Human ecology 1

What is ecology?

Ecology is the scientific study of the relationships between organisms and their environment, including both biotic (living) and abiotic (non-living) components that influence survival, reproduction, and adaptation.

What is human ecology?

Human ecology examines how humans interact with their biological, social, and physical environments, including how humans adapt to and modify their surroundings.

What is meant by ‘environment’ in ecology?

The environment refers to the external conditions, resources, and stimuli with which an organism interacts, influencing its survival and reproduction.

What are the main branches or subfields of ecology?

• Autecology: The study of individual species and their adaptations.

• Synecology: The study of groups of organisms in relation to their environment (communities and ecosystems).

• Human ecology: The study of humans as biological organisms within ecological systems.

What are abiotic and biotic factors?

• Abiotic factors: Non-living environmental components such as temperature, light, water, and nutrients.

• Biotic factors: Living components, including other organisms (predators, prey, competitors, symbionts).

What is the ecological hierarchy from smallest to largest?

1. Individual (organism)

2. Population

3. Community

4. Ecosystem

5. Biome

6. Biosphere

What is an ecosystem?

An ecosystem is a biological system composed of interacting organisms (biotic) and their physical environment (abiotic), connected by energy flow and nutrient cycles.

How does energy flow through an ecosystem?

• Energy enters via photosynthesis (producers convert sunlight into chemical energy).

• It moves through trophic levels: producers → consumers → decomposers.

• Energy is lost as heat at each level (Second Law of Thermodynamics).

• Diagrammatically shown as a pyramid of energy flow.

What is nutrient cycling?

The continuous movement of elements like carbon, nitrogen, and phosphorus between living organisms and the environment via biogeochemical cycles.

What is carrying capacity (K)?

The maximum population size that an environment can sustain indefinitely, determined by resource availability and environmental constraints.

What is human carrying capacity?

The number of humans that Earth can sustainably support, depending on resource consumption, technology, and environmental impact.

What is evolution?

Evolution is the change in genetic composition of a population over successive generations, driven by mechanisms such as mutation, selection, gene flow, and drift.

Who first proposed the theory of natural selection?

Charles Darwin and Alfred Russel Wallace independently proposed natural selection as the primary mechanism of evolution.

What is natural selection?

The process by which individuals with advantageous traits survive and reproduce more successfully than others, leading to the increase of those traits in the population over time.

What are the key conditions for natural selection?

• Variation: Individuals differ in traits.

• Heritability: Traits are genetically inherited.

• Differential reproduction: Individuals with beneficial traits reproduce more.

• Change over time: Traits that enhance fitness become more common.

What is adaptation?

A heritable trait that enhances an organism’s ability to survive and reproduce in a particular environment.

What is fitness?

In evolutionary biology, fitness refers to the relative reproductive success of an individual — how well its traits contribute to survival and reproduction compared to others.

What are the types of natural selection?

• Directional selection: Favors one extreme phenotype.

• Stabilizing selection: Favors intermediate traits, reducing variation.

• Disruptive selection: Favors both extremes, increasing variation.

What is sexual selection?

A form of natural selection that arises from differences in mating success, favoring traits that increase attractiveness or competition for mates (e.g., peacock tails, human courtship displays).

What is gene flow?

The exchange of genetic material between populations due to migration, which can increase variation and reduce genetic differences between groups.

What is genetic drift?

Random changes in allele frequencies due to chance events, especially in small populations, leading to loss of genetic variation.

What is mutation?

A change in DNA sequence, creating new genetic variation that serves as raw material for evolution.

What is the difference between microevolution and macroevolution?

• Microevolution: Small-scale genetic changes within a population.

• Macroevolution: Large-scale changes that result in the formation of new species.

What is speciation?

The process by which new species arise due to reproductive isolation and divergent evolution.

What are adaptive radiations?

Rapid diversification of a single ancestral species into many new species, each adapted to a different ecological niche (e.g., Darwin’s finches).

What is convergent evolution?

When unrelated species evolve similar traits due to similar environmental pressures (e.g., wings in bats and birds).

What is coevolution?

Mutual evolutionary influence between two interacting species (e.g., predator–prey, pollinator–plant relationships).

What is human evolution?

The process of biological and cultural change in humans over time, shaped by natural selection, environmental pressures, and cultural behaviors.

What is adaptation in human ecology?

A process by which humans adjust physiologically, genetically, behaviorally, or culturally to environmental conditions.

What are the main types of human adaptation?

