Chapter 27: Population Growth and Regulation

Introduction to Population Concepts

• Understanding changes in population size:
  • Births and deaths affect population size.
  • Immigration (individuals coming in) and emigration (individuals leaving).
  • Population: all members of a species living in a particular area.

Mathematical Concepts of Population Growth

• Growth rate (R):
  • Calculated as birth rate minus death rate.
  • Positive growth rate: more births than deaths.
  • Negative growth rate: more deaths than births.
• Population growth (G):
  • Number of individuals added = growth rate x initial population size.
• Exponential growth:
  • Constant positive growth rate results in a J-shaped curve.

Biotic Potential

• Maximum rate a population can grow.
• Influenced by factors such as:
  • Age of reproduction.
  • Frequency of reproduction.
  • Number of offspring per reproduction.
  • Reproductive lifespan.
• Low biotic potential: slower population growth.

Environmental Resistance and Carrying Capacity

• Environmental resistance:
  • Factors that limit population growth.
  • Living sources: predation, competition.
  • Non-living sources: natural events (e.g., weather, wildfires).
• Boom and bust cycles:
  • Rapid growth followed by a sudden die-off, often cyclic.
• Carrying capacity (K):
  • Maximum population environment can support.
  • Logistic growth results in an S-shaped curve.

Density Factors

• Density-independent factors:
  • Affect population size regardless of density (e.g., climate).
• Density-dependent factors:
  • More intense as population density increases (e.g., predation, competition).
• Intraspecific vs. interspecific competition:
  • Intraspecific: within same species.
  • Interspecific: between different species.

Life History Strategies

• R-selected species:
  • Rapid reproduction in unpredictable environments.
  • Short lifespan, many offsprings, little parental care.
• K-selected species:
  • Stable environments, slow maturation.
  • Long lifespan, fewer offspring, significant parental care.
• Survivorship curves:
  • Constant loss, early loss, and late loss patterns.

Spatial Distribution of Populations

• Distribution patterns:
  • Uniform, random, and clumped.
• Advantages and disadvantages of each pattern.

Human Population Changes

• Historical context:
  • Small populations for millennia.
  • Technological and agricultural advancements increased populations.
  • Industrial Revolution and medical advances (e.g., antibiotics) accelerated growth.
• Replacement Level Fertility (RLF):
  • Average of two children per couple.
• Population stages:
  • Pre-industrial: balanced birth and death rates.
  • Transitional: high birth, declining death rates.
  • Industrial: lower birth and death rates.
  • Post-industrial: low birth and death rates.
• Population growth and structure:
  • Rapid growth: broader base.
  • Stable growth: straight sides.
  • Declining growth: narrow base.

Ecological Footprint and Future Implications

• U.S. population:
  • Large ecological footprint due to high resource consumption.
• Implications for future planetary stability.