Ecological Tolerance - AP Environmental Science

1. A tolerance curve for a yeast strain shows fermentation rate versus sugar concentration. Rate is maximal at 8–12%, reduced at 4–8% and 12–16%, and zero below 4% or above 16%. Which sugar concentration is most likely to be a zone of stress?
   Answer: 14% Ecological tolerance describes the spectrum of abiotic factors, like sugar concentration, that an organism can endure, from lethal limits to optimal conditions. The tolerance curve maps performance, such as fermentation rate, showing zero at extremes, reduced in stress zones, and maximal in the optimal range. Here, the yeast's optimal range is 8–12% sugar, with stress zones at 4–8% and 12–16%, and zero outside those. A concentration of 14% falls in the 12–16% stress zone, where fermentation is reduced but possible. Thus, choice C is correct as it identifies a stress zone. This demonstrates how organisms can persist in suboptimal conditions but with impaired function, which is key in environmental science for understanding adaptation.
2. Two fish species have tolerance curves for dissolved oxygen (DO, mg/L). Species X has 0% survival below 2 and above 14, with maximum survival at 8. Species Y has 0% survival below 5 and above 12, with maximum survival at 9. In a lake that seasonally drops to 3 mg/L DO, which prediction is most supported?
   Answer: Species X is more likely to survive than Species Y because 3 mg/L is above X's lower limit but below Y's lower limit Ecological tolerance is the ability of a species to persist under varying environmental conditions, defined by lower and upper limits. A tolerance curve graphs survival or performance against the factor, with an optimal peak, stress zones, and limits where survival is impossible. Here, Species X tolerates 2–14 mg/L DO with max at 8, while Y tolerates 5–12 mg/L with max at 9, so at 3 mg/L, X is above its lower limit (stressed but survivable) but Y is below its lower limit (unsurvivable). Thus, X is more likely to survive than Y in low DO conditions. This prediction is supported by comparing tolerance ranges. Choice C correctly captures this competitive advantage for X.
3. A tolerance curve for a soil bacterium shows enzyme activity versus pH. Activity is maximal at pH 7.0, half-maximal at pH 6.0 and 8.0, and zero at pH 5.0 and 9.0. Which pair best represents the limits of tolerance?
   Answer: pH 5.0 and pH 9.0 Ecological tolerance encompasses the environmental extremes a species can handle, key to its ecological niche. A tolerance curve plots performance like enzyme activity, peaking optimally, decreasing in stress, and hitting zero at limits. Here, activity is maximal at pH 7.0, half at 6.0 and 8.0, and zero at 5.0 and 9.0, so limits are pH 5.0 and 9.0. These points mark where activity ceases entirely. Other pairs are within stress or optimal zones. Choice B best represents the tolerance limits.
4. An organism has a tolerance curve for temperature with lower and upper limits at 0°C and 40°C, and an optimal range at 18–22°C. Which temperature is most likely to produce the lowest performance while still allowing survival?
   Answer: 2°C Ecological tolerance encompasses the range of conditions, such as temperature, where an organism can survive, though performance varies. A tolerance curve illustrates this with limits at 0°C and 40°C where performance is zero, stress zones with reduced performance, and an optimal range at 18–22°C for peak performance. The temperature of 2°C is within the tolerance limits but in the lower stress zone, yielding the lowest performance while still allowing survival. Temperatures like 45°C exceed the upper limit, making survival impossible. Choice B correctly identifies this. Such curves aid in predicting species' responses to climate variability.
5. A tolerance curve for a bird species shows nesting success versus average spring temperature. Nesting success is maximal at 12–16°C, reduced at 8–12°C and 16–20°C, and near zero below 8°C or above 20°C. If climate change increases spring temperature from 15°C to 19°C, what is the best prediction?
