V. POPULATION ATTRIBUTES
A WHAT IS A POPULATION?
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| FEATURE | DETAIL |
|---|---|
| Definition | A group of individuals of the same species living in a specific geographical area at a specific time ⭐ |
| Examples | All cormorants in a wetland; Teakwood trees in a forest tract; Bacteria in a culture plate; Lotus in a pond |
| Ecological significance | Population ecology links ecology to population genetics & evolution ⭐ |
| Key fact | Natural selection operates at the population level ⭐ |
B POPULATION vs INDIVIDUAL ATTRIBUTES
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| ATTRIBUTE | INDIVIDUAL | POPULATION |
|---|---|---|
| Births / Deaths | Has births & deaths | Has birth rates & death rates (per capita) ⭐ |
| Sex | Either male or female | Has a sex ratio ⭐ |
| Age | Has an age | Has age distribution ⭐ |
⚡ EXAM TRAP: NEET 2020
Population attributes = Natality, Mortality, Sex ratio, Age distribution. Species interaction is NOT a population attribute — it is a community attribute.
C BIRTH & DEATH RATE CALCULATIONS
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| SCENARIO | CALCULATION | ANSWER |
|---|---|---|
| 20 lotus plants → 8 new added | Birth rate = 8/20 | 0.4 offspring per lotus per year |
| 40 fruitflies → 4 died in a week | Death rate = 4/40 | 0.1 individuals per fruitfly per week |
| 80 Drosophila → 8 died in a week | Death rate = 8/80 | 0.1 individuals per Drosophila per week ⭐ |
⚡ EXAM TRAP: NEET 2022
Death rate = 8/80 = 0.1 individuals per Drosophila per week.
D AGE PYRAMIDS
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| PYRAMID TYPE | SHAPE | GROWTH STATUS | AGE GROUP PATTERN |
|---|---|---|---|
| Expanding | Triangular ⭐ | Growing population | Pre-reprod. > Reprod. > Post-reprod. |
| Stable | Bell-shaped ⭐ | Stationary population | Pre-reprod. ≈ Reprod. |
| Declining | Urn-shaped ⭐ | Shrinking population | Pre-reprod. < Reprod. |
⚡ EXAM TRAP: NEET 2018, 2023, 2013, 2012
Three types of age pyramids — expanding (triangular, growing), stable (bell-shaped), declining (urn-shaped).
E POPULATION DENSITY
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| FEATURE | DETAIL |
|---|---|
| Designated as | N |
| Can be measured as | Number, Biomass, or Percent cover ⭐ |
| Biomass example | Single huge banyan vs 200 Parthenium plants — biomass is more meaningful |
| Indirect estimation | Tiger census — based on pug marks & fecal pellets ⭐ |
| Relative density | e.g., fish caught per trap = good enough measure |
VI. POPULATION GROWTH
A FOUR BASIC PROCESSES
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| PROCESS | EFFECT ON DENSITY | DETAIL |
|---|---|---|
| Natality (Birth rate) | Increases ⭐ | Number of births added per unit time |
| Immigration (I) | Increases ⭐ | Individuals coming into population from elsewhere |
| Mortality (Death rate) | Decreases ⭐ | Number of deaths per unit time |
| Emigration (E) | Decreases ⭐ | Individuals leaving population |
⚡ EXAM TRAP: NEET 2018
Natality = Birth rate.
⚡ EXAM TRAP: NEET 2020
Immigration has a positive impact on population density.
B POPULATION DENSITY EQUATION
🔑 Equation: Nt+1 = Nt + [(B + I) – (D + E)]
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| COMPONENT | EFFECT |
|---|---|
| (B + I) | Increase density ⭐ |
| (D + E) | Decrease density ⭐ |
| Population grows when | (B + I) > (D + E) |
⚡ EXAM TRAP: NEET 2013, 2024
Population density equation; Births + Immigration increase; Deaths + Emigration decrease.
