Inland waters: < 5 ppt
  • Sea: 30-35 ppt
  • Hypersaline lagoons: > 100 ppt
• Euryhaline: Tolerant of a wide range of salinities (e.g., Salmon).
• Stenohaline: Restricted to a narrow range of salinities (e.g., Goldfish).

C. Light & Soil

Light: Plants produce food through photosynthesis, a process which is only possible when sunlight is available as a source of energy. Small plants (herbs/shrubs) in forests are adapted to photosynthesize optimally under very low light. Animals use diurnal and seasonal variations in light intensity and duration (photoperiod) for timing their foraging, reproductive and migratory activities.

Soil: The nature and properties of soil vary in different places. Vegetation in any area is determined by soil composition, grain size and aggregation (percolation/water holding capacity), pH, mineral composition and topography.

Kangaroo Rat (Deserts)

In North American deserts, the Kangaroo rat meets all its water requirements through its internal fat oxidation (water is a by-product). It also concentrates its urine to minimize water loss.

Desert Plants (Xerophytes)

• Thick cuticle on leaf surfaces.
• Stomata arranged in deep pits (sunken) to minimize water loss through transpiration.
• CAM pathway (Crassulacean Acid Metabolism) enables stomata to remain closed during day.
• Opuntia: Leaves reduced to spines; photosynthesis by flattened stems (phylloclade).

Allen's Rule

Mammals from colder climates generally have shorter ears and limbs to minimize heat loss.

Altitude Sickness

At high altitude (e.g., Rohtang Pass, >3500m), body compensates low oxygen availability by:
1. Increasing Red Blood Cell production.
2. Decreasing binding affinity of hemoglobin.
3. Increasing breathing rate.

A. Exponential Growth (Geometric)

Resource (food/space) availability is unlimited. Equation:

dN/dt = (b - d)N = rN

Where 'r' is intrinsic rate of natural increase. The curve is J-shaped.

Significance of 'r': Measure of biotic potential. Value for Norway rat = 0.015, Flour beetle = 0.12.

B. Logistic Growth (Verhulst-Pearl)

Resources are limited. Leads to competition. Populations grow until they reach Carrying Capacity (K). Equation:

dN/dt = rN [(K - N) / K]

The curve is Sigmoid (S-shaped). This is more realistic.

Details on Interactions

Gause's Competitive Exclusion Principle: Two closely related species competing for the same limiting resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually. However, resource partitioning (MacArthur's warblers) allows coexistence.

Brood Parasitism: Examples: Cuckoo lays eggs in Crow's nest. The eggs resemble host eggs vertically.

Sexual Deceit (Mutualism): Mediterranean orchid Ophrys employs 'sexual deceit' to get pollinated by a species of bee. One petal bears an uncanny resemblance to the female of the bee.

