Chapter 11: Organism and Population

Introduction

Biological Hierarchy and Ecology

• Living world is diverse and complex with levels: macromolecules, cells, tissues, organs, organisms, populations, communities, ecosystems, biomes.
• Ecology: Study of interactions among organisms and with abiotic environment.
• Term coined by Ernst Haeckel (1866); Ramdeo Misra is Father of Ecology in India.
• Ecological hierarchy: Levels of ecological organisation; individual organism is the basic unit.

Memory Aids

• Ecology = Organism + Environment interactions.
• Hierarchy: Organism → Population → Community → Ecosystem → Biome.

Quick Checkpoints

• What is ecological hierarchy?
• Who coined the term ecology?
• Basic unit of ecological organisation?

Organism and its Environment

Organismic Ecology and Biomes

• Physiological ecology studies organism adaptations for survival and reproduction.
• Seasonal and annual precipitation variations form major biomes: desert, rainforest, tundra.
• Local variations create diverse habitats within biomes.
• Life exists in extreme habitats: deserts, rainforests, deep ocean, polar regions, thermal springs, intestines.
• Key habitat factors: temperature, water, light, soil.
• Habitat includes abiotic (physico-chemical) and biotic components (pathogens, predators, competitors).
• Organisms evolve adaptations via natural selection to optimize survival and reproduction.
• Niche: Range of tolerance, resource use, and functional role of an organism.
• Weather: short-term atmospheric conditions; Climate: long-term regional atmosphere.
• Microclimate: local climatic conditions.
• Habitat: specific locality where a community lives.
• Niche: specific part of habitat occupied by a species; no two species share the same niche.
• Niche overlap: sharing resources; Niche density: species abundance in habitat.

Memory Aids

• Habitat = Where organism lives; Niche = How organism lives.
• Weather = short term; Climate = long term.
• Niche is unique to each species.

Quick Checkpoints

• Define niche and habitat.
• Difference between weather and climate?
• What factors define a niche?

Major Abiotic Factors

Temperature

• Ranges from subzero in polar/high altitudes to >50°C in tropical deserts; thermal springs exceed 100°C.
• Affects enzyme kinetics, metabolism, activity, physiology.
• Thermal tolerance influences species distribution.
• Types by temperature tolerance:
  • Eurythermal: tolerate wide temperature range (e.g., mammals, birds, Artemesia tridentata).
  • Stenothermal: tolerate narrow temperature range (e.g., polar bear, lizards).
• Types by body temperature regulation:
  • Poikilothermal: body temp varies with environment; ectothermic (e.g., reptiles, amphibians).
  • Homoiothermal: constant body temp; endothermic (e.g., birds, mammals).
• Temperature affects photosynthesis, respiration, reproduction, growth in plants; metabolism, distribution, behavior in animals.

Water

• Water quality (pH, chemical composition) important for aquatic life.
• Salinity varies: <5 ppt inland, 30-35 ppt sea, >100 ppt hypersaline lagoons.
• Euryhaline: tolerate wide salinity range (e.g., salmon).
• Stenohaline: tolerate narrow salinity range (e.g., shark).
• Freshwater and marine animals face osmotic challenges crossing habitats.
• Terrestrial plants by moisture availability:
  • Hygrophytes: wet areas, soft stems, large leaves with hydathodes.
  • Mesophytes: moist habitats, luxuriant growth (most crops).
  • Xerophytes: dry habitats, water loss adaptations (e.g., Acacia, Casuarina).

Light

• Life processes depend on light intensity, duration, quality.
• Photosynthesis requires sunlight; shade plants adapt to low light.
• Photoperiod cues animal behavior: foraging, migration, reproduction.
• Deep oceans (>500 m) are dark; different light zones exist in lakes/oceans.

Soil

• Soil: upper weathered humus layer supporting terrestrial plants.
• Properties depend on climate, weathering, soil type (transported/sedimentary).
• Soil characteristics (composition, grain size, pH, minerals) affect vegetation.
• Soil profile: vertical layers (horizons) O, A, B, C, R.
• O horizon: organic litter; A horizon: topsoil rich in organic matter; B horizon: subsoil with clay, iron; C horizon: weathered rock; R horizon: bedrock.

Memory Aids

• Temperature: Eurythermal = wide range; Stenothermal = narrow range.
• Water: Euryhaline = wide salinity tolerance; Stenohaline = narrow.
• Soil horizons: O (organic), A (topsoil), B (subsoil), C (weathered rock), R (bedrock).

Quick Checkpoints

• Define eurythermal and stenothermal organisms.
• What are the soil horizons?
• How does salinity affect aquatic organisms?