   Answer: Nesting success decreases because conditions shift from optimal to a zone of stress Ecological tolerance outlines the environmental range for successful reproduction, like temperature for nesting. The curve shows maximal success at 12–16°C, stress at 8–12°C and 16–20°C, and near zero outside. Shifting from 15°C (optimal) to 19°C enters the upper stress zone, decreasing success. Survival isn't impossible until above 20°C. Choice B predicts this outcome. This is relevant for modeling climate change impacts on wildlife.
6. A plant's tolerance curve for soil moisture shows best growth at 25–40% water content, reduced growth at 15–25% and 40–55%, and no growth below 15% or above 55%. If a drought lowers soil moisture from 30% to 20%, which change is most likely?
   Answer: Growth decreases because conditions shift from optimal range to a zone of stress Ecological tolerance is the range of abiotic factors allowing growth and reproduction in a species. A tolerance curve illustrates optimal growth, stress-induced reductions, and limits where growth stops. For this plant, best growth is at 25–40% moisture, reduced at 15–25% and 40–55%, and none outside 15–55%. Shifting from 30% (optimal) to 20% enters the lower stress zone, decreasing growth due to drought stress. Survival remains possible, but performance drops. Choice B aptly describes this shift to stress.
7. A tolerance curve for a soil worm shows activity versus soil temperature. Activity is nonzero from 2–28°C, with an optimal range of 12–18°C. During winter, soil temperature stays at 4°C for several days. Which outcome is most likely?
   Answer: Activity is reduced because 4°C is in the lower zone of stress but within tolerance limits Ecological tolerance is the temperature span for activity in worms. Nonzero from 2–28°C, optimal 12–18°C. 4°C is lower stress, reducing activity but survivable. Not optimal or beyond limits. Choice B likely. Shows winter resilience.
8. A tolerance curve for a stream macroinvertebrate shows abundance versus pH. Abundance is highest from pH 6.8–7.6, reduced from 6.0–6.8 and 7.6–8.4, and zero below 6.0 and above 8.4. Which pH value is most likely to produce the greatest abundance?
   Answer: pH 7.2 Ecological tolerance outlines the environmental parameters a species can endure, crucial for abundance and distribution. The tolerance curve peaks in the optimal range where abundance is greatest, flanked by stress zones with lower abundance, and ends at tolerance limits with zero abundance. For this macroinvertebrate, abundance is highest at pH 6.8–7.6, reduced at 6.0–6.8 and 7.6–8.4, and zero outside 6.0–8.4. The pH 7.2 falls squarely in the optimal range, likely yielding the greatest abundance. Other options are either in stress zones or closer to limits. This makes choice B the best for maximal abundance.
9. A tolerance curve for a frog species shows tadpole survival versus water temperature. Survival is nonzero from 10–28°C, with maximum survival from 18–22°C. Which temperature is most likely in the zone of stress (not optimal, but survivable)?
   Answer: 12°C Ecological tolerance refers to the span of conditions supporting species survival, often visualized in curves. The tolerance curve features an optimal range for max survival, stress zones with reduced but positive survival, and limits with zero survival. For the frog, survival is nonzero from 10–28°C and maximal at 18–22°C, so stress zones are 10–18°C and 22–28°C. 12°C falls in the lower stress zone, where survival is possible but not optimal. Temperatures like 30°C are beyond limits, and 20°C or 19°C are optimal. Choice B correctly identifies a stress zone temperature.
10. Two insect species have tolerance ranges for temperature. Species A survives 5–35°C (optimal 20–25°C). Species B survives 12–30°C (optimal 18–22°C). On a cold night at 8°C, which statement is most accurate?
    Answer: Species A can survive (likely stressed), while Species B is below its lower limit of tolerance Ecological tolerance defines survivable environmental ranges, influencing species resilience to changes. Tolerance curves show broad or narrow ranges, with optimal sub-ranges for peak performance. Species A tolerates 5–35°C (optimal 20–25°C), so at 8°C it is stressed but within limits. Species B tolerates 12–30°C, so 8°C is below its lower limit, preventing survival. This highlights A's wider tolerance for cold. Choice B correctly predicts A's survival advantage.
