Topics to be Learn :

  • Introduction
  • Organisms and the environment around
  • Major Abiotic Factors
  • Adaptation
  • Population
  • Population Interactions

Introduction

  • Diversity in natural world.
  • Levels of organization: macromolecules, cells, tissues, organs, individual organism, population, communities, ecosystems, and biomes.
  • Ecology: Study of interactions among organisms and their physical environment.
  • Term ecology: First used by Reiter, introduced by E. Haeckel.
  • Sequential levels of ecological organizations: Organism, Populations, Communities, Biomes.
  • Organism: Basic unit of ecological hierarchy.
  • Population: Organisms of same kind in a geographical area.
  • Community: Populations of different species in an area.
  • Land biome: Large regional unit with specific climatic zone, major vegetation, and fauna.

Organisms and the Environment

  • Ecology at organism level: Study of animal or plant physiology, adaptation, survival, and propagation.
  • Earth's rotation and tilt cause seasons.
  • Seasons create major biomes: desert, tropical rainforest, temperate forest, coniferous forest, grassland, tundra.
  • Habitat variations within biomes create a variety of habitats.
  • Habitat: Place where a species lives.
  • Factors affecting habitat presence: Sunlight, rainfall, temperature, soil, topography.
  • Types of habitats: Arboreal, terrestrial, aerial, aquatic.
  • Microhabitat: Immediate surroundings of an organism.

Other Terms

  • Ethology: Study of animal behavior in relation to environment.
  • Bionomics: Study of organism-environment relationships.
  • Environmental biology (Modern ecology): Study of organism-surroundings interrelationships.
  • Biosphere: All earth's ecosystems.

Habitat and Niche

Habitat

  • Definition: Place where a species lives.
  • Factors: Sunlight, rainfall, temperature, soil, topography.
  • Types: Arboreal, terrestrial, aerial, aquatic.
  • Microhabitat: Immediate surroundings of an organism.

Niche

  • Definition: Functional role of an organism in its environment.
  • Term: Coined by J. Grinnell.
  • Includes: Diet, shelter, link with physical and biological environment.
  • Comparison:
    • Habitat: Postal address.
    • Niche: Profession of organism.

Types of Niches

  • Spatial or Habitat Niche: Physical space occupied by organisms.
  • Trophic Niche: Based on organism's trophic level in a food chain.
  • Multidimensional or Hypervolume Niche: Considers abiotic and biotic factors, forming a hypervolume showing organism's position in environmental gradient.
  • Fundamental Niche: Niche in absence of competitors.
  • Realized Niche: Niche with competitors and available resources.

Characteristics of Ecological Niche

  • Describes organism's link with physical and biological environment.
  • Indicates organism's survival and fulfillment of needs.
  • Helps understand energy flow in food chains and webs.
  • If a niche is vacant, other organisms fill it.
  • Specific to each species, reducing competition.
  • Example: Birds in same habitat have different niches based on eating habits.

Differences Between Habitat and Niche

Habitat

Niche

Area where species lives and interacts

How an organism lives in environmental conditions

Consists of numerous niches

Does not contain multiple components

Influenced by abiotic factors

Involves flow of energy through ecosystem

Supports numerous species

Supports a single species

Physical place

Activity performed by organisms

Not species specific

Species specific

Major Abiotic Factors

Key Abiotic Factors: Ambient temperature, Availability of water, Light, Type of soil.

1. Temperature

  • Variation: Decreases from equator to poles and from plains to mountain tops.
  • Extreme Temperatures:
    • Polar areas and high altitude: Below 0°C.
    • Tropical deserts: > 50°C in summer.
    • Thermal springs: 80 to 100°C.
    • Deep sea hydrothermal vents: ~ 400°C.
  • Effect:
    • Distribution of animals and plants.
    • Kinetics of enzymes, affecting basal metabolism and physiological functions.
  • Thermal Tolerance:
    • Eurythermal: Wide temperature tolerance.
    • Stenothermal: Narrow temperature range.

