Ecological tolerance is the range of environmental conditions (temperature, salinity, light, flow rate, etc.) a species or individual can survive in before injury or death—think optimal range, zone of physiological stress, and zones of intolerance (Shelford’s Law of Tolerance). Some species are eurythermal or euryhaline (wide tolerance); others are stenothermal or stenohaline (narrow tolerance). Concepts like acclimation/acclimatization and critical thermal maximum/minimum show how organisms respond to short- or long-term change. You need this for APES because Topic 2.4 (ERT-2.F) is tested: it links tolerance to ecological niches, species distributions, and responses to disturbances and climate change—common multiple-choice and free-response themes. Review the CED keywords and examples so you can explain how shifting temps or salinity change species ranges. For a focused review, see the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz). For broader Unit 2 review and practice Qs, check the unit page (https://library.fiveable.me/ap-environmental-science/unit-2) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Ecological tolerance is the range of abiotic conditions an organism can survive. For an individual, tolerance is physiological: it has an optimal range, a zone of physiological stress, and limits where injury or death occur (think tolerance curves and Shelford’s Law of Tolerance). Individuals can shift their personal curve short-term by acclimation or acclimatization (e.g., a person adjusting to heat). For a species, tolerance describes the combined range across all individuals and populations—it’s broader because genetic variation and local adaptations let some members survive conditions others can’t. So a species may be eurythermal (wide temp. range) even if some individuals are stenothermal (narrow). Same idea for salinity: euryhaline vs stenohaline. This distinction matters on the AP exam: know terms like optimal range, zone of physiological stress, critical thermal max/min, acclimation vs adaptation, and how tolerance shapes a species’ ecological niche (see the Topic 2.4 study guide for review: https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz). For more practice, check Unit 2 and the practice bank (https://library.fiveable.me/ap-environmental-science/unit-2; https://library.fiveable.me/practice/ap-environmental-science).

Short answer: it’s not just temperature. Ecological tolerance is the range of environmental conditions (temperature, salinity, flow rate, sunlight, etc.) an organism can endure before injury or death—Shelford’s Law of Tolerance (CED EK ERT-2.F.1). Use terms like range of tolerance, optimal range, zone of physiological stress, and tolerance curve to describe how performance changes. Thermal tolerance (eurythermal vs. stenothermal) and salinity tolerance (euryhaline vs. stenohaline) are common examples, but light, pH, oxygen, and flow can matter too. Tolerance applies to individuals and to species (EK ERT-2.F.2). Organisms can acclimate or acclimatize within limits; beyond critical thermal maximum/minimum they’ll die. For AP review, see the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and Unit 2 overview (https://library.fiveable.me/ap-environmental-science/unit-2). Practice questions are at (https://library.fiveable.me/practice/ap-environmental-science).

Think of an organism’s tolerance curve like a bell: the full range of conditions it can survive (Shelford’s Law of Tolerance) is the range of tolerance—from the critical minimum to the critical maximum for a factor (temperature, salinity, light, etc.). The optimal range is the narrow middle of that curve where the organism performs best: highest growth, reproduction, and fitness. Outside the optimal range but still inside the range of tolerance is the zone of physiological stress—the organism survives but with reduced function. Past the tolerance limits (critical thermal min/max, intolerance) injury or death follows. This applies to individuals and to species (some are eurythermal or stenothermal, euryhaline or stenohaline). For AP prep, link this to ERT-2.F and how tolerance curves are used on multiple-choice or free-response items (see the Topic 2.4 study guide: https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz). For extra practice, try related questions at Fiveable’s AP practice page (https://library.fiveable.me/practice/ap-environmental-science).

