SajjadAhmad wrote:
The phrase “alternative stable state” in ecology refers to the tendency of many ecosystems to have different, stable configurations of biotic and abiotic conditions across large time scales separated by what are called regime or phase shifts. Alternative stable state theory claims that instead of a forest transitioning slowly along a gradient toward a different stable state, that forest will reach a crucial tipping point (known as an ecological threshold) as deforestation occurs. Any change beyond this threshold will lead to a rapid change towards the second stable state of the biome in question, in this case a grassland.
Ecologists typically describe this theory with an analogy: Picture a set of three hills, between which are two valleys with a ball sitting in one of them that you want to push into the other. If you don’t push enough, the ball just rolls back down to where it started, but if you give the ball a big enough push, it will roll all the way into the valley on the other side of the hill. From there, it would require a similarly big push to get the ball back to where it started. Stable states are the valleys – where the balls want to stay if no outside forces are involved. However, if there is a big enough change in the environment to cause the ball to roll all the way up the hill to its highest point (the ecological threshold), the ball can be forced from one valley into another relatively quickly – this is a phase shift.
Until recently, most work discussing alternative stable states was theoretical – the idea of purposefully changing an environment to this extent was considered unthinkable – but several cases of confirmed alternative stable states have been reported. For example, disrupting the balance of phosphorous in a clearwater lake can lead to out-of-control phytoplankton blooms. Reducing this addition of phosphorous has so far not been an effective way of stopping the phytoplankton blooms, leading researchers to think that the ecosystem has been pushed into a new local equilibrium. This idea of hysteresis – that the state of an environment depends at least in part on its history and not just its current state – is at the core of many debates surrounding alternative stable state theory. However, whether most ecosystems that can exist under multiple stable states will readily convert between the two is still an open debate.
1. Which one of the following scenarios is most analogous to the type of ecological change predicted by alternative stable state theory?
A. After 30 years working at a bank, a man quits suddenly after a severe illness and then spends the rest of his life working as a patient advocate.
B. The stock market slowly rises over a 10-year period and then crashes precipitously after unexpected news regarding the health of the economy.
C. Over a period of a few years, a company switches from manufacturing a particular software product to consulting on that product after sales slowed.
D. The price of a certain stock that has been constant for months spikes dramatically on rumors of a takeover bid but then quickly returns to the old price after the rumor is debunked.
E. The ecology of a lake slowly changes as silt deposits increase from frequent flooding, but the lake returns to its original state as floodwaters recede.
2. Which of the following is confirmed in the passage as causing a phase shift in the environment?
A. the addition of phosphorous to a lake
B. the blooming of phytoplankton in a lake
C. the movement of balls over a hill
D. the presence of drought conditions in a certain region
E. the repeated logging of certain forests
3. The primary purpose of the passage is to
A. highlight the uncertainties and debates relating to a particular theory.
B. suggest that the alternative stable state theory is incomplete.
C. argue that the alternative stable state theory is primarily correct.
D. provide a thorough understanding of an important ecological theory.
E. give several detailed examples of the alternative stable state theory.
para1 : the introduce to the theory and concept of “alternative stable state” and how its transitioning pattern works, in that its phase shift occur rapidly rather than continually
para2 : take the analogy to hills and valleys as an example to further illustrate the concept of “phase shift”
para3 : though the passage as a whole affirmed the reported cases on the theory, he still hold a objective tone by raising the idea of hysteresis, in that further give the open debatable issue of whether, in reality, most ecosystems can exist under this theoretical ideal multiple stable states mention in para1&2
1. Which one of the following scenarios is most analogous to the type of ecological
change(THIS IS THE POINT) predicted by alternative stable state theory?
The theory is about…. Any change beyond this threshold will lead to a rapid change towards the second stable state of the biome in question, in this case a grassland.
refer to the analogous example, the hill and valleys, in para2
A. After 30 years working at a bank, a man quits suddenly after a severe illness and then spends the rest of his life working as a patient advocate.
spends the rest of his life working as a patient advocate.
…..CHANGE TO SECOND, OR SAY ANOTHER, STABLE STATE, correct
B. The stock market slowly rises over a 10-year period and then crashes precipitously after unexpected news regarding the health of the economy.
(BUT HOW IS THE “CHANGE” TO ANOTHER STATE?, IT ONLY SAYS THE CRASH HAPPEN SUDDENLY HOWEVER NOT MENTION ANYTHING ABOUT ITS AFTERMATH)
C. Over a period of a few years, a company switches from manufacturing a particular software product to consulting on that product after sales slowed.
this choice only address the “change” –and here we know, from “over a period…” not a sudden change--in the verb of “switch”, but how the things go after the change, is it stable or unstable, we do not know
D. The price of a certain stock that has been constant for months spikes dramatically on rumors of a takeover bid but then quickly
returns to the old price(SO STILL NO CHANGE IS CONCERNED HERE) after the rumor is debunked.
E. The ecology of a lake slowly changes(must be sudden, as the analogus require)) as silt deposits increase from frequent flooding, but the lake
returns to its original state(SO NO CHANGE IS CONCERNED HERE) as floodwaters recede.
2. Which of the following is confirmed in the passage as causing a phase shift in the environment?
A. the addition of phosphorous to a lake …..correct
B. the blooming of phytoplankton in a lake
C. the movement of balls over a hill
D. the presence of drought conditions in a certain region
E. the repeated logging of certain forests
para2
Until recently, most work discussing alternative stable states was theoretical – the idea of purposefully changing an environment to this extent was considered unthinkable – but several cases of confirmed alternative stable states have been reported. For example, disrupting the balance of phosphorous in a clear water lake can lead to out-of-control phytoplankton blooms. Reducing this addition of phosphorous has so far not been an effective way of stopping the phytoplankton blooms, leading researchers to think that the ecosystem has been pushed into a new local equilibrium.
here we had to find a choice that is the cause of “phase shift/effect”, which, in the example of para2, is phytoplankton blooms, from the third sentence we could clearly see that it’s the disruption of the balance of phosphorus which cause the phytoplankton blooms, thus only the quantity change of phosphorus will effect the cause, (A) be the correct answer
3. The primary purpose of the passage is to
A. highlight the uncertainties and debates relating to a particular theory.
although the author, in the last sentence of para3, say that this alternative stable states theory is still open to debate, also nowhere in the passage mention about uncertainties, and though the last sentence of para3 say this theory is “open to debate, the author doesn’t intend to “highlight” this debate, rather he’s quite neutral and objective in his tone
B. suggest that the alternative stable state theory is incomplete.
There’s nowhere in the passage says that this theory is “incomplete”
C. argue that the alternative stable state theory is primarily correct.
The purpose to this passage doesn’t intend to argue about anything or judge whether it be correct or not, and it says in the last sentence of para3 that this theory is “open to debate”, we could see the author is quite neutral to this point
D. provide a thorough understanding of an important ecological theory.
….correct, best fit to overall gist of this passage, the last sentence says its “open to debate”, this imply that the author is still quite objective to the viewing of this theory
E. give several detailed examples of the alternative stable state theory.
the whole passage only offer one example in para2 to analogize the theory in para1
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Updated on: 03 Jun 2023, 10:19
57%
(03:28) wrong 
35%
(medium)