2. Water

  • Importance: Second most important factor for organisms.
  • Origination: Life originated and sustained in water.
  • Availability:
    • Varies by geographical regions.
    • Influences plant distribution and productivity.
  • Salinity:
    • Inland waters: < 5 ppt.
    • Sea: 30 — 35 ppt.
    • Hypersaline lagoons: 100 ppt.
  • Salinity Tolerance:
    • Euryhaline: Wide salinity tolerance.
    • Stenohaline: Narrow salinity range.

3. Light

  • Importance: Ultimate source of energy.
  • Adaptations: Plants in forests adapt to low light conditions under tall trees.
  • Effects: Photosynthesis, Diurnal and seasonal rhythms in animals.
  • Dark Environments: Oceanic depths (>500m): perpetually dark, inhabited by carnivorous organisms.

4. Soil

  • Influence: Climate determines soil nature and properties.
  • Variation:
    • Weathering process, type, and pattern of soil development.
    • Soil composition, aggregation, and grain size.
  • Effect:
    • Percolation and water holding capacity.
    • Vegetation and faunal pattern.
  • Aquatic Environment: Sediment characteristics determine resident benthic animals.
Types of Organisms According to Abiotic Factors

  • Regulate:


    • Maintain homeostasis through physiological and behavioral changes.
    • Examples:
    • Birds and mammals maintain constant body temperature and osmotic concentration.
    • Perform thermoregulation or osmoregulation.

  • Conform:


    • Unable to maintain a constant internal environment; body parameters change according to external environment.
    • Examples:
    • Poikilothermic animals unable to maintain body temperature.
    • Some aquatic animals adjust osmotic concentration of body fluids.
    • Few conformers can regulate parameters within a limited range.

  • Migrate:


    • Temporarily move from stressful habitat to more favorable habitat.
    • Examples:
    • Birds undertake long-distance migrations during severe winter.
    • Return to original habitat when conditions improve.

  • Suspend:


    • Suspend life activities for a particular period to cope with stressful conditions.
    • Examples:
    • Seeds remain dormant during unfavorable period and resume growth when conditions improve (dormancy).
    • Hibernation and aestivation:
    • Hibernation: Seen in animals like polar bears to escape severe winter.
    • Aestivation: Seen in animals like snails and fish to escape severe summer.
    • Metabolic activities suspended during these periods.
Adaptation

Definition: Attribute of the organism (morphological, physiological, and behavioral) enabling survival and reproduction in its habitat.

Types of Adaptations

1. Physiological Adaptations

  • Thermoregulation: Control of body temperature.
  • Osmoregulation: Control of water and salt balance.

2. Behavioral Adaptations

  • Migration: Response to severe winter temperatures.
  • Hibernation and Aestivation: Periods of dormancy.
  • Desert Lizards:
    • Bask in sun to absorb heat.
    • Move into shade to avoid overheating.
    • Burrow into sand to escape heat.

3. Morphological Adaptations

  • Structural changes enhancing survival.
  • Desert Plants:
    • Thick cuticle and deep stomatal pits to minimize water loss.
    • CAM(Crassulacean acid metabolism) pathway for closed stomata during daytime.
    • Reduced leaves to spines (e.g., Opuntia).
  • Mammals from Colder Climates: Shorter snout, ears, tail, and limbs to minimize heat loss (Allen's Rule).
  • Aquatic Mammals in Polar Seas: Thick layer of fat (blubber) for insulation against cold.
Population
  • Definition: Group of organisms in a well-defined geographical area sharing or competing for similar resources, potentially interbreeding.
  • Population Ecology: Links ecology to population dynamics, genetics, and evolution.

Population Attributes

  • Size and Density: Basic physical characteristics of population.
  • Natality, Mortality, Immigration, Emigration, Age Pyramids, Expanding Population, Population Growth Forms, Biotic Potential: Other characteristics.

Natality

  • Natality: Birth rate of a population, leading to increased population density.
  • Crude Birth Rate: Number of births per 1000 population/year.
  • Specific Birth Rate: Birth rate relative to a specific criterion (e.g., age).
  • Absolute Natality: Births under ideal conditions.
  • Realized Natality: Births under environmental pressures.