Some species have wider ecological tolerance because of differences in physiology, genetics, and life history that let them survive a broader range of conditions. Shelford’s Law of Tolerance explains this: each species has minimum and maximum limits (critical thermal minimum/maximum for temperature) and an optimal range. Eurythermal or euryhaline species tolerate wide temperature or salinity ranges; stenothermal/stenohaline species tolerate narrow ranges. Mechanisms include genetic adaptations (evolved enzymes, membrane composition), phenotypic plasticity like acclimation/acclimatization, and behaviors (migration, burrowing) that avoid stress. Wider tolerance expands an organism’s realized niche and makes it more resilient to environmental change; narrow tolerance increases physiological stress and extinction risk. For AP exam connections, this matches EK ERT-2.F.1–2 and vocab you should know (tolerance curve, zone of physiological stress). Review the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and more Unit 2 resources (https://library.fiveable.me/ap-environmental-science/unit-2) or practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Ecological tolerance is the range of environmental conditions (temperature, salinity, sunlight, flow rate, etc.) a species or individual can survive in before injury or death. Shelford’s Law of Tolerance says each species has an optimal range (best performance), a zone of physiological stress (can survive but with reduced function), and zones of intolerance. Example: a stenothermal fish tolerates only a narrow temp range (cold-water trout), while a eurythermal species tolerates wide swings (carp). Salinity example: stenohaline marine fish can’t handle fresh water, but euryhaline species like salmon can. Organisms can sometimes acclimate or acclimatize, shifting their tolerance limits a bit; but they still have critical thermal maximum/minimum points beyond which they die. This concept shows up on the AP exam under ERT-2.F (describe range of tolerance, tolerance curve, thermal/salinity terms). Review the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz), the Unit 2 overview (https://library.fiveable.me/ap-environmental-science/unit-2), and try practice problems (https://library.fiveable.me/practice/ap-environmental-science) to prep.

If an organism goes outside its ecological tolerance limits it moves out of its optimal range into the zone of physiological stress—and if conditions keep getting worse it reaches intolerance and can be injured or die. Shelford’s Law of Tolerance describes this: each abiotic factor (temperature, salinity, sunlight, flow rate) has an optimal range, a stress range, and limits beyond which the organism can’t survive. Individuals can sometimes acclimate or acclimatize (short-term physiological adjustments) and some species are broad-tolerant (eurythermal, euryhaline) while others are narrow-tolerant (stenothermal, stenohaline). Ecologically, if many individuals or a whole species can’t tolerate changed conditions, populations decline or shift their range, altering community structure and the species’ niche. For AP purposes, this is covered under EK ERT-2.F (know tolerance curves, critical thermal max/min, and the difference between individual vs. species responses). Review Topic 2.4 on Fiveable for a quick study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and try practice questions at (https://library.fiveable.me/practice/ap-environmental-science).

In lab experiments scientists measure ecological tolerance by exposing organisms to controlled gradients of an environmental factor (temperature, salinity, light, flow) and tracking responses like survival, growth, reproduction, or behavior. Typical steps: set up multiple treatment levels (e.g., 5–10 temperature points or salinity steps) with replicates (3–5 per level), include a control, and maintain all other variables constant. Record endpoints such as % survival, time to death, growth rate, or reproductive output, then plot a tolerance curve to show optimal range, zone of physiological stress, and limits (Shelford’s Law of Tolerance). For thermal studies researchers often find critical thermal maximum/minimum (CTmax/CTmin) by gradually ramping temperature until physiological failure. Don’t forget acclimation time and statistical analysis to detect significant differences. This is exactly the kind of experimental design you might be asked to create on FRQ 1 (design an investigation) on the AP exam. For a quick review, check the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and practice designing experiments at (https://library.fiveable.me/practice/ap-environmental-science).

High tolerance species (broad range)—eurythermal/euryhaline examples: - American green crab and many estuarine oysters tolerate wide salinity swings (euryhaline). - Humans and rats tolerate a broad temperature range compared with many species (eurythermal). These species have wide “range of tolerance” and large optimal zones on a tolerance curve (Shelford’s Law of Tolerance). Low tolerance species (narrow range)—stenothermal/stenohaline examples: - Coral reef-building corals are stenothermal: small temperature increases cause bleaching (zone of physiological stress). - Freshwater fish like trout are often stenohaline/stenothermal—they need cool, well-oxygenated water and die outside narrow ranges. Remember acclimation/acclimatization can shift an organism’s tolerance a bit (e.g., some fish acclimating to seasonal temps), but critical thermal maximum/minimum still limit survival. For an AP review of these terms and practice questions, see the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and more practice at (https://library.fiveable.me/practice/ap-environmental-science).

Think of ecological tolerance as the environmental “speedometer” and “salt gauge” for an organism—salinity and flow rate are just two abiotic factors that have a range where an organism does best (optimal), a zone of stress, and limits where it dies (Shelford’s Law of Tolerance). Salinity: some organisms are stenohaline (narrow salinity tolerance) and die if salinity shifts a little; euryhaline species tolerate big changes (e.g., estuary fish). Salinity affects osmoregulation—too salty or too fresh forces extra energy for ion/water balance, causing stress or mortality. Flow rate: low flow can reduce oxygen/nutrient delivery and increase siltation; high flow can physically dislodge organisms or increase energy costs for feeding/holding position. Both factors shape an organism’s niche and population distribution; they’re fair game on AP questions about tolerance, stress, and acclimation. For a quick topic review, see the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and more unit practice (https://library.fiveable.me/practice/ap-environmental-science).

