Organisms and Populations

Ecology is a subject which studies the interactions among organisms and between the organism and its physical (abiotic) environment. Ecology is basically concerned with four levels of biological organisation: – 

• Organisms: Individual living being that has ability to act or function independently.

• Populations: relation b/w the number of individuals of a population and the area they occupy.

• Communities: Many species interdependent; named after major species. Interaction takes place b/w species in communities. Types of communities:

1. 1. Major Community: primary aggregation: large-sized, well organized and relatively independent. They depend only on the sun’s energy and are independent of the inputs from neighbouring community; For example, Tropical evergreen forest.

• Minor Community: Secondary aggregation on major community. Dependent on neighbouring communities and not individually self-sustaining; For Example: Lichens (Algae & Fungi), 

• Ecosystem: A structural & functional unit of biosphere consisting of a community of living beings & the physical environment, both interacting & exchanging material b/w them. 

Organism & its environment: 

There are seasonal variations and annual variations in biomes due to different weather and climatic conditions (physico-chemical (or abiotic) conditions). 

Major Abiotic Factors: 

• Temperature:  Changes with latitudes, seasons. But sometimes unique habitats Occur: For example, hot springs, deep sea hydrothermal vents etc. with average temperature of 100oC. Thermal variations affect the kinetics of enzymes and through it the basal metabolism, activity and other physiological functions.

• Eurythermal: Organisms which can thrive in a wide range of temperature.

• Stenothermal: Many organisms are restricted to a narrow range of temperatures. 

• Water: For aquatic organisms living in oceans, lakes and rivers; 

• Quality (pH, chemical composition) of water becomes important.

• Salt concentration (Salinity in o/oo): less than 5 o/oo in inland waters. 30-35 o/oo in the sea & >100 o/oo in some hypersaline lagoons. Tolerance towards salinity:

1. 1. 1. • Euryhaline: Animals that can adapt to wide range of salinities
         • Stenohaline: Animals that can tolerate only low range of Salinities.

• Light: Many plants are also dependent on sunlight to meet their photoperiodic requirement. For many animals too, light is important in that they use the diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities. The availability of light on land is closely linked with that of temperature since the sun is the source for both. 

But, deep (>500m) in the oceans, the environment is perpetually dark and its inhabitants are unaware of the Sun. Red pigment can absorb high energy light; Thus, Red algae is found deepest in the sea.

• Soil: Dependent on climate, weathering process; Randomness in soil composition, grain size and aggregation determine the percolation & water holding capacity of the soils. pH, mineral content, topography determines the type of vegetation.

Response to Abiotic Components:

• Homeostasis: (imagine temperature) the tendency toward a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes.
  • Organism try to maintain the constancy of its internal environment (a process called homeostasis) despite varying external environmental conditions that tend to upset its homeostasis.

1. Regulate:  by means of physiological and behavioural means which ensures constant body temperature (Thermoregulation), constant osmotic concentrations (Osmoregulation) etc. 
   • All birds & mammals, & very few lower vertebrates are invertebrate species are capable of regulation. Thus, mammals thrive everywhere.
   • Humans maintain a temperature of 37oC. By shivering and sweat. 
2. Conform: 99% of animals and nearly all plants can’t maintain a constant internal environment. They change their physiological conditions with ambient environment: Conformers.
   • In Aquatic animals, osmotic concentration of the body fluids changes with ambient water osmotic concentration.
   • Thermoregulation is energetically expensive for most of the animals, thus body temp changes with ambient temp. heat loss is a function of surface area. Small animals have large surface area with respect to their body volume. They tend to lose heat more.
     • Particularly true for small animals like shrews & humming birds. No thermoregulations
     • There are no small animals in polar regions.
   • Some species thermoregulate their temp in a small range and conform beyond it.
3. Migrate: Temporarily move from stressful habitat to a more hospitable area and return when stressful period is over.
   • Thousands of Siberian Cranes migrate to areas of north India, like Keoladeo National Park (Bharatpur) in Rajasthan.
4.  Suspend: 
   • In Bacteria, fungi & lower plants, various kinds of thick-walled spores are formed which help them to survive unfavourable conditions – these germinate on availability of suitable environment.
   • In higher plants, seeds and some other vegetative reproductive structures serve as means to tide over periods of stress besides helping in dispersal – they germinate to form new plants under favourable moisture and temperature conditions. They do so by reducing their metabolic activity and going into a state of ‘dormancy’.
   • In Animals: 
     • hibernation during winter is an example of escape in time. For example, Polar Bear.
     • Some snails and fish go into aestivation(dormancy) to avoid summer–related problems-heat and desiccation. 
   • Many zooplankton species in lakes and ponds are known to enter diapause, a stage of suspended development.