11. Two frog species have the following temperature tolerance information: - Species A: survives 8–26°C; optimal 16–20°C. - Species B: survives 14–32°C; optimal 24–28°C. A pond is consistently 18°C during the breeding season. Which claim is most supported?
    Answer: Species A should have higher fitness because 18°C falls within its optimal range, while Species B is in a zone of stress. Ecological tolerance curves help predict competitive outcomes by showing which species perform best under specific conditions. Species A survives from 8-26°C with optimal performance at 16-20°C, while Species B survives from 14-32°C with optimal performance at 24-28°C. At the pond's consistent 18°C temperature, Species A is within its optimal range (18°C falls within 16-20°C) and should exhibit maximum growth, reproduction, and overall fitness. In contrast, Species B is below its optimal range and likely in a zone of stress, as 18°C is well below its preferred 24-28°C range but still within its survival limits. When one species is in optimal conditions while another is stressed, the optimally-suited species typically has competitive advantages in resource acquisition and reproduction. Option B correctly predicts Species A's higher fitness due to optimal conditions versus Species B's stressed state.
12. A tolerance curve for a pine seedling shows survival versus soil moisture. Survival is nonzero from 10–60%, maximal from 25–40%. Which statement best describes 55% soil moisture?
    Answer: It is in a zone of stress, so survival is possible but performance is reduced Ecological tolerance is the ability of an organism to withstand variations in environmental factors, such as soil moisture, without dying. A tolerance curve visually represents this, with the x-axis as the factor and y-axis as a performance metric like survival, peaking in the optimal range and declining in stress zones until reaching zero at tolerance limits. For the pine seedling, 55% moisture is within the nonzero survival range of 10–60% but outside the maximal range of 25–40%, indicating a zone of stress. In this zone, survival is possible but growth or performance is reduced compared to optimal conditions. Choice B accurately describes this scenario. Understanding these curves helps predict how species respond to environmental changes like drought or flooding.
13. A tolerance curve for a river mussel shows filtration rate versus turbidity (NTU). Filtration is maximal at 0–10 NTU, reduced at 10–25 NTU, and near zero above 25 NTU. Which turbidity level is most likely to cause the greatest filtration rate?
    Answer: 5 NTU Ecological tolerance defines the boundaries of environmental conditions, like turbidity, that allow an organism to function effectively. The tolerance curve is a graphical tool showing performance metrics, such as filtration rate, with an optimal peak, declining stress zones, and limits where the metric hits zero. For the river mussel, maximal filtration occurs at 0–10 NTU, making 5 NTU within this optimal range for the greatest rate. Choices like 20 NTU or 25 NTU are in reduced or near-zero zones, respectively. Thus, choice A is supported. This concept is crucial for assessing water quality impacts on aquatic species.
14. A tolerance curve for a shrimp species shows survival versus salinity. Survival is nonzero from 8–32 ppt, maximal from 18–24 ppt. In water at 9 ppt, which statement is most accurate?
    Answer: The shrimp is in a zone of stress near the lower limit, so survival is possible but reduced Ecological tolerance is the range for survival, like salinity for shrimp. The curve indicates nonzero from 8–32 ppt, maximal 18–24 ppt. 9 ppt is near lower limit, in stress with reduced survival. Not optimal or beyond limits. Choice B is accurate. Useful for aquaculture management.
15. A tolerance curve for a lake zooplankton shows population growth rate versus salinity (ppt). Growth is positive from 0–6 ppt, maximal from 1–3 ppt, and negative (declining population) from 3–6 ppt; at 6 ppt growth is zero and above 6 ppt individuals do not survive. At 5 ppt, which is most likely?