1. Genetic adaptation – evolutionary change through natural selection.

2. Developmental adaptation – irreversible changes during growth (e.g., lung capacity at altitude).

3. Acclimatization (physiological) – reversible changes to short-term environment.

4. Cultural adaptation – behavioral changes through technology, shelter, clothing, etc.

What is Bergmann’s Rule?

In cold climates, populations of a species tend to have larger body sizes to conserve heat; in warm climates, smaller bodies dissipate heat more effectively.

What is Allen’s Rule?

Populations in cold climates have shorter limbs and extremities to reduce heat loss, while those in hot climates have longer limbs to increase heat dissipation.

What are examples of human thermoregulation adaptations?

• Cold adaptation: Increased basal metabolic rate (BMR), vasoconstriction, fat insulation.

• Heat adaptation: Sweating, vasodilation, lower BMR.

• Cultural adaptation: Clothing, shelter, and fire use.

How have humans adapted to high altitudes?

• Physiological: Increased red blood cell production, higher ventilation rate.

• Developmental: Larger chest size and lung capacity in native populations (e.g., Andes, Himalayas).

• Cultural: High-altitude agriculture, dietary adjustments.

How have humans adapted to solar radiation?

• Skin pigmentation: Balances protection from UV damage and vitamin D synthesis.

• Melanin: Acts as a natural sunscreen, preventing folate degradation.

How do folate and vitamin D relate to skin color evolution?

• High UV: Darker skin protects folate from UV degradation.

• Low UV: Lighter skin enhances vitamin D synthesis to prevent rickets.
  This demonstrates evolutionary compromise between folate protection and vitamin D production.

What is population ecology?

Population ecology studies the size, density, distribution, and growth of populations and how they interact with their environment.

What factors influence population size?

• Birth rate (natality)

• Death rate (mortality)

• Immigration

• Emigration

Population change = (births + immigration) − (deaths + emigration).

What are density-dependent and density-independent factors?

• Density-dependent factors: Effects increase with population density (e.g., competition, predation, disease).

• Density-independent factors: Effects are unrelated to density (e.g., temperature, natural disasters).

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What are the patterns of population growth?

1. Exponential growth: Rapid increase under unlimited resources; represented by a J-shaped curve.

2. Logistic growth: Growth slows as population approaches carrying capacity (K); forms an S-shaped curve.

What is environmental resistance?

Environmental factors (predation, limited food, disease, competition) that limit population growth and prevent indefinite exponential increase.

What is ecological succession?

The gradual change in community composition over time following disturbance or formation of new habitat.

• Primary succession: Starts on bare rock (e.g., volcanic island).

• Secondary succession: Occurs in previously occupied areas after disturbance (e.g., fire, flood).

What are biomes?

Large-scale ecological units defined by climate, vegetation, and fauna, such as tropical rainforest, desert, tundra, and grassland.

How does latitude affect biome distribution?

Climate and vegetation vary with latitude:

• Near the equator: tropical forests (high temperature and rainfall).

• Mid-latitudes: grasslands and temperate forests.

• High latitudes: tundra and polar deserts.
  This pattern is driven by solar radiation and precipitation.

How does altitude mimic latitude in biome distribution?

As altitude increases, temperature and air pressure decrease, producing vertical zonation similar to latitudinal gradients — e.g., tropical → temperate → alpine → snowline on mountains.

What are trophic levels?

Hierarchical levels of energy transfer in an ecosystem:

1. Producers (autotrophs) – capture energy via photosynthesis.

2. Primary consumers (herbivores).

3. Secondary and tertiary consumers (carnivores).

4. Decomposers – recycle nutrients from dead matter.

What is an energy pyramid?

A diagram showing the amount of energy available at each trophic level — energy decreases by ~90% between levels due to metabolic heat loss.

What are food chains and food webs?

• Food chain: Linear sequence of feeding relationships.

• Food web: Complex, interconnected feeding network showing real ecological relationships.

What is the Second Law of Thermodynamics in ecology?

Energy transformations are inefficient — some energy is always lost as heat, meaning ecosystems require constant energy input (sunlight) to sustain life.

What is homeostasis in ecology?

The tendency of ecosystems to maintain stability through internal feedback mechanisms that resist change.

What is a feedback system?

A self-regulating process in which the output of a system feeds back into the system to influence its subsequent behavior.

What is negative feedback?

A stabilizing mechanism that counteracts deviations from equilibrium — e.g., body temperature regulation, predator-prey cycles.