A. Both A and R are true and R is the correct explanation of A.

B. Both A and R are true but R is NOT the correct explanation of A.

C. A is true but R is false.

D. A is false but R is true.

A. Sex ratio

B. Natality

C. Mortality

D. Death of an individual

A. Both A and R are true and R is the correct explanation of A.

B. Both A and R are true but R is NOT the correct explanation of A.

C. A is true but R is false.

D. A is false but R is true.

A. Commensalism

B. Amensalism

C. Parasitism

D. Predation

A. Soil and Light

B. Temperature and Precipitation

C. Water and Wind

D. Temperature and Soil

A. Both A and R are true and R is the correct explanation of A.

B. Both A and R are true but R is NOT the correct explanation of A.

C. A is true but R is false.

D. A is false but R is true.

A. No two species can occupy the same niche indefinitely for the same limiting resources.

B. Larger organisms exclude smaller ones through interference.

C. More abundant species will exclude the less abundant species through competition.

D. Competition for the same resources excludes species having different food preferences.

A. Sunken stomata

B. Thick cuticle

C. CAM pathway

D. High surface area leaves

A. Both A and R are true and R is the correct explanation of A.

B. Both A and R are true but R is NOT the correct explanation of A.

C. A is true but R is false.

D. A is false but R is true.

A. Declining population

B. Stable population

C. Expanding population

D. None of these

A. Competition

B. Predation

C. Brood Parasitism

D. Mutualism

A. Respiration rate

B. Intrinsic rate of natural increase

C. Carrying capacity

D. Mortality rate

A. Both A and R are true and R is the correct explanation of A.

B. Both A and R are true but R is NOT the correct explanation of A.

C. A is true but R is false.

D. A is false but R is true.

A. Commensalism

B. Mutualism

C. Parasitism

D. Amensalism

A. Yucca

B. Fig

C. Ophrys

D. Lotus

A. Both A and R are true and R is the correct explanation of A.

B. Both A and R are true but R is NOT the correct explanation of A.

C. A is true but R is false.

D. A is false but R is true.

A. dN/dt = rN (K-N)/K

B. dN/dt = rN (K/N)

C. dN/dt = rN (N-K)/K

D. dN/dt = rN

A. Suspended development

B. Active growth

C. Migration

D. Aging

A. Conformers

B. Regulators

C. Partial regulators

D. Euryhaline

A. Both A and R are true and R is the correct result of A.

B. Both A and R are true but R is NOT related to A.

C. A is true but R is false.

D. A is false but R is true.

Ecology is a subject which studies the interactions among organisms and between the organism and its physical (abiotic) environment. It is basically concerned with four levels of biological organization: organisms, populations, communities and biomes. Ramdeo Misra is revered as the Father of Ecology in India.

Biome formation is primarily driven by annual variations in the intensity and duration of temperature and annual variations in precipitation. Major biomes of India include Tropical rain forest, Deciduous forest, Desert, and Sea coast. Regional and local variations within each biome lead to the formation of a wide variety of habitats.

A few organisms can tolerate and thrive in a wide range of temperatures; they are called eurythermal. But, a vast majority of them are restricted to a narrow range of temperatures; such organisms are called stenothermal. The levels of thermal tolerance determine to a large extent their geographical distribution.

Salinity is measured in parts per thousand (ppt). For inland waters it is less than 5 ppt. For the sea it is 30-35 ppt. For some hypersaline lagoons it is greater than 100 ppt. Some organisms are euryhaline (tolerant to wide salinity) while others are stenohaline (restricted to narrow range).

Light is important for photosynthesis. Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesize optimally under very low light conditions. Animals use diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities.

Some organisms are able to maintain homeostasis by physiological (sometimes behavioural also) means which ensures constant body temperature, constant osmotic concentration, etc. All birds and mammals, and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation).

About 99 per cent of animals and nearly all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. In aquatic animals, the osmotic concentration of the body fluids changes with that of the ambient water osmotic concentration. These animals and plants are simply conformers.

Thermoregulation is energetically expensive for many organisms. This is particularly true for small animals like shrews and humming birds. Heat loss or heat gain is a function of surface area. Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside. This is why small animals are rarely found in polar regions.

The organism can move away temporarily from the stressful habitat to a more hospitable area and return when stressful period is over. Every winter the famous Keoladeo National Park (Bharatpur) in Rajasthan hosts thousands of migratory birds coming from Siberia and other extremely cold northern regions.

Under unfavourable conditions many zooplankton species in lakes and ponds are known to enter diapause, a stage of suspended development. This is different from hibernation (winter sleep, e.g., bears) and aestivation (summer sleep, e.g., snails and fish), although all are ways to survive unfavorable periods.

The Kangaroo rat in North American deserts is capable of meeting all its water requirements through its internal fat oxidation (in which water is a byproduct). It also has the ability to concentrate its urine so that minimal volume of water is used to remove excretory products.

In Opuntia, leaves are reduced to spines to reduce water loss. The photosynthetic function is taken over by the flattened stems (phylloclade). Many desert plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits (sunken) to minimise water loss through transpiration.

Mammals from colder climates generally have shorter ears and limbs to minimise heat loss. This is called Allen's Rule. In the polar seas aquatic mammals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat.

At high altitude places (>3,500m Rohtang Pass), we experience altitude sickness (nausea, fatigue, heart palpitations). This is because in the low atmospheric pressure of high altitudes, the body does not get enough oxygen. The body compensates by increasing RBC production, decreasing binding affinity of hemoglobin and increasing breathing rate.

