1. Ecology Fundamentals, Biological Hierarchy & Abiotic Factors
A. Introduction to Ecology
- Ecology Term: Coined by Reiter (often credited to Ernst Haeckel). Father of Indian Ecology: Prof. Ramdeo Misra.
- Study Definition: Interaction among organisms and between organisms and their physical abiotic environment. Ecology at the organismic level is essentially physiological ecology.
- Levels of Biological Organization:
$$\mathbf{\text{Organism (Basic Unit)} \to \text{Population} \to \text{Community} \to \text{Ecosystem} \to \text{Landscape} \to \text{Biome} \to \text{Biosphere}}$$
- Major Biomes of India: Tropical Rain Forest, Deciduous Forest, Desert, Sea Coast.
- Habitat vs. Niche:
• Habitat: Specific physical location where an organism lives (sum total of biotic & abiotic factors).
• Ecological Niche: Functional role of an organism in an ecological system, including range of conditions tolerated and resources utilized. No two species can occupy the exact same niche indefinitely!
B. Major Abiotic Factors (Temperature & Water)
- 1. Temperature (Most Ecologically Relevant Factor): Affects enzyme kinetics, basal metabolism, and physiological functions. Ranges from sub-zero polar regions ($<0^\circ\text{C}$) to deep hydrothermal vents ($>100^\circ\text{C}$).
• Eurythermal: Organisms capable of tolerating a wide range of temperatures (e.g., Mammals, Birds).
• Stenothermal: Organisms restricted to a narrow range of temperatures (e.g., Reptiles, Amphibians, Polar bear).
• Biogeographical Limits: Mango trees cannot grow in temperate countries (Canada/Germany); Tuna fish rarely caught beyond tropical latitudes.
- 2. Water ($2^{\text{nd}}$ Most Important Factor): Life originated in water. Plant productivity and distribution heavily dependent on water availability.
• Salinity Limits (parts per thousand – ppt): Inland waters $<5\text{ ppt}$, Oceans $30\text{–}35\text{ ppt}$, Hypersaline lagoons $>100\text{ ppt}$.
• Euryhaline: Tolerates wide range of salinity (e.g., Salmon fish).
• Stenohaline: Tolerates narrow range of salinity (e.g., Goldfish, Sharks).
2. Abiotic Factors (Light & Soil) & Responses to Environment
A. Light & Soil Characteristics
- Light (Visible Spectrum 400–700 nm – PAR): Essential for photosynthesis, photoperiodism (flowering response in plants, seasonal breeding in animals), and diurnal/nocturnal activity rhythms.
• Zonation in Lakes: Littoral zone, Limnetic zone, Euphotic zone (max light), Disphotic/Twilit zone, Profundal/Benthic zone (darkness, inhabited by Red Algae with r-phycoerythrin).
- Soil (Edaphic Factor): Depends on climate, weathering of rocks, and pedogenesis (humification).
• Soil Composition: $50\%$ mineral/organic matter, $25\%$ water, $25\%$ air. Loamy Soil is best for plant growth.
B. Organismal Responses to Abiotic Stress
| Response Type | Physiological / Behavioral Mechanism | Representative Examples |
|---|---|---|
| 1. Regulators | Maintain constant internal environment (Homeostasis) via physiological osmoregulation & thermoregulation. High energy cost. | Birds, Mammals, very few lower vertebrates/invertebrates. |
| 2. Conformers | Cannot maintain constant internal environment; internal temperature/osmotic conc. changes with ambient environment. | $99\%$ of Animals and nearly all Plants. |
| 3. Partial Regulators | Regulate internal environment up to a certain threshold limit, beyond which they conform. | Certain aquatic species & primitive mammals. |
| 4. Migrate | Move temporarily from stressful habitat to a hospitable area and return when stressful period is over. | Siberian Cranes migrating thousands of kilometers to Keoladeo National Park (Bharatpur, Rajasthan) during winter. |
| 5. Suspend | • Thick-walled Spores: Bacteria, Fungi, Algae. • Dormancy / Vegetative prop: Higher plants. • Hibernation (Winter sleep): Bears. • Aestivation (Summer sleep): Snails & Fishes. • Diapause (Suspended development): Zooplankton species. | Microbes, Plants, Bears, Snails, Zooplankton. |
3. Adaptations & Ecological Rules
A. Adaptations to Extreme Environments
- Physiological Adaptation (Kangaroo Rat in North American Deserts): Meets all water requirements through internal fat oxidation (releasing metabolic water) and concentrates urine to excrete minimal water.
