Organisms and Populations — Revision Notes

⚡ 30-Second Revision

Organism — Individual unit, adapts to environment.
Population — Group of same species in an area.
Abiotic Factors — Temperature, water, light, soil.
Adaptations — Morphological (structure), Physiological (function), Behavioral (action).
Regulators — Maintain homeostasis (e.g., mammals, birds).
Conformers — Internal environment changes with external (most plants, animals).
Responses — Migration, Hibernation (winter sleep), Aestivation (summer sleep), Diapause (suspended development).
Population Attributes — Density ($N$), Natality ($b$), Mortality ($d$), Sex Ratio, Age Distribution.
Exponential Growth (J-curve) — Unlimited resources. $dN/dt = rN$. $N_t = N_0 e^{rt}$.
Logistic Growth (S-curve) — Limited resources, reaches Carrying Capacity ($K$). dN/dt = rN left(\frac{K-N}{K}\right). Max growth at $N=K/2$.
Interspecific Interactions

- Predation: (+/-) Tiger-deer. - Competition: (-/-) Two species for same resource. Gause's Principle, Resource Partitioning. - Parasitism: (+/-) Lice on humans, Cuckoo-crow (brood parasitism). - Commensalism: (+/0) Orchid on mango, Barnacles on whale. - Mutualism: (+/+) Lichens, Mycorrhizae, Fig-wasp. - Amensalism: (-/0) Penicillin-bacteria.

2-Minute Revision

This chapter covers how individual organisms cope with environmental challenges and how populations of a single species behave. Organisms adapt to abiotic factors like temperature, water, light, and soil through structural (morphological), functional (physiological), or behavioral changes.

Some organisms are 'regulators,' maintaining a constant internal state, while most are 'conformers,' allowing their internal state to fluctuate. Under stress, organisms may migrate, hibernate, aestivate, or enter diapause.

Populations are characterized by density, birth rate (natality), death rate (mortality), sex ratio, and age distribution. Population growth can be exponential (J-shaped curve) with unlimited resources, or logistic (S-shaped curve) when resources are limited, eventually stabilizing at the carrying capacity ($K$).

Crucially, species interact in various ways: predation (one benefits, one harmed), competition (both harmed), parasitism (one benefits, one harmed), commensalism (one benefits, one neutral), mutualism (both benefit), and amensalism (one harmed, one neutral).

Remember key examples for each interaction and the implications of Gause's Competitive Exclusion Principle and resource partitioning.

5-Minute Revision

Begin by recalling the hierarchy of ecological organization: organism, population, community, ecosystem, biome, biosphere. Focus on the first two. For 'Organisms,' remember how individuals respond to abiotic factors (temperature, water, light, soil).

Distinguish between 'regulators' (e.g., mammals, birds maintaining homeostasis) and 'conformers' (most plants and animals whose internal conditions match external). Note temporary responses like migration (e.

g., Siberian cranes), and dormancy states like hibernation (winter sleep, e.g., bears), aestivation (summer sleep, e.g., snails), and diapause (suspended development, e.g., zooplankton). Adaptations can be morphological (e.

g., desert plants with thick cuticles), physiological (e.g., high altitude sickness adaptation), or behavioral (e.g., desert lizards basking).

For 'Populations,' understand their attributes: population density ($N$), natality (birth rate), mortality (death rate), immigration, emigration, sex ratio, and age distribution (represented by age pyramids).

Population growth models are critical: Exponential growth (J-shaped curve) occurs with unlimited resources, described by $dN/dt = rN$ or $N_t = N_0 e^{rt}$. Logistic growth (S-shaped curve) is more realistic, considering limited resources and environmental resistance, stabilizing at the **carrying capacity ($K$)**.

The equation is dN/dt = rN left(\frac{K-N}{K}\right). Remember that the maximum growth rate in logistic growth occurs when $N = K/2$. Also, differentiate between r-selected (many small offspring, short lifespan) and K-selected species (few large offspring, long lifespan).