A population has certain attributes that an individual organism does not. An individual may have births and deaths, but a population has birth rates and death rates. In a population these rates refer to per capita births and deaths. Another attribute characteristic of a population is sex ratio. An individual is either a male or a female but a population has a sex ratio.

If the age distribution (per cent individuals of a given age or age group) is plotted for the population, the resulting structure is called an age pyramid. For human population, the age pyramids generally show age distribution of males and females in a diagram. The shape of the pyramids reflects the growth status of the population - (a) whether it is growing (expanding), (b) stable or (c) declining.

Population density (N) is the number of individuals of a species per unit area or volume. Total number is not always the most appropriate measure. For 200 parthenium plants and 1 huge banyan tree, stating banyan is low density underestimates its role. In such cases, the percent cover or biomass is more meaningful.

Total number is again not an easily adaptable measure if the population is huge and counting is impossible or very time-consuming (e.g. dense bacterial culture). In such cases, relative density is used. For example, the tiger census in our national parks and tiger reserves is often based on pug marks and fecal pellets.

The size of a population for any species is not a static parameter. It keeps changing depending on factors including food availability, predation pressure and adverse weather. The fluctuations give us some idea of whether the population is flourishing or declining.

Natality (B) refers to the number of births during a given period in the population that are added to the initial density. Mortality (D) is the number of deaths in the population during a given period. Immigration (I) and Emigration (E) also affect population density. Nt+1 = Nt + [(B+I) - (D+E)].

Resource (food and space) availability is obviously essential for the unimpeded growth of a population. Ideally, when resources in the habitat are unlimited, each species has the ability to realize fully its innate potential to grow in number, as Darwin observed. This results in exponential or geometric growth. J-shaped curve.

In the equation dN/dt = (b-d)N, let (b-d) = r, then dN/dt = rN. The 'r' in this equation is called the 'intrinsic rate of natural increase' and is a very important parameter chosen for assessing impacts of any biotic or abiotic factor on population growth. For Norway rat r=0.015, flour beetle r=0.12.

No population of any species in nature has at its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. Eventually, the 'fittest' individual will survive and reproduce. This leads to logistic growth. Sigmoid curve.

In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. Let us call this limit as nature's carrying capacity (K) for that species in that habitat. The logistic growth model fits this constraint (dN/dt = rN((K-N)/K)).

Populations evolve to maximize their reproductive fitness (Darwinian fitness, high r value). Some organisms breed only once in their lifetime (Pacific salmon fish, bamboo) while others breed many times during their lifetime (most birds and mammals). Some produce a large number of small-sized offspring (Oysters, pelagic fishes).

Predators play important roles:
1. Conduits for energy transfer across trophic levels.
2. Keep prey populations under control.
3. Maintain species diversity in a community by reducing intensity of competition among competing prey species (e.g., Pisaster starfish).

The prickly pear cactus introduced into Australia in the early 1920s caused havoc by spreading rapidly into millions of hectares of rangeland. Finally, the invasive cactus was brought under control only after a cactus-feeding predator (a moth) from its natural habitat was introduced into the country.

Prey species have evolved defenses. Camouflage (cryptic coloration) helps frogs and insects avoid detection. Monarch butterfly is highly distasteful to its predator (birds) because of a special chemical acquired during its caterpillar stage by feeding on a poisonous weed.

Plants cannot run away from herbivores. They use morphological (Thorns of Acacia, Cactus) and chemical defenses. Calotropis produces highly poisonous cardiac glycosides. Nicotine, Caffeine, Quinine, Strychnine, Opium, etc., are produced by plants as defenses against grazers and browsers.

Interaction where both species suffer (-/-). Competition is best defined as a process in which the fitness of one species (measured in terms of 'r') is significantly lower in the presence of another species. It occurs when closely related species compete for the same resources that are limiting, but can also occur between unrelated species (e.g., Flamingoes vs Fish for plankton).

This principle states that two closely related species competing for the same limiting resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true if resources are limiting, but not otherwise.