Responses to Abiotic Factors

Homeostasis and Coping Mechanisms

• Homeostasis: maintaining internal stability despite external changes.
• Organism responses:
  • Regulators: maintain constant internal conditions (e.g., birds, mammals).
  • Conformers: internal conditions vary with environment (99% animals, most plants).
  • Partial regulators: regulate partially, conform beyond limits.
  • Migrate: move to favorable habitats temporarily.
  • Suspend: escape unfavorable conditions via hibernation, aestivation, diapause.

Memory Aids

• Regulators = constant internal state.
• Conformers = internal state matches environment.
• Partial regulators = intermediate response.
• Suspension = hibernation, aestivation, diapause.

Quick Checkpoints

• What is homeostasis?
• Difference between regulators and conformers?
• Examples of suspension strategies?

Adaptations

Plant Adaptations

• Adaptation: traits enabling survival and reproduction.
• Sun plants (heliophytes): adapted to bright sunlight.
• Shade plants (sciophytes): adapted to low light.
• Xerophytes: dry habitat adaptations; types:
  • Ephemerals (drought escapers)
  • Annuals (drought evaders)
  • Succulents (drought resistants)
  • Non-succulent perennials (drought endurers)
• Desert plants: thick cuticle, sunken stomata, CAM photosynthesis, leaf spines (e.g., Opuntia).
• Hydrophytes: mucilage-covered, reduced roots, aerenchyma present.
• Halophytes: tolerate saline soils, salt secretion, succulence, pneumatophores.

Animal Adaptations

• Adaptations can be short-term (tanning, heartbeat) or long-term (beak, claw).
• Most animal adaptations are physiological and behavioral.
• Camouflage: blending with environment to avoid detection.
• Mimicry: resemblance to another species for protection.
• Desert animals reduce water loss and tolerate arid conditions (e.g., kangaroo rat).
• Behavioral adaptations include activity timing and habitat use.

Memory Aids

• Allen's rule: shorter ears/limbs in cold climates.
• Bergman rule: larger body size in cold regions.
• Gloger's rule: darker skin in warm, humid areas.
• Jordan's rule: more vertebrae in cold-water fish.
• Rensch's rule: narrow wings in cold-area birds.

Quick Checkpoints

• Types of xerophytes?
• Difference between camouflage and mimicry?
• Examples of animal behavioral adaptations?

Populations

Population Attributes

• Population: Group of individuals of a species in a defined area sharing resources and potentially interbreeding.
• Includes asexual groups for ecological studies (e.g., bacteria in culture).
• Population has birth rate and death rate (per capita births and deaths).
• Sex ratio: Proportion of males and females in population (e.g., 60% females, 40% males).
• Age structure: Distribution of individuals in pre-reproductive, reproductive, and post-reproductive stages.
• Age pyramid types: Triangular (growing), Bell-shaped (stable), Urn-shaped (declining).
• Local population (demes): Subgroups in a specific area.
• Sister populations: Same species in different locations.
• Demography: Study of population size.

Memory Aids

• Population = Group + Interbreeding + Shared area.
• Sex ratio = % females vs males.
• Age pyramid shapes indicate growth trends.
• Demography = Population size study.

Quick Checkpoints

• What defines a population?
• How is sex ratio expressed?
• What are the three age groups in a population?
• What does a triangular age pyramid indicate?

Population Growth

Population Dynamics

• Population size changes over time due to food, predation, weather.
• Population density changes by natality (births), immigration (in), mortality (deaths), emigration (out).
• Population density = number of individuals per unit area or volume.
• Population size often estimated by indirect signs (e.g., tiger pug marks).

Memory Aids

• Population density = N.
• Increase factors: Natality + Immigration.
• Decrease factors: Mortality + Emigration.
• Indirect counting used for large populations.

Quick Checkpoints

• What factors increase population density?
• How is population density defined?
• Why use indirect methods for population size?

Growth Models

Exponential Growth

• Occurs when resources are unlimited.
• Population grows rapidly in J-shaped curve.
• Growth rate depends on intrinsic rate and current population size.

Logistic Growth

• Growth slows as population nears carrying capacity (K).
• Produces S-shaped (sigmoid) curve.
• More realistic model due to limited resources.

Memory Aids

• Exponential = unlimited growth, J-curve.
• Logistic = limited growth, S-curve, carrying capacity K.
• Carrying capacity = max population environment supports.

Quick Checkpoints

• What shape is exponential growth curve?
• What limits logistic growth?
• Define carrying capacity.

Life History Variation

Reproductive Strategies

• Populations evolve to maximize reproductive fitness (Darwinian fitness).
• Some species breed once; others breed multiple times.
• Offspring size and number vary: many small or few large.
• Life history traits adapt to habitat constraints.
• Biotic potential: max reproductive capacity in optimal conditions.
• k-selected species: large size, few offspring, long lifespan, low metabolism.
• r-selected species: small size, many offspring, short lifespan, high metabolism.

Memory Aids

• k-selected = K for "Kare" (care, fewer offspring).
• r-selected = Rapid reproduction, many offspring.
• Biotic potential = max reproduction under ideal conditions.