Adaptations: 

Any attribute of the organism (morphological, physiological, behavioural) that enables the organism to survive and reproduce in its habitat. These are the responses to ambient changes; It includes all the above four responses.

Many adaptations are evolutionary and thus genetic. FOR EXAMPLE, 

• Kangaroo rat can oxidise its fat to produce water in dry seasons. It can also concentrate its urine to save water. It is found in tropical deserts of North America in Mexico and USA.
• Desert plants 
  • Many have a thick cuticle on their leaf surfaces & stomata arranged in deep pits to reduce transpiration losses. 
  • They also have a special photosynthetic pathway (CAM) that enables their stomata to remain closed during day time. 
  • Sometimes leaves are reduced to spines and photosynthetic function is taken over by fattened stems.
• Mammals from colder climates have shorter ears and limbs to minimise heat loses. (Allen’s rule)
  • At high altitudes: The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding capacity of haemoglobin and by increasing breathing rate.
• There are microbes (archaebacteria) that flourish in hot springs and deep-sea hydrothermal vents where temperatures far exceed 100oC.
• Desert lizards lack the physiological ability that mammals have to deal with the high temperatures fairly constant by behavioural means. They bask in sun & absorb heat when body temperature drops below comfort zone.

Populations: 

• Same definitions of birth rates, death rates, fertility rate, sex ratio etc. Then construct population pyramid and in it divide population horizontally into pre-reproductive, Reproductive & post-reproductive populations.
• Population studies tell a lot about status of habitat, impact of predator or effect of pesticide application, we evaluate them in terms of any change in population size.

• Percentage cover is sometimes more important than population. For example, Banyan trees are large in size and have low population density. But it has a large canopy and a large biomass size. It can’t be compared with 200 Parthenium plants.
• Sometimes population is not calculated; Population density is enough; For example, No. of fishes in a fish net.
• Population growth: fluctuates with:
  • Natality: No. of births during a period in population that are added to initial density.
  • Mortality: no. of deaths in population during a given period.
  • Immigration: No. of individuals of same species that have come into habitat from elsewhere during the time period under consideration.
  • Emigration: No. of individuals who left the habitat during the time period in consideration.

Types of growth:

• Exponential growth: When resources in a habitat are unlimited, each species have ability to realise fully its innate potential to grow in number.

• Logistic growth: Resources are limited. There is a limit called carrying capacity (K) for the species. Lag phase, exponential phase and static phase.

Life History Variations: Populations maximise their reproductive fitness: Darwinian fitness, in the habitat which they live. Under a particular set of selection pressures, organisms evolve towards the most efficient reproductive strategy.

• Some organisms breed only once in their lifetime: Pacific Salmon fish, bamboo.
• Some breed many times: most birds & mammals.
• Some produce large no. of small-sized offspring: Oysters, pelagic fishes.
• Some small no. of large offspring: birds, mammals.

Population interactions: 

Interspecific interactions arise from the interaction of populations of two different species (opp. Intraspecific). They could be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both. 

Assigning a ‘+’ sign for beneficial interaction, ‘-’ sign for detrimental and 0 for neutral interaction.

Symbiosis refers to a close, long-term interaction between two different species. 

Mutualism: 

Mutualism is a relationship that benefits both of the interacting species.