⚡ EXAM TRAP: RE-NEET 2026
When the per-capita birth rate equals the per-capita death rate, r = 0 and the population size stays unchanged. A population of 10 million cells with birth rate 0.002 and death rate 0.002 remains 10 million after 10 generations.
🔑 Normal conditions: Births & deaths are most important. Special conditions: In newly colonised habitats, immigration may contribute more than birth rates.
C GROWTH MODELS
C1. Exponential / Geometric Growth (J-shaped curve) ⭐⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Condition | Resources are unlimited ⭐ |
| Curve shape | J-shaped ⭐ |
| Equation | dN/dt = rN ⭐⭐ |
| Integral form | Nt = N0 ert ⭐ |
| r | Intrinsic rate of natural increase = b – d ⭐ |
| e | Base of natural logarithms (2.71828) |
| Key concept | Every species has innate potential to grow exponentially when resources are unlimited |
r VALUES — SELECTED ORGANISMS ⭐
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| ORGANISM | r VALUE |
|---|---|
| Norway rat | 0.015 |
| Flour beetle | 0.12 |
| Human population (India, 1981) | 0.0205 |
⚡ EXAM TRAP: NEET 2016, 2021, 2023
Exponential growth — dN/dt = rN; J-shaped curve; unlimited resources; r = intrinsic rate of natural increase.
C2. Logistic Growth (S-shaped / Sigmoid curve) ⭐⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Condition | Resources are limited ⭐ |
| Curve shape | Sigmoid (S-shaped) ⭐ |
| Also called | Verhulst–Pearl Logistic Growth ⭐ |
| Equation | dN/dt = rN[(K – N)/K] ⭐⭐⭐ |
| K | Carrying capacity — maximum population size the habitat can support ⭐ |
| Considered | More realistic model (resources finite & become limiting) ⭐ |
PHASES OF LOGISTIC GROWTH ⭐⭐
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| PHASE | DETAIL |
|---|---|
| Lag phase | Initial slow growth |
| Acceleration | Rapid growth phase |
| Deceleration | Growth rate slows as resources deplete |
| Asymptote | Population reaches carrying capacity (K) ⭐; growth rate becomes zero ⭐ |
⚡ EXAM TRAP: NEET 2016, 2017
Logistic growth — S-shaped; Verhulst-Pearl; dN/dt = rN[(K–N)/K]; asymptote when N = K.
⚡ EXAM TRAP: NEET 2024
Graph labelling — Curve a (J-shape) = Exponential; Curve b (S-shape) = Logistic.
⚡ EXAM TRAP: NEET 2026
The Verhulst-Pearl logistic growth equation is dN/dt = rN[(K – N)/K].
⚡ EXAM TRAP: NEET 2025
The Verhulst-Pearl logistic growth equation is dN/dt = rN[(K – N)/K] — note both N and the bracket term. dN/dt = r[(K–N)/K] without N is the standing distractor.
D EXPONENTIAL vs LOGISTIC GROWTH — COMPARISON
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| FEATURE | EXPONENTIAL (J-SHAPED) | LOGISTIC (S-SHAPED) |
|---|---|---|
| Resources | Unlimited | Limited |
| Curve | J-shaped | Sigmoid (S-shaped) |
| Equation | dN/dt = rN | dN/dt = rN[(K–N)/K] |
| Carrying cap. (K) | Not considered | Included |
| Realistic? | Less realistic | More realistic ⭐ |
| Growth pattern | Continuous increase | Lag → Accel. → Decel. → Asymptote |
| Asymptote | Never reached | Reached at N = K |
⚡ EXAM TRAP: RE-NEET 2026
The logistic growth model is considered more realistic than the exponential model BECAUSE resources are finite — the reason is the correct explanation of the assertion.