    Answer: The population may survive but is stressed and likely declining Ecological tolerance influences population dynamics under stressors like salinity. The tolerance curve graphs growth rate, positive optimally, negative in stress (declining but survivable), zero or negative beyond limits. Positive growth 0–6 ppt, maximal 1–3 ppt, negative 3–6 ppt, zero at 6 ppt, no survival above. At 5 ppt, in stress zone with declining population but possible survival. This indicates stress without immediate extinction. Choice B predicts this stressed state accurately.
16. A tolerance curve for a moss shows water retention performance versus humidity (%). Performance is maximal at 70–90%, reduced at 50–70% and 90–95%, and near zero below 50% or above 95%. Which humidity is most likely to cause reduced but nonzero performance?
    Answer: 60% Ecological tolerance affects moisture-dependent species like moss. The tolerance curve illustrates optimal humidity for retention, reduced in stress, near zero at limits. Maximal at 70–90%, reduced 50–70% and 90–95%, near zero below 50% or above 95%. 60% is in lower stress, with reduced but nonzero performance. This allows function under moderate dryness. Choice B likely causes this reduced performance.
17. Two plant species have tolerance curves for soil pH. Species 1: survival from pH 4.5–7.5 (optimal 5.5–6.5). Species 2: survival from pH 6.0–8.5 (optimal 7.0–7.8). In a soil with pH 5.0, which prediction is best?
    Answer: Species 1 can survive (likely stressed or near optimal), while Species 2 is below its lower limit of tolerance Ecological tolerance varies between species, affecting coexistence in habitats. Tolerance curves compare ranges, showing survival possibilities. Species 1 survives pH 4.5–7.5 (optimal 5.5–6.5), so at 5.0 it is within limits, likely stressed. Species 2 survives 6.0–8.5, so 5.0 is below its lower limit, preventing survival. This gives Species 1 an edge in acidic soils. Choice B correctly predicts Species 1's survival over 2.
18. Two amphibian species have tolerance curves for pH. Species P survives pH 5.0–7.5 (optimal 6.0–6.8). Species Q survives pH 6.5–9.0 (optimal 7.2–8.0). If acid rain lowers a pond to pH 5.6, which statement is most supported?
    Answer: Species P can survive (possibly stressed), while Species Q is below its lower limit of tolerance Ecological tolerance varies by species for factors like pH. Curves show P survives 5.0–7.5 (optimal 6.0–6.8), Q 6.5–9.0 (optimal 7.2–8.0). At 5.6, P is stressed but within, Q below lower limit. Not both optimal or dead. Choice B is supported. Illustrates acid rain selectivity.
19. Two species have tolerance curves for salinity. Species M survives 0–15 ppt (optimal 2–6 ppt). Species N survives 10–35 ppt (optimal 20–28 ppt). In an estuary at 12 ppt, which statement is most accurate?
    Answer: Species M is within its tolerance range (likely stressed), and Species N is within its tolerance range (likely stressed) Ecological tolerance is the span of conditions, such as salinity, in which species can persist, varying by optimal and stress zones. Tolerance curves for Species M (0–15 ppt, optimal 2–6) and N (10–35 ppt, optimal 20–28) show both can survive at 12 ppt, though M is above its optimal and N below, likely stressing both. Neither is beyond limits nor in optimal ranges. Choice A accurately reflects this. Overlapping tolerances like this enable species coexistence in dynamic environments like estuaries.
20. A tolerance curve for a beetle shows activity level versus temperature. Activity is highest at 30°C, reduced at 20°C and 40°C, and zero at 10°C and 50°C. Which statement correctly identifies the limits of tolerance?
    Answer: 10°C and 50°C Ecological tolerance defines activity limits for insects like beetles. The tolerance curve peaks at optimal temperature, reduces in stress, zeros at limits. Highest at 30°C, reduced at 20°C and 40°C, zero at 10°C and 50°C. Limits are 10°C and 50°C, where activity ceases. These are the extremes of tolerance. Choice C identifies the limits correctly.

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