Mortality

  • Mortality: Death rate of a population.
  • Mortality Rate: Deaths per 1000 individuals per year.
  • Absolute Mortality: Deaths under ideal conditions.
  • Realized Mortality: Deaths under environmental pressures.

Sex Ratio

  • Sex Ratio: Ratio of males to females in a population.
  • Evolutionary Stable Strategy (ESS): Males and females in a 1:1 ratio.

Age Distribution and Age Pyramid

 Age Distribution: Pre-reproductive (0-14 years), Reproductive (15-44 years), Post-reproductive (45—85+ years).

  • Age Pyramid: Graphical representation showing age distribution.

Population Size or Population Density (N)

  • Population Density: Number of individuals per unit space in a given time.
  • Biomass is a more meaningful measure of population size.

Population Growth

  • Population size changes over time due to various factors like food availability, predation, and weather.
  • Fluctuations in population density occur due to four basic processes:
    1. New Births                2. Immigration                3. Deaths                     4. Emigration
  • Immigration (I): Number of individuals entering the habitat from elsewhere during a specific time.
  • Emigration (E): Number of individuals leaving the habitat during a specific time.
  • Population growth increases with new births and immigration, and decreases with deaths and emigration.
  • Formula for calculating population density at time 't + 1':
    Nt+1 = Nt + [(B + I) - (D + E)]
Growth Models

Exponential Growth

  • Occurs when resources are abundant.
  • Population grows continuously without hindrance.
  • Each species realizes its full potential to grow.
  • Leads to enormous population densities in a short time.
  • Example: Human population.
  • Shows a J-shaped curve.

 

Logistic Growth

  • Occurs when populations have limited resources.
  • Competition exists between individuals for these limited resources.
  • Populations have a maximum possible number they can support (carrying capacity, K).

 
  • Phases of logistic growth:
    1. Lag phase
    2. Phase of acceleration
    3. Phase of deceleration
    4. Asymptote (population density reaches carrying capacity)
  • Verhulst-Pearl Logistic Growth: Plot of population size (N) against time (t) results in a sigmoid curve.
  • More realistic model as it considers finite resources.
  • Always shows a sigmoid curve.
Population Interactions

  • In Nature:

    • Animals, plants, and microbes interact to form biological communities.
    • Every species requires interactions with at least one other species for its food.
    • Even autotrophic plant species need soil microbes for nutrient absorption and animal agents for pollination.

  • Types of Interactions:

    • Intraspecific: Interaction between organisms of the same species.
    • Interspecific: Interaction between members of different species.
    • Interspecific interactions occur between two or more organisms, which could be plants, animals, or both.

  • Nature of Interactions:

    • Mutualism: (+)(+) - Both species benefit.
    • Competition: (−)(−) - Both species lose.
    • Predation: (+)(−) - One species benefits (predator) while the other is harmed (prey).
    • Parasitism: (+)(−) - One species benefits (parasite) while the other is harmed (host).
    • Commensalism: (+)(O) - One species benefits, and the other is neither benefited nor harmed.
    • Amensalism: (−)(O) - One species is harmed, and the other is unaffected.

    + = benefited, − = inhibited, O = not affected

Mutualism

  • Definition:

    Mutualism is an obligatory and interdependent interaction where both species benefit.

  • Examples:

    • Lichens: Mutualistic relationship between fungus and photosynthetic algae or cyanobacteria.
    • Plant-animal interactions: Animals help in pollination and seed dispersal, while plants provide pollen, nectar, and nutritious fruits.
    • Animal-animal interactions: Many instances of mutualism observed.

Competition

  • Definition:

    Competition occurs when both species involved are at a loss.
    • Examples: Flamingos and resident fish compete for zooplankton in shallow creeks.
    • Even if resources are abundant, interference or inhibitory presence reduces feeding efficiency, as seen with leopards avoiding hunting near lion prides.

  • Gause's Competitive Exclusion Principle:

    • States that closely related species competing for the same resources cannot co-exist indefinitely.
    • Predicts the eventual elimination of the competitively inferior species.
    • However, recent studies show that such gross generalizations about competition may not always hold true.