E NEET CALCULATION PRACTICE
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| PROBLEM (PYQ) | SOLUTION | ANSWER |
|---|---|---|
| Net increase: Natality=250, Immigration=20, Mortality=240, Emigration=30 | (250+20) – (240+30) = 270 – 270 | 0 (NEET 2013) |
| 8 flies died out of 80 in a week | 8/80 | 0.1 per week (NEET 2022) |
| 250 snails → 2500 in a year | Increase = 2250; Rate = 2250/250 | 9 offspring per snail per year (NEET 2023) |
| b = d (e.g. 10 million cells; b = 0.002, d = 0.002) | r = b – d = 0 | Population remains constant regardless of number of generations ⭐⭐⭐ |
F LIFE HISTORY VARIATION
REPRODUCTIVE STRATEGIES
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| STRATEGY | DESCRIPTION | EXAMPLES |
|---|---|---|
| Semelparous | Breed only once in lifetime ⭐ | Pacific Salmon, Bamboo |
| Iteroparous | Breed many times during lifetime | Most birds & mammals |
OFFSPRING STRATEGIES ⭐⭐
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| STRATEGY | OFFSPRING | SIZE | EXAMPLES |
|---|---|---|---|
| r-strategy (r-selected) | Large number ⭐ | Small-sized | Oysters, Pelagic fishes ⭐ |
| K-strategy (K-selected) | Small number | Large-sized | Birds, Mammals |
⚡ EXAM TRAP: NEET 2016
r-selected species — large number of small-sized progeny (Oysters, Pelagic fishes).
VII. POPULATION INTERACTIONS
MASTER TABLE — INTERACTION TYPES ⭐⭐⭐
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| INTERACTION | SPECIES A | SPECIES B | DESCRIPTION |
|---|---|---|---|
| Mutualism | + | + | Both species benefit |
| Competition | – | – | Both species harmed |
| Predation | + | – | Predator benefits, Prey harmed |
| Parasitism | + | – | Parasite benefits, Host harmed |
| Commensalism | + | 0 | One benefits, Other unaffected |
| Amensalism | – | 0 | One harmed, Other unaffected |
⚡ EXAM TRAP: NEET 2022, 2021, 2018, 2016, 2015
Know all six interaction types with signs.
⚡ EXAM TRAP: NEET 2026
Both species benefit in mutualism; in parasitism only one species benefits and the other is harmed; in amensalism one species is harmed and the other is unaffected.
⚡ EXAM TRAP: NEET 2026
In commensalism one species benefits and the other is UNAFFECTED. Commensalism is not a both-benefit interaction. Parasitism and commensalism cannot be grouped together as one benefits, other harmed.
⚡ EXAM TRAP: RE-NEET 2026 (Match-the-list)
Both species harmed ↔ Competition; one harmed and the other benefited ↔ Predation; both benefited ↔ Mutualism; one benefited while the other has no effect ↔ Commensalism.
🔑 Common feature: Predation, Parasitism, and Commensalism share a characteristic — the interacting species live closely together.
A PREDATION (+/–)
ROLES OF PREDATION ⭐⭐
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| ROLE | DETAIL |
|---|---|
| Energy transfer | Transfers energy from lower trophic levels → higher trophic levels ⭐ |
| Population control | Predators keep prey populations under control ⭐ |
| Maintain species diversity | By reducing intensity of competition among competing prey species ⭐ |
🔑 Even a sparrow eating a seed is predation; for plants, herbivores are predators.
EXOTIC SPECIES & PREDATOR CONTROL ⭐⭐
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| EXAMPLE | DETAIL |
|---|---|
| Prickly pear cactus (Australia, 1920s) | Introduced, spread rapidly (no natural predators); controlled only by introducing cactus-feeding moth (Cactoblastis) ⭐ — example of biological control |
| Principle | Biological control methods in agriculture based on ability of predators to regulate prey populations ⭐ |
PISASTER (STARFISH) EXPERIMENT ⭐⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Location | Rocky intertidal communities, American Pacific Coast |
| Role | Pisaster = important keystone predator ⭐ |
| Experiment | When all starfish removed from enclosed area |
| Result | >10 species of invertebrates became extinct within a year due to interspecific competition ⭐ |
⚡ EXAM TRAP: NEET 2022, 2024
Pisaster removal → >10 species extinct; predators maintain species diversity.
