Niche and Population dynamics

1. Key Definitions

• Habitat

  • Physical environment where an organism lives

• Population

  • Group of same species in a given area

• Biotic factors

  • Living components (plants, animals, microbes)

• Abiotic factors

  • Nonliving components (light, water, temperature, soil)

2. Ecological Niche

• Niche = organism’s role + interactions in ecosystem

  • Where it lives

  • What it eats

  • How it behaves

  • Interactions with other species

• Includes:

  • Resource use

  • Trophic role

  • Activity patterns

• Example (snail):

  • Eats plants (herbivore/decomposer role)

  • Food source for predators

3. Competitive Exclusion Principle

• No two species can occupy the same niche in the same habitat simultaneously

• Outcomes:

  • One species outcompetes the other

  • One species shifts niche (resource partitioning)

4. Population Characteristics

A. Geographic Distribution

• Range where a population lives

• Influenced by:

  • Climate

  • Resources

  • Habitat conditions

B. Demography (Population Size Changes)

• Natality → births

• Mortality → deaths

• Immigration → entering population

• Emigration → leaving population

Population growth:

• Births > deaths → increase

• Deaths > births → decrease

C. Population Density

• Number of individuals per unit area

• Measured using:

  • Sampling

  • Mark–recapture method

D. Dispersion Patterns

• Clumped → groups (most common)

• Uniform → evenly spaced

• Random → unpredictable spacing

5. Population Growth Models

A. Exponential Growth (J Curve)

• Rapid increase under ideal conditions

• Formula concept:

  • Growth rate proportional to population size

• Requirements:

  • Unlimited resources

  • No predators/disease

• Example: bacteria, invasive species

B. Logistic Growth (S Curve)

• Growth slows as resources become limited

• Stabilizes at carrying capacity (K)

• Carrying capacity (K):

  • Maximum population environment can support

6. Limiting Factors

A. Density-Dependent

• Effect increases with population size

• Includes:

  • Competition

  • Predation

  • Disease

  • Parasitism

B. Density-Independent

• Affect populations regardless of size

• Includes:

  • Weather

  • Natural disasters

  • Human activity

7. Predator–Prey Dynamics

• Cyclical relationship:

  • Prey ↑ → Predator ↑

  • Predator ↑ → Prey ↓

  • Prey ↓ → Predator ↓

8. Life History Strategies

r-Strategists

• High reproduction rate

• Short lifespan

• Little parental care

• Rapid growth (J curve)

• Examples:

  • Bacteria, insects, weeds

K-Strategists

• Low reproduction rate

• Long lifespan

• High parental care

• Stable populations (S curve)

• Examples:

  • Elephants, whales, trees

9. Carrying Capacity and Environmental Resistance

• Environmental resistance:

  • Limits population growth (food, space, disease)

• Population stabilizes when:

  • Growth rate = 0

  • Reaches carrying capacity

10. Core Ecological Principles

• Ecosystems require balance

• Populations regulated by:

  • Resource availability

  • Competition

  • Predation

• Growth patterns:

  • Unlimited → exponential

  • Limited → logistic

• Species survive by:

  • Adapting

  • Competing

  • Finding unique niches

11. Conservation Insight

• Loss of one species/resource → affects entire ecosystem

• Understanding population dynamics:

  • Helps prevent collapse

  • Supports biodiversity conservation