Ecological tolerance matters for climate change because it tells you the range of conditions (temperature, salinity, sunlight, etc.) a species can survive before hitting physiological stress or death (Shelford’s Law of Tolerance). Species with narrow ranges (stenothermal or stenohaline) have small buffers and are more likely to hit their critical thermal maximum/minimum as climates warm, so they may decline, shift range, or go extinct. Eurythermal/euryhaline species tolerate wider changes and often cope better. Acclimation or acclimatization can help individuals temporarily, but whole populations may still be vulnerable if conditions move outside the tolerance curve or shift the species’ niche. On the AP exam, expect questions linking tolerance to range shifts, habitat loss, or ecosystem impacts (use these terms on FRQs). For a quick review of this Topic, see the APES Ecological Tolerance study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Ecological tolerance shapes where individuals and species can live, so it directly affects population distribution and biodiversity. Shelford’s Law of Tolerance says each species has an optimal range, a zone of physiological stress, and limits beyond which it can’t survive (use tolerance curves, thermal/salinity examples). Populations concentrate where conditions fall in the optimal range; marginal conditions reduce abundance or force behavioral/physiological acclimation. Species with broad tolerance (eurythermal, euryhaline) can occupy more habitats, increasing regional species richness, while specialists (stenothermal, stenohaline) have narrow ranges and smaller, patchier distributions—raising vulnerability and lowering local biodiversity. On the AP exam, expect prompts to “describe” tolerance or to link tolerance to ecological niche and population patterns (ERT-2.F.1–2). For a focused review see the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and wider Unit 2 overview (https://library.fiveable.me/ap-environmental-science/unit-2). For extra practice, check Fiveable’s APES practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Ecological tolerance is the range of environmental conditions (temperature, salinity, light, flow, etc.) a species or individual can survive in before injury or death—Shelford’s Law of Tolerance. Within that range there’s an optimal zone, a zone of physiological stress, and limits beyond which the species is intolerant. Species with broad tolerance (eurythermal, euryhaline) can live in many habitats and are more likely to survive environmental changes; specialists with narrow tolerance (stenothermal, stenohaline) survive only in specific habitats and are more vulnerable. Acclimation or acclimatization can shift individual tolerance temporarily, but not always enough for long-term survival. For APES, know these terms and how tolerance shapes an ecological niche and species distribution—this shows up in Unit 2 questions. Review the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Short answer: It can change—but how and how fast depends on scale. The CED says tolerance applies to individuals and species (EK ERT-2.F.2). Individuals can shift their tolerance short-term by acclimation or acclimatization (physiological adjustments over hours–weeks, e.g., increasing heat shock proteins or adjusting blood chemistry). Populations can shift tolerance long-term by genetic adaptation through natural selection over many generations (evolution), producing traits like greater thermal or salinity tolerance. Shelford’s Law of Tolerance and tolerance curves capture these ideas (optimal range, zone of physiological stress, critical thermal max/min). Some species are eurythermal/euryhaline (wide ranges) and can adjust more easily; stenothermal/stenohaline species have narrow ranges and are less able to change quickly. Review the Topic 2.4 study guide for examples and AP-style wording (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Think of ecological tolerance as Shelford’s Law of Tolerance: organisms have a range (minimum → optimal → maximum) for key abiotic factors. To remember the factors, use a short mnemonic: "TSF S" = Temperature, Salinity, Flow (or wind/current), Sunlight—plus pH, dissolved oxygen, and nutrients. Quiz yourself by drawing a tolerance curve and labeling where eurythermal/stenothermal or euryhaline/stenohaline species fall. Memorize a few CED keywords (optimal range, zone of physiological stress, critical thermal max/min, acclimation) and link each to an example (e.g., salmon need specific flow rate and temp). On the exam, expect multiple-choice or a stimulus showing a tolerance curve or species response—practice reading graphs. For more focused review and examples, see the Topic 2.4 study guide (https://library.fiveable.me/ap-environmental-science/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz), the Unit 2 overview (https://library.fiveable.me/ap-environmental-science/unit-2), and lots of practice problems (https://library.fiveable.me/practice/ap-environmental-science).