⚡ EXAM TRAP: NEET 2023
Keystone species = species that controls relative abundance of others (e.g., Pisaster).
PREY DEFENCES ⭐⭐
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| DEFENCE | EXAMPLE |
|---|---|
| Cryptic colouration (Camouflage) | Some insects & frogs — avoid detection by predators ⭐ |
| Chemical defence (Poisonous) | Monarch butterfly — distasteful to birds due to special chemical acquired by feeding on poisonous weed as caterpillar ⭐ |
PLANT DEFENCES AGAINST HERBIVORY ⭐⭐⭐
⭐ ~25% of insects are phytophagous (feed on plant sap & parts).
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| DEFENCE TYPE | EXAMPLES |
|---|---|
| Morphological defences | Thorns — Acacia, Cactus ⭐ |
| Chemical defences | Toxins that make herbivore sick, inhibit feeding/digestion, disrupt reproduction, or kill |
CHEMICAL DEFENCE EXAMPLES ⭐⭐
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| CHEMICAL / PLANT | DETAIL |
|---|---|
| Calotropis | Produces cardiac glycosides ⭐ — highly poisonous; cattle & goats never browse on it |
| Nicotine | Plant defence chemical (commercially extracted) |
| Caffeine | Plant defence chemical |
| Quinine | Plant defence chemical |
| Strychnine | Plant defence chemical |
| Opium | Plant defence chemical |
⚡ EXAM TRAP: NEET 2023
Calotropis produces cardiac glycosides — defence against herbivores.
B COMPETITION (–/–)
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| FEATURE | DETAIL |
|---|---|
| Darwin said | Struggle for existence and Survival of the fittest — interspecific competition is a potent force in organic evolution ⭐ |
| Definition | Process where fitness of one species (measured as r) is significantly lower in presence of another species |
KEY CONCEPTS ⭐⭐
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| CONCEPT | DETAIL |
|---|---|
| Not just related species | Totally unrelated species can also compete for same resource ⭐ |
| Example | Flamingoes & resident fishes in South American lakes — compete for zooplankton ⭐ |
| Resources need not be limiting | Interference competition — feeding efficiency reduced by inhibitory presence of other species even when resources are abundant ⭐ |
⚡ EXAM TRAP: NEET 2013, 2024
Unrelated species can compete — flamingoes vs fishes for zooplankton.
GAUSE COMPETITIVE EXCLUSION PRINCIPLE ⭐⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Statement | Two closely related species competing for the same resources cannot co-exist indefinitely ⭐ |
| Outcome | The competitively inferior one will be eliminated ⭐ |
| True if | Resources are limiting |
⚡ EXAM TRAP: NEET 2016, 2023, 2024
Gause Competitive Exclusion Principle — two closely related species competing for the same resources cannot co-exist indefinitely.
EXAMPLES OF COMPETITIVE EXCLUSION ⭐⭐
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| EXAMPLE | DETAIL |
|---|---|
| Abingdon tortoise (Galapagos) | Became extinct within a decade after goats introduced — goats had greater browsing efficiency ⭐ |
| Connell experiment (Scotland) | Rocky sea coasts — larger barnacle Balanus dominates intertidal area → excludes smaller Chthamalus ⭐ |
| General pattern | Herbivores & plants more adversely affected by competition than carnivores ⭐ |
⚡ EXAM TRAP: NEET 2024
Abingdon tortoise extinct due to goat competition; Balanus excludes Chthamalus.
COMPETITIVE RELEASE ⭐
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| FEATURE | DETAIL |
|---|---|
| Definition | When a competitively superior species is removed → the restricted species expands its range dramatically ⭐ |
⚡ EXAM TRAP: NEET 2024
Competitive release — restricted species expands its range when the superior competitor is removed.