Finally, master interspecific interactions:

Predation (+/-) — Lion and deer.
Competition (-/-) — Two species for same food. Remember Gause's Competitive Exclusion Principle and resource partitioning.
Parasitism (+/-) — Tapeworm in human, Cuckoo and crow (brood parasitism).
Commensalism (+/0) — Orchid on mango tree, Barnacles on whale.
Mutualism (+/+) — Lichens, Mycorrhizae, Fig and fig wasp.
Amensalism (-/0) — Penicillin inhibiting bacteria. Focus on specific examples for each interaction type.

Prelims Revision Notes

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Ecology — Study of interactions between organisms and environment.
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Levels of Organization — Organism $\rightarrow$ Population $\rightarrow$ Community $\rightarrow$ Ecosystem $\rightarrow$ Biome $\rightarrow$ Biosphere.
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Abiotic Factors — Temperature (most important), Water, Light, Soil.

* Eurythermal/Stenothermal: Wide/narrow temperature tolerance. * Euryhaline/Stenohaline: Wide/narrow salinity tolerance.

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Responses to Abiotic Stress

* Regulate: Maintain homeostasis (e.g., mammals, birds). Energetically expensive. * Conform: Internal conditions change with external (most plants, 99% animals). * Partial Regulators: Regulate over a limited range.

* Migration: Temporary movement to favorable areas (e.g., Siberian cranes). * Suspension: Dormancy. * Hibernation: Winter sleep (e.g., bears). * Aestivation: Summer sleep (e.g., snails, fish).

* Diapause: Suspended development (e.g., zooplankton).

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Adaptations — Evolutionary changes for survival.

* Morphological: Structural (e.g., desert plants with thick cuticle, sunken stomata; polar bear fur). * Physiological: Functional (e.g., kangaroo rat internal water production; high altitude RBC increase). * Behavioral: Actions (e.g., desert lizard basking/burrowing).

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Population Attributes

* **Density ($N$)**: Number of individuals per unit area/volume. * **Natality ($b$)**: Birth rate. * **Mortality ($d$)**: Death rate. * **Immigration ($I$)**: Influx of individuals. * **Emigration ($E$)**: Outflux of individuals. * Population change: $N_{t+1} = N_t + [(b+I) - (d+E)]$. * Sex Ratio: Males:Females. * Age Pyramids: Pre-reproductive, Reproductive, Post-reproductive groups. Indicate growth status (expanding, stable, declining).

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Population Growth Models

* Exponential Growth (J-shaped): Unlimited resources. $dN/dt = rN$. $N_t = N_0 e^{rt}$. $r$ = intrinsic rate of natural increase. * Logistic Growth (S-shaped): Limited resources, environmental resistance. dN/dt = rN left(\frac{K-N}{K}\right). $K$ = Carrying Capacity. Max growth at $N=K/2$.

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Life History Variations — r-selected (many small offspring, short life) vs. K-selected (few large offspring, long life).
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Interspecific Interactions

* Predation (+/-): Predator benefits, prey harmed. Important for energy transfer, population control. * Competition (-/-): Both harmed. Gause's Competitive Exclusion Principle (no two species can coexist if competing for identical resources).

Resource Partitioning (coexistence by niche differentiation). * Parasitism (+/-): Parasite benefits, host harmed. Ectoparasites (on surface), Endoparasites (inside). Brood parasitism (e.g., cuckoo).

* Commensalism (+/0): One benefits, other unaffected (e.g., orchid on mango, barnacles on whale). * Mutualism (+/+): Both benefit (e.g., lichens, mycorrhizae, fig-wasp). * Amensalism (-/0): One harmed, other unaffected (e.

g., penicillin mold, black walnut tree).

Vyyuha Quick Recall

To remember the types of interspecific interactions and their outcomes:

Predation: Plus/Minus (Predator gains, Prey loses) Competition: Crash/Crash (Both lose) Parasitism: Plus/Minus (Parasite gains, Host loses) Commensalism: Cool/Neutral (One gains, other unaffected) Mutualism: Mutually Beneficial (Both gain) Amensalism: Affected/Neutral (One loses, other unaffected)

PCP CMA (like a doctor's certification + a common abbreviation) helps recall the interaction types, and the 'outcome words' help remember the +/-/0 effects.