Limiting Factors Have Ranges of Tolerance
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
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.
- Measure soil pH at each quadrat, analyze correlations between soil pH and plant distribution
Using Sensors to Measure Abiotic Variables
- Advantages
- Accuracy: Minimizes human error.
- Continuous Data Logging: Records long-term trends (e.g., temperature, light).
- Portability: Sensor devices are easy to transport and use in the field.
A light intensity sensor can quantify how much sunlight penetrates a forest canopy, explaining the distribution of shade-tolerant plants on the forest floor.
Common MistakeA common mistake when using sensors is neglecting to calibrate them before use. Always ensure sensors are properly calibrated to obtain accurate readings.
Real-World Applications of Tolerance Ranges
- Conservation Biology
- Predicting how species migrate or adapt under climate change.
- Identifying when a habitat’s conditions exceed a species’ tolerance range.
- Agriculture: Selecting crop varieties suited to local soil pH or climate, improving yield.
- Disease Control: Targeting vectors (e.g., mosquitoes) within their optimal conditions to reduce disease spread.
- How might the concept of tolerance ranges challenge the idea of fixed species distributions?
- Consider how human activities, such as urbanization or climate change, might alter the abiotic factors that define these ranges.
Investigating Tolerance in Semi-Natural Habitats
- Transect Studies
- Use soil pH or light sensors to measure environmental gradients across meadows, forest edges, or pond margins.
- Correlate species distribution with data to see how limiting factors shape community composition.
- Insight: Field work reveals how environmental filters determine which species flourish, survive at the margins, or fail beyond their tolerance limits.
What abiotic variable would you expect to have the greatest influence on plant distribution in a coastal dune ecosystem? Why?