RESOURCE PARTITIONING (MacARTHUR) ⭐⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Mechanism | To avoid competition → species choose different feeding times or foraging patterns ⭐ |
| MacArthur showed | Five closely related warbler species co-existed on the same tree due to behavioural differences in foraging activities ⭐ |
| Promotes | Co-existence rather than exclusion ⭐ |
⚡ EXAM TRAP: NEET 2021, 2019, 2022, 2024
MacArthur Resource Partitioning — 5 warbler species on same tree; different foraging patterns → co-existence.
C PARASITISM (+/–)
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| FEATURE | DETAIL |
|---|---|
| Definition | Parasite benefits (+); Host is harmed (–) |
| Benefit to parasite | Free lodging and meals ⭐ |
| Host-specificity | Many parasites are host-specific (parasitise only a single species) |
| Co-evolution | Host evolves defence → Parasite evolves counter-mechanisms ⭐ |
PARASITE ADAPTATIONS ⭐⭐⭐
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| ADAPTATION | DETAIL |
|---|---|
| Loss of unnecessary sense organs ⭐ | Simplified morphology |
| Presence of adhesive organs / Suckers ⭐ | To cling to host |
| Loss of digestive system ⭐ | Absorb pre-digested food from host |
| High reproductive capacity ⭐ | Ensure transmission |
⚡ EXAM TRAP: NEET 2013
Parasite adaptations — loss of sense organs, adhesive organs, loss of digestive system, high reproductive capacity.
EFFECTS OF PARASITES ON HOST ⭐
- Reduce survival, growth & reproduction of host
- Reduce host population density
- Make host more vulnerable to predation (physically weak)
ECTOPARASITES (EXTERNAL) ⭐⭐
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| EXAMPLE | DETAIL |
|---|---|
| Lice on humans | Feed on external surface |
| Ticks on dogs | External parasite |
| Copepods on marine fish | Ectoparasitic |
| Cuscuta on hedge plants ⭐ | Parasitic plant; lost chlorophyll & leaves; derives nutrition from host ⭐ |
🔑 Female mosquito is NOT considered a parasite — although it needs blood for reproduction (it is a temporary contact, not true parasitism).
ENDOPARASITES (INTERNAL) ⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Location | Inside host body — liver, kidney, lungs, RBCs, etc. |
| Life cycle | More complex due to extreme specialisation ⭐ |
| Morphology | Greatly simplified ⭐ |
| Reproductive potential | Emphasised (high) ⭐ |
COMPLEX LIFE CYCLES — EXAMPLES
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| PARASITE | INTERMEDIATE HOSTS / VECTORS |
|---|---|
| Human liver fluke (Trematode) | Two intermediate hosts — Snail & Fish ⭐ |
| Malarial parasite | Vector — Mosquito |
BROOD PARASITISM ⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Definition | Parasitic bird lays eggs in nest of host bird ⭐ |
| Host incubation | Lets host incubate the eggs |
| Evolutionary adaptation | Parasitic bird eggs evolved to resemble host eggs in size & colour ⭐ — to reduce chance of detection |
| Classic example | Cuckoo (Koel) lays eggs in Crow nest ⭐ |
⚡ EXAM TRAP: NEET 2023
Brood parasitism — Cuckoo (Koel) in Crow nest; eggs resemble host eggs.
D COMMENSALISM (+/0)
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| FEATURE | DETAIL |
|---|---|
| Definition | One species benefits (+); Other is neither harmed nor benefited (0) ⭐ |
EXAMPLES ⭐⭐⭐
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| EXAMPLE | BENEFITED | UNAFFECTED |
|---|---|---|
| Orchid (epiphyte) on Mango branch ⭐ | Orchid (gets support & light) | Mango tree |
| Barnacles on Whale back ⭐ | Barnacles (get transport) | Whale |
| Cattle Egret & Grazing Cattle ⭐ | Egret (insects flushed out by cattle) | Cattle |
| Sea Anemone & Clown Fish ⭐ | Clown fish (protection from predators by stinging tentacles) | Sea anemone |
⚡ EXAM TRAP: NEET 2013, 2019, 2020, 2023
Know all four commensalism examples — Orchid-Mango, Barnacle-Whale, Egret-Cattle, Clownfish-Anemone.