- Morphological / Anatomical (Desert Plants – Opuntia): Thick leaf cuticle, sunken stomata, leaves modified into spines, $C_4 / \text{CAM}$ pathway (scotoactive stomata open at night), photosynthetic flattened stems (Phylloclades).
- Behavioral Adaptation (Desert Lizard): Basks in sun to absorb heat when body temperature drops below comfort zone; moves to shade or burrows underground when ambient temperature rises.
- High Altitude Acclimatization ($>3500\text{ meters}$ at Rohtang Pass): Low atmospheric pressure causes altitude sickness (nausea, fatigue, heart palpitations). Body compensates by:
1. Increasing Red Blood Cell (RBC) production.
2. Increasing breathing rate.
3. Decreasing binding affinity of Hemoglobin for $\text{O}_2$.
B. Key Ecological Rules
| Ecological Rule | Core Principle / Rule Description |
|---|---|
| Allen’s Rule | Mammals from colder climates generally have shorter ears (pinnae) and shorter limbs to minimize heat loss. |
| Bergmann’s Rule | Warm-blooded animals (birds and mammals) in colder climates tend to have larger body sizes ($\text{low Surface Area / Volume ratio}$) to conserve body heat. |
| Jordan’s Rule | Fishes in colder waters tend to have more vertebrae and larger body size than those in warmer waters. |
| Rensch’s Rule | Birds in colder environments have narrower, shorter wings compared to broader wings in warmer environments. |
4. Population Attributes, Age Pyramids & Growth Models
A. Population Attributes & Calculations
- Populations have attributes distinct from individual organisms: Birth Rate (Natality), Death Rate (Mortality), Sex Ratio, and Age Structure.
- Calculations:
• Natality Rate: $\text{BR} = \frac{\text{Final Population} – \text{Initial Population}}{\text{Initial Population}}$. (e.g., Lotus pond increases from $20 \to 28 \implies \text{BR} = \frac{8}{20} = \mathbf{0.4\text{ offsprings/lotus/year}}$).
• Mortality Rate: $\text{DR} = \frac{\text{Initial} – \text{Final}}{\text{Initial}}$. (e.g., $4$ out of $40$ fruit flies die $\implies \text{DR} = \frac{4}{40} = \mathbf{0.1\text{ deaths/fly/week}}$).
- Age Pyramids (Pre-reproductive, Reproductive, Post-reproductive):
• Triangular Shape: Expanding / Growing population ($\text{Pre-rep} > \text{Rep}$; e.g., India).
• Bell Shape: Stable population ($\text{Pre-rep} = \text{Rep}$; e.g., USA, Germany).
• Urn Shape: Declining population ($\text{Pre-rep} < \text{Rep}$; e.g., Japan, Scandinavian countries).
- Population Density Measurement: Direct counting, Biomass/dry weight (more meaningful for single large Banyan tree vs 200 Parthenium plants), Relative density (bacteria in petri dish), Indirect estimation (Tiger pug marks or fecal pellets).
B. Population Growth Mechanics & Formula
$$\mathbf{N_{t+1} = N_t + [(B + I) – (D + E)]}$$
$N_t = \text{Initial Density}$, $B = \text{Births}$, $I = \text{Immigration}$, $D = \text{Deaths}$, $E = \text{Emigration}$.