Species facing competition might evolve mechanisms that promote co-existence rather than exclusion. One such mechanism is 'resource partitioning'. If two species compete for the same resource, they could avoid competition by choosing different times for feeding or different foraging patterns (MacArthur showed this with warblers).

Interaction where one species (parasite) benefits and the other (host) is harmed (+/-). Parasites have evolved adaptations: 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.

Ectoparasites feed on the external surface of the host (Lice on humans, Ticks on dogs, Copepods on marine fish, Cuscuta on hedge plant). Endoparasites live inside the host body (Liver fluke, Plasmodium, Tapeworm). Endoparasites typically have simplified morphology but complex life cycles.

Brood parasitism in birds is a fascinating example of parasitism in which the parasitic bird lays its eggs in the nest of its host and lets the host incubate them. During evolution, the eggs of the parasitic bird have evolved to resemble the host's egg in size and colour to reduce chances of rejection (Cuckoo and Crow).

Interaction where one species benefits and the other is neither harmed nor benefited (+/0). Examples: Orchid growing as an epiphyte on a mango branch (Orchid benefits, Mango unaffected). Barnacles growing on the back of a whale. Cattle egret and grazing cattle. Sea anemone and Clown fish.

Interaction confers benefits on both the interacting species (+/+). Examples: Lichens (intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria). Mycorrhizae (association between fungi and roots of higher plants). The fungi help the plant in absorption of essential nutrients from soil while the plant provides fungi with energy-yielding carbohydrates.

In many cases of mutualism, the evolution of the flower and its pollinator species is tightly linked with one another. Example: Fig trees and the pollinator species of wasp. There is a one-to-one relationship. The wasp pollinates the fig while searching for sites to lay eggs; the fig provides seeds for larvae nourishment.

The Mediterranean orchid Ophrys employs 'sexual deceit' to get pollinated by a species of bee. One petal of its flower bears an uncanny resemblance to the female of the bee in size, colour and markings. The male bee is attracted to what it perceives as a female and 'pseudocopulates', transferring pollen.

Interaction one species is harmed whereas the other is unaffected (-/0). An example is the mould Penicillium which secretes penicillin, killing bacteria, but the mould itself is unaffected.

The Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, apparently due to the greater browsing efficiency of the goats. This is an evidence for competition (Interference competition).

Predators act as 'conduits' for energy transfer across trophic levels. If the sun is the source of energy, and plants fix it, the energy is trapped in plants (herbivores). Predators (carnivores) are needed to transfer this energy to higher trophic levels.

Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria. The fungus helps in the absorption of nutrients and provides shelter, while the algae prepare food for the fungus. They are good pollution indicators.

In the rocky intertidal communities of the American Pacific Coast, the starfish Pisaster is an important predator. When all the starfish were removed from an enclosed area, more than 10 species of invertebrates became extinct within a year, because of inter-specific competition. This shows predators maintain species diversity.

The logistic growth equation is dN/dt = rN(K-N)/K.
N = Population density at time t
r = Intrinsic rate of natural increase
K = Carrying capacity This is considered a more realistic growth model because resources are finite.

Desert plants have a special photosynthetic pathway (CAM - Crassulacean Acid Metabolism) that enables their stomata to remain closed during the day (to reduce water loss) and open at night for CO2 fixation. This is a crucial physiological adaptation for xeric conditions.

In the aquatic environment, the sediment characteristics often determine the type of benthic animals that can thrive there. This shows that soil composition is a key abiotic factor even in aquatic ecosystems, influencing the distribution of bottom-dwelling organisms.

An age pyramid with a narrow base (fewer pre-reproductive individuals than reproductive ones) indicates a declining population. This shape is often called urn-shaped. A bell-shaped pyramid indicates a stable population where pre-reproductive and reproductive individuals are almost equal.

Cuscuta (dodder) is a parasitic plant that is commonly found growing on hedge plants. It has lost its chlorophyll and leaves in the course of evolution. It derives its nutrition from the host plant which it parasitises. It is a stem parasite.

Mycorrhiza is a mutualistic association between fungi and the roots of higher plants. The fungi help the plant in the absorption of essential nutrients (phosphorus) from the soil while the plant provides the fungi with energy-yielding carbohydrates.