AP Bio Unit 8

1. Ecosystem Interactions

Biotic Interactions

• Predation: One organism captures and consumes another (e.g., wolves preying on deer).

• Competition: Two or more species or individuals compete for limited resources like food, water, or shelter.

  • Intraspecific: Within the same species.

  • Interspecific: Between different species.

• Mutualism: Both species benefit (e.g., bees pollinating flowers).

• Commensalism: One organism benefits while the other is unaffected (e.g., barnacles on whales).

• Parasitism: One organism benefits at the expense of another (e.g., ticks feeding on mammals).

Abiotic Interactions

• Effects of nonliving factors like sunlight, temperature, water, and soil on organismal behavior, distribution, and survival.

• Adaptations to Abiotic Factors:

  • Desert plants conserve water (e.g., succulents).

  • Animals migrate or hibernate to survive seasonal changes.

2. Energy Flow and Nutrient Cycling

Energy Flow in Ecosystems

• Trophic Levels:

  • Primary Producers: Autotrophs like plants and algae (photosynthesis).

  • Primary Consumers: Herbivores feeding on producers.

  • Secondary/Tertiary Consumers: Carnivores and omnivores consuming other animals.

  • Decomposers: Break down organic material and recycle nutrients (e.g., fungi, bacteria).

• Energy Transfer:

  • ~10% of energy moves up each trophic level; the rest is lost as heat (Second Law of Thermodynamics).

  • Energy pyramids show the decrease in energy available at higher levels.

Nutrient Cycles

1. Carbon Cycle:

   • Photosynthesis removes CO2 from the atmosphere.

   • Cellular respiration, decomposition, and combustion release CO2 back into the atmosphere.

2. Nitrogen Cycle:

   • Nitrogen Fixation: Bacteria convert atmospheric N2 into usable forms (ammonia or nitrate).

   • Nitrification: Conversion of ammonia to nitrites/nitrates by bacteria.

   • Denitrification: Bacteria return nitrogen to the atmosphere.

3. Phosphorus Cycle:

   • Does not involve a gas phase; phosphorus moves from rocks to soil, water, plants, and animals.

3. Population Ecology

Population Dynamics

• Exponential Growth: Occurs under ideal conditions with unlimited resources (J-shaped curve).

• Logistic Growth: Growth slows as population approaches carrying capacity (S-shaped curve).

• Carrying Capacity (K): Maximum population size that an environment can sustain.

Factors Affecting Population Growth

• Density-Dependent Factors: Competition, predation, disease, parasitism.

• Density-Independent Factors: Natural disasters, temperature extremes, human activities.

Population Demographics:

• Age Structure: Distribution of individuals among different age groups.

• Survivorship Curves:

  • Type I: High survival in early/mid-life (e.g., humans).

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

  • Type III: High mortality in early life (e.g., fish, plants).

4. Global Change

Human Impacts on Ecosystems

• Habitat Destruction: Deforestation, urbanization, and agriculture reduce biodiversity.

• Pollution: Plastics, chemical runoff, and air pollution harm ecosystems.

• Overexploitation: Overfishing and hunting reduce population sizes and disrupt ecosystems.

• Climate Change: Rising CO2 levels drive global warming, causing altered weather patterns, melting ice, and sea level rise.

Invasive Species:

• Non-native species disrupt local ecosystems by outcompeting native species or introducing new predators.

Conservation Biology:

• Strategies to protect biodiversity include:

  • Restoration Ecology: Rehabilitating degraded ecosystems.

  • Protected Areas: National parks, wildlife reserves.

  • Sustainable Practices: Responsible resource use to minimize ecological impact.

AP-Level Practice Questions

Multiple-Choice Questions

1. Which of the following best describes the 10% rule in energy transfer within an ecosystem?

   • A. Only 10% of energy is used by producers for photosynthesis.

   • B. 10% of energy transfers to each trophic level while 90% is lost as heat.

   • C. 10% of energy is lost during respiration.

   • D. 10% of energy is stored as biomass.

   Correct Answer: B

2. What is the primary role of decomposers in an ecosystem?

   • A. Fix nitrogen into a usable form.

   • B. Convert sunlight into chemical energy.

   • C. Break down organic material to recycle nutrients.

   • D. Consume herbivores to maintain population balance.

   Correct Answer: C

3. Which survivorship curve is characterized by high early mortality followed by lower mortality rates for survivors?

   • A. Type I

   • B. Type II

   • C. Type III

   • D. Logistic growth curve

   Correct Answer: C