C. Growth Models: Exponential vs. Logistic
| Feature | Exponential Growth (Geometric) | Logistic Growth (Verhulst-Pearl) |
|---|---|---|
| Resource Availability | Unlimited resources (idealized, unrealistic). | Limited resources (realistic in nature). Includes Carrying Capacity ($K$). |
| Differential Equation | $$\mathbf{\frac{dN}{dt} = rN}$$ ($r = b – d = \text{intrinsic rate of natural increase}$) | $$\mathbf{\frac{dN}{dt} = rN \left(\frac{K – N}{K}\right)}$$ ($\frac{K – N}{K} = \text{Environmental Resistance}$) |
| Integral Form & Curve | $N_t = N_0 e^{rt}$; J-shaped Curve. | $N_t = \frac{K}{1 + e^{-rt}}$; S-shaped / Sigmoid Curve. |
5. Life History Variation & Population Interactions (Part 1)
A. $r$-Selected vs. $K$-Selected Species
| Trait | $r$-Selected Species (Opportunistic) | $K$-Selected Species (Equilibrium) |
|---|---|---|
| Environment & Lifespan | Unstable, unpredictable; short lifespan. | Stable, predictable; long lifespan. |
| Offspring Number & Size | Produce many small-sized offspring (e.g., Oysters, Pelagic fishes, Insects, Bacteria). Breeds once in lifetime (e.g., Pacific Salmon, Bamboo). | Produce few large-sized offspring (e.g., Birds, Mammals, Elephants). Breeds many times in lifetime. |
B. Predation ($+/-$) & Defense Mechanisms
- Ecological Roles of Predators: Energy transfer across trophic levels, keeping prey populations under control, and maintaining species diversity by reducing interspecific competition (e.g., Starfish Pisaster removal from American Pacific coast caused extinction of $>10$ invertebrate species).
- Biological Pest Control: Prickly pear cactus invasion in Australia (1920s) controlled by introducing natural predator Cactoblastis moth.
- Phytophagous Insects: $25\%$ of insects feed on plant sap/tissues. Plants defend via thorns (Acacia, Cactus) or chemical cardiac glycosides (Calotropis), nicotine, opium, caffeine, quinine.
- Prey Defenses:
• Camouflage / Crypsis: Frogs, Grasshoppers, Praying mantis.
• Monarch Butterfly: Distasteful to bird predators due to toxic cardiac glycoside acquired during caterpillar stage by feeding on poisonous weed.
• Batesian Mimicry: Harmless Viceroy Butterfly mimics unpalatable Monarch butterfly.
6. Competition, Commensalism, Parasitism & Mutualism
A. Competition ($-\!/-\!$) & Gause’s Competitive Exclusion Principle
- Occurs between closely related or unrelated species (e.g., Flamingoes and resident fishes competing for zooplankton in South American lakes) competing for limited resources.
- Gause’s Principle: Two closely related species competing for the same limited resources cannot co-exist indefinitely; competitively inferior species is eliminated (e.g., Introduction of Abingdon Goat in Galapagos Islands led to extinction of Abingdon Tortoise due to greater browsing efficiency; Balanus barnacle excluding Chthamalus on Scottish coast).
- Competitive Co-existence (MacArthur’s Resource Partitioning): Species avoid competition and co-exist by choosing different foraging times or patterns (e.g., 5 closely related species of Warbler birds co-existing on the same tree).
B. Commensalism ($+/0$) & Amensalism ($-/0$)
- Commensalism ($+/0$): One species benefits, other is unaffected.
• Epiphytic Orchids on Mango branch.
• Barnacles attached to back of Whale.
• Cattle Egret birds foraging close to grazing Cattle.
• Clown fish sheltered inside tentacles of Sea Anemone.
- Amensalism ($-/0$): One species is harmed, other is unaffected.
• Antibiosis: Penicillium producing penicillin inhibiting bacterial growth.
• Allelopathy: Black Walnut tree releasing juglone chemical inhibiting nearby plants.
C. Parasitism ($+/-$) & Mutualism ($+/+$)
- Parasitism ($+/-$): Parasite benefits at cost of host. Ectoparasites (Lice, Ticks on dogs, Copepods on marine fish, Cuscuta stem parasite) vs Endoparasites (Liver fluke, Tapeworm).
• Female Mosquito: Not considered a parasite (only requires blood vector for egg nourishment, not nutrition).
• Brood Parasitism: Parasitic bird lays eggs in nest of host bird (e.g., Cuckoo / Koel and Crow).
- Mutualism ($+/+$): Both interacting species benefit mutually.
• Mycorrhizae: Fungi (Glomus) $+$ Roots of Higher Plants (absorbs Phosphorus).
• Lichens: Fungus (Mycobiont) $+$ Algae/Cyanobacteria (Phycobiont).
• Co-evolution / Obligate Mutualism: Fig tree and Blastophaga wasp (wasp pollinates fig, fig provides egg-laying site in seeds); Yucca plant and Pronuba moth.
• Pseudocopulation (Sexual Deceit): Mediterranean Orchid Ophrys mimics female Colpa bee appearance to ensure pollination by male bees.