⚡ EXAM TRAP: NEET 2025
Epiphytes growing on a mango branch are an example of commensalism.
E MUTUALISM (+/+)
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| FEATURE | DETAIL |
|---|---|
| Definition | Both interacting species are benefited ⭐ |
EXAMPLES ⭐⭐⭐
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| EXAMPLE | SPECIES A | SPECIES B | DETAIL |
|---|---|---|---|
| Lichens | Fungi | Algae / Cyanobacteria ⭐ | Intimate mutualistic relationship |
| Mycorrhizae | Fungi | Roots of higher plants ⭐ | Fungi help absorb nutrients; Plant gives carbohydrates |
| Fig & Wasp | Fig tree | Wasp (specific species) ⭐ | Tight 1:1 relationship; Wasp pollinates fig; Fig provides oviposition site & seeds for larvae |
| Yucca & Moth | Yucca plant | Moth ⭐ | Neither can complete life cycle without the other |
| Plant-Pollinator | Plants | Animals | Plants offer pollen & nectar as rewards ⭐ |
| Plant-Seed disperser | Plants | Animals | Plants offer juicy, nutritious fruits ⭐ |
⚡ EXAM TRAP: NEET 2019, 2020
Lichens (Fungi + Algae); Mycorrhizae (Fungi + Roots).
⚡ EXAM TRAP: NEET 2017, 2019, 2020, 2023
Mycorrhizae = mutualism between fungi & roots of higher plants.
⚡ EXAM TRAP: NEET 2018
Yucca & Moth — neither can complete life cycle without the other.
⚡ EXAM TRAP: NEET 2024
Fig & Wasp — tight one-to-one relationship.
⚡ EXAM TRAP: NEET 2025
The fig wasp and fig tree exhibit a mutual relationship — the fig provides the wasp a place to lay eggs and the fig gets pollinated by the wasp.
OPHRYS — SEXUAL DECEIT ⭐⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Organism | Mediterranean Orchid Ophrys ⭐ |
| Mechanism | Sexual deceit for pollination ⭐ |
| How it works | One petal resembles female bee in size, colour & markings ⭐ |
| Male bee | Attracted → pseudocopulates with flower → dusted with pollen ⭐ |
| Pollination | When same bee pseudocopulates with another flower → transfers pollen |
| Co-evolution | If female bee colour pattern changes → pollination success reduced → unless orchid co-evolves to maintain resemblance ⭐ |
⚡ EXAM TRAP: NEET 2026
Ophrys and bumblebee is the example of sexual deceit; female wasp and fig = mutualism; sea anemone and clown fish = commensalism; cuckoo and crow = brood parasitism.
🔑 Cheaters: Some animals try to steal nectar without aiding pollination — this is why plant-animal interactions involve co-evolution.
F AMENSALISM (–/0)
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| FEATURE | DETAIL |
|---|---|
| Definition | One species is harmed (–); Other is unaffected (0) ⭐ |
| Example | Antibiotic production — Penicillium harms bacteria; Penicillium is unaffected ⭐ |
⚡ EXAM TRAP: NEET 2018, 2021
Amensalism — one harmed, other unaffected; example: Penicillium vs bacteria.