Quick Checkpoints

• What is biotic potential?
• Difference between k-selected and r-selected species?
• How do life history traits relate to habitat?

Population Interactions

Types of Interactions

• Intra-specific: within same species.
• Inter-specific: between different species.
• Positive interactions: mutualism, proto-cooperation, commensalism.
• Negative interactions: amensalism, competition, parasitism, predation.
• Interactions summarized by + (benefit), - (harm), 0 (neutral).

Memory Aids

• + / + = Mutualism
• - / - = Competition
• + / - = Predation or Parasitism
• + / 0 = Commensalism
• - / 0 = Amensalism

Quick Checkpoints

• What is intra-specific interaction?
• Give examples of positive interactions.
• What does + / - interaction indicate?

Predation

Predator-Prey Relationship

• Predators capture, kill, and eat prey species.
• Transfers energy to higher trophic levels and controls prey population.
• Herbivores are ecologically predators of plants.
• Invasive species spread fast due to lack of natural predators.
• Predators regulate prey populations, maintaining species diversity.
• Predators are 'prudent' to avoid overexploiting prey.
• Prey defenses: camouflage, toxicity (e.g., Monarch butterfly).
• Plants defend with thorns and chemical toxins (e.g., cardiac glycosides).

Memory Aids

• Predation = predator kills prey.
• Prey defenses: camouflage, poison.
• Plants use thorns and chemicals for defense.
• Predators maintain ecosystem balance.

Quick Checkpoints

• What is predation?
• How do prey avoid predation?
• Why are predators called prudent?

Competition

Competition Types

• Active demand for common resources by individuals of same or different species.
• Intraspecific: within species, more severe.
• Interspecific: between species, less severe.
• Competitive release: species expands range when competitor removed.
• Gause's competitive exclusion: two species cannot coexist if competing for same resource indefinitely.
• Resource partitioning: species avoid competition by using different resources or times.

Memory Aids

• Intraspecific = same species competition.
• Interspecific = different species competition.
• Competitive exclusion = no coexistence with same niche.
• Resource partitioning avoids competition.

Quick Checkpoints

• Define intraspecific competition.
• What is competitive exclusion principle?
• How do species avoid competition?

Parasitism

Parasite-Host Relationship

• Parasite obtains food from host, usually smaller and lives on/in host.
• Adaptations: loss of sense organs, adhesive organs, loss of digestive system, high reproduction.
• Ectoparasites: live on host surface (e.g., lice, ticks, Cuscuta).
• Endoparasites: live inside host (e.g., liver, blood parasites), complex life cycles.
• Brood parasitism: parasitic bird lays eggs in host nest; eggs mimic host eggs.

Memory Aids

• Ectoparasites: outside host.
• Endoparasites: inside host.
• Brood parasitism: egg mimicry in birds.

Quick Checkpoints

• What adaptations do parasites have?
• Difference between ectoparasites and endoparasites?
• What is brood parasitism?

Commensalism

One Benefits, Other Neutral

• One species benefits; other neither harmed nor benefited.
• Examples: orchid on mango, barnacles on whale, cattle egret with cattle.
• Sea anemone and clown fish: fish protected, anemone unaffected.
• Epiphytes: attach to trees but photosynthesize, called ectocommensals.

Memory Aids

• Commensalism = one benefits, other neutral.
• Epiphytes are ectocommensals.
• Classic example: cattle egret and cattle.

Quick Checkpoints

• What is commensalism?
• Give an example of ectocommensal.
• How does clown fish benefit in commensalism?

Mutualism

Mutually Beneficial Obligatory Relationship

• Both species benefit and cannot live separately.
• Examples: lichens (fungus + algae), mycorrhizae (fungi + plant roots).
• Plant-animal mutualism: pollination and seed dispersal with rewards.
• Fig tree and wasp: wasp pollinates and lays eggs; fig provides food and shelter.
• Ophrys orchid uses sexual deceit to attract bee pollinator.

Memory Aids

• Mutualism = both benefit, obligatory.
• Lichens = fungus + algae symbiosis.
• Fig-wasp = tight one-to-one pollination.
• Sexual deceit = orchid mimics female bee.

Quick Checkpoints

• What defines mutualism?
• Give examples of mutualistic relationships.
• How does fig-wasp mutualism work?

Amensalism

One Species Inhibits Another

• One species inhibits growth or survival of another without benefit or harm to itself.
• Example: Grevillea robusta produces chemicals inhibiting nearby seedlings.

Memory Aids

• Amensalism = one harmed, other unaffected.
• Example: chemical inhibition by plants.

Quick Checkpoints

• What is amensalism?
• Give an example of amensalism in plants.

Additional Note

• Protocooperation: Both benefit but can live separately (e.g., tick bird and rhinoceros).