Ecological Tolerance
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AP Environmental Science › Ecological Tolerance
A tolerance curve for a freshwater trout shows survival versus water temperature. Survival is maximal at 12–16°C, reduced at 6–12°C and 16–20°C, and zero below 6°C or above 20°C. Which temperature best represents the upper limit of tolerance?
20°C
6°C
16°C
12°C
Explanation
Ecological tolerance defines survival limits, like temperature for trout. The curve shows maximal 12–16°C, stress 6–12°C and 16–20°C, zero outside 6–20°C. 20°C is the upper limit. Others are within or below. Choice B represents it. Critical for fisheries under warming.
A tolerance curve for a cactus shows growth versus nighttime temperature. Growth is maximal at 15–20°C, reduced at 5–15°C and 20–30°C, and zero below 5°C or above 30°C. Which nighttime temperature would most likely cause the cactus to experience stress but still grow?
3°C
27°C
18°C
32°C
Explanation
Ecological tolerance encompasses conditions for growth, such as nighttime temperature. The curve peaks at 15–20°C, stresses at 5–15°C and 20–30°C, zeros outside 5–30°C. 27°C is in upper stress, allowing growth but stressed. 32°C is beyond. Choice C fits. Relevant for desert plant ecology.
A tolerance curve for a coastal grass shows survival versus salinity. Survival is highest at 10–20 ppt, reduced at 5–10 ppt and 20–30 ppt, and zero below 5 ppt or above 30 ppt. Which salinity would most likely produce the lowest survival while still being within tolerance limits?
31 ppt
15 ppt
29 ppt
6 ppt
Explanation
Ecological tolerance influences coastal species' salinity endurance. The tolerance curve peaks highly, reduces towards limits, zeros outside. Highest 10–20 ppt, reduced 5–10 and 20–30 ppt, zero below 5 or above 30. 29 ppt is in upper reduced zone, near limit, likely lowest survival within tolerance. This is due to approaching zero at 30 ppt. Choice C produces lowest within-limits survival.
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?
pH 7.2
pH 8.2
pH 8.6
pH 6.4
Explanation
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.
A tolerance curve for a kelp species shows photosynthesis versus light intensity. Photosynthesis is maximal at 200–400 µmol photons m$^{-2}$ s$^{-1}$, reduced at 100–200 and 400–600, and near zero below 100 or above 600. Which light intensity is most likely to be in the upper zone of stress?
150
300
500
650
Explanation
Ecological tolerance is the light intensity range for photosynthesis in kelp. The curve peaks at 200–400, stresses at 100–200 and 400–600, near zero outside. 500 is in upper stress. 650 beyond. Choice C correct. Aids in understanding marine productivity.
A tolerance curve for a coral species shows calcification rate versus water temperature. Calcification is maximal at 25–27°C, reduced at 23–25°C and 27–29°C, and near zero at 22°C and 30°C. If ocean temperature rises from 26°C to 28°C, what is the best interpretation?
No change is expected because tolerance curves are flat near the optimum
The coral moves from a zone of stress into the optimal range, so calcification increases
The coral moves from optimal range into a zone of stress, so calcification decreases
The coral crosses the upper limit of tolerance, so calcification becomes impossible at 28°C
Explanation
Ecological tolerance outlines conditions for species processes like calcification in corals. The tolerance curve shows optimal temperatures, stress zones with reduced rates, and limits nearing zero. Maximal at 25–27°C, reduced at 23–25°C and 27–29°C, near zero at 22°C and 30°C. Rising from 26°C (optimal) to 28°C shifts to upper stress, decreasing calcification. This is due to thermal stress affecting symbiosis. Choice A interprets this transition correctly.
A tolerance curve for a lichen species shows growth versus air pollution (arbitrary units). Growth is highest at 0–10 units, reduced at 10–25 units, and zero above 25 units. Which condition represents the zone of stress?
0 units
30 units
5 units
15 units
Explanation
Ecological tolerance is the spectrum of conditions a species can endure, vital for ecosystem roles. Tolerance curves depict growth versus factors like pollution, with optimal low-pollution, stress at moderate, and limits at high. Here, highest growth at 0–10 units, reduced (stress) at 10–25, zero above 25. The zone of stress is 10–25 units, where growth persists but diminishes. 15 units falls in this range. Choice B represents the stress zone condition.
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?
The worms cannot survive because 4°C is above the upper limit of tolerance
The worms cannot survive because 4°C is below the lower limit of tolerance
Activity is reduced because 4°C is in the lower zone of stress but within tolerance limits
Activity is near maximum because 4°C is close to the optimum
Explanation
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.
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?
20°C
2°C
19°C
45°C
Explanation
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.
A tolerance curve for a tidepool crab shows survival versus salinity (ppt). Survival is highest at 30–34 ppt, reduced at 20–30 ppt and 34–40 ppt, and zero below 20 ppt and above 40 ppt. After heavy rain, salinity drops to 18 ppt. What is the best prediction?
Survival increases because lower salinity reduces osmotic stress for marine crabs
Survival drops to near zero because 18 ppt is below the lower limit of tolerance
Survival decreases but remains possible because 18 ppt is in a zone of stress
Survival remains high because 18 ppt is within the optimal range
Explanation
Ecological tolerance is the range of an abiotic factor where a species can live, influencing its habitat distribution. The tolerance curve shows high survival in the optimal range, reduced in stress zones, and zero at the limits. For the crab, optimal survival is at 30–34 ppt, reduced at 20–30 and 34–40 ppt, and zero below 20 or above 40 ppt. Dropping to 18 ppt crosses below the lower limit of 20 ppt, where survival is zero. This predicts near-zero survival due to osmotic imbalance. Choice C correctly identifies this as exceeding the tolerance limit.