Limiting Factors Have Ranges of Tolerance
Definition
Range of tolerance
Each species survives within specific minimum and maximum values of certain abiotic factors, its range of tolerance. Outside this range, survival is impossible.
- Within the tolerance range lies an optimal zone for growth, reproduction, and overall success.
- Temperature: Polar bears thrive in Arctic cold but perish in tropics, tropical frogs die in freezingconditions.
- Soil pH: Blueberries prefer acidic soils (pH 4–5) and struggle in neutral/alkaline soils.
- Light Intensity: Shade-loving ferns wilt under intense sunlight, whereas sunflowers require bright, directlight.
Limiting Factors and Their Role in Distribution
Definition
Limiting factor
A limiting factor is any abiotic or biotic variable that restricts a species’ growth, reproduction, or distribution if it goes beyond the species’ tolerance range.
- Key Abiotic Limiting Factors
- Temperature: Influences enzyme activity and metabolism.
- Water Availability: Too little or too much can hamper survival.
- Light Intensity: Critical for photosynthesis and animal visibility.
- Soil pH/Salinity: Affects nutrient availability and water uptake.
- Oxygen Levels: Essential in aquatic habitats, where oxygen solubility changes with temperature.
When analyzing species distributions, focus on the limiting factor that most deviates from the species’ tolerance range.
Investigating Tolerance Using Transects
- Purpose: Transects help ecologists study how species distributions correlate with abiotic factors over an environmental gradient.
- Types of Transects
- Line Transect: A tape is laid out, organisms touching the line are recorded.
- Belt Transect: A wider strip is assessed, often using quadrats to estimate abundance.
- Observational Transect: An observer walks a defined route noting target species.
- Example: Correlating Plant Distribution with Soil pH
- Lay a belt transect along a slope transitioning from acidic to neutral soil.
- Place quadrats at regular intervals, record plant species and abundance.
