UNIT 3 5 for 5

Chapter Summary

• Populations in ecosystems change over time in response to environmental factors.

• Populations are limited by resource availability and space.

• Focus on both natural and human populations.

Key Ideas

• Populations change over time due to various factors.

• Human populations also change in reaction to social and cultural factors.

Key Terms

• Age-structure diagrams: Visual representations showing the distribution of various age groups in a population.

• Biotic potential: The maximum number of offspring a species can produce under ideal conditions.

• Carrying capacity: The maximum number of organisms an ecosystem can support over time.

• Demographic transition: Changes in population growth as a country develops economically.

• Population overshoot: Occurs when a population exceeds its carrying capacity.

• R-selected species: Species that produce many offspring with little to no parental care, typically adapted to unstable environments.

• Rule of 70: A formula to estimate the doubling time of a population based on its growth rate.

• Specialist: A species that has specific habitat and dietary requirements.

• Total fertility rate (TFR): Average number of children a woman will have in her lifetime, based on current age-specific fertility rates.

• Density-dependent factors: Influences on population growth that change as the density of the population changes.

• Density-independent factors: Influences on population growth that occur regardless of the population density.

• Type I survivorship curve: Characterized by high survival rates until old age (e.g., humans).

• Generalist: A species that can thrive in a wide variety of environmental conditions and can make use of a variety of resources.

• Type II survivorship curve: Mortality rate is constant regardless of age (e.g., songbirds).

• Infant mortality rate: The number of infants dying before their first birthday per 1,000 live births.

• Type III survivorship curve: High mortality rate for the young (e.g., frogs).

• K-selected species: Organisms that produce few offspring with significant parental investment, often found in stable environments.

Generalist and Specialist Species

• Generalist species:

  • Adaptable to changing habitats.

  • Example: can change diet if food availability changes.

• Specialist species:

  • Require specific conditions and food sources.

  • More vulnerable to changes in the environment.

k-Selected vs. r-Selected Species

• k-Selected species (Kangaroo):

  • Characteristics:

  • Large size.

  • Few offspring per year.

  • Long parental care (11-18 months).

  • Stable environments.

  • Specialized diet.

  • Long lifespan (12-18 years).

• r-Selected species (Cockroach):

  • Characteristics:

  • Small size.

  • High number of offspring (up to 16 eggs at a time).

  • Short lifespan (about six months).

  • Mature quickly and reproduce often.

  • Minimal or no parental care.

Biotic Potential

• The theoretical maximum reproductive rate of a population.

• Graph representation: Exponential growth represented as the letter J (Figure 7.1).

• Example: Roaches have high biotic potential vs. kangaroos, which have low biotic potential.

Survivorship Curves

• Type I:

  • Characteristic of k-selected species.

  • E.g., humans; high survival in early life stages.

• Type II:

  • Constant mortality rate throughout life.

  • E.g., songbirds.

• Type III:

  • Characteristic of r-selected species.

  • E.g., frogs; high mortality in young.

Carrying Capacity

• Definition: The number of organisms an ecosystem can sustainably support.

• Graph usually shows population growth in relation to its carrying capacity (Figure 7.3).

• Possible outcomes:

  • Population overshoot leads to dieback.

  • Lag time before the decline appears due to reproductive time lag.

Population Growth and Resource Availability

• Populations grow when resources are abundant and decline when scarce.

• Dieback occurs if:

  • Limited resources prevent reproduction.

  • Decreased reproductive rates.

• Percent change formula:
  $\text{Percent change} = \frac{\text{New value} - \text{Old value}}{\text{Old value}} \times 100\%$

• Positive result indicates population increase; negative indicates decrease.

Age-Structure Diagrams

• Graphical representations with:

  • X-axis: size of population (in numbers or percentages).

  • Left side: males; right side: females; bottom: children; top: elderly.

• Types of Growth:

  • Rapid Growth: Characterized by a broad base (e.g., Kenya).

  • Slow Growth: More column-shaped pyramid (e.g., USA).

  • Zero/Stable Growth: Similar number of children and adults (e.g., Japan).

  • Declining/Negative Growth: Fewer children than adults (e.g., Germany).

Total Fertility Rate (TFR)

• Definition: Total number of children a woman is likely to have during her lifetime given current age-specific fertility rates.

• Influenced by:

  • Age of first childbirth.

  • Availability of education and healthcare.

  • Use of birth control.

• TFR of 2.0 indicates replacement-level fertility stabilizing population growth.

Infant Mortality Rate

• Definition: Number of infants dying before age one per 1,000 live births.

• High rates indicate poor health care and nutrition.

• In developing nations, high infant mortality leads to higher TFR as families have more children to ensure some survive.

Human Population Dynamics

• Influenced by:

  • Birth rates.

  • Death rates.

  • Access to healthcare.

  • Education, especially for women and girls.

  • Age of marriage.

• Malthusian Theory (1798):

  • Proposed that population grows exponentially while food grows linearly leading to eventual resource shortages.

Density-Dependent and Density-Independent Factors

• Density-dependent factors:

  • Increase in impact as population grows (e.g., diseases).

• Density-independent factors:

  • Affect populations regardless of density (e.g., natural disasters).

Rule of 70

• Formula:
  $\text{Number of years to double} = \frac{70}{\text{annual percentage growth rate}}$

• Used to determine how quickly a population will double in size.

Demographic Transition Model

• Framework for understanding population changes across four stages:

  • Stage 1: Preindustrial, high birth and death rates.

  • Stage 2: Transitional, high birth rates, decreasing death rates.

  • Stage 3: Industrial, declining birth rates and steady death rates.

  • Stage 4: Postindustrial, low birth rates, low death rates, declining population.

Review Questions and Answers

• Multiple-Choice Questions: Test understanding of concepts related to population dynamics.

• Free-Response Questions: Require identification and explanation of r- and k-selected species, calculations of percent change, and description of survival curves.

Important Concepts Review

• Generalist vs. Specialist: Generalists are adaptable; specialists have specific needs.

• K-selected vs. r-selected: K-selected species have low reproductive rates and invest in offspring; r-selected species reproduce quickly with little care.

• Biotic potential, carrying capacity, and population dynamics are crucial for understanding ecological stability and changes in population sizes.