VIII. RAPID REVISION — KEY COMPARISON TABLES
TABLE 1: Exponential vs Logistic Growth
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| FEATURE | EXPONENTIAL | LOGISTIC |
|---|---|---|
| Resources | Unlimited | Limited |
| Curve | J-shaped | S-shaped (Sigmoid) |
| Equation | dN/dt = rN | dN/dt = rN[(K–N)/K] |
| Integral | Nt = N0 ert | — |
| K | Not applicable | Included |
| Realistic | Less | More |
| Named after | — | Verhulst-Pearl |
| Asymptote | Never | At N = K |
TABLE 2: Semelparous vs Iteroparous
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| FEATURE | SEMELPAROUS | ITEROPAROUS |
|---|---|---|
| Breeding frequency | Once in lifetime | Many times |
| Examples | Pacific salmon, Bamboo | Most birds & mammals |
TABLE 3: r-strategy vs K-strategy
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| FEATURE | R-SELECTED | K-SELECTED |
|---|---|---|
| Offspring number | Large | Small |
| Offspring size | Small | Large |
| Examples | Oysters, Pelagic fishes | Birds, Mammals |
TABLE 4: All Six Population Interactions
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| INTERACTION | SIGN (A/B) | KEY EXAMPLE |
|---|---|---|
| Mutualism | +/+ | Lichens, Mycorrhizae, Fig-Wasp |
| Competition | –/– | Flamingoes vs Fish; Abingdon tortoise vs Goats |
| Predation | +/– | Tiger-Deer; Pisaster-Invertebrates |
| Parasitism | +/– | Cuscuta; Cuckoo-Crow; Liver fluke |
| Commensalism | +/0 | Orchid-Mango; Barnacle-Whale; Egret-Cattle; Clownfish-Anemone |
| Amensalism | –/0 | Penicillium vs Bacteria |
TABLE 5: Plant Defences Against Herbivory
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| TYPE | EXAMPLES |
|---|---|
| Morphological | Thorns (Acacia, Cactus) |
| Chemical | Cardiac glycosides (Calotropis); Nicotine; Caffeine; Quinine; Strychnine; Opium |
TABLE 6: Ectoparasites vs Endoparasites
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| FEATURE | ECTOPARASITES | ENDOPARASITES |
|---|---|---|
| Location | External surface | Inside host body |
| Life cycle | Simpler | More complex |
| Morphology | Less simplified | Greatly simplified |
| Reproductive capacity | High | Very high (emphasised) |
| Examples | Lice, Ticks, Copepods, Cuscuta | Liver fluke, Malarial parasite |
TABLE 7: Commensalism Examples — Quick Reference
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| EXAMPLE | BENEFITED | UNAFFECTED |
|---|---|---|
| Orchid on Mango | Orchid | Mango |
| Barnacles on Whale | Barnacles | Whale |
| Cattle Egret + Cattle | Egret | Cattle |
| Clownfish + Sea Anemone | Clownfish | Sea Anemone |
TABLE 8: Mutualism Examples — Quick Reference
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| EXAMPLE | PARTNER A | PARTNER B |
|---|---|---|
| Lichens | Fungi | Algae / Cyanobacteria |
| Mycorrhizae | Fungi | Roots of higher plants |
| Fig & Wasp | Fig tree | Wasp species (1:1) |
| Yucca & Moth | Yucca | Moth |
| Ophrys & Bee | Orchid | Bee (sexual deceit) |
IX. COMMON EXAM TRAPS — QUICK REFERENCE
CONSOLIDATED PYQ Q&A TABLE ⭐⭐⭐
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| TRAP / QUESTION | CORRECT ANSWER |
|---|---|
| Population attributes include? | Birth rate, Death rate, Sex ratio, Age distribution |
| Species interaction — population attribute? | No (community attribute) |
| Age pyramid for growing population? | Triangular (Expanding) |
| Age pyramid for declining population? | Urn-shaped |
| Population density measured as? | Number, Biomass, Percent cover |
| Tiger census based on? | Pug marks & Fecal pellets |
| B + I increase or decrease density? | Increase |
| D + E increase or decrease density? | Decrease |