Parasitism

  • Definition:

    • Parasitism is a relationship where one organism, the parasite, benefits at the expense of the other, the host.
    • It has evolved in various taxonomic groups from plants to higher vertebrates.

  • Effects on Host:

    • Harmful Effects: Most parasites harm the host by reducing its survival, growth, and reproduction.
    • Fatal: Some parasites can be fatal, leading to the death of the host.
    • Reduced Population Density: Parasites reduce the population density of host species.
    • Increased Vulnerability: Hosts become more vulnerable to predation due to physical weakness caused by parasites.

  • Special Adaptations of Endoparasites:

    • Loss of Sense Organs: Endoparasites lose unnecessary sense organs.
    • Adhesive Organs: Possess adhesive organs or suckers to cling to the host.
    • Loss of Digestive System: Endoparasites often lack a digestive system.
    • High Reproductive Capacity: They have a high reproductive capacity.
    • Complex Life Cycles: Often involve intermediate hosts or vectors to facilitate transfer.

Ectoparasites

  • Definition:

    Ectoparasites feed on the external surface of the host organism.

  • Examples:

    • Human Lice and Dog Ticks: Parasites that infest humans and dogs, respectively.
    • Cuscuta: A parasitic plant that has lost its chlorophyll and leaves, obtaining nutrition from its host plant.

Brood Parasitism

  • Definition:

    Brood Parasitism is a type of parasitic behavior.

  • Example: Asian Koel

    • Behavior: Koel lays its eggs in the nest of crows, exploiting them as host birds.
    • Egg Resemblance: Koel's eggs resemble the host's eggs in size and color, reducing detection by the crow.
    • Advantage: Koel's eggs hatch before the host's, giving the parasitic bird an advantage.

Predation
  • Roles of Predators:
    • Population Control: Predators keep prey populations under control, preventing overpopulation and ecosystem instability.
    • Maintaining Species Diversity: By reducing competition among prey species, predators help maintain species diversity in a community.
    • Pest Control: Predators control pest species, offering natural biological control measures in ecosystems (e.g., frogs controlling locust populations).
    • Limiting Invasive Species: Predators control invading exotic species, preventing their rapid spread.

Defence Mechanisms of Prey Species

  • Camouflage:

    Prey species use camouflage for concealment, blending into their environment to avoid detection.

  • Speed:

    Prey may move at faster speeds to escape predators.

  • Cryptic Coloration:

    Some prey species have cryptic coloration to avoid detection (e.g., insects and frogs).

  • Chemical Defence:

    • Prey may have bad taste due to accumulated chemicals, making them unpalatable to predators.
    • Example: The Monarch butterfly stores a special chemical during its caterpillar stage, making it distasteful to predators.

Defence Mechanisms in Plants Against Herbivores

  • Thorns:

    Thorns, like those seen in cacti or acacias, make plants inedible, serving as a common morphological defence.

  • Chemical Defence:

    Plants produce and store toxic and unpalatable chemicals to deter herbivores.
    Examples:
    • Calotropis: Produces highly poisonous cardiac glycosides.
    • Secondary Metabolites: Plants produce substances like nicotine, caffeine, quinine, strychnine, and opium, which deter grazers and browsers.

Commensalism

  • Definition: Interaction between two species where one benefits and the other is neither harmed nor benefited.

Examples of Commensalism

  1. Orchid Epiphytes:

    • Orchids grow as epiphytes on large trees, obtaining support without harming the tree.
    • The tree is neither benefited nor harmed, while the orchid gains support.

  2. Cattle Egret and Cattle:

    • Cattle egrets forage near cattle, which disturb insects hiding in the grass.
    • Egrets capture these insects, benefiting from the cattle's movement, while cattle are unaffected.

  3. Clownfish and Sea Anemone:

    • Clownfish seek protection in sea anemones' stinging tentacles.
    • The clownfish gains protection from predators, while the sea anemone is unharmed.

Fun Facts

  • Hypsometer: Instrument used to measure the height of forest trees.
  • World Environment Day: June 5th
  • World Population Day: July 11th
  • World Earth Day: April 22nd
  • World Ozone Day: September 16th