Unit 3: Populations

Topic 3.1: Generalist and Specialist Species

• Generalist Species:

  • Broad niches

  • Thrive in changing habitats

• Specialist Species:

  • Narrow niches

  • Advantageous in constant habitats

• Native Species:

  • Thrive in their specific ecosystem

• Nonnative Species:

  • Introduced intentionally or accidentally into an ecosystem

Topic 3.2: K- and r-Selected Species

• K-selected Species:

  • Large size

  • Few offspring per reproductive event

  • Stable environments

  • Significant energy investment per offspring

  • Long maturation and lifespan

  • Parental care is crucial

  • High competition for resources

• r-selected Species:

  • Small size

  • Many offspring

  • Minimal energy investment per offspring

  • Early maturation and short lifespan

  • Reproduce once or very few times

  • Low competition for resources

• Biotic Potential:

  • Maximum reproductive rate under ideal conditions

• Invasive Species:

  • More adversely affects K-selected species compared to r-selected species

Topic 3.3: Limits of Population Growth

• Population: A group of interbreeding individuals of the same species.

• Population Size: Number of individuals at a given time.

• Distributions:

  • Clumped

  • Uniform

  • Random

• Growth Variables:

  • Birth

  • Death

  • Immigration (moving into a population)

  • Emigration (exiting a population)

Topic 3.4: Survivorship Curves

• Survivorship Curve: Indicates survival rates from birth to maximum age for a cohort (group of same age).

• Types of Curves:

  • Type I: K-selected species (e.g., humans) typically have high survivorship until old age followed by high mortality.

  • Type II: Constant mortality rate throughout life (e.g., birds).

  • Type III: High mortality early in life (e.g., trees, r-selected species).

Topic 3.5: Carrying Capacity

• Carrying Capacity (K): Maximum sustainable population size for a species in a habitat.

• Overshoot: Occurs when the population exceeds K, leading to dieback.

• Environmental Resistance: Sum of all limiting factors (e.g., sunlight, water, nutrients, predators).

Topic 3.6: Population Growth and Resource Availability

• Limited by environmental factors and resource availability.

• Abundance of resources can accelerate growth; limited resources lead to mortality and decreased fecundity.

• J-Shaped Curve: Exponential growth, exceeding carrying capacity.

• S-Shaped Curve: Logistic growth, fluctuating around carrying capacity.

Topic 3.7: Age Structure Diagrams

• Analysis of growth rates through age structure shapes:

  • Rapid growth has a higher proportion of youth.

• Age Structure Categories:

  • Pre-Reproductive: Ages 0-14

  • Reproductive: Ages 15-44

  • Post-Reproductive: Ages 45+

• Notable Trends: Aging populations in developed countries (e.g., US Baby Boomers).

Topic 3.8: Total Fertility Rate (TFR)

• Influenced by:

  • Age of first childbirth

  • Educational opportunities for women

  • Access to family planning and healthcare

• Replacement-Level Fertility Rates: Average number needed to replace population (2.1 to maintain stability).

• Notable Trends: Global TFR dropped from 5.0 to 2.5 from 1955 to 2017.

Topic 3.9: Human Population Dynamics

• Influencing factors:

  • Birth and death rates

  • Access to family planning and healthcare

  • Environmental limits (Earth's carrying capacity)

  • Density-independent factors (natural disasters)

  • Density-dependent factors (resource availability)

• Rule of 70: Used to estimate population doubling time by dividing 70 by growth rate percentage.

Topic 3.10: Demographic Transition

• Transition from high to low birth and death rates as countries develop.

• Characteristic stages:

  1. Preindustrial: High birth and death rates, slow growth.

  2. Early Transitional: Death rates drop; population grows.

  3. Late Transitional: Birth rates decline; rapid growth continues.

  4. Industrial: Both rates drop; growth slows.

  5. Postindustrial: Population stabilizes or declines.

Topic 3.11: Women in the World

• Education and empowerment correlate with lower fertility rates.

• Statistics show disparities:

  • 30% of girls in secondary education

  • Women work 66% of hours but earn only 10% of income

  • Women as 70% of global poor and 66% of illiterate adults.

• Family planning initiatives aim to educate and empower women.