• Lichens: mutualistic relationship b/w a fungus & a photosynthesising algae or cyanobacteria.
• Mycorrhizae: relation b/w fungi & roots of higher plants. Fungi help plant in absorption of essential nutrients from soil while plants provide energy yielding carbohydrates.
• Plant animal relation: coevolution of insects in pollination.

Competition: 

Darwin: Survival of fittest: interspecific competition is a potent force in organic evolution. It is believed that competition occurs when closely related species compete for the same resources that are limiting, Not entirely true.

• Totally unrelated species may also compete for same resources.
  • Antibiosis in Algae.
• Resources need not to be limiting for competition to occur. [Fitness: ‘r’ is the deciding factor]. Sometimes eventual elimination of a less-fit species occurs. Sometimes competition is not conclusive.
• Different species may also avoid competition by choosing different time/area to feed themselves. 
  • In Fisheries: fishes are introduced in a pond in such a way that a species feed itself at the bottom and another species feed itself on the top.

Predation: 

All communities that eat other communities. Heterotrophs. May it be herbivores type or Carnivorous. They keep the population under control. 

• Biological control methods adopted to regulate prey population based on predation.
• Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species.
• Prey species have evolved various defences to lessen the impact of predation. Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator. Some are poisonous and therefore avoided by the predators.
• Nearly 25% of all insects are phytophagous: feeding on plant sap & other parts of plants.

Parasitism: 

Many parasites have evolved host-specific in a way that both host and the parasite tend to co-evolve. 

• If the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to counteract and neutralise them.
• In accordance with their life styles, parasites evolved special adaptations such as the 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.
• The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of its primary host.
  • Human liver fluke: depends on two intermediate hosts (a snail & a fish) to complete its life cycle.
  • Malarial parasite needs a vector(mosquito) to spread to other hosts.
• Majority of parasites harm the host; They may reduce the survival, growth & reproduction of the host & reduce its population density.
• Brood parasitism: birds lay eggs in the nest of the host & lets the host incubate them; For example, cuckoo (koel) 
• Facultative (no necessity of host) & Obligatory (needs host at any need); 
• Ectoparasites: That feed on surface of the host organisms. For example, Lice.
  • Cuscuta, a parasitic plant found growing on hedge plants, has lost its chlorophyll & leaves in the course of evolution. It derives its nutrition from the host plant which it parasitizes. 
• Endoparasites: live in the body of host at different sites: Liver, Kidney, lungs, RBCs. 
  • Commensalism: one species benefits & other is neither harmed, and nor benefited;
    • An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither mango tree nor the whale derives any apparent benefit.
    • Betel consuming on a Cow dung.
  • Amensalism: One of the species is harmed/destroyed, but other is unaffected.
  • Neutralism: One species does not affect the other in any way.
  • Antibiosis: One is negatively affected: Predation and parasitism.

What is the significance of studying organisms and populations in the UPSC syllabus?

Understanding organisms and populations helps UPSC aspirants grasp ecological concepts such as species interactions, adaptation, biodiversity, and population dynamics, crucial for environmental studies and policy-making topics in the syllabus.

How do environmental factors influence organism adaptations, relevant for UPSC?

Environmental factors like temperature, water availability, sunlight, and altitude influence organism adaptations, such as camels developing humps to store fat or plants in deserts adapting thick leaves. Recognizing these adaptations can help aspirants answer ecology-based questions effectively.

Can you explain population interactions frequently asked in UPSC exams?

Population interactions include mutualism, competition, predation, parasitism, commensalism, and amensalism. Understanding these interactions helps aspirants analyze ecological balance, species survival strategies, and biodiversity conservation policies.

What is population growth, and why is it relevant to India’s ecological concerns in UPSC?

Population growth refers to changes in population size over time, influenced by factors like birth rate, death rate, immigration, and emigration. In India, managing human population growth and wildlife populations is central to sustainability and conservation efforts, making it a key topic for UPSC aspirants.

Why is the concept of ecological niche important in understanding biodiversity for UPSC preparation?

An ecological niche defines the functional role of a species within an ecosystem, including its habitat, food preferences, and interactions with other species. This concept is essential for understanding biodiversity, competition, and coexistence, frequently highlighted in UPSC examinations.