| If per-capita birth rate = death rate, population after n generations? | Unchanged (r = 0) ⭐⭐⭐ |
| Exponential growth curve shape? | J-shaped |
| Logistic growth curve shape? | S-shaped (Sigmoid) |
| More realistic growth model? | Logistic (resources limited / finite) ⭐⭐⭐ |
| Why is logistic growth more realistic? | Because resources are finite ⭐⭐⭐ |
| Logistic / Verhulst-Pearl growth equation? | dN/dt = rN[(K – N)/K] ⭐⭐⭐ |
| Is dN/dt = r[(K–N)/K] (without N) correct? | No — the N term must be present ⭐⭐⭐ |
| K in logistic equation? | Carrying capacity |
| Asymptote reached when? | N = K (growth rate = zero) |
| Verhulst-Pearl growth is? | Logistic growth |
| r = ? | Intrinsic rate of natural increase (b – d) |
| Semelparous examples? | Pacific Salmon, Bamboo |
| r-selected examples? | Oysters, Pelagic fishes |
| K-selected examples? | Birds, Mammals |
| Both species benefit? | Mutualism (+/+) ⭐⭐⭐ |
| Both species harmed? | Competition (–/–) ⭐⭐⭐ |
| One harmed, one benefited? | Predation / Parasitism (+/–) ⭐⭐⭐ |
| One benefited, other unaffected? | Commensalism (+/0) ⭐⭐⭐ |
| One harmed, other unaffected? | Amensalism (–/0) ⭐⭐⭐ |
| Do both species benefit in commensalism? | No — one is unaffected ⭐⭐⭐ |
| Amensalism example? | Penicillium vs Bacteria |
| Predator that maintains species diversity? | Pisaster (Starfish) — keystone predator |
| Pisaster removal result? | >10 invertebrate species extinct within a year |
| Prickly pear cactus controlled by? | Cactus-feeding moth (Cactoblastis) |
| ~25% insects are? | Phytophagous |
| Calotropis produces? | Cardiac glycosides |
| Plant defence chemicals? | Nicotine, Caffeine, Quinine, Strychnine, Opium |
| Thorns are defence of? | Acacia, Cactus |
| Gause Principle? | Two closely related species with same resources cannot co-exist indefinitely |
| Abingdon tortoise — why extinct? | Goats introduced (greater browsing efficiency) |
| Competitive release means? | Restricted species expands when superior competitor removed |
| Connell experiment showed? | Balanus excludes Chthamalus |
| MacArthur studied? | 5 warbler species on same tree — resource partitioning |
| Resource partitioning promotes? | Co-existence |
| Herbivores & plants vs carnivores — who more affected by competition? | Herbivores & plants |
| Parasite adaptations? | Loss of sense organs, Adhesive organs, Loss of digestive system, High reproductive capacity |
| Cuscuta — lost what? | Chlorophyll & leaves |
| Brood parasitism example? | Cuckoo (Koel) → Crow nest ⭐⭐ |
| Eggs in brood parasitism evolved to? | Resemble host eggs in size & colour |
| Human liver fluke intermediate hosts? | Snail & Fish |
| Female mosquito — parasite? | No (not considered a parasite) |
| Orchid / epiphyte on Mango — what interaction? | Commensalism ⭐⭐⭐ |
| Barnacles on Whale — interaction? | Commensalism |
| Cattle Egret + Cattle — interaction? | Commensalism |
| Clownfish + Sea Anemone — interaction? | Commensalism ⭐⭐ |
| Lichens — interaction type? | Mutualism |
| Mycorrhizae — interaction type? | Mutualism |
| Fig wasp and fig tree? | Mutualism — egg-laying site for wasp, pollination for fig ⭐⭐⭐ |
| Ophrys orchid pollination? | Sexual deceit — petal resembles female bee ⭐⭐⭐ |
| Example of sexual deceit? | Ophrys and bumblebee ⭐⭐⭐ |
| Pseudocopulation done by? | Male bee on Ophrys orchid flower |
| Co-evolution example? | Ophrys + female bee colour patterns |
| Cuckoo and crow? | Brood parasitism ⭐⭐ |
| Plants offer what to pollinators? | Pollen & Nectar |
| Plants offer what to seed dispersers? | Juicy, Nutritious fruits |