Overview
This lecture introduces ecological range of tolerance, explains how environmental conditions affect species survival, and offers strategies for writing strong, specific answers on this topic in free-response questions (FRQs).
Ecological Range of Tolerance
- Ecological tolerance is the range of environmental conditions (e.g., temperature, salinity, pH, sunlight) an organism or species can endure before injury or death.
- Both species and individuals have their own specific tolerance ranges for different environmental factors.
- Example: Salmon species tolerate temperatures from 6–22°C, but individuals may have slightly different limits due to genetic variation.
- Genetic diversity within a species increases a population's resilience to environmental changes, like global warming.
Zones within Range of Tolerance
- The optimal zone is where organisms thrive; they survive, grow, and reproduce with the highest population numbers.
- The range of physiological stress is where organisms can survive but experience stress, such as infertility, lack of growth, or reduced activity.
- The zone of intolerance is where conditions cause organism death, often due to specific factors like thermal shock or lack of resources.
Writing Tips for FRQs: Ecological Tolerance
- When discussing a disturbance (human or natural), connect it to ecological range of tolerance for a more complete answer.
- Stronger answers link disturbances to climate change, such as how increased CO₂ levels raise global temperatures.
- Explain how moving outside tolerance ranges leads to population decline or die-offs.
Adding Specificity to FRQs
- Instead of just saying organisms died, cite the specific physiological stress causing mortality (e.g., suffocation, thermal shock, dehydration).
- Example: Global warming → warmer water → less dissolved oxygen → fish suffocate.
- Example: Drought → reduced rainfall → less soil moisture → plants can't absorb water → plants die.
Key Terms & Definitions
- Ecological tolerance — The range of environmental conditions an organism or species can endure before injury or death.
- Optimal zone — The range of conditions where a species thrives, grows, and reproduces.
- Range of physiological stress — Conditions where survival is possible but organisms experience stress and reduced performance.
- Zone of intolerance — Conditions outside tolerance where organisms cannot survive.
- Genetic diversity — Variation in genes among individuals in a population, increasing resilience to change.
- Physiological stressor — A specific cause (e.g., lack of oxygen, thermal shock) that impairs survival or reproduction.
Action Items / Next Steps
- Practice reading the provided passage on salmon thermal tolerance.
- Identify and write one sentence stating the author’s claim in